Basics of computer hardware
A computer is a programmable machine (or more precisely, a programmable sequential state machine). There are two basic kinds of computers: analog and digital.
Analog computers are analog devices. That is, they have continuous states rather than discrete numbered states. An analog computer can represent fractional or irrational values exactly, with no round-off. Analog computers are almost never used outside of experimental settings.
A digital computer is a programmable clocked sequential state machine. A digital computer uses discrete states. A binary digital computer uses two discrete states, such as positive/negative, high/low, on/off, used to represent the binary digits zero and one.
The French word ordinateur, meaning that which puts things in order, is a good description of the most common functionality of computers.
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what are computers used for?
Computers are used for a wide variety of purposes.
Data processing is commercial and financial work. This includes such things as billing, shipping and receiving, inventory control, and similar business related functions, as well as the “electronic office”.
Scientific processing is using a computer to support science. This can be as simple as gathering and analyzing raw data and as complex as modelling natural phenomenon (weather and climate models, thermodynamics, nuclear engineering, etc.).
Multimedia includes content creation (composing music, performing music, recording music, editing film and video, special effects, animation, illustration, laying out print materials, etc.) and multimedia playback (games, DVDs, instructional materials, etc.).
parts of a computer
The classic crude oversimplication of a computer is that it contains three elements: processor unit, memory, and I/O (input/output). The borders between those three terms are highly ambigious, non-contiguous, and erratically shifting.
hardware subsystems of a computer
A slightly less crude oversimplification divides a computer into five elements: arithmetic and logic subsystem, control subsystem, main storage, input subsystem, and output subsystem.
* processor
* arithmetic and logic
* control
* main storage
* external storage
* input/output overview
* input
* output
processor
The processor is the part of the computer that actually does the computations. This is sometimes called an MPU (for main processor unit) or CPU (for central processing unit or central processor unit).
A processor typically contains an arithmetic/logic unit (ALU), control unit (including processor flags, flag register, or status register), internal buses, and sometimes special function units (the most common special function unit being a floating point unit for floating point arithmetic).
Some computers have more than one processor. This is called multi-processing.
The major kinds of digital processors are: CISC, RISC, DSP, and hybrid.
CISC stands for Complex Instruction Set Computer. Mainframe computers and minicomputers were CISC processors, with manufacturers competing to offer the most useful instruction sets. Many of the first two generations of microprocessors were also CISC.
RISC stands for Reduced Instruction Set Computer. RISC came about as a result of academic research that showed that a small well designed instruction set running compiled programs at high speed could perform more computing work than a CISC running the same programs (although very expensive hand optimized assembly language favored CISC).
DSP stands for Digital Signal Processing. DSP is used primarily in dedicated devices, such as MODEMs, digital cameras, graphics cards, and other specialty devices.
Hybrid processors combine elements of two or three of the major classes of processors.
For more detailed information on these classes of processors, see processors.
arithmetic and logic
An arithmetic/logic unit (ALU) performs integer arithmetic and logic operations. It also performs shift and rotate operations and other specialized operations. Usually floating point arithmetic is performed by a dedicated floating point unit (FPU), which may be implemented as a co-processor.
An arithmetic/logic unit (ALU) performs integer arithmetic and logic operations. It also performs shift and rotate operations and other specialized operations. Usually floating point arithmetic is performed by a dedicated floating point unit (FPU), which may be implemented as a co-processor.
control
Control units are in charge of the computer. Control units fetch and decode machine instructions. Control units may also control some external devices.
A bus is a set (group) of parallel lines that information (data, addresses, instructions, and other information) travels on inside a computer. Information travels on buses as a series of electrical pulses, each pulse representing a one bit or a zero bit (there are trinary, or three-state, buses, but they are rare). An internal bus is a bus inside the processor, moving data, addresses, instructions, and other information between registers and other internal components or units. An external bus is a bus outside of the processor (but inside the computer), moving data, addresses, and other information between major components (including cards) inside the computer. Some common kinds of buses are the system bus, a data bus, an address bus, a cache bus, a memory bus, and an I/O bus.
For more information, see buses.
main storage
Main storage is also called memory or internal memory (to distinguish from external memory, such as hard drives).
RAM is Random Access Memory, and is the basic kind of internal memory. RAM is called “random access” because the processor or computer can access any location in memory (as contrasted with sequential access devices, which must be accessed in order). RAM has been made from reed relays, transistors, integrated circuits, magnetic core, or anything that can hold and store binary values (one/zero, plus/minus, open/close, positive/negative, high/low, etc.). Most modern RAM is made from integrated circuits. At one time the most common kind of memory in mainframes was magnetic core, so many older programmers will refer to main memory as core memory even when the RAM is made from more modern technology. Static RAM is called static because it will continue to hold and store information even when power is removed. Magnetic core and reed relays are examples of static memory. Dynamic RAM is called dynamic because it loses all data when power is removed. Transistors and integrated circuits are examples of dynamic memory. It is possible to have battery back up for devices that are normally dynamic to turn them into static memory.
ROM is Read Only Memory (it is also random access, but only for reads). ROM is typically used to store thigns that will never change for the life of the computer, such as low level portions of an operating system. Some processors (or variations within processor families) might have RAM and/or ROM built into the same chip as the processor (normally used for processors used in standalone devices, such as arcade video games, ATMs, microwave ovens, car ignition systems, etc.). EPROM is Erasable Programmable Read Only Memory, a special kind of ROM that can be erased and reprogrammed with specialized equipment (but not by the processor it is connected to). EPROMs allow makers of industrial devices (and other similar equipment) to have the benefits of ROM, yet also allow for updating or upgrading the software without having to buy new ROM and throw out the old (the EPROMs are collected, erased and rewritten centrally, then placed back into the machines).
