Wasted Neurons Wednesday - The Architecture of MS-DOS

I have a lot of neurons wasted on MS-DOS. Probably more than for any other technology I've ever worked with.

Which is a bit ironic, as most people would say that the entire problem with MS-DOS is that there's so little of it...

And I'll admit that I would agree MS-DOS has an architecture in the same way that a bivouac has - there's the beginnings of something there, but it's not exactly going to fill a textbook.

Wasted Neurons Wednesday - COM and EXE files

These days, all Windows programs are .EXE files. But back in the days of DOS, there were also .COM files.

Why no .COM files anymore?

The answer lies with the precursor of MS-DOS - CP/M.

MS-DOS was not actually written by Microsoft - IBM had tried to get CP/M for their new PC, but couldn't agree on the royalty rates. As a hedge bet, they asked Microsoft for an operating system - so Microsoft first licensed, then bought outright someone else's CP/M clone and resold it to IBM!

Wasted Neurons Wednesday - RAM and the IBM Compatible PC

The IBM PC was powered by an Intel 8088 processor.

That processor could address 1Mb of memory. Yes, a whole luxurious megabyte! Trust me, that was a big figure in 1981.

However, you didn't get the whole megabyte. Oh no. Things like video cards and the built-in BASIC need some RAM to use, so IBM reserved the upper 384Kb of RAM for that purpose. That gave the machine 640Kb of RAM to play with.

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