MICROPROCESSOR AN OVERVIEW A microprocessor is a multipurpose, programmable, clock driven, register based device that takes input and provides output.

MICROPROCESSOR AN OVERVIEW A microprocessor is a multipurpose, programmable,

clock driven, register based device that takes input and provides output. A microprocessor incorporates most or all of the functions of a computer's central processing unit (CPU) on a single integrated circuit (IC, or microchip). The first microprocessors emerged in the early 1970s and were used for electronic calculators, using binary-coded decimal (BCD) arithmetic in 4-bit words. Other embedded uses of 4-bit and 8-bit microprocessors, such as terminals, printers, various kinds of automation etc., followed soon after. Affordable 8-bit microprocessors with 16-bit addressing also led to the first general-purpose microcomputers from the mid-1970s on.

CPU ARCHITECTUREThe processor (really a short form for

microprocessor and also often called the CPU or central processing unit) is the central component of the PC. This vital component is in some way responsible for every single thing the PC does. It determines, at least in part, which operating systems can be used, which software packages the PC can run, how much energy the PC uses, and how stable the system will be, among other things. The processor is also a major determinant of overall system cost: the newer and more powerful the processor, the more expensive the machine will be.

For some years two families of microprocessor dominated the PC industry - Intel's Pentium and the Apple/IBM/Motorola alliance's PowerPC - each CPU being a prime example of the competing CPU architectures of the time, CISC and RISC.

CISC - Complex Instruction Set ComputerCISC is the traditional architecture of a

computer, in which the CPU uses microcode to execute very comprehensive instruction set. These may be variable in length and use all addressing modes, requiring complex circuitry to decode them.

For a number of years, the tendency among computer manufacturers was to build increasingly complex CPUs that had ever-larger sets of instructions. In 1974, John Cocke of IBM Research decided to try an approach that dramatically reduced the number of instructions a chip performed. By the mid-1980s this had led to a number of computer manufacturers reversing the trend by building CPUs capable of executing only a very limited set of instructions.

RISC - Reduced Instruction Set ComputerRISC CPUs keep instruction size constant,

ban the indirect addressing mode and retain only those instructions that can be overlapped and made to execute in one machine cycle or less. One advantage of RISC CPUs is that they can execute their instructions very fast because the instructions are so simple. Another, perhaps more important advantage, is that RISC chips require fewer transistors, which makes them cheaper to design and produce.

CPU Basic StructureCore: The heart of a modem CPU is the

execution unit.The Pentium microprocessor has two parallel integer pipeplines enabling it to read , interpret , exeute and dispatch two instruction simultaneously.

Branch Predictor : The branch predictor unit tries to guess which sequence will be executed each time the program contains a conditional jump, so that the prefetch and decode unit can get instruction ready in advance.

Floating Point: The third execution unit in a pentium microprocessor, where non –integer calculations are performed .

Level 1 Cache: the Pentium has two on –chip caches of 8kb each, one for code and one for data, which are far quicker than the larger external secondary cache (L2 Cache).

Bus Interface: This brings a mixture of code and data in the CPU , seperates the two ready for use and then recombines then and sends them back out.

Moore's law

describes a long-term trend in the history of computing hardware. The number of transistors that can be placed inexpensively on an integrated circuit has doubled approximately every two years. The trend has continued for more than half a century and is not expected to stop until 2015 or later.

Microprocessor Progression: Intel

The first microprocessor to make it into a home

computer was the Intel 8080, a complete 8-bit computer on one chip, introduced in 1974. The first microprocessor to make a real splash in the market was the Intel 8088, introduced in 1979 and incorporated into the IBM PC (which first appeared around 1982).

The Intel 8080 was the first microprocessor in a home computer.

Clock speed is the maximum rate that the chip can be clocked at. Clock speed will make more sense in the next section.