Registers and flags are a special kind of memory that exists inside a processor. Typically a processor will have several internal registers that are much faster than main memory. These registers usually have specialized capabilities for arithmetic, logic, and other operations. Registers are usually fairly small (8, 16, 32, or 64 bits for integer data, address, and control registers; 32, 64, 96, or 128 bits for floating point registers). Some processors separate integer data and address registers, while other processors have general purpose registers that can be used for both data and address purposes. A processor will typically have one to 32 data or general purpose registers (processors with separate data and address registers typically split the register set in half). Many processors have special floating point registers (and some processors have general purpose registers that can be used for either integer or floating point arithmetic). Flags are single bit memory used for testing, comparison, and conditional operations (especially conditional branching). For a much more advanced look at registers, see registers.
For more information on memory, see memory
external storage
External storage (also called auxillary storage) is any storage other than main memory. In modern times this is mostly hard drives and removeable media (such as floppy disks, Zip disks, optical media, etc.). With the advent of USB and FireWire hard drives, the line between permanent hard drives and removeable media is blurred. Other kinds of external storage include tape drives, drum drives, paper tape, and punched cards. Random access or indexed access devices (such as hard drives, removeable media, and drum drives) provide an extension of memory (although usually accessed through logical file systems). Sequential access devices (such as tape drives, paper tape punch/readers, or dumb terminals) provide for off-line storage of large amounts of information (or back ups of data) and are often called I/O devices (for input/output).
input/output overview
Most external devices are capable of both input and output (I/O). Some devices are inherently input-only (also called read-only) or inherently output-only (also called write-only). Regardless of whether a device is I/O, read-only, or write-only, external devices can be classified as block or character devices.
A character device is one that inputs or outputs data in a stream of characters, bytes, or bits. Character devices can further be classified as serial or parallel. Examples of character devices include printers, keyboards, and mice.
A serial device streams data as a series of bits, moving data one bit at a time. Examples of serial devices include printers and MODEMs.
A parallel device streams data in a small group of bits simultaneously. Usually the group is a single eight-bit byte (or possibly seven or nine bits, with the possibility of various control or parity bits included in the data stream). Each group usually corresponds to a single character of data. Rarely there will be a larger group of bits (word, longword, doubleword, etc.). The most common parallel device is a printer (although most modern printers have both a serial and a parallel connection, allowing greater connection flexibility).
A block device moves large blocks of data at once. This may be physically implemented as a serial or parallel stream of data, but the entire block gets transferred as single packet of data. Most block devices are random access (that is, information can be read or written from blocks anywhere on the device). Examples of random access block devices include hard disks, floppy disks, and drum drives. Examples of sequential access block devcies include magnetic tape drives and high speed paper tape readers.
input
Input devices are devices that bring information into a computer.
Pure input devices include such things as punched card readers, paper tape readers, keyboards, mice, drawing tablets, touchpads, trackballs, and game controllers.
Devices that have an input component include magnetic tape drives, touchscreens, and dumb terminals.
output
Output devices are devices that bring information out of a computer.
Pure output devices include such things as card punches, paper tape punches, LED displays (for light emitting diodes), monitors, printers, and pen plotters.
Devices that have an output component include magnetic tape drives, combination paper tape reader/punches, teletypes, and dumb terminals.
more details
For a more detailed of the basic parts of a computer, see the following sections:
* processors
o CISC
o RISC
o DSP
o Hybrid
* buses
o kinds of buses
o bus standards
* memory
o memory hardware issues
+ main storage
+ external storage
o basic memory software approaches
+ static and dynamic approaches
+ absolute addressing
+ overlay
+ relocatable software
+ demand paging and swapping
+ program counter relative
+ base pointers
+ indirection, pointers, and handles
+ stack frames
+ virtual memory
o OS memory services
o memory maps
o low memory
For a more detailed examination of how processors work, see assembly language (huge web page) or subsections below:
* intro to assembly language
* data representation and number systems
* registers
* addressing modes
* executable instructions (huge web page, subdivided below)
* data and address movement
* integer arithmetic
* floating arithmetic
* binary coded decimal
* advanced math
* data conversion
* logical operations
* shift and rotate
* bit and bit field manipulation
* character and string
* table operations
* high level language support
* program control and condition codes
* input/output
* system control
* coprocessor and multiprocessor
* trap generating
further reading: books:
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further reading: books: general
Structured Computer Organization, 4th edition; by Andrew S. Tanenbaum; Prentice Hall; October 1998; ISBN 0130959901; Paperback; 669 pages; $95.00; used by CS 308-273A (Principles of Assembly Languages) at McGill University School of Computer Science
Computers: An Introduction to Hardware and Software Design; by Larry L. Wear, James R. Pinkert (Contributor), William G. Lane (Contributor); McGraw-Hill Higher Education; February 1991; ISBN 0070686742; Hardcover; 544 pages; $98.60; used by CS 308-273A (Principles of Assembly Languages) at McGill University School of Computer Science
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one level up
Hardware Level of Operating System
peer level
* processors
* processes or jobs
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* memory
* memory maps
* low memory
* character codes
Thursday, April 1, 2010
Bio-Molecular Computing
Definition
Molecular computing is an emerging field to which chemistry, biophysics, molecular biology, electronic engineering, solid state physics and computer science contribute to a large extent. It involves the encoding, manipulation and retrieval of information at a macromolecular level in contrast to the current techniques, which accomplish the above functions via IC miniaturization of bulk devices. The biological systems have unique abilities such as pattern recognition, learning, self-assembly and self-reproduction as well as high speed and parallel information processing. The aim of this article is to exploit these characteristics to build computing systems, which have many advantages over their inorganic (Si,Ge) counterparts.
DNA computing began in 1994 when Leonard Adleman proved thatDNA computing was possible by finding a solution to a real- problem, a Hamiltonian Path Problem, known to us as the Traveling Salesman Problem,with a molecular computer. In theoretical terms, some scientists say the actual beginnings of DNA computation should be attributed to Charles Bennett's work. Adleman, now considered the father of DNA computing, is a professor at the University of Southern California and spawned the field with his paper, "Molecular Computation of Solutions of Combinatorial Problems." Since then, Adleman has demonstrated how the massive parallelism of a trillion DNA strands can simultaneously attack different aspects of a computation to crack even the toughest combinatorial problems.
