Central Processing Unit (CPU)

The CPU in a PC is the Microprocessor (80386, 80486, Pentium, Cyrix 5x86, etc.). You should be aware that there are several brands of CPU's. The most popular as of 1997 are probably the Pentium (many versions), AMD K series, CYRIX Mx series, and Motorola microprocessors. CPU's are primarily of two types: Socket 7 and Single Edge Contact (SEC). Intel CPU's prior to the Pentium II were Socket 7, as are the CYRIX and AMD CPUs. The Pentium II is a SEC CPU, and it is believed that in the future most if not all Intel CPUs will be SEC design.

In my opinion, the CPU is the "brain" of the computer; however, even your brain needs some stimuli to process information. So, the CPU needs an electrical system, an input (senses), etc. to work; just like your body needs direction and motivation to do things. Electricity, in computers, is like the heart, blood, and calories(energy) in your body.

A CPU that has no operating system is useless. It is like your brain on the day you were born - all you knew was to eat; the CPU along with the BIOS at boot time, knows only that it has to load an Operating System and check out its parts. As you grew older, you learned; as the operating system is loaded the computer learns enough to operate. Enough.

EVERY PART of a PC must be functioning to truly process data into information!

and

When you turn on your computer, something called the "BOOT PROCESS" takes place. The boot process is essentially the following:

  1. The CPU is cleared, the CPU register is set to F000 hex, which is the address of the BIOS ROM chip.
  2. The boot program in ROM BIOS is loaded into memory.
  3. The boot program performs a set of "Power On Self-Tests (POST)" to determine if all its parts are in working order.

  4. The disk drives (normally A: and C:) are checked for a boot record. When found, it loads the "Boot Record" into memory at address 7C00, and BIOS then transfers control to the boot record address.
  5. The boot record then loads IO.SYS file which contains extensions to the ROM BIOS, and includes a program called SYSINIT that handles the rest of the boot process. The boot record is then replaced in RAM by other program code.
  6. SYSINIT assumes control and loads MSDOS.SYS into RAM. MSDOS.SYS assists BIOS to manage files, execute programs, and handle hardware interrupts.
  7. SYSINIT finds the "config.sys" file and uses MSDOS.SYS to execute the commands in the "config.sys" file.
  8. SYSINIT then tells MSDOS.SYS to load the "command.com" into memory. Part of the command.com is loaded into memory as part of BIOS. Then the internal DOS commands from "Command.COM" loads into conventional RAM.
  9. The third part of COMMAND.COM finds the "autoexec.bat" file and executes it.
  10. The PC is now fully booted!

    This is the basics of how an INTEL processor BOOTs. Newer processor will have minor differences and some different control procedures.

No matter the brand, they are all cute little chips, with many "pins", which in newer machines, fit in "ZIF" sockets and are removeable.

Several vendors including the above manufacture upgrade models of CPUs: Courtesy of Kingston Technologies, Inc.

YOU CANNOT PUT JUST ANY "UPGRADE" IN ANY PC. YOU MUST BUY ONE THAT IS COMPATIBLE WITH YOUR MOTHERBOARD, YOUR CLOCK SPEED, YOUR BIOS, ETC.

An Intel Pentium Microprocessor (CPU) as shown above, has multiple components as follows:

  1. Bus Interface Unit (BUI) - links the CPU with the rest of the PC. It retrives the instruction from RAM and gives it to the Prefetch unit. The BUI has a 64-bit path (bus) to RAM. It also has two other 64-bit paths to the "code cache" and the "data cache". These are 8KB storage units used for instructions and data. The code and data remain in these cache areas until needed by other CPU components.
  2. Branch Predictor Unit. This has a direct interface to the "code cache" and to the Instruction Prefetch and Decode Unit. It looks at the code, to determine which of the two ALUs can handle them most efficeitnly. It attempts to keep each of the ALUs working constantly.

