THE CENTRAL PROCESSING UNIT (CPU)

All computers have a Central Processing Unit (CPU). At one time a CPU could take up several aisles in a large computer room.

Today's computers (even the most powerful supercomputers) rely on CPU's that may be no larger than a postage stamp. It's a miracle of miniaturization.

WHAT A CPU DOES FOR A LIVING – How it works & what goes on

  • Fetch, decode, execute and more - instruction set
  2. DECODE
The instruction is decoded into
a form the ALU can process.		 3. EXECUTE
The ALU executes the
instruction.

  1. FETCH
The next instruction is
fetched from memory.		 4. STORE
Results from the instruction
execution are stored in memory.		  

Families

  • 8088, 80286, 80386, 80486, 80586 (Pentium), 80686 (PII-III), 80786 (P4). Sometimes called the x86 architecture.
  • AMD, INTEL, CYRIX, TRANSMETA, VIA
  • IC - Integrated circuit
  • Instruction set – the CPU’s "verbs"
    • Architecture determines the efficiency of instruction
    • RISC (Reduced Instruction Set Computer – PowerPC or Compaq (DEC) Alpha, DAC processors)
    • CISC (Complex Instruction Set Computer – Intel 80386)
    • Hybrid (486 and up)
  • Enhancements
    • MMX (1997 - 166Mhz - P55C) – 57 new multimedia instructions - Intel
    • 3D-Now! - AMD
    • SSE (Streaming SIMD Extensions) - 70 new. – Intel

    • In most programs, floating-point calculations are used for generating data, while SIMD calculations are used for displaying it
    • SSE2 (Pentium 4) – 144 new. – Intel
    • For the most part, programs must be written to take advantage of these enhancements

 

Registers - small amount of memory space on a CPU set aside as a kind of address book, limited data-store and alert notification point.

  • Stores very specialized data.
  • Temporary scratch pad for CPU
  • The CPU's "little black book"
  • Width (number of bits in the register) helps determine "power" of CPU.
    • Word size
    • Microprocessors currently use 8, 16 and 32-bit (integer) registers
    • But 64-bit is just around the corner



  • External data bus - the pins and wire tracings that the CPU uses to move data to and from the chipset and main memory. Very A+
    • Also known as the front-side bus (FSB)
    • Microprocessors currently use a 64-bit FSB
    • CPU speed is set from (based on) the speed of this bus
    • This bus MOVES data
    • It has been Very A+ to know the FSB speed of typical CPUs
      • Pentium and PII slower than 350MHz are at 66MHz FSB
      • 350MHz and over can use 100MHz and up (to 200MHz (or 800MHz quad-pumped))
  • Address bus - the pins and wire tracings that the CPU uses to "dial up" a specific RAM location.
    • Width determines max amount of memory that a CPU can access.
    • Microprocessors currently use a 32 or 36-bit address bus.
    • This bus tells data "where to go!"
  • Processor "modes" - Memory access and protection features
    • Real mode
      • All x86 CPUs
      • Traditional memory management
      • Good for one program at a time
    • Protected mode
      • Needed for multiple programs running a the same time
      • All 286 CPUs and newer
      • Advanced memory management
      • Virtual-real mode for 386s and up
  • System clock – historically an oscillating quartz crystal

    • Regulates and synchronizes
    • PLL (Phase Lock Loop) – integrated in IC chip
    • CPUs now run at some multiple of the system clock
  • Math coprocessor - support processor
    • Specialized to handle floating-point math (large numbers and numbers with decimals).
    • Integral in 486DX and up
    • Separate processor 486SX and older
  • Cache - Cache memory is a special high-speed memory designed to supply the processor with the most frequently requested instructions and data.

    Instructions and data located in cache memory can be accessed many times faster than instructions and data located in main memory. The more instructions and data the processor can access directly from cache memory, the faster the computer runs as a whole.

    • Memory mantra - CPU fast, RAM slow!
    • It's a party…
      • Corner store =
      • Refrigerator =
      • Beverage =
      • Host =
      • Your name here =
    • Level 1 is on CPU
      • From 8k to 64k
      • Began with x486
    • Level 2 may be on CPU
      • If not, then on mobo or processor card
      • SRAM (Static RAM)
      • Inclusive / exclusive
    • Write through - cache reads
    • Write back - caches reads and writes

     

    It is Very A+ to know what cache is and typical amounts of L1 and L2 cache on popular CPUs.

    Virtual memory - uses secondary storage as primary storage.

    • x386 and up
    • Swap file

     

  • P-Rating - comparison to Intel - Very A+
    • Better performance at same clock speed
    • It’s sorta back with the Athlon XP (extra performance).

    AMD XP1600 runs at 1.4 GHz clock speed – but outperforms Intel by about 20% - 1.6GHz
    • Dual (or quad or more!) pipeline - true multitasking Very A+
      • Super scalar
      • Like an assembly line
      • RISC-like hybrids
      • Dual pipes on Pentium, and Quad (and up) in PIIs and newer
      • Intel Hyper-Threading makes a single CPU act like more

         

      Putting it all together…

      CONFIGURING THE SYSTEM – installing a CPU

      Configuration data may be saved by setting DIP switches (dual inline packages), using jumpers or software.

      DIPs - A DIP switch is a chip with several small "levers" or switches on it.

      To change a configuration using a DIP, simply slide the switch to one side or the other. There are usually markings on the DIP that tells you whether you are sliding the switch to the ON or OFF position. The correct positions of the switches for a particular hardware device should be listed in that hardware device's manual.

