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The Perfect IBM PC AT

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First post, by Great Hierophant

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If you want a perfect, i.e. the most powerful IBM PC AT system ever made, you have to start with the last models. There are three models to the AT, but only the third can operate normally at 8MHz. Here is how the eight slots (all full-length) should be used:

Floppy/Fixed Disk Adapter (16-bit, 2 floppy, 2 half-height hard drives)
16MB ISA Parity Memory Expansion Card (16-bit probably, only 15MB recognized)
Serial/Parallel Adapter
Serial/Parallel Adapter (PC BIOS supports maximum of two Serial, three Parallel)
Roland MPU-IPC (true MPU-401 capability w/breakout box)
Sound Blaster 1.0 (for Adlib, Sound Blaster DSP and Game Blaster)
IBM Enhanced Graphics Adapter w/256 KB RAM upgrade (for 640x350x16 graphics)
Hercules Graphics Card Plus (for monochrome text + graphics + third parallel)

As far as drives go, you will need one 1.2MB 5.25" Floppy and one 1.44MB 3.5" Floppy (supported in BIOS, requires non-IBM setup program). There should be room for two hard drives, so you will need two of the 30MB hard drives IBM made available for the late model ATs. Finally, you will need a 80287 math co-processor for the socket rated at 8MHz.

Of course, you will need to attach the right kind of peripherals to this device. The Hercules should ideally be connected to an 5151 Monochrome Display and the EGA to the 5154 Enhanced Color Display. The Roland must be connected to an MT-32, early revision. The Keyboard must be a 101-Enhanced keyboard (use a Model M PS/2 keyboard and the appropriate cable.) The mouse should be a Microsoft Serial Mouse.

For games that do not require a 386 for protected mode or a VGA, this is undoubtedly the most powerful and compatible PC ever made. It should run any of DOS game that does not require either type of hardware. It may not run the game as quickly as you may like. In fact, as the AT has a speed limiter, it won't ever run any faster.

Reply 1 of 9, by HunterZ

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I had a 286 clone by Wyse that ran at 8MHz, but my cousins had a different brand that I think ran at 12MHz (http://www.computerhope.com/jargon/num/80286.htm) - were faster ATs like that all clones?

Also, I got my Wyse 286 around 1986-1987 and used it all the way until the early 90s (got a 386 a little after Wolfenstein 3-D came out). 5-7 years is an unprecedented amount of time these days for going without a PC upgrade.

Reply 2 of 9, by 5u3

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HunterZ wrote:

were faster ATs like that all clones?

Intels 80286 CPUs reached up to 12 MHz, IBM made licensed 286 CPUs with only 6 and 8 MHz. The faster clones with 16, 20 and 25 MHz were all from other manufacturers like AMD and Harris.
I think IBMs original "TTL graveyard" board design was too unreliable at higher speeds. This problem was solved when C&T released the first NEAT chipset, making faster clones possible.

Reply 3 of 9, by Great Hierophant

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If the AT is somewhat too slow for you, then I present the next dream machine, the IBM PS/2 Model 40slc. This is the best model for PS/2 gaming because it is the last that comes with ISA slots. The 386slc operates at 20MHz and has the 16/24bit bus of the 386sx, but it also has 8KB of internal cache for improved performance. It comes with PS/2 keyboard and mouse ports as well as a serial and a parallel port. It contains 16-bit IBM VGA on the motherboard (VGA was designed to interface to 8-bit slots, so we will see a speed boost.) It can be expanded to 16MB using PS/2 SIMMs and has a socket for a 80387 math co-processor. Finally, it should come with an 80MB hard drive and a 2.88MB Floppy Drive.

Most importantly, it has five 16-bit ISA slots in addition to all the motherboard ports. With all those ports, you should have enough to house all the sound cards you can fit inside.

Reply 4 of 9, by HunterZ

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That is impressive. Speaking of the PS/2, I got my hands on one once several years ago but ended up tossing it out due to the fact that the motherboard seemed bad and it had an MCA bus (which I'd never heard of before at the time), making all the expansion cards useless except in other PS/2 computers.

