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A Modern Accelerator Board

lyonadmiral

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I'm curious about this because I see allot of hobbyist projects such as XT-IDE and XT-FD, but I wonder what kind of engineering feat would be necessary to build a modern accelerator card for the PC/XT bus? Now I know the bottleneck is the bus itself, but if you were to just use the ISA bus just for offloading instructions to and output from the accelerator.
 

framer

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Back in the day we had few choices to speed the XT up and AT cost $$$$. Today just buy a 286 or 386 to run programs that you need speed for. The XT-IDE was a great project because old MFM & RLL drives were getting rare and unreliable with age. My 2cents...

framer
 

Maverick1978

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I'm curious about this because I see allot of hobbyist projects such as XT-IDE and XT-FD, but I wonder what kind of engineering feat would be necessary to build a modern accelerator card for the PC/XT bus? Now I know the bottleneck is the bus itself, but if you were to just use the ISA bus just for offloading instructions to and output from the accelerator.
It would be a very cool engineering feat, but I fear, impractical, as the demand would be low - certainly much lower than simply purchasing a 286 or 386 motherboard to swap into a case for use (or keeping a 2nd or 3rd computer, which let's face it, most of us have no problem doing)

The beauty of XT-IDE and its ilk are that it fills a need for the computers we have now, to allow us to continue using them. Accels were just to stave off the expense of purchasing a whole new system at a huge cost for a little longer.

This reminds me that I still need to take some time out and connect up those Sota ISA accels I got off of ebay earlier in the year (both a 286 and a 386 board, each of which will work in 8086 and 8088 systems)
 

Chuck(G)

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How modern? At some point, it's gilding the lily because ISA bandwidth limitations would be a real wet blanket. Unless you were going for a very modest improvement, the engineering (both hardware and software) would be substantial. Accelerator cards never were very inexpensive--they died out mostly because you could replace an entire motherboard more cheaply.
 

pearce_jj

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Just thinking out loud, but what about a small PCB to plug in the CPU sockets that has a 386 and some 8-to-16 bit mux logic on it? As said the bus is the issue, so going with 4.77MHz 8 bit then the closer to 4 clocks per instruction on average, the closer the system will be to it's limits.

No idea of feasibility, just thinking out loud really.
 

Trixter

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How modern? At some point, it's gilding the lily because ISA bandwidth limitations would be a real wet blanket.

This is evidenced in some of the TOPBENCH results. There is a 5150 with an accelerator, then on top of that the accelerator itself was upgraded with a make-it-486. The performance hits an upper limit well below that of an actual 486 (in fact, below a 386 IIRC.
 

krebizfan

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What software is intended to be run on this accelerator? What I remember was that games which adjusted play based on benchmarking got it completely wrong when run on an accelerator. The software couldn't see how slow all the other system components were.

The IBM PC accelerators market seemed to have a dodge to get a slightly better system without having to get purchase approval like a complete replacement computer required.
 

mac512

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For a time now i've been thinking of replacing the motherboard in my 5150 for a 386/486 board. What i want is more speed and more software compatibility, while retaining the coolness of the 5150 (and avoiding the shipping costs to Chile for an XT/AT case). I know the 5150 has only 5 expansion slots that are more separated from each other than the slots i the 5160 and newer computers. Is there some way that i can acomplish this motherboard swap?

This may be off topic. If it is please forgive me and let me know to stat a new thread.

Thanks.

Jose
 

modem7

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For a time now i've been thinking of replacing the motherboard in my 5150 for a 386/486 board. What i want is more speed and more software compatibility, while retaining the coolness of the 5150 (and avoiding the shipping costs to Chile for an XT/AT case). I know the 5150 has only 5 expansion slots that are more separated from each other than the slots i the 5160 and newer computers. Is there some way that i can acomplish this motherboard swap?
Some motherboard makers offered 'replacement' motherboards. As an example, the one shown [here] replaces an XT motherboard.