Adleman's Traveling Salesman Problem:
The objective is to find a path from start to end going through all the points only once. This problem is difficult for conventional computers to solve because it is a "non-deterministic polynomial time problem" . These problems, when they involve large numbers, are intractable with conventional computers, but can be solved using massively parallel computers like DNA computers. The Hamiltonian Path problem was chosen by Adleman because it is known problem.
The following algorithm solves the Hamiltonian Path problem:
1.Generate random paths through the graph.
2.Keep only those paths that begin with the start city (A) and conclude with the
end city (G).
3.If the graph has n cities, keep only those paths with n cities. (n=7)
4.Keep only those paths that enter all cities at least once.
5.Any remaining paths are solutions.
The key was using DNA to perform the five steps in the above algorithm. Adleman's first step was to synthesize DNA strands of known sequences, each strand 20 nucleotides long. He represented each of the six vertices of the path by a separate strand, and further represented each edge between two consecutive vertices, such as 1 to 2, by a DNA strand which consisted of the last ten nucleotides of the strand representing vertex 1 plus the first 10 nucleotides of the vertex 2 strand. Then, through the sheer amount of DNA molecules (3x1013 copies for each edge in this experiment!) joining together in all possible combinations, many random paths were generated. Adleman used well-established techniques of molecular biology to weed out the Hamiltonian path, the one that entered all vertices, starting at one and ending at six. After generating the numerous random paths in the first step, he used polymerase chain reaction (PCR) to amplify and keep only the paths that began on vertex 1 and ended at vertex 6. The next two steps kept only those strands that passed through six vertices, entering each vertex at least once. At this point, any paths that remained would code for a Hamiltonian path, thus solving the problem.
Molecular computing is an emerging field to which chemistry, biophysics, molecular biology, electronic engineering, solid state physics and computer science contribute to a large extent. It involves the encoding, manipulation and retrieval of information at a macromolecular level in contrast to the current techniques, which accomplish the above functions via IC miniaturization of bulk devices. The biological systems have unique abilities such as pattern recognition, learning, self-assembly and self-reproduction as well as high speed and parallel information processing. The aim of this article is to exploit these characteristics to build computing systems, which have many advantages over their inorganic (Si,Ge) counterparts.
DNA computing began in 1994 when Leonard Adleman proved thatDNA computing was possible by finding a solution to a real- problem, a Hamiltonian Path Problem, known to us as the Traveling Salesman Problem,with a molecular computer. In theoretical terms, some scientists say the actual beginnings of DNA computation should be attributed to Charles Bennett's work. Adleman, now considered the father of DNA computing, is a professor at the University of Southern California and spawned the field with his paper, "Molecular Computation of Solutions of Combinatorial Problems." Since then, Adleman has demonstrated how the massive parallelism of a trillion DNA strands can simultaneously attack different aspects of a computation to crack even the toughest combinatorial problems.
Adleman's Traveling Salesman Problem:
The objective is to find a path from start to end going through all the points only once. This problem is difficult for conventional computers to solve because it is a "non-deterministic polynomial time problem" . These problems, when they involve large numbers, are intractable with conventional computers, but can be solved using massively parallel computers like DNA computers. The Hamiltonian Path problem was chosen by Adleman because it is known problem.
The following algorithm solves the Hamiltonian Path problem:
1.Generate random paths through the graph.
2.Keep only those paths that begin with the start city (A) and conclude with the
end city (G).
3.If the graph has n cities, keep only those paths with n cities. (n=7)
4.Keep only those paths that enter all cities at least once.
5.Any remaining paths are solutions.
The key was using DNA to perform the five steps in the above algorithm. Adleman's first step was to synthesize DNA strands of known sequences, each strand 20 nucleotides long. He represented each of the six vertices of the path by a separate strand, and further represented each edge between two consecutive vertices, such as 1 to 2, by a DNA strand which consisted of the last ten nucleotides of the strand representing vertex 1 plus the first 10 nucleotides of the vertex 2 strand. Then, through the sheer amount of DNA molecules (3x1013 copies for each edge in this experiment!) joining together in all possible combinations, many random paths were generated. Adleman used well-established techniques of molecular biology to weed out the Hamiltonian path, the one that entered all vertices, starting at one and ending at six. After generating the numerous random paths in the first step, he used polymerase chain reaction (PCR) to amplify and keep only the paths that began on vertex 1 and ended at vertex 6. The next two steps kept only those strands that passed through six vertices, entering each vertex at least once. At this point, any paths that remained would code for a Hamiltonian path, thus solving the problem.
Worldwide Inter operatibility for Microwave Access
Introduction
In recent years, Broadband technology has rapidly become an established, global commodity required by a high percentage of the population. The demand has risen rapidly, with a worldwide installed base of 57 million lines in 2002 rising to an estimated 80 million lines by the end of 2003. This healthy growth curve is expected to continue steadily over the next few years and reach the 200 million mark by 2006. DSL operators, who initially focused their deployments in densely-populated urban and metropolitan areas, are now challenged to provide broadband services in suburban and rural areas where new markets are quickly taking root. Governments are prioritizing broadband as a key political objective for all citizens to overcome the "broadband gap" also known as "digital divide".
Wireless DSL (WDSL) offers an effective, complementary solution to wireline DSL, allowing DSL operators to provide broadband service to additional areas and populations that would otherwise find themselves outside the broadband loop. Government regulatory bodies are realizing the inherent worth in wireless technologies as a means for solving digital-divide challenges in the last mile and have accordingly initiated a deregulation process in recent years for both licensed and unlicensed bands to support this application. Recent technological advancements and the formation of a global standard and interoperability forum - WiMAX, set the stage for WDSL to take a significant role in the broadband market. Revenues from services delivered via Broadband Wireless Access have already reached $323 million and are expected to jump to $1.75 billion.