Reply 5 of 9, by 5u3

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Great Hierophant wrote:

If the AT is somewhat too slow for you, then I present the next dream machine, the IBM PS/2 Model 40slc.

Back in the days I had a similar machine, a Compaq ProLinea 3/25zs. I used it for a long time, from 1992 to 1996, and I would have kept it for playing old games, but it died due to lightning striking a power line transformer nearby. It would have been ideal for vintage games (by 1993 standards, it was already too slow for new ones), the only disadvantage was the really small proprietary slimline desktop case which provided only two ISA slots and two 3.5" bays 😒.

Specs:
Intel 386SX-25
Western Digital 76C10A chipset with integrated IDE/FDD and I/O (2 serial, 1 parallel, PS/2 keyboard/mouse)
Western Digital 90C30 integrated Paradise VGA with 512k RAM
Four 30pin SIMM slots (2x1 MB SIMMs installed)
80 MB harddisk, 1.44 MB floppy

Some features of this system were very cool for vintage games compatibility: The clock speed could be adjusted via keyboard shortcuts - neat! 😁 When booting from floppy, the system automatically slowed down to avoid problems with PC booters and copy protection mechanisms. The integrated VGA was not very fast, but emulated Hercules, CGA and EGA perfectly. There was a special Compaq DOS included, with a lot of extra features, like improved memory drivers and utilities for better software compatibility. Sadly, most of them only worked on the Compaq, because they depended on the installed hardware.

Reply 6 of 9, by eesz34

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5u3 wrote on 2005-12-07, 23:19:
Back in the days I had a similar machine, a Compaq ProLinea 3/25zs. I used it for a long time, from 1992 to 1996, and I would ha […]
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Great Hierophant wrote:

If the AT is somewhat too slow for you, then I present the next dream machine, the IBM PS/2 Model 40slc.

Back in the days I had a similar machine, a Compaq ProLinea 3/25zs. I used it for a long time, from 1992 to 1996, and I would have kept it for playing old games, but it died due to lightning striking a power line transformer nearby. It would have been ideal for vintage games (by 1993 standards, it was already too slow for new ones), the only disadvantage was the really small proprietary slimline desktop case which provided only two ISA slots and two 3.5" bays 😒.

Specs:
Intel 386SX-25
Western Digital 76C10A chipset with integrated IDE/FDD and I/O (2 serial, 1 parallel, PS/2 keyboard/mouse)
Western Digital 90C30 integrated Paradise VGA with 512k RAM
Four 30pin SIMM slots (2x1 MB SIMMs installed)
80 MB harddisk, 1.44 MB floppy

Some features of this system were very cool for vintage games compatibility: The clock speed could be adjusted via keyboard shortcuts - neat! 😁 When booting from floppy, the system automatically slowed down to avoid problems with PC booters and copy protection mechanisms. The integrated VGA was not very fast, but emulated Hercules, CGA and EGA perfectly. There was a special Compaq DOS included, with a lot of extra features, like improved memory drivers and utilities for better software compatibility. Sadly, most of them only worked on the Compaq, because they depended on the installed hardware.

Hi, replying to a really old post I know, but do you remember the keyboard combination to change the CPU speed? I have one of these now and can't find any information *anywhere* on these sorts of particulars.

Reply 8 of 9, by eesz34

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Ringding wrote on 2022-02-21, 08:00:

It might have been Ctrl + Alt + +/- on the numeric block. At least I think it was this on my 286.

I did a quick test of this, and no go. Granted I only tested by doing "type somelongfile.txt" and the speed didn't change. I tried Ctrl-Alt along with plus or minus on the numeric keypad, with the numlock on and off. Tried the +/- to the left of the backspace too. Tried Ctrl-Alt-h and l.

It does have an option in the BIOS for startup speed, so it seems it can do it.