Introduction
Whether you're planning to build your own computer or you simply would like to know more about how computers of old and new work then this page is for you. First let me start by pointing out a strange occurrence that has risen with regards to the term 'PC' which means 'Personal Computer.' Actually, thanks to Microsoft, when most people use the term PC they don't just mean a personal computer but also, a computer that uses a version of Microsoft's Windows operating system (WIndows 98, Windows XP, and so on).
Computer Basics
You may wonder what is the most important part of a computer; the answer is debatable. The CPU (Central Processing Unit, such as a Pentium) is the brains of the computer so without it the computer wouldn't start because there's no one to tell the other components what to do. But even if the CPU was installed but the PSU (Power Supply Unit) wasn't connected or working then nothing would happen if you tried to turn the computer on. Another very important part of a computer is the RAM (Random Access Memory), although the CPU has its own, tiny amount of internal RAM only a small amount of data can be stored there at one time so without the external RAM (external to the CPU) the computer wouldn't be able to do much.
A CPU must have insructions, the start up code, ready for it as soon as the power is turned on; these startup instructions are stored in the BIOS (Basic Input/Output System) which is stored in a ROM (Read Only Memory) chip. The BIOS of modern computers can be changed, such as to update it to provide new features or to fix bugs, however, this opens up the possibility of a corrupted BIOS which would stop the computer from starting.
The BIOS will check the system is running as it should and will display a limited amount of information about the hardware on screen, like how much RAM there is and if there are any errors. There will also be a setup configuration utility, usually accessed by pressing a certain button after power up, that allows the user to adjust settings such as the date and time, and what integrated devices should be enabled.
When the BIOS is checking the hardware it runs what is known as its POST (Power-On Self Test) and will test the RAM and look for connected peripherals, namely floppy drive, harddrive, CD-ROM and the like. As soon as it has done that and there aren't any serious problems, the BIOS will load the operating system (e.g., Windows) from the harddrive (or other device). The operating system can't be loaded first since, even if there were no need for tests, code either in ROM or RAM has to be available as startup code to load data from a peripheral like a harddrive.
Anyone who has had keyboard troubles or pressed a key on the keyboard when a computer starts up will be faced with the puzzling error message that reports a keyboard error and asks the user to press any key to continue despite the keyboard not working. The keyboard always has been for most computers the one input device you need more than any other but still that's no excuse for that stupid error message.
Amstrad PCW16
Amstrad were always one for providing to their customers exactly what they needed and their range of computers known as the PCW (Personal Computer Word processor) had everything you needed to use a computer immediately. The PCW16, known also as Anne, had a monitor built into the computer as well as a 1.44MB 3.5 inch floppy disk drive.
This computer came out in 1996 and made use of the 8-bit Z80 CPU running at 16MHz. In addition to using floppies, the PCW16 had also 1MB of flash memory built in which could be used to save files. The operating system, or at least the visual side, was called Rosanne and functions as a typical GUI (Graphical User Interface).
BBC Microcomputer
In the 80's the BBC (British Broadcasting Corporation) wanted to make sure that computers were used for educating people-funny now that they make do with modern PCs. Actually, the BBC microcomputer was made by Acornsoft who also produced other versions such as Acorn Electron which was a more basic version of the original BBC microcomputer.
This microcomputer was huge, almost as big as the Commodore Amiga 500, but the BBC microcomputer had everything you could need. Using an 8-bit 6502 CPU, with the ability to add a second CPU (like a Z80 8-bit microprocessor or even a 16-bit microprocessor), with a fast BASIC and many different display modes it was a real winner.
The BASIC that was standard supported assembler which was a great bonus although not terribly easily integrate with a BASIC program due to the way the assembler was loaded. Inside the machine it had a number of chip sockets to allow the BASIC to be replaced with another programming language or any other software. This expansion, however, was also the cause of a serious flaw in its design: many users would lean on the keyboard which would put pressure onto the socketed chips, casuing anything from sudden crashes to the computer not starting up at all until the problem was fixed.
For me, and I'm sure may others, one of the most memorable things about the BBC microcomputer is how it starts up with a loud BLEEP! This bleep was actually an indictaion that the computer had started up without any troubles, that and the on-screen text.
Commodore 64
One of the most famous microcomputers of its time, its no wonder that the Commodore 64 was so popular (and is still today if you're a fan of retro) considering how well it was made.
With 64KB of RAM (hence its name, although not much was spare for BASIC users), sprites and great sound it was a winning combination. As an 8-bit computer using a version of the 6502 microprocessor it performed well running programs that wouldn't look out of place in an office, but it was best for playing video games on. Like most microcomputers programs could be loaded from an extrernal cassette tape player or floppy disk drive, as well as a cartridge plugged into the expansion port of the Commodore 64.
Commodore Plus 4
The Commodore Plus 4 was a cut down version of the Commodore 64 and although it lacked sprites and the sound abilities of the Commodore 64 it had a number of advantages other than its smaller size.
The reason for the Plus 4 in its name is due to the 4 pieces of software that are built into the mircocomputer. The Commodore Plus 4 did not use standard connectors for joysticks and other devices (perhaps to save space) which caused a few problems. The good things about this microcomputer is that it has arrow keys on the keyboard and best of all, a built-in machine code monitor (strangely the manual mentions how to activate the machine code monitor but has no information about the individual commands). When turning on or restarting the Commodore Plus 4 the machine code monitor could be entered instead of starting in the BASIC environment or it could be activated at any other time, switching between BASIC and the machine code monitor.
Repairs
One day your computer may be as fine as can be the next day it stops working or behaves oddly, especially if you have Windows as your operating system. The key to fixing the computer is first to work out if the fault or faults are because of a hardware or software problem, or even a combination of both.
Let me give you an example, I have an old computer running Windows 98 SE that I have in addition to my main computer. Recently the Windows 98 computer would start up fine but after loading Windows or a few moments later the much feared blue screen would pop up, or sometimes the less serious explorer has performed an illegal operation error. A clue to what was wrong was that the errors were random and they had only started to appear recently.
Although software including drivers could be to blame, a dodgy power supply or faulty memory (RAM) were just as likely. I ruled out the PSU as it was of the type that is supposed to provide a power good signal to the motherboard that would prevent the computer from starting if the voltages were not a the right level. I also remembered that I had added extra memory recently so I removed the second DIMM memory stick. Now there were no errors, even after using the computer for some while just to make sure that removing the bad RAM really had caused so much trouble.
All content of this and related pages is copyright (c) James S. 2007-2008
