COMPUTER ARCHITECTURE AND ORGANISATION J.P.HAYS PDF

A processor only understands instructions encoded in some numerical fashion, usually as binary numbers. Software tools, such as compilers , translate those high level languages into instructions that the processor can understand. Besides instructions, the ISA defines items in the computer that are available to a program—e. Instructions locate these available items with register indexes or names and memory addressing modes. The ISA of a computer is usually described in a small instruction manual, which describes how the instructions are encoded.

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A processor only understands instructions encoded in some numerical fashion, usually as binary numbers. Software tools, such as compilers , translate those high level languages into instructions that the processor can understand. Besides instructions, the ISA defines items in the computer that are available to a program—e. Instructions locate these available items with register indexes or names and memory addressing modes. The ISA of a computer is usually described in a small instruction manual, which describes how the instructions are encoded.

Also, it may define short vaguely mnemonic names for the instructions. The names can be recognized by a software development tool called an assembler. An assembler is a computer program that translates a human-readable form of the ISA into a computer-readable form. Disassemblers are also widely available, usually in debuggers and software programs to isolate and correct malfunctions in binary computer programs.

ISAs vary in quality and completeness. A good ISA compromises between programmer convenience how easy the code is to understand , size of the code how much code is required to do a specific action , cost of the computer to interpret the instructions more complexity means more hardware needed to decode and execute the instructions , and speed of the computer with more complex decoding hardware comes longer decode time.

Memory organization defines how instructions interact with the memory, and how memory interacts with itself. During design emulation , emulators can run programs written in a proposed instruction set. Modern emulators can measure size, cost, and speed to determine whether a particular ISA is meeting its goals. Main article: Microarchitecture Computer organization helps optimize performance-based products.

For example, software engineers need to know the processing power of processors. They may need to optimize software in order to gain the most performance for the lowest price. For example, in a SD card, the designers might need to arrange the card so that the most data can be processed in the fastest possible way. Computer organization also helps plan the selection of a processor for a particular project. Multimedia projects may need very rapid data access, while virtual machines may need fast interrupts.

Sometimes certain tasks need additional components as well. For example, a computer capable of running a virtual machine needs virtual memory hardware so that the memory of different virtual computers can be kept separated. Computer organization and features also affect power consumption and processor cost.

Implementation[ edit ] Once an instruction set and micro-architecture have been designed, a practical machine must be developed. This design process is called the implementation. Implementation is usually not considered architectural design, but rather hardware design engineering.

Implementation can be further broken down into several steps: Logic implementation designs the circuits required at a logic-gate level Circuit implementation does transistor -level designs of basic elements e. Physical implementation draws physical circuits. The different circuit components are placed in a chip floorplan or on a board and the wires connecting them are created. Design validation tests the computer as a whole to see if it works in all situations and all timings.

Once the design validation process starts, the design at the logic level are tested using logic emulators. However, this is usually too slow to run realistic test. Most hobby projects stop at this stage. The final step is to test prototype integrated circuits, which may require several redesigns For CPUs , the entire implementation process is organized differently and is often referred to as CPU design.

Design goals[ edit ] The exact form of a computer system depends on the constraints and goals. Computer architectures usually trade off standards, power versus performance, cost, memory capacity, latency latency is the amount of time that it takes for information from one node to travel to the source and throughput.

Sometimes other considerations, such as features, size, weight, reliability, and expandability are also factors. The most common scheme does an in-depth power analysis and figures out how to keep power consumption low while maintaining adequate performance. Performance[ edit ] Modern computer performance is often described in instructions per cycle IPC , which measures the efficiency of the architecture at any clock frequency; a faster IPC rate means the computer is faster.

Older computers had IPC counts as low as 0. Superscalar processors may reach three to five IPC by executing several instructions per clock cycle. This refers to the cycles per second of the main clock of the CPU. However, this metric is somewhat misleading, as a machine with a higher clock rate may not necessarily have greater performance. As a result, manufacturers have moved away from clock speed as a measure of performance. Other factors influence speed, such as the mix of functional units , bus speeds, available memory, and the type and order of instructions in the programs.

There are two main types of speed: latency and throughput. Latency is the time between the start of a process and its completion. Throughput is the amount of work done per unit time. Interrupt latency is the guaranteed maximum response time of the system to an electronic event like when the disk drive finishes moving some data.

Performance is affected by a very wide range of design choices — for example, pipelining a processor usually makes latency worse, but makes throughput better.

Computers that control machinery usually need low interrupt latencies. These computers operate in a real-time environment and fail if an operation is not completed in a specified amount of time. For example, computer-controlled anti-lock brakes must begin braking within a predictable and limited time period after the brake pedal is sensed or else failure of the brake will occur.

Benchmarking takes all these factors into account by measuring the time a computer takes to run through a series of test programs. Often the measured machines split on different measures. For example, one system might handle scientific applications quickly, while another might render video games more smoothly. Main articles: Low-power electronics and Performance per watt Power efficiency is another important measurement in modern computers.

A higher power efficiency can often be traded for lower speed or higher cost. Modern circuits have less power required per transistor as the number of transistors per chip grows.

However the number of transistors per chip is starting to increase at a slower rate. Therefore, power efficiency is starting to become as important, if not more important than fitting more and more transistors into a single chip.

Recent processor designs have shown this emphasis as they put more focus on power efficiency rather than cramming as many transistors into a single chip as possible. Shifts in market demand[ edit ] Increases in clock frequency have grown more slowly over the past few years, compared to power reduction improvements.

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