If such a replacement motherboard is an AT class one (replacing a PC or XT class one), then other things need to be considered:
1. Keyboard needs to be replaced with an AT class one.
2. Power supply may need to be upgraded.

Regarding point 2 above. I saw a few cases where the power supply was not upgraded to an AT class one, and what happened was that the computer intermittently lost its CMOS settings.
 

mac512

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Keyboard and PSU swap: OK! But i still have the 5 to 8 slots issue. Should i modify the PC (5150) case to put in an AT motherboard due to the different space between slots?

Thanks.

Jose
 

mmruzek

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This is an interesting topic. Just as a point of interest here is a photo of several different types of accelerator boards for the 8088 CPU that I have picked up over the years...

The top 2 boards are Breakthru 286 boards. The board on the bottom left is a Tiny Turbo 286. There is no maker's mark on the final board (that I can see), although I notice it is sporting an 80287 math chip in addition to the processor.

All these boards are designed to be plugged into an ISA card slot and have a ribbon cable with 40 pin connector for replacing the original motherboard cpu.

Michael

accel.jpg
 

Agent Orange

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mmruzek

Just wondering if you actually have those boards in your goody locker? I would be interested in dealing for the 286 Tiny Turbo.
 

modem7

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Keyboard and PSU swap: OK! But i still have the 5 to 8 slots issue. Should i modify the PC (5150) case to put in an AT motherboard due to the different space between slots?
You also need to worry about motherboard size, motherboard mounting holes, position of keyboard hole in case.

Why not simply get an IBM AT, or an AT clone?
 

modem7

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All these boards are designed to be plugged into an ISA card slot and have a ribbon cable with 40 pin connector for replacing the original motherboard cpu.
And perhaps one or more of them will, at power-on, run at 'slow' speed until the POST is finished (running the POST faster than what it was designed for can cause problems).
 

per

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All these boards are designed to be plugged into an ISA card slot and have a ribbon cable with 40 pin connector for replacing the original motherboard cpu.
Orchid made some accelerators that did not connect to the CPU with a ribbon cable. These accelerators got their own RAM, and work as their own computer-on-a-card. All I/O access done by the CPU on the card are registered and forwarded to the host CPU by using registers and interrupts, and the host CPU then does the actual I/O operation.

In other words, the host system itself is converted to become somewhat of a "southbridge" while the main excecution happens within the accelerator at full speed.
 

lyonadmiral

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Orchid made some accelerators that did not connect to the CPU with a ribbon cable. These accelerators got their own RAM, and work as their own computer-on-a-card. All I/O access done by the CPU on the card are registered and forwarded to the host CPU by using registers and interrupts, and the host CPU then does the actual I/O operation.

In other words, the host system itself is converted to become somewhat of a "southbridge" while the main excecution happens within the accelerator at full speed.

That's the type of project I was interested in...
 

mac512

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You also need to worry about motherboard size, motherboard mounting holes, position of keyboard hole in case.

Why not simply get an IBM AT, or an AT clone?

Not an easy task here in Chile! And shipping from the US is very expensive.

Thanks.

Jose
 

pearce_jj

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PC/XT 5160 has standard slot spacing and looks essentially identical so maybe go with that?
 

modem7

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PC/XT 5160 has standard slot spacing and looks essentially identical so maybe go with that?
Comparison of 5150 and 5160 slots (and keyboard connector position).

5160_to_5150_slot_comparison.jpg
 

Trixter

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Not an easy task here in Chile! And shipping from the US is very expensive.

Agreed, but you will have to essentially cut and remove the entire back metal where the slots are to accomodate a standard ATX 8-slot motherboard, as well as drill and finish new screw holes. Destroying a classic case just so you can put in a modern motherboard seems tragic, but then again, it is yours and you can do with it whatever you like.

If I were to pursue this project, I would try to trade my 5150 for a 5160 with someone else. That way there should be little to no modification required of the case, although you will still have to make at least an additional hole for the PS/2 mouse connector and cut out a space for the other back connectors on the board. But the main slots/holes should line up.
 
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