E-Mail Newsletters
There are several ways to get a fast Internet connection to the middle of nowhere. Until not too long ago, the only answer would have been "cable" - that is, laying lines. Cable TV companies, who would be the ones to do this, had been weighing the costs and benefits. However this would have taken years for the investment to pay off. So while cable companies might be leading the market for broadband access to most people (of the 41% of Americans who have high-speed Internet access, almost two-thirds get it from their cable company), they don't do as well to rural areas. And governments that try to require cable companies to lay the wires find themselves battling to force the companies to take new customers. Would DSL be a means of achieving this requisite of broadband and bridging the digital divide?
The lines are already there, but the equipment wasn't always the latest and greatest, even then. Sending voice was not a matter of big concern, but upgrading the system to handle DSL would mean upgrading the central offices that would have to handle the data coming from all those farms. The most rattling affair is that there are plenty of places in cities that can't handle DSL, let alone the countryside. Despite this, we'll still read about new projects to lay cable out to smaller communities, either by phone companies, cable companies, or someone else. Is this a waste of money? Probably because cables are on their way out. Another way to get broadband to rural communities is the way many folks get their TV: satellite, which offers download speeds of about 500 Kbps -faster than a modem, but at best half as fast as DSL - through a satellite dish. But you really, really have to want it. The system costs $600 to start, then $60 a month by the services provided by DIRECWAY in the US.
There are other wireless ways to get broadband access.
MCI ("Microwave Communications Inc.") was originally formed to compete with AT & T by using microwave towers to transmit voice signals across the US. Unlike a radio (or a Wi-Fi connection), those towers send the signal in a straight line -unidirectional instead of omni directional. That's sometimes called fixed wireless or point-to-point wireless. One popular standard for this is called LMDS: local multipoint distribution system. Two buildings up to several miles apart would have microwave antennas pointing at each other.
WiMAX:
WiMax delivers broadband to a large area via towers, just like cell phones. This enables your laptop to have high-speed access in any of the hot spots. Instead of yet another cable coming to your home, there would be yet another antenna on the cell-phone tower. This is definitely a point towards broadband service in rural areas.
In recent years, Broadband technology has rapidly become an established, global commodity required by a high percentage of the population. The demand has risen rapidly, with a worldwide installed base of 57 million lines in 2002 rising to an estimated 80 million lines by the end of 2003. This healthy growth curve is expected to continue steadily over the next few years and reach the 200 million mark by 2006. DSL operators, who initially focused their deployments in densely-populated urban and metropolitan areas, are now challenged to provide broadband services in suburban and rural areas where new markets are quickly taking root. Governments are prioritizing broadband as a key political objective for all citizens to overcome the "broadband gap" also known as "digital divide".
Wireless DSL (WDSL) offers an effective, complementary solution to wireline DSL, allowing DSL operators to provide broadband service to additional areas and populations that would otherwise find themselves outside the broadband loop. Government regulatory bodies are realizing the inherent worth in wireless technologies as a means for solving digital-divide challenges in the last mile and have accordingly initiated a deregulation process in recent years for both licensed and unlicensed bands to support this application. Recent technological advancements and the formation of a global standard and interoperability forum - WiMAX, set the stage for WDSL to take a significant role in the broadband market. Revenues from services delivered via Broadband Wireless Access have already reached $323 million and are expected to jump to $1.75 billion.
E-Mail Newsletters
There are several ways to get a fast Internet connection to the middle of nowhere. Until not too long ago, the only answer would have been "cable" - that is, laying lines. Cable TV companies, who would be the ones to do this, had been weighing the costs and benefits. However this would have taken years for the investment to pay off. So while cable companies might be leading the market for broadband access to most people (of the 41% of Americans who have high-speed Internet access, almost two-thirds get it from their cable company), they don't do as well to rural areas. And governments that try to require cable companies to lay the wires find themselves battling to force the companies to take new customers. Would DSL be a means of achieving this requisite of broadband and bridging the digital divide?
The lines are already there, but the equipment wasn't always the latest and greatest, even then. Sending voice was not a matter of big concern, but upgrading the system to handle DSL would mean upgrading the central offices that would have to handle the data coming from all those farms. The most rattling affair is that there are plenty of places in cities that can't handle DSL, let alone the countryside. Despite this, we'll still read about new projects to lay cable out to smaller communities, either by phone companies, cable companies, or someone else. Is this a waste of money? Probably because cables are on their way out. Another way to get broadband to rural communities is the way many folks get their TV: satellite, which offers download speeds of about 500 Kbps -faster than a modem, but at best half as fast as DSL - through a satellite dish. But you really, really have to want it. The system costs $600 to start, then $60 a month by the services provided by DIRECWAY in the US.
There are other wireless ways to get broadband access.
MCI ("Microwave Communications Inc.") was originally formed to compete with AT & T by using microwave towers to transmit voice signals across the US. Unlike a radio (or a Wi-Fi connection), those towers send the signal in a straight line -unidirectional instead of omni directional. That's sometimes called fixed wireless or point-to-point wireless. One popular standard for this is called LMDS: local multipoint distribution system. Two buildings up to several miles apart would have microwave antennas pointing at each other.
WiMAX:
WiMax delivers broadband to a large area via towers, just like cell phones. This enables your laptop to have high-speed access in any of the hot spots. Instead of yet another cable coming to your home, there would be yet another antenna on the cell-phone tower. This is definitely a point towards broadband service in rural areas.
AC Performance Of Nanoelectronics
Definition
Nano electronic devices fall into two classes: tunnel devices and ballistic transport devices. In Tunnel devices single electron effects occur if the tunnel resistance is larger than h/e = 25 K §Ù. In Ballistic devices with cross sectional dimensions in the range of quantum mechanical wavelength of electrons, the resistance is of order h/e = 25 K §Ù. This high resistance may seem to restrict the operational speed of nano electronics in general. However the capacitance values and drain source spacing are typically small which gives rise to very small RC times and transit times of order of ps or less. Thus the speed may be very large, up to THz range. The goal of this seminar is to present the models an performance predictions about the effects that set the speed limit in carbon nanotube transistors, which form the ideal test bed for understanding the high frequency properties of Nano electronics because they may behave as ideal ballistic 1d transistors.
