Basics

Overview

The Central Processing Unit (CPU) controls and manipulates data, and may be thought of as the "brain" of a computer. The main areas in a CPU are;

[CPU interation]

It directs the step-by-step operation of the entire computing system
fetches, decodes and executes machine language instructions by prompting ALU or I/O processor

does comparisons, addition, subtraction, multiplication and division, fixed and floating point arithmetic when requested by CPU

Holds data and instructions after input until needed by the CPU. Inputs are received from Disk, Keyboard, Mouse, other peripherals

Stores information as a pattern of connections in an array of possible connections
the information is usually only set once during the life of the device
non-volatile - retains information with or without power.

Stores data/programs and instructions as a pattern of charges in a series of cells
provides the quickest access, the information is easily changed
Contents are changeable.
volatile - all information is lost when power is lost, so stores short term data which is required quickly but not permenant.
New machines are sold with millions of bytes (MB) of RAM already installed. (1997 typically 16MB)

[4MB 72pin SIMM]

4MB RAM 32bit (Non-parity) 72 pin SIMM (Single inline memory module)

Is interrupted by the keyboard whenever a key is pressed or released.
The key maybe interpreted as part of a command or the content of some file.
Is interrupted by the mouse whenever it is moved or a button is pressed or released.
The mouse pointer on the screen will be moved to match its movement.
Mouse actions may be used to have the CPU start application programs or select a command from a menu bar or highlight and move text in a file.
Uses memory to hold a copy of the program that is currently being run and to keep track of the current state of files that are being changed.
Uses disk drives to store the contents of data files that are not currently being changed and to store programs that are not currently being run.

The CPU keeps a copy in RAM of the data and instructions (program) that is currently being used.
When the data is changed and the CPU is asked to save it, then a copy of the new version of the file is sent to the disk for long term storage.
When a new program needs to be run then a copy of it is read from the disk to the RAM for the CPU to run it.
When a program requires data that was stored earlier, then the CPU reads a copy of it from the disk.

Unit of measurement for indicating the frequency of electrical vibration cycles per second.
One Hertz (Hz) equals one cycle per second. (Megahertz = Million electrical vibration cycles per second)
Named after Heinrich R. Hertz, a German physicist, who first detected electromagnetic waves in 1883.
The original IBM-Personal Computers in the early 1980's were controlled by Central Processing Units (CPU's) that were synchronized with clock crystals vibrating at 4.77 megahertz.
The bandwidth of your computer monitor is also measured in MHz.
Megahertz ratings are not an accurate measure of microcomputer performance. Many other elements have an effect on speed. For example the Pentium processor has a superscalar architecture, giving it the ability to execute multiple instructions in a single clock cycle.
Example
Pentium 90mhz, considered minimum multimedia developers CPU (1995).

Million Instructions per second
average number of machine language instructions a computer can perform or execute in one second.
It can be shown that the same computer can execute two different loops of code to estimate MIPS, and their execution times will differ significantly. MIPS should therefore be used only as a very general measure of performance between different types of computers. In order to obtain accurate performance data to compare similar computers, each subsystem must be isolated, and practically speaking, this is an almost impossible task
sometimes thought of "meaningless indicator of processor speed!!!
Example
Pentium 66MHz, runs at 112 MIPS.

Since both measurements have their limitations, other measures are continually being developed;

More realistic benchmark testing occurs at the application level.
Intel use their iCOMP index (INTEL COMPARATIVE MICROPROCESSOR PERFORMANCE INDEX). It is an Intel developed tool for comparing the performance of their processors.

1. PC switch turned on

2. Signal sent to CPU to clear registers

3. Program counter set to F000 (address of first instruction of a program in ROM (called BIOS)).

4. BIOS invokes power on self tests (POSTs) which checks;

CPU
system bus (circuits connecting components)
timer (clock)
display RAM and adapter. (Display adapter contains its own BIOS and this becomes part of the overall BIOS (VDU awakes at this point!))
RAM
keyboard
disk drives (signal sent to see what replies)
CMOS settings (validates what was found during the checks with what is recorded in CMOS - a trickle fed memory that retains its data even when the computer is turned off)
additional BIOS instructions. (Such as those contained in other adapter cards, like SCSI disk drive adapter). These are added to the overall BIOS.

Merging of Hewlett-Packard & Intel CISC & RISC technologies.
64 bit reduces memory-to-processor latency.
Allows processing of Windows and unix applications by the same CPU.
Predicts and speculates which instructions to perform (unlike sequential processing).
Reduces the number of processing paths (branches).
Merced expected 1999.