Data Width is the width of the ALU. An 8-bit ALU can add/subtract/multiply/etc. two 8-bit numbers, while a 32-bit ALU can manipulate 32-bit numbers. An 8-bit ALU would have to execute four instructions to add two 32-bit numbers, while a 32-bit ALU can do it in one instruction. In many cases, the external data bus is the same width as the ALU, but not always. The 8088 had a 16-bit ALU and an 8-bit bus, while the modern Pentiums fetch data 64 bits at a time for their 32-bit ALUs.

MIPS stands for "millions of instructions per second" and is a rough measure of the performance of a CPU. Modern CPUs can do so many different things that MIPS ratings lose a lot of their meaning, but you can get a general sense of the relative power of the CPUs from this column.

CPU EvolutionThe 4004 CPU was the forerunner of all of

today's Intel offerings and, to date, all PC processors have been based on the original Intel designs. The first chip used in an IBM PC was Intel's 8088. This was not, at the time it was chosen, the best available CPU, in fact Intel's own 8086 was more powerful and had been released earlier. The 8088 was chosen for reasons of economics: its 8-bit data bus required less costly motherboards than the 16-bit 8086.

More transistors also allow for a technology called pipelining. In a pipelined architecture, instruction execution overlaps. So even though it might take five clock cycles to execute each instruction, there can be five instructions in various stages of execution simultaneously. That way it looks like one instruction completes every clock cycle.

Many modern processors have multiple instruction decoders, each with its own pipeline. This allows for multiple instruction streams, which means that more than one instruction can complete during each clock cycle. This technique can be quite complex to implement, so it takes lots of transistors.

Multi-tasking

Multitasking, in an operating system, is allowing a user to perform more than one computer task (such as the operation of an application program) at a time. The operating system is able to keep track of where you are in these tasks and go from one to the other without losing information. Microsoft Windows 2000, IBM's OS/390, and Linux are examples of operating systems that can do multitasking (almost all of today's operating systems can). When you open your Web browser and then open word at the same time, you are causing the operating system to do multitasking.

A multi-core processor is a processing system composed of two or more independent cores. One can describe it as an integrated circuit to which two or more individual processors (called cores in this sense) have been attached. Manufacturers typically integrate the cores onto a single integrated circuit die (known as a chip multiprocessor or CMP), or onto multiple dies in a single chip package.

A many-core processor is one in which the number of cores is large enough that traditional multi-processor techniques are no longer efficient — this threshold is somewhere in the range of several tens of cores — and probably requires a network on chip.

A multi-core processor is an integrated circuit (IC) to which two or more processors have been attached for enhanced performance, reduced power consumption, and more efficient simultaneous processing of multiple tasks (see parallel processing).

A dual-core processor contains two cores, a quad-core processor contains four cores, and a hexa-core processor contains six cores. A multi-core processor implements multiprocessing in a single physical package. Designers may couple cores in a multi-core device together tightly or loosely. For example, cores may or may not share caches, and they may implement message passing or shared memory inter-core communication methods.

Hyper-threading

Hyper-threading (officially Hyper-Threading Technology, and abbreviated HT Technology, HTT or HT) is Intel's term for its simultaneous multithreading implementation in its Atom, Core i3, Core i5, Core i7, Itanium, Pentium 4 and Xeon CPUs.

Hyper-threading is an Intel-proprietary technology used to improve parallelization of computations (doing multiple tasks at once) performed on PC microprocessors. For each processor core that is physically present, the operating system addresses two virtual processors, and shares the workload between them when possible. Hyper-threading requires not only that the operating system support multiple processors, but also that it be specifically optimised for HTT, and Intel recommends disabling HTT when using operating systems that have not been so optimized.

Intel Pentium 4 processor that incorporates Hyper-Threading Technology

Hyper-threading works by duplicating certain sections of the processor—those that store the architectural state—but not duplicating the main execution resources. This allows a hyper-threading processor to appear as two "logical" processors to the host operating system, allowing the operating system to schedule two threads or processes simultaneously.

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