  3. Fetch/Decode Unit.
    1. Instruction Prefetch Unit (buffer) - retrieves the code from the Branch Predictor unit, and queues instructions for processing by the decode unit.
    2. DeCode Unit - the Instruction Prefetch Unit gives the instruction to the decode unit. The Decode Unit then translates the instruction and gives it to the execution unit, or in case of floating or decimal numbers it gives them to the Floating Point Unit.

  4. Execution Unit - coordinates the steps to complete each instruction.

  1. Control Unit -It tells the Protection Test Unit where the operands of an instruction are located in DATA cache, or RAM.
  2. Protection Test Unit - makes sure the operations are legal.
  3. Registers - data to be processed is moved into the registers.
  4. Arithmetic Logic Unit - Normally, in older processors, there is just one of these; however, in the Pentium there are two ALU processors. They process the information in the registers according to the instruction being executed. It then lets the control unit handle the results of the instruction. The control unit uses the Bus Interface to send the results to memory, storage device, etc.
  5. Floating Point Unit. Handles any numbers with decimal fractions (67.45, 5E-10, etc.).

The microprocessor is just one of many components on the "motherboard". Without all the other parts such as BIOS, CMOS, the BUS, memory, etc. the CPU does not function. AND - the parts will not function without a CPU!

Each type of microprocessor (CPU) has been produced in more advanced versions over the past 25 or so years. The following will give you an idea of how two different vendor's products evolved:

INTEL PROCESSOR Models and Descriptions

Motorola Processor Models and Descriptions

CPU COMPARISONS:

CPUSPEED(MHz)BUSINTERNAL CACHEMMXSUPERSCALARRISCBrch.Pred.Chipset
Pentium100,133,166,200UNKYESat 166,200Not ReallyNOUNKunk
Pentium w/MMX150,200,233DIBL1(32KB),L2(512KB)YESYESNOYESTRITON HX
Pentium Pro166 to 200DIBL1(32KB),L2(256KB)on chip NOYESYESYESI440FX
Pentium II233,266,300DIBL1(32KB),L2(512KB)off chipYESYESYESYESUNK
Cyrix 6x86110 to 150PCIL1(16KB),256(L2)NOYESYESYESUNK
Cyrix M2166 to 233PCI L1(64KB)YESYESYESYESUNK
Cyrix MediaGX120 to 200PCIL1(16KB)YESUNKUNKYESCx5510
AMD K590 to 133UNKL1 and L2NOYESYESYESUNK
AMD K6 MMX166 to 300UNK64KB(L1),512KB(L2)YESYESYESYESVP2
AMD K6166 to 233UNK64KB(L1),512KB(L2)YESYESYESYESVP2
Intel Deschutes300 to 433Scheduled in 1998
NOTE: Some of the systems specifications are slightly misleading. For instance, a Pentium Pro with 256MB of L2 Cache which runs at the 200MHz speed of the processor since it is on chip; while the Pentium II at 233MHZ had a separate L2 cache chip running at 116.5MHz which effectively slows it below the total performance of the Pentium Pro 200. This will soon be rectified you can be sure, and the 266 and 300 MHz Pentium II will also have improved performance. And you can be sure that Pentium II processor will rapidly make the other Pentium Processors obsolete. However, other upgrades to 1998-2000 processors will make the Pentium II rather blaise.

NOTES:

  1. Chipsets are extremely important, but are often dependent on vendors who build the computers or makes the "motherboard". You may have to shop or research to get the proper chip set. "www.sysdoc.pair.com" is an excellent source of information on chip sets.
  2. Buses, such as PCI, VESA, etc., are vendor dependent.
  3. Type of RAM may be vendor dependent - EDO, SDRAM.
  4. Amount of RAM is dependent on the motherboard used by a vendor.
  5. Some motherboards allow only 128 MB RAM, while others can go to 512 MB RAM, and a Micronics "Stingray" can have up to 1 GB.
  6. MMX technology (a combination of high-speed circuits, MMX oriented software, and a set of 57 new processor instructions available to software designers) enhances performance greatly, expecially in the Pentium II processors at higher CPU speeds. MMX technology does supposedly require the serious investment of graphic accelerator cards, sound cards, and MPEG chips. Great for graphics applications.

Basic PC Components