Ballistic Transport- An Outline
When carriers travel through a semiconductor material, they are likely to be scattered by any number of possible sources, including acoustic and optical phonons, ionized impurities, defects, interfaces, and other carriers. If, however, the distance traveled by the carrier is smaller than the mean free path, it is likely not to encounter any scattering events; it can, as a result, move ballistically through the channel. To the first order, the existence of ballistic transport in a MOSFET depends on the value of the characteristic scattering length (i.e. mean free path) in relation to channel length of the transistor.
This scattering length, l , can be estimated from the measured carrier mobility where t is the average scattering time, m* is the carrier effective mass, and vth is the thermal velocity. Because scattering mechanisms determine the extent of ballistic transport, it is important to understand how these depend upon operating conditions such as normal electric field and ambient temperature.
Dependence On Normal Electric Field
In state-of-the-art MOSFET inversion layers, carrier scattering is dominated by phonons, impurities (Coulomb interaction), and surface roughness scattering at the Si-SiO2 interface. The relative importance of each scattering mechanism is dependent on the effective electric field component normal to the conduction channel. At low fields, impurity scattering dominates due to strong Coulombic interactions between the carriers and the impurity centers. As the electric field is increased, acoustic phonons begin to dominate the scattering process. At very high fields, carriers are pulled closer to the Si-SiO2 gate oxide interface; thus, surface roughness scattering degrades carrier mobility. A universal mobility model has been developed to relate field strength with the effective carrier mobility due to phonon and surface roughness scattering:
Dependence On Temperature
When the temperature is changed, the relative importance of each of the aforementioned scattering mechanisms is altered. Phonon scattering becomes less important at very low temperatures. Impurity scattering, on the other hand, becomes more significant because carriers are moving slower (thermal velocity is decreased) and thus have more time to interact with impurity centers. Surface roughness scattering remains the same because it does not depend on temperature. At liquid nitrogen temperatures (77K) and an effective electric field of 1MV/cm, the electron and hole mobilities are ~700 cm2/Vsec and ~100 cm2/Vsec, respectively. Using the above equations, the scattering lengths are approximately 17nm and 3.6nm.These scattering lengths can be assumed to be worst-case scenarios, as large operating voltages (1V) and aggressively scaled gate oxides (10Å) are assumed. Thus, actual scattering lengths will likely be larger than the calculated values.
Further device design considerations in maximizing this scattering length will be discussed in the last section of this paper. Still, the values calculated above are certainly in the range of transistor gate lengths currently being studied in advanced MOSFET research (<50nm).>
To accurately determine the extent of ballistic transport evident in a particular transistor structure, Monte Carlo simulation methods must be employed. Only by modeling the random trajectory of each carrier traveling through the channel can we truly assess the extent of ballistic transport in a MOSFET.
Nano electronic devices fall into two classes: tunnel devices and ballistic transport devices. In Tunnel devices single electron effects occur if the tunnel resistance is larger than h/e = 25 K §Ù. In Ballistic devices with cross sectional dimensions in the range of quantum mechanical wavelength of electrons, the resistance is of order h/e = 25 K §Ù. This high resistance may seem to restrict the operational speed of nano electronics in general. However the capacitance values and drain source spacing are typically small which gives rise to very small RC times and transit times of order of ps or less. Thus the speed may be very large, up to THz range. The goal of this seminar is to present the models an performance predictions about the effects that set the speed limit in carbon nanotube transistors, which form the ideal test bed for understanding the high frequency properties of Nano electronics because they may behave as ideal ballistic 1d transistors.
Ballistic Transport- An Outline
When carriers travel through a semiconductor material, they are likely to be scattered by any number of possible sources, including acoustic and optical phonons, ionized impurities, defects, interfaces, and other carriers. If, however, the distance traveled by the carrier is smaller than the mean free path, it is likely not to encounter any scattering events; it can, as a result, move ballistically through the channel. To the first order, the existence of ballistic transport in a MOSFET depends on the value of the characteristic scattering length (i.e. mean free path) in relation to channel length of the transistor.
This scattering length, l , can be estimated from the measured carrier mobility where t is the average scattering time, m* is the carrier effective mass, and vth is the thermal velocity. Because scattering mechanisms determine the extent of ballistic transport, it is important to understand how these depend upon operating conditions such as normal electric field and ambient temperature.
Dependence On Normal Electric Field
In state-of-the-art MOSFET inversion layers, carrier scattering is dominated by phonons, impurities (Coulomb interaction), and surface roughness scattering at the Si-SiO2 interface. The relative importance of each scattering mechanism is dependent on the effective electric field component normal to the conduction channel. At low fields, impurity scattering dominates due to strong Coulombic interactions between the carriers and the impurity centers. As the electric field is increased, acoustic phonons begin to dominate the scattering process. At very high fields, carriers are pulled closer to the Si-SiO2 gate oxide interface; thus, surface roughness scattering degrades carrier mobility. A universal mobility model has been developed to relate field strength with the effective carrier mobility due to phonon and surface roughness scattering:
Dependence On Temperature
When the temperature is changed, the relative importance of each of the aforementioned scattering mechanisms is altered. Phonon scattering becomes less important at very low temperatures. Impurity scattering, on the other hand, becomes more significant because carriers are moving slower (thermal velocity is decreased) and thus have more time to interact with impurity centers. Surface roughness scattering remains the same because it does not depend on temperature. At liquid nitrogen temperatures (77K) and an effective electric field of 1MV/cm, the electron and hole mobilities are ~700 cm2/Vsec and ~100 cm2/Vsec, respectively. Using the above equations, the scattering lengths are approximately 17nm and 3.6nm.These scattering lengths can be assumed to be worst-case scenarios, as large operating voltages (1V) and aggressively scaled gate oxides (10Å) are assumed. Thus, actual scattering lengths will likely be larger than the calculated values.
Further device design considerations in maximizing this scattering length will be discussed in the last section of this paper. Still, the values calculated above are certainly in the range of transistor gate lengths currently being studied in advanced MOSFET research (<50nm).>
To accurately determine the extent of ballistic transport evident in a particular transistor structure, Monte Carlo simulation methods must be employed. Only by modeling the random trajectory of each carrier traveling through the channel can we truly assess the extent of ballistic transport in a MOSFET.
Computer Forensics
Definition
The proliferation of computer use in today's networked society is creating some complex side effects in the application of the age-old greed, jealousy, and revenge. Criminals are becoming much more sophisticated in committing crimes. Computers are being encountered in almost every type of criminal activity. Gangs use computers to clone mobile telephones and to re-encode credit cards. Drug dealers use computers to store their transaction ledgers. Child pornography distributors use the Internet to peddle and trade their wares. Fraud schemes have been advertised on the Internet. Counterfeiters and forgers use computers to make passable copies of paper currency or counterfeit cashiers checks, and to create realistic looking false identification.
In addition, information stored in computers has become the target of criminal activity. Information such as social security and credit card numbers, intellectual property, proprietary information, contract information, classified documents, etc., have been targeted. Further, the threat of malicious destruction of software, employee sabotage, identity theft, blackmail, sexual harassment, and commercial and government espionage is on the rise. Personnel problems are manifesting themselves in the automated environment with inappropriate or unauthorized use complaints resulting in lawsuits against employers as well as loss of proprietary information costing millions of dollars. All of this has led to an explosion in the number and complexity of computers and computer systems encountered in the course of criminal or internal investigations and the subsequent seizure of computer systems and stored electronic communications.
Computer evidence has become a 'fact of life' for essentially all law enforcement agencies and many are just beginning to explore their options in dealing with this new venue. Almost overnight, personal computers have changed the way the world does business. They have also changed the world's view of evidence because computers are used more and more as tools in the commission of 'traditional' crimes. Evidence relative to embezzlement, theft, extortion and even murder has been discovered on personal computers. This new technology twist in crime patterns has brought computer evidence to the forefront in law enforcement circles.
Computer forensics is simply the application of disciplined investigative techniques in the automated environment and the search, discovery, and analysis of potential evidence. It is the method used to investigate and analyze data maintained on or retrieved from electronic data storage media for the purposes of presentation in a court of law, civil or administrative proceeding. Evidence may be sought in a wide range of computer crime or misuse cases.Computer forensics is rapidly becoming a science recognized on a par with other forensic sciences by the legal and law enforcement communities. As this trend continues, it will become even more important to handle and examine computer evidence properly. Not every department or organization has the resources to have trained computer forensic specialists on staff.
Computer Forensic Process
As in any investigation, establishing that an incident has occurred is the first key step. Secondly, the incident needs to be evaluated to determine if computer forensics may be required. Generally, if the computer incident resulted in a loss of time or money, or the destruction or compromise of information, it will require the application of computer forensic investigative techniques. When applied, the preservation of evidence is the first rule in the process. Failure to preserve evidence in its original state could jeopardize the entire investigation. Knowledge of how the crime was initiated and committed may be lost for good. Assignment of responsibility may not be possible if evidence is not meticulously and diligently preserved.The level of training and expertise required to execute a forensics task will largely depend on the level of evidence required in the case. If the result of the investigation were limited to administrative actions against an employee, the requirement would be lower than taking the case to court for civil or criminal litigation.
The proliferation of computer use in today's networked society is creating some complex side effects in the application of the age-old greed, jealousy, and revenge. Criminals are becoming much more sophisticated in committing crimes. Computers are being encountered in almost every type of criminal activity. Gangs use computers to clone mobile telephones and to re-encode credit cards. Drug dealers use computers to store their transaction ledgers. Child pornography distributors use the Internet to peddle and trade their wares. Fraud schemes have been advertised on the Internet. Counterfeiters and forgers use computers to make passable copies of paper currency or counterfeit cashiers checks, and to create realistic looking false identification.
In addition, information stored in computers has become the target of criminal activity. Information such as social security and credit card numbers, intellectual property, proprietary information, contract information, classified documents, etc., have been targeted. Further, the threat of malicious destruction of software, employee sabotage, identity theft, blackmail, sexual harassment, and commercial and government espionage is on the rise. Personnel problems are manifesting themselves in the automated environment with inappropriate or unauthorized use complaints resulting in lawsuits against employers as well as loss of proprietary information costing millions of dollars. All of this has led to an explosion in the number and complexity of computers and computer systems encountered in the course of criminal or internal investigations and the subsequent seizure of computer systems and stored electronic communications.
Computer evidence has become a 'fact of life' for essentially all law enforcement agencies and many are just beginning to explore their options in dealing with this new venue. Almost overnight, personal computers have changed the way the world does business. They have also changed the world's view of evidence because computers are used more and more as tools in the commission of 'traditional' crimes. Evidence relative to embezzlement, theft, extortion and even murder has been discovered on personal computers. This new technology twist in crime patterns has brought computer evidence to the forefront in law enforcement circles.
Computer forensics is simply the application of disciplined investigative techniques in the automated environment and the search, discovery, and analysis of potential evidence. It is the method used to investigate and analyze data maintained on or retrieved from electronic data storage media for the purposes of presentation in a court of law, civil or administrative proceeding. Evidence may be sought in a wide range of computer crime or misuse cases.Computer forensics is rapidly becoming a science recognized on a par with other forensic sciences by the legal and law enforcement communities. As this trend continues, it will become even more important to handle and examine computer evidence properly. Not every department or organization has the resources to have trained computer forensic specialists on staff.
