Normally you'd need to replace the quartz as well to increase the speed of the CPU (you could probably even oc it ) ... but on your card I can't figure out where it is (if there's even one. Maybe they're generating the 8Mhz with the 4.77MHz speed of the ISA ?)

Deksor wrote:

Normally you'd need to replace the quartz as well to increase the speed of the CPU (you could probably even oc it ) ... but on your card I can't figure out where it is (if there's even one. Maybe they're generating the 8Mhz with the 4.77MHz speed of the ISA ?)

That's what stumped me too. I was thinking I'd be able to buy a cheap CPU and a crystal, swap them out and see what happened, but there's nothing on the board that looks like a crystal to me.

If it is using the main crystal and there's no way to change the card to allow faster CPUs, I'll probably have to leave it be. I don't really want to "overclock" the rest of the system in any way, so I wouldn't go as far as replacing the crystal on the motