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Hello,
You may find that silly, but I would like to know what are the AT, XP and PC and what is/are the difference(s) between them. I keep on seeing them in a lot of tutorials about the DMA or the keyboard.
Thank you in advance.

You mean AT, XT, and PC.

First came the IBM PC (Personal Computer, 1981, 8088 CPU).

Then came the IBM XT (Extended Technology, 1983).

Then came the IBM AT (Advanced Technology, 1984, 80286 CPU).

Then they ran out of stupid abbreviations and shifted to a new pattern of confusing people, mostly based on the CPU type.

Solar wrote: You mean AT, XT, and PC.

First came the IBM PC (Personal Computer, 1981, 8088 CPU).

Then came the IBM XT (Extended Technology, 1983).

Then came the IBM AT (Advanced Technology, 1984, 80286 CPU).

You sure about the XT and PC? In my mind they were identical, with the XT being the real name and the PC being the streetname. The XT having only 8086 and 8088 (and a few 80186's) with the AT taking all else for its account.

I think they stopped naming the computer after the processor after they found out that the AT wasn't that much better than the PC/XT since it still had the same peripherals at the older speed, plus the slow bus.

I googled some website that claimed the XT being the PC with hard drive added.

Dunno. Does it really matter today? About as much as that there actually was a Zorro I bus (in the Amiga 1000)...

Solar wrote: I googled some website that claimed the XT being the PC with hard drive added.

Doubt that. We had an XT at home (so I was told, I was 9) and it didn't have a hard drive. Then again, I wouldn't know, was still trying to build lego mansions at that time. Oh, and code small C64 basic games

Dunno. Does it really matter today? About as much as that there actually was a Zorro I bus (in the Amiga 1000)...

and that's the part that's just too bad, they're all 20+ year old computers. In a way not relevant...

As a sidenote, Amiga's are also that old. Does that make them obsolete? for what I hear, mostly from you , they still work better than windows boxes.

They are obsolete.

The "Classic" line (1992 design) is built around the 68k, with PPC 603e and 604e "expansion cards" being available, and a highly integrated set of "custom chips".

The AmigaOne and Pegasos, both stepping to the plate claiming to be the Amiga successor, are both sub-1GHz PPC mobo's with little "flair" to them since all the rest is stock hardware.

The OS 3.x running on the "Classic" line doesn't have memory protection or multiuser capabilities. USB support was added only recently.

But boy, does the OS have some true design gems under it's hood. It is, at the same time, one of the cleanest, intuitive, and most maintainable on-drive setups I've ever seen.

Sorry, but whenever the subject comes to Amigas I get sentimental.

The PC used an 8088 - 8 bit data bus.
2 floppy's, cassette recorder (!!!), no hard disk,256k of memory,
CGA (ugh) or MGA.

The XT used an 8086, but retained the 8 bit expansion bus and could use 512k of memory. A lot of XT clones used EGA even though it wasn't shipped by IBM as such.
The XT was also the first IBm to ship with a hard drive - the circuitry was built into the motherboard and set the ST-506 standard we use today (with LBA modifications).

The XT/286 used a 286, implemented more ciruity in VLSI, but added nothing new. 8 bit expansion, 512k memory

The AT used the 80286, EGA, 16-bit ISA bus and usually shipped with a full 512k of memory. The hard disk used by IBM was a conner and suffered from massive faults (Conner no longer exists - got bought by Seagate).

None of this takes into account clones etc who usually met the standards + some.

PS/2's used 8086, 286, 386 and 486 processors. The main change with these was Microchannel Expansion Bus and the EDSI hard disk interface.
Microchannel lives on in RS/6000 workstations.

I own 3 Amiga 500's. All are dedicating their lives to satellite signal research.

I can dribble on more if you want, but my feet are gettiing wet.

Keep safe.

Solar wrote: I googled some website that claimed the XT being the PC with hard drive added.

Not exactly; while the XT was the first IBM model with a hard drive option (10M or 20M), it just as often shipped with a pair of full-height FDDs (the models with hard drives had only one floppy drive). The real differences were the double-density floppy drives, larger bus (8 slots instead of five) power supply (200w instead of 150w, IIRC) and memory capacity (it could load 512k on the motherboard, whereas the original 5150 could only fit 64k, and the 5150-2 could fit 256k), plus a few refinements in the case design (mostly relating to the differences above).

The original DeskPro used the XT configuration, and as a result, the vast majority of 8088 based clones followed suit. Hence, most 8088 clones were technically referred to as 'XT type' models, especially if they designed to fit the so-called 'XT case' design.

The AT, in addition to being a true 16-bit system, had a larger case, and was designed with half-height drives in mind (though they could of course use full height drives); they had five half height drive slots, and 250w power supplies. This configuration became known as the 'AT case', and most 80286 and later clone boards were designed for it, prior to the introduction of ATX cases in the mid-1990s.

C&CW.

PS: No, the original PC's model number (5150) has no connection with the common US police radio code for 'psychotic requiring restraint'... tempting as the thought might sound.

Schol-R-LEA wrote:
This configuration became known as the 'AT case', and most 80286 and later clone boards were designed for it, prior to the introduction of ATX cases in the mid-1990s.

You forgot the "Baby-AT" case (BAT) that had its time in between the AT and the ATX (AT eXtended) cases.

That's true, I'd forgotten about that.