      DIPpy facts:

      • Bank of switches
      • Either on or off
      • Don’t set with pencil - graphite is a conductor of electricity
      • Must remove computer case first - it’s a hardware thing
      • Need documentation - you saved it, right?
      • No pieces to loose - this is a good thing

       

      Jumpers

      Jumpers are pins sticking up side by side. You simply place covers (or shunts) over the pins to make the connection (jumper on) or remove the cover to break the connection (jumper off).

      Most manuals will show jumpers labeled something like JP1 or JP12. Some jumper banks may have 3 or more pins.

      In this case, your manual will help identify where pin 1 is so you can then set jumpers 1 and 2 on, or 2 and 3 on etc.

      Jumper Facts

      • Not covered is OFF (0)
      • Covered is ON (1)
      • Often used to convey type, speed and voltage of CPU to system
      • The small plastic removable piece is called a shunt
      • Need manual - although settings are often silk-screened onto the circuit board. BYOMG - Bring your own magnifying glass!

      The polite technician places the jumper over a single pin for the off position. That way it is there for the next technician to utilize… This is called the parked position.

      Jumpers and DIPs often correspond to a binary number. Very A+

      Many modern systems can be set via software – soft settings.


      INSTALLING YOUR CPU

      You need to set up three things:
      1. Speed of FSB – the metronome of the computer
        • Note: some components will run at a multiple of FSB
        • Note: some components will run at a fraction of FSB

         

         

         


      2. Multiplier – CPUs now process faster than the metronome

       
    1. Voltage – they need some DC to work!

     

    CPU SPEED AS A MULTIPLE OF BUS SPEED

    A single motherboard can adapt to the speed settings of many different CPUs.

    Modern CPUs can run internaly many times faster than the FSB. "Multiplier" circuitry is then used to allow the CPU to process internal data at one rate while accessing the FSB at another.

    My 500MHz CPU runs at a FSB speed of 100MHz. This essentially means that the CPU can only access the FSB every 5th processing cycle.

    OK, so give me the juice!

    Your CPU needs just a small amount of electricity to function - around 3v dc.

    • Since different CPU's need different amounts of "juice" and a single motherboard can accommodate different CPU's, those voltage amounts are set via jumpers or DIPs or even in software.

    Sometimes the CPU (core) needs one voltage but its I/O requires a different voltage - this is called a dual voltage system.

    Sometimes the CPU can set the voltage itself (see PII).

     

    Voltage
    • Set jumpers for voltage too
    • Voltage regulator (VRM) - Very A+

    First law of thermodynamics:

    Energy can be changed from one form or another, but cannot be created or destroyed.

    Single: 5v or ~2 through 3.5
    Split (dual plane): 5v     and ~2 through 3.5
    Cryptically encoded on CPU or refer to mobo manual.

     

    Where CPUs live and their footprints - Very A+

    CPU removal tools - chip pullers

    SOCKETS

    LIF and ZIF sockets

    SPGA (Staggered Pin Grid Array)

    PPGA (Plastic Pin Grid Array - CPU on bottom)

    FC-PGA (Flip Chip Pin Grid Array - CPU on top)

    BGA (Ball Grid Array – pins everywhere!)
    • Socket 4 - 273 pins (Pentiums 60-66)
    • Socket 5 - 320 pins (K5 and Pentium 75-133)
    • Socket 7 - 321 pins (K5-K6 and Pentium 75-300)
    • Socket 8 - 387 pins (Pentium Pro)
    • Socket 370 - duh… (Celeron and "flip chip" PIIIs)
    • Socket A - 462 pins - AMD Duron and Athlon (T-bird and XP)
    • Socket 423 - For Pentium 4
    • Socket 478 - For Pentium 4 and Celeron
    • Socket 418 – Intel Itanium
    • Socket 603/604 - Pentium XEON
    • Socket 940 / 754 – AMD Opteron, Athlon 64FX, Athlon 64

     

    SLOTS

    SECC (Single Edge Contact Cartridge - covered CPU)

    SEP (Single Edge Processor - no cover for CPU)
    • Slot 1 - Pentium II - Celeron - Pentium III (to about 800MHz)
    • Slot 2 - Pentium XEON
    • Slot A - AMD Athlon

     

    Keep your cool - Very A+

    CPU's can generate a great deal of heat. All those millions of internal transistors can contain tiny points of electricity. Most modern CPU's require a fan and even a metal heat sink to keep themselves cool. Thermal paste & liquid coolers are additional tools in the cooling process.

    • Safe operating temperatures depend on CPU. 80 – 130 degrees Fahrenheit.
    • Temperature sensing may be done via software that reads special chips or you can add extra hardware. Thermistors.

    Thermal paste / thermal goo / Meyers calls it heat dope

    Types of cooling
    • Passive cooling – heat sink
    • Active cooling – heat sink and fan(s)
    • Liquid cooling (A+ 2003)
      • Uses water, pump, radiator, reservoir, fan, blocks and more…
      • Both kinds of cool!

     

    Historically speaking - talking 'bout my ggggeneration!

    1st

    8088 (8086)

    2nd

    80286 (1st protected mode)

    3rd

    80386 sx (16-bit data bus) – Virtual Memory

     

    80386 dx (32-bit data bus)

    4th

    80486 sx (no integral mathco)

     

    80486 dx (integral mathco)

    5th

    80586 Pentium (super scalar)

    6th

    80686 Pentium Pro / II / III

    7th

    80786 Athlon, P4

    Edited (2003) By Vlad Magero