Computer Forensic Process
As in any investigation, establishing that an incident has occurred is the first key step. Secondly, the incident needs to be evaluated to determine if computer forensics may be required. Generally, if the computer incident resulted in a loss of time or money, or the destruction or compromise of information, it will require the application of computer forensic investigative techniques. When applied, the preservation of evidence is the first rule in the process. Failure to preserve evidence in its original state could jeopardize the entire investigation. Knowledge of how the crime was initiated and committed may be lost for good. Assignment of responsibility may not be possible if evidence is not meticulously and diligently preserved.The level of training and expertise required to execute a forensics task will largely depend on the level of evidence required in the case. If the result of the investigation were limited to administrative actions against an employee, the requirement would be lower than taking the case to court for civil or criminal litigation.
Next Generation Secure Computing Base
INTRODUCTION
Microsoft's next-generation secure computing base aims to provide robust access control while retaining the openness of personal computers. Unlike closed systems, an NGSCB platform can run any software, but it provides mechanisms that allow operating systems and applications to protect themselves against other software running on the same machine. For example, it can make home finance data inaccessible to programs that the user has not specifically authorized.
To enable this mode of operation, NGSCB platforms implement
" Isolation among operating systems and among processes. OS isolation is related to virtual machine monitors. However, some key NGSCB innovations make it more robust than traditional VMMs by enabling a small machine monitor to isolate itself and other high-assurance components from the basic input/output system (BIOS), device drivers, and bus master devices.
" Hardware and software security primitives that allow software modules to keep secrets and authenticate themselves to local and remote entities. These primitives maintain the trustworthiness of OS access protections without preventing the platform from booting other operating systems.
We refer to a security regimen that allows any software to run but requires it to be identified in access-control decisions as authenticated operation, and we call a hardware-software platform that supports authenticated operation a trusted open system.
A variety of commercial requirements and security goals guided the NGSCB system design. The main commercial requirement was for an open architecture that allows arbitrary hardware peripherals to be added to the platform and arbitrary software to execute without involving a central authority. Furthermore, the system had to operate in the legacy environment of personal computers. While we introduced changes to core platform components, most of the PC architecture remained unmodified. The system had to be compatible with the majority of existing peripherals. Finally, the hardware changes had to be such that they would not have a significant impact on PC production costs.
Our main security goal was assurance. Assurance is not any particular security function. It refers to the degree of confidence the owner of a system can have in its correct behavior especially in the presence of attacks. A further goal was to enable authenticated operation.
The hardware platforms are not required to provide protection against hardware tampering. Protection against tampering costs money, and it is clear that most security attacks facing users are launched by malicious software, or are remotely launched and exploit bugs in otherwise benign software. However, we anticipate platforms will be deployed that are also robust against hardware attacks, especially in high-security corporate and government settings.
AUTHENTICATED OPERATION
Traditional access-control systems protect data against unauthorized access through an authentication mechanism such as a password, biometric data, or smart card. Each access request triggers a system component, the guard, that is part of the trusted computing base. The guard grants or denies access, and can audit access requests according to the user, the request, and the system's access-control policy.
Authenticated operation bases access-control decisions in part on the identity of the program making a request. For example, a user can restrict access to files containing financial data to only certain authorized programs.
It is straightforward to extend most existing user-based access-control systems to code-based access models. For example, a resource can have an access-control list that grants access only to a list of programs rather than to users who run these programs. We expect that most systems built to support authenticated operation will base access-control decisions on both program and user resource requests
Microsoft's next-generation secure computing base aims to provide robust access control while retaining the openness of personal computers. Unlike closed systems, an NGSCB platform can run any software, but it provides mechanisms that allow operating systems and applications to protect themselves against other software running on the same machine. For example, it can make home finance data inaccessible to programs that the user has not specifically authorized.
To enable this mode of operation, NGSCB platforms implement
" Isolation among operating systems and among processes. OS isolation is related to virtual machine monitors. However, some key NGSCB innovations make it more robust than traditional VMMs by enabling a small machine monitor to isolate itself and other high-assurance components from the basic input/output system (BIOS), device drivers, and bus master devices.
" Hardware and software security primitives that allow software modules to keep secrets and authenticate themselves to local and remote entities. These primitives maintain the trustworthiness of OS access protections without preventing the platform from booting other operating systems.
We refer to a security regimen that allows any software to run but requires it to be identified in access-control decisions as authenticated operation, and we call a hardware-software platform that supports authenticated operation a trusted open system.
A variety of commercial requirements and security goals guided the NGSCB system design. The main commercial requirement was for an open architecture that allows arbitrary hardware peripherals to be added to the platform and arbitrary software to execute without involving a central authority. Furthermore, the system had to operate in the legacy environment of personal computers. While we introduced changes to core platform components, most of the PC architecture remained unmodified. The system had to be compatible with the majority of existing peripherals. Finally, the hardware changes had to be such that they would not have a significant impact on PC production costs.
Our main security goal was assurance. Assurance is not any particular security function. It refers to the degree of confidence the owner of a system can have in its correct behavior especially in the presence of attacks. A further goal was to enable authenticated operation.
The hardware platforms are not required to provide protection against hardware tampering. Protection against tampering costs money, and it is clear that most security attacks facing users are launched by malicious software, or are remotely launched and exploit bugs in otherwise benign software. However, we anticipate platforms will be deployed that are also robust against hardware attacks, especially in high-security corporate and government settings.
AUTHENTICATED OPERATION
Traditional access-control systems protect data against unauthorized access through an authentication mechanism such as a password, biometric data, or smart card. Each access request triggers a system component, the guard, that is part of the trusted computing base. The guard grants or denies access, and can audit access requests according to the user, the request, and the system's access-control policy.
Authenticated operation bases access-control decisions in part on the identity of the program making a request. For example, a user can restrict access to files containing financial data to only certain authorized programs.
It is straightforward to extend most existing user-based access-control systems to code-based access models. For example, a resource can have an access-control list that grants access only to a list of programs rather than to users who run these programs. We expect that most systems built to support authenticated operation will base access-control decisions on both program and user resource requests
Computer Intelligence Applications
INTRODUCTION
The word 'robot' evokes many different thoughts and images, perhaps conflicting ones. Some may think of a metal humanoid, others of an industrial arm, and yet more may think, unfortunately, of a lost job. In the field of medical robotics, the word robot is just as fuzzily defined, with many different applications. These range from simplistic laboratory robots, to highly complex surgical robots that can either aid a human surgeon or execute operations by themselves.
