Resources - Cascade et al

Virus simulations.

Chapter 15

Much had been made by the company by associating the scary word 'virus' with a program that dropped the letters down a text screen - this being similar in one respect to what the non-replicating part of the cascade virus does.

There were a number of a big differences though:

My program	Cascade
Drew company logo on screen	Used existing characters on screen
Characters would 'fall' up, down, left or right	Characters only fell to bottom of screen
Once they had 'fallen', they would then 'churn' around, like socks in a tumble drier	They just sat there
Never did anything but draw on screen	Could self-replicate and 'infect' other programs
Program came to an end	Virus would stay resident in memory and continue infection

Clearly, if someone was honestly mistaking it for the real cascade virus, they would have to be an imbecile.

Cascade dates from a time when people's displays were character-only and were 80 wide by 25, 43 or 50 lines tall - no graphics. So, what does the real, non-replicating part of the cascade look like?

These are screenshots from programs by the British Computer Virus Research Centre.

Cascade sits in the background and here, as an example, I have produced a directory listing.

One by one, the characters fall to the bottom of the screen and several minutes later, it looks something like this.

There are other viruses that have visual output from this period in what is now called 'computer history' - it seems so recent.

This one is the Ambulance virus. It draws an ambulance which runs across the bottom of the screen with the sound of a German two-tone siren coming from the computer's speaker.

Of course, viruses are just small computer programs - the only special thing about them is that they propagate on their own - and at some stage, someone had the brilliant idea of taking the ambulance virus and modifying it so that there was a brick wall on the right-hand side of the screen.

The ambulance appears on the left as usual, drives across the screen with two-tone siren sounding from the computer's speaker and then it smashes into the brick wall.

Being code, they can have errors in them as well. Dr Alan Solomon (Aaron Shimsom in the book) was looking at the code for the Tequila virus when he noticed some code at the end of the virus that was never used. It turned out to be a 80x25 representation of the Mandelbrot set which, if you do make it use that code, looks like the image on the right.

The Mandelbrot set is of curiosity to many programmers and others because it is a fractal - you can see on the right, a higher resolution version of the set. It had recently been discovered and for the first time, the personal computer gave people at home the ability to produce it for themselves.

Being fractal, you can zoom in on it and see things that look very similar.

Just keep on zooming.

You can, if you know what to look for, tell your whereabouts on the set by looking at the structure of the 'threads' that go off from any particular 'gingerbread man' in the set.

	The solicitor and Snaith carried on with their charade, claiming Bexley’s threats were just the beneficent Mr Bexley being concerned about my welfare.

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