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Technical 
The Internal Components
In the left margin you will find links to all the component
pages to date. I plan to add more pages over the next few months or so.
PC Components - A Technical Insight
The following pages contain technical information about the main components
found in a standard personal computer.
Introduction
Since the release of the original IBM PC new and enhanced components
have been added to the basic design. The rapid advances of the personal
computer were partly because of software demands placed on hardware, such
as graphical user interfaces (GUI's) or memory hungry applications and
new technologies and design techniques processor, motherboard, component
and peripheral manufacturers standardised.
Overview
The components I am referring to are usually integrated on the motherboard.
The processor and support circuits, memory (RAM and ROM), the input/output
interface (including the serial and parallel ports, keyboard interface,
disk interface, graphics interface, etc.) and buses (the data bus, the
address and control bus). There was no real time clock on the original
PC and had to be manufactured on an expansion card and placed in one of
the motherboard expansion slots. (One of the early upgrades available
for PC compatibles).
A computer carries out a series of commands called a program. The processor
is designed and organised with the ability to do this. The processor can
also read and write to memory because instructions and data used by programs
is temporarily held there, secondly the processor is capable of understanding
and carry out the series of instructions. The processor is also able to
instruct other components on what to do and therefore manage the computers
operation.
Although the processor makes a distinction between instructions and data
, memory does not (apart from cache). Memory is temporary (unlike ours)
and needs constant reminding by dedicated circuitry (except for static
ROM). Most memory needs a constant power and hence is referred to as volatile,
memory that does not need power to retain data is known as non-volatile
(straight forward when there was only one main type of ROM and RAM). Memory
is the workspace that programs use when running. The size of workspace
is equivalent to the amount of memory installed. The memory can be written
to, read from and over written (there is no need for the memory to be
cleared first), by both the processor and the input / output devices.
The input/output devices form a window between the system and the outside
world allowing communication with the memory and processor. A bridge between
the user and the computer. I/O devices (peripherals) include the keyboard,
the monitor, mouse, printer, modem, network and disk storage devices.
PC components are connected together by the bus architecture which can
be thought of as a highway along which devices communicate. The original
PC bus architecture was 8 bits wide and could transfer about 1 MB per
second compared to a modern 64 bit bus which can transfer data in excess
of 500 MB per second. Modern applications place a heavy demand on the
bus architecture. New bus designs made applications not previously
possible, such as multimedia available on the PC. Pentium processors are
able to support multiprocessor buses and many motherboard designs are
able to accommodate two or more processors. When systems have multiple
bus types in a single design there are devices that bridge between the
bus types. New buses will appear that support new designs such as SIMPL,
HydraXS and VBus.
The computer case or box houses the motherboard, devices, drives and a
power supply (PSU). There are several popular types of case available,
such as desktop, mini-desktop, slimline desktop, tower, mini tower and
midi tower. All the components need power to function. AC current is converted
to DC and output at voltages of 5, 12 and 3.3 and a fixed polarity of
either positive or negative. Power supply units are rated in watts.
To better understand how the industry arrived at its present state of
supporting multiple processor types and speeds, multiple physical packaging
styles and bus architectures read New to
PC's User Guide. Below are block diagrams illustrating the layout
of the different bus architectures. Click on a diagram to view it full size.
The PC and PC XT block diagram :
Click for full size image
A typical system used four expansion slots
1. Floppy Disk Controller
2. Hard Disk Drive controller
3. The Display adapter
4. Combined Serial and Parallel Port Adapter
The PC AT ISA block diagram :
Click for full size image
8 slots with two usually used
1. EGA or VGA display controller adapter
2. Multi I/O Port adapter with
- 2 serial ports
- a parallel port
- floppy disk drive interface
- IDE interface for hard disk drives
- a Game Port
VESA Local Bus system block diagram :
Click for full size image
A typical system may use 2 VL expansion slots
1. Multi I/O with EIDE
2. SVGA (Super-Video Graphics Array) Display Adapter
PCI ISA Bus Block diagram :
Click for full size image
One of the PCI slots is placed close to one ISA slot and share the (but
not at the same time) a back-plate.
Some motherboards only offer two ISA slots and as many as five PCI slots.
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