KNOW ABOUT PROCESSORS PC MAINTENANCE

MOTHERBOARDS AND COMPONENTS

1. PROCESSORS

The computer will not run without a CPU. The CPU is often referred to as the

brains of a computer. On the motherboard, the CPU is contained on a single

integrated circuit called the microprocessor. The CPU contains two basic

components, a control unit and an Arithmetic/Logical Unit (ALU).

A control unit instructs the computer system on how to follow the program

instructions. It directs the movement of data to and from processor memory. The

control unit temporarily holds data, instructions, and processed information in its

arithmetic/logic unit. In addition, it directs control signals between the CPU and

external devices such as hard disks, main memory, and I/O ports.

The Arithmetic/Logic Unit (ALU) performs both arithmetic and logical operations.

Arithmetic operations are fundamental math operations like addition, subtraction,

multiplication, and division. Logical operations such as the AND, OR, and XOR

are used to make comparisons and decisions. Logical operations determine how

a program is executed.

The processor handles most of the operations that are required of the computer

by processing instructions, sending signals out, checking for connectivity, and

ensuring that operations and hardware are functioning properly. The processor

acts as a messenger to components such as the RAM, the monitor, and the disk

drives.

The microprocessor is connected to the rest of the computer system through

three buses. The buses are the data bus, the address bus, and the control bus.

External Data Bus - Wires on the motherboard used by the CPU to communicate with

peripherals and ROM. Address Bus - Wires on the motherboard used by the CPU to

communicate and access memory through the Memory Controller Chip (MCC). How

much memory a CPU can access depends on how many wires are in the address bus.

Control Unit - The control unit is the circuitry that controls the flow of information

through the processor, and coordinates the activities of the other units within it.

There are many different companies that produce CPUs. They include Intel,

Advanced Micro Devices (AMD), and Cyrix. Intel is credited with making the first

modern, silicon-based CPU chip in 1971.

ROLES

• Performance: The processor is probably the most important single determinant

of system performance in the PC. While other components also play a key role in

determining performance, the processor's capabilities dictate the maximum

performance of a system. The other devices only allow the processor to reach its

full potential.

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• Software Support: Newer, faster processors enable the use of the latest software.

In addition, new processors such as the Pentium with MMX Technology, enable

the use of specialized software not usable on earlier machines.

• Reliability and Stability: The quality of the processor is one factor that

determines how reliably your system will run. While most processors are very

dependable, some are not. This also depends to some extent on the age of the

processor and how much energy it consumes.

• Energy Consumption and Cooling: Originally processors consumed relatively

little power compared to other system devices. Newer processors can consume a

great deal of power. Power consumption has an impact on everything from

cooling method selection to overall system reliability.

• Motherboard Support: The processor you decide to use in your system will be a

major determining factor in what sort of chipset you must use, and hence what

motherboard you buy. The motherboard in turn dictates many facets of your

system's capabilities and performance.

Native Execution Steps

Native execution processors are those that run standard x86 code directly, without

translation to RISC-like micro-instructions. The actual stages used in execution vary by

the individual processor, with some more advanced ones using more, smaller steps than

others. However, they basically follow the same general path through the processor.

These are the main steps followed; note that they are normally pipelined in a modern

CPU:

• Fetch: The first step is to load the instruction into the execution unit so it can be

executed. Since memory is so slow compared to the processor, this stage doesn't

involve a direct read from memory. Rather, special control circuitry loads larger

blocks (16 or 32 bytes) of instruction data from memory and into the primary

instruction cache. This data is then available for rapid feeding to the execution

units as needed. Some processors have prefetch units that do this.

• Decode: The decode stage is used to examine the instruction loaded and

determine how large it is, whether or not it requires an access to memory to read

data for execution, etc. Some processors employ multiple decoders to increase

performance.

• Address Generate: Some instructions operate on memory locations while others

do not. For those that access memory, the address of the location is generated in

this stage based on information given as part of the instruction.

• Execute: The instruction is actually executed here, based on information

processed from the earlier steps.

• Write-Back: After the instruction is executed, it produces some sort of a result.

In this stage, the results is written back either to an internal register or the system

memory. Again, system memory is very slow so the result isn't really written to it

directly but rather to a write buffer, where it is held until it can be written to

system memory or the cache.

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The CPU executes a program, which is a sequence of stored instructions. Each model of

processor has an instruction set, which it executes. The CPU executes the program by

processing each piece of data as directed by the program and the instruction set. While

the CPU is executing one step of the program, the remaining instructions and the data are

stored nearby in a special memory called cache. There are two major CPU architectures

related to instruction sets:

• Reduced Instruction Set Computer (RISC) – Architectures use a

relatively small set of instructions, and RISC chips are designed to

execute these instructions very rapidly.

