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cozzyd

I assume named after the involuntary commitment section of California law (portmanteaued with Area51...pretty clever).

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the IBM 5150 was the first XT class computer, which created the IBM PC standard still used today.

Ah, that's much more plausible!

5150 is PC, XT is 5160, and AT is 5170.

Thus not XT class, but PC class.

The 5160 barely had any improvements. Except for extra slots and including a hard drive, it was essentially the same. The AT had real performance improvements. I remember using one in 1987 or so at my dad’s office.

Correct, as "XT" stands for eXtended Technology. You can't extend it without having the basic technology first. The 5150, aka the PC, was that basic technology. However, in terms of CPU, graphics, sound and all other aspects relevant to this demo, the 5150 and 5160 are interchangeable.

The main differences between 5150 and 5160 are: 5160 upgraded from 5 to 8 ISA slots (also changing the size of the bracket, which has been the standard ever since, even today with PCI-e 5.0). 5160 removed the cassette port. 5160 came with a harddisk as standard (and as a result, a more powerful PSU, as the stock PSU of a 5150 was insufficient for a HDD, and generally required an upgrade).

Memory-wise, there are various different revisions of 5150 and 5160 boards, which can take different amounts of memory onboard. For the 5150, the early revisions took 16k-64k, the later revisions took 64k-256k. For the 5160, the early revisions took 64k-256k, the later revisions took 256k-640k. In all cases it is possible to add additional memory up to 640k via an ISA card. So it is possible to have a 5150 configuration with the full 640k that the most high-spec 5160 had.

Then there is also the IBM 5155, the 'portable' PC. This is essentially a 5160 motherboard in a modified case, with an integrated CRT. As such, it is also fully compatible with the 5150 and 5160, and can run these demos flawlessly.

> In all cases it is possible to add additional memory up to 640k via an ISA card.

Was there any performance difference if you added memory in an ISA card as opposed to directly on the motherboard?

Not on the original PC/XT machines, as the ISA bus was basically the CPU data bus. So regardless of whether you had memory on board or on an ISA card, data transfers were exactly the same speed. On later machines, the CPU would be clocked faster than the ISA bus, so this was no longer true.

"5160 came with a harddisk as standard"

This was true at release but the 5160 was eventually available in a configuration with no hard drive and dual floppies.

I stand corrected, thank you.

As I remember it, the term "XT class" was used back in the day to distinguish between "AT class" PCs and those prior - i.e. to mean an IBM PC, XT or comparable machine. So (weirdly enough) the 5150 was considered XT class despite predating the XT (they're almost identical as far as software is concerned anyway). The term "PC class" wasn't a thing because PC came to be shorthand for any IBM PC/XT/AT or later x86 machine. Some more powerful machines like the Amstrad PC1512 (with an 8MHz 8086) were also considered XT class - these machines could run games like Bruce Lee and Digger which were designed for the PC/XT (and which were too fast on AT and later machines), though the gameplay was quicker than they were designed for so were extra-challenging.

Yeah, that seemed to be the usage in most contemporary literature/magazines. There are also those other architectural factors like the bus width, the number of PICs, the keyboard subsystem and so on, which is why you could have "XT-class" 8086 and even 286 machines (like a Tandy 1000 model or two).

What may also have had an impact was that clones were generally XT-clones (using the newer, smaller ISA card layout, and no cassette port), not PC-clones. And indeed, they were specifically advertised as 'XT-clone', 'XT-class' and such. So the 5150 is really the oddball here. Back in the old days I understood the usage as follows: 'PC' was a catch-all term for all IBM PC-compatible machines that ran DOS. 'XT' was the term used for machines with an 8088 (or sometimes V20) CPU (and of course there was the 'Turbo XT' subclass for CPUs running at more than 4.77 MHz). 'AT' was the term for 286 machines. After that era, people just identified PCs by the CPU used, so you had '386es', '486es', 'Pentiums' etc.

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