The idea of robotics in surgery got its start in the military. The idea was to develop technology where a surgeon could perform an operation from a remote location on an injured soldier in the battlefield. This concept has evolved into robotics to enhance surgical performance. In this instance, a robotic arm called Endowrist performs the procedure with the surgeon guiding the robotic arm from a location in or adjacent to the operating room. The surgeon sits at a station peering at a monitor that shows a magnified view of the surgical field. A computer mimics and enhances his hand movements. The computer in this instance makes the movements more precise by dampening even a tiny tremor in the surgeon's hands, which might increase the difficulty in performing procedures under high power microscopic magnification. Examples of such procedures now being performed that were extremely difficult if not impossible before this technology are fallopian tube repair in women, microsurgery on the fetus, and minimally invasive coronary bypass surgery. The Zeus robot made by Computer Motion and a similar device, the Endowrist made by Intuitive Surgical are now in clinical trials for the above-mentioned procedures. Even with the robot to enhance the surgeon's ability, a great deal of practice is required to master the technique.
The reasons behind the interest in the adoption of medical robots are multitudinous. There is a great analogy to be found with the automation involved in the manufacturing industry. That is not to say that the issues of medical robotics are the same, but that the advantages to be gained are similar. Robots provide industry with something that is, to them, more valuable than even the most dedicated and hard-working employee - namely speed, accuracy, repeatability, reliability, and cost-efficiency. A robotic aid, for example, one that holds a viewing instrument for a surgeon, will not become fatigued, for however long it is used. It will position the instrument accurately with no tremor, and it will be able to perform just as well on the 100th occasion as it did on the first. The use of robotics and computers in minimally invasive spine surgery has resulted in more accurate surgical procedures, shortened operative time and fewer complications. It is expected that Computer Enhanced Image Guidance Systems will improve the precision of these procedures as a result of real time 3-D imaging at the time of the surgery. Diagnostic studies will be digitally transmitted to the operating room and projected to monitors to further aid the surgeon in performing the correct procedure with minimal trauma to the patient
SURGICAL NAVIGATION SYSTEM
A surgical navigation system has been built that is currently used regularly for neurosurgical cases such as tumor resection at Brigham and Women's Hospital. The system consists of a portable cart containing a Sun UltraSPARC workstation and the hardware to drive the laser scanner and Flashpoint tracking system (Image Guided Technologies, Boulder, CO). On top of the cart is mounted an articulated extendible arm to which a bar is attached to house the laser scanner and Flashpoint cameras. The three linear Flashpoint cameras are inside the bar. The laser is attached to one end of the bar, and a video camera to the other. The joint between the arm and scanning bar has three degrees-of-freedom to allow easy placement of the bar in desired configurations
The word 'robot' evokes many different thoughts and images, perhaps conflicting ones. Some may think of a metal humanoid, others of an industrial arm, and yet more may think, unfortunately, of a lost job. In the field of medical robotics, the word robot is just as fuzzily defined, with many different applications. These range from simplistic laboratory robots, to highly complex surgical robots that can either aid a human surgeon or execute operations by themselves.
The idea of robotics in surgery got its start in the military. The idea was to develop technology where a surgeon could perform an operation from a remote location on an injured soldier in the battlefield. This concept has evolved into robotics to enhance surgical performance. In this instance, a robotic arm called Endowrist performs the procedure with the surgeon guiding the robotic arm from a location in or adjacent to the operating room. The surgeon sits at a station peering at a monitor that shows a magnified view of the surgical field. A computer mimics and enhances his hand movements. The computer in this instance makes the movements more precise by dampening even a tiny tremor in the surgeon's hands, which might increase the difficulty in performing procedures under high power microscopic magnification. Examples of such procedures now being performed that were extremely difficult if not impossible before this technology are fallopian tube repair in women, microsurgery on the fetus, and minimally invasive coronary bypass surgery. The Zeus robot made by Computer Motion and a similar device, the Endowrist made by Intuitive Surgical are now in clinical trials for the above-mentioned procedures. Even with the robot to enhance the surgeon's ability, a great deal of practice is required to master the technique.
The reasons behind the interest in the adoption of medical robots are multitudinous. There is a great analogy to be found with the automation involved in the manufacturing industry. That is not to say that the issues of medical robotics are the same, but that the advantages to be gained are similar. Robots provide industry with something that is, to them, more valuable than even the most dedicated and hard-working employee - namely speed, accuracy, repeatability, reliability, and cost-efficiency. A robotic aid, for example, one that holds a viewing instrument for a surgeon, will not become fatigued, for however long it is used. It will position the instrument accurately with no tremor, and it will be able to perform just as well on the 100th occasion as it did on the first. The use of robotics and computers in minimally invasive spine surgery has resulted in more accurate surgical procedures, shortened operative time and fewer complications. It is expected that Computer Enhanced Image Guidance Systems will improve the precision of these procedures as a result of real time 3-D imaging at the time of the surgery. Diagnostic studies will be digitally transmitted to the operating room and projected to monitors to further aid the surgeon in performing the correct procedure with minimal trauma to the patient
SURGICAL NAVIGATION SYSTEM
A surgical navigation system has been built that is currently used regularly for neurosurgical cases such as tumor resection at Brigham and Women's Hospital. The system consists of a portable cart containing a Sun UltraSPARC workstation and the hardware to drive the laser scanner and Flashpoint tracking system (Image Guided Technologies, Boulder, CO). On top of the cart is mounted an articulated extendible arm to which a bar is attached to house the laser scanner and Flashpoint cameras. The three linear Flashpoint cameras are inside the bar. The laser is attached to one end of the bar, and a video camera to the other. The joint between the arm and scanning bar has three degrees-of-freedom to allow easy placement of the bar in desired configurations
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