• Complex Instruction Set Computer (CISC) – Architectures use a broad

set of instructions, resulting in fewer steps per operation.

MMX is a set of multimedia instructions built into Intel processors. MMX enabled

microprocessors can handle many common multimedia operations that are normally

handled by a separate sound or video card. However, only software especially written to

call MMX instructions can take advantage of the MMX instruction set.

The latest processor technology has resulted in CPU manufacturers finding ways to

incorporate more than one CPU core onto a single chip. Many CPUs are capable of

processing multiple instructions concurrently:

• Single Core CPU – One core inside a single CPU chip that handles all of

the processing capability. A motherboard manufacturer may provide

sockets for more than one single processor, providing the ability to build a

powerful, multi-processor computer.

• Dual Core CPU – Two cores inside a single CPU chip in which both cores

can process information at the same time.

Processor slots and sockets

• ZIF (Zero Insertion Force): for tight connection and a special lever to tighten and

loosen

• LIF (Low Insertion Force) not very tight and has no lever

Processor Modes

Processor modes refer to the various ways that the processor creates an operating

environment for itself. Specifically, the processor mode controls how the processor sees

and manages the system memory and the tasks that use it. There are three different modes

of operation, that resulted from the evolution of the PC from its humble beginnings with

the Intel 8088 chip.

Real Mode - The mode of memory access used by the CPU in DOS. CPU can only

access 1MB of memory and can only run one program at a time.

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Protected Mode - The mode of memory access used by the CPU to address more than

1MB of memory and run more than one program at a time by “protecting” the part of

memory each program is running in from use by another program.

Virtual Memory - When CPU uses a portion of a hard drive storage device as memory.

Appears just like regular memory to the operating system.

Clock Speed - The speed at which a CPU can perform calculations and access

peripherals or memory. This is controlled by the oscillating System Crystal located on the

motherboard.

386 Enhanced Mode - Same as protected mode, but added the enhanced features of

Virtual Memory and Virtual 8086.

Math Coprocessor - A processor other than the CPU that is used to perform high level

math functions.

Internal Cache - On board RAM built into the CPU. This allows the CPU to store

commands internally and execute them when it has time. Also called Level one (L1)

cache.

External Cache - The same as L1 cache, only it is a special RAM chip that sits on the

motherboard.

PROCESSOR HISTORY AND INFORMATION

Below is a listing of all known manufacturers made to date. The following list lists the

processors manufactured in date order as well as a brief description of the technology and

advances of each of the processors.

INTEL 4004 - Microprocessor introduced in 1970 with the speed of 108KHz was the

worlds first microprocessor.

INTEL 8080 - Microprocessor introduced in 1974 running at the speed of 2 MHz was

used in the world's first PC, the Altair.

INTEL 8086 (Code Name: P1)- Microprocessor first introduced in 1976. The 80086 had

a 16-bit architecture that allowed it to work with 16-bit binary numbers and pass them

through a 16-bit data bus. The 8086 was available in clock speeds of 5MHz, 8MHz, and

10MHz.

MOTOROLA 6800 - Microprocessor released in 1979 was later chosen by Apple for the

Macintosh computer.

INTEL 8087 - Floating-point math compressor compliant with the 8086 / 8080

microprocessor family.

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INTEL 8088 - Microprocessor released in 1979. The 8088 was the first Processor used in

the original IBM PC and XT personal computers because it was less expensive than the

8086 microprocessor because of the availability of less expensive eight-bit data bus

supporting chips made it the microprocessor for the IBM PC. The 8088 was available in

speeds from 4.77 MHz and 8MHz.and used the 16-bit architecture allowing it to work

internally with 16-digit numbers. The 8088 had the ability of addressing up to 1MB of

RAM.

INTEL 80286 (Code Name: P2) - Microprocessor introduced by Intel in 1982. Which

commonly is referred to as the 286 processor. The 286 processor supported 16-bit

architecture, supported virtual memory, and was available in clock speeds of 8MHz,

10MHz, and 12MHz. The 286 was around 20 times faster then the predecessor 8088.

INTEL 80287 - A compliant processor to the 286. A floating-point math coprocessor.

Specially designed 286 chips have the capability of placing the optional 80287 processor

on top of it. Giving the computer a math coprocessor.

INTEL 80386DX (Code Name: P3) - Microprocessor manufactured in 1985 was the

next generation of Intel processors. The 80386DX included the math compressor unlike

the 80386SX and still featured the 32-bit architecture and built-in multitasking. The chip

was available in clock speeds of 16MHz, 20MHz, 25MHz, and 33MHz.

SPARC - Released in 1987 is short for Scaleable Processor ARChiture by Sun - used

RISC (Reduced Instruction Set) to speed up processing.

INTEL 80486DX (Code Name: P4) - Microprocessor released April 10th 1989. The

486DX featured a built-in memory cache and 32-bit architecture. It had more than three

times the computing power of the 386DX and was available in clock speeds of 25MHz,

33MHz, and 50MHz.

INTEL 80386SX - Microprocessor introduced in 1989 was the next generation of Intel

processors. The 80386SX lacked a math coprocessor however still featured the 32-bit

architecture and built-in multitasking. The chip was available in clock speeds of 16MHz,

20MHz, 25MHz, and 33MHz.

INTEL 80386SL - Microprocessor introduced in 1990 which used low power

consumption and was used mainly in portable computers.

INTEL 80486SX (Code Name: P45 / P23 ) - Microprocessor introduced in April 1991

which is a less expensive version of the 80486DX. It lacked the math coprocessor of the

80486DX and ran at lower clock speeds then the DX it ran at 16MHz, 20MHz, 25MHz,

or 33 MHz.

INTEL 80486DX2 (Code Name: P24 / P24S) - Microprocessor first introduced in

March 2, 1992. It was based upon the popular 486DX however featured internal clock

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speeds that doubled that of the system that operated it. Thus, a DX2 on a system with a

33MHz bus would run at 66MHz. Also known as the i486DX2.

INTEL 80486DX4 (Code Name: P24C / P24CT)- Microprocessor first introduced in

1994. The 486DX4 would triple that of the system that operated it.

INTEL PENTIUM (Code Name: P5 (Pentium 60 - 66MHz))- Microprocessor

introduced March 22, 1993 designed to replace the 486 processors. The new Pentium had

an additional 1.9 million transistors when compared to the 80486DX. The Pentium has a

32-bit address bus and a 64-bit data bus, and it can operate at speeds of 60MHz to

200MHz. The Pentium was released in three generations. The first-generation of Pentium

processors was the Pentium 60 and 66 MHz. These chips used a 273-pin PGA form factor

and ran on 5v power. Intel announced the release of a second-generation introduced

March 7, 1994 included new processors from 75, 90, 100, 120, 133, 150, 166, and 200

MHz. The processors used 296-pin SPGA form factor that is physically incompatible

with the first generation versions. The third-generation of Pentium processors code

named P55C were introduced January 1997, which incorporated the new technology

MMX. The Pentium MMX processors were available 166, 200, 233 MHz, and 266 MHz

mobile version.

INTEL PENTIUM PRO (Code Name: P6) - Microprocessor which was designed for

the corporate users and for high-end servers and workstations, preferably those using

Windows NT. The Pentium Pro CPUs are extremely fast with 32-bit applications and 3-

D image processing and rendering when compared to previous Intel processors. The chip

runs at 166MHz and higher

INTEL PENTIUM II (Code Name: Klamath) - Initially the Pentium II 233MHz was

released in 1997 and introduced a new physical architecture which encased a circuit

board within a plastic case. With this new technology this allowed the chip to be easily

added and removed. However previous owners of Pentium motherboard could not

upgrade to this new type of chip unless the motherboard they had included a SLOT 1

technology. The Pentium II runs from 233MHz to 450MHz.

INTEL PENTIUM III - Initially the Pentium III 500 MHz was released in 1999 shortly

after its released Intel introduced the Pentium III 550 MHz processor. The Pentium III

chip continued to use the SLOT 1 and could be used on previous Pentium II

motherboards with BIOS support. Before its release a big controversy concerning

privacy. The Intel Pentium III chips have a ID for each chip helping to authenticate

peoples purchase over the Internet. However many argued that this was another way for

someone to find out personal information about the individual without there consent.

Intel disabled this feature by default and allowed it to be released after released the chip.

Processor Slots

Slot-type processors were only on the market for a year. Intel moved from the

socket configuration to a processor packaged in a cartridge that fits into a slot in

the motherboard for its Pentium II processor. Similarly, AMD has progressed

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from Slot A, similar to Slot 1, to Socket A for its high-end AMD Athlon and Duron

processors.

AMD Processors

The best performing AMD processors are the Athlon, Athlon XP, Thunderbird, and

Duron series. They, along side the Intel Pentium IIIs, are currently the most used

microprocessors in high-end desktop systems, workstations, and servers. The AMD

Athlon processor system bus is designed for scalable multiprocessing. The number of

AMD Athlon processors in a multiprocessor system is determined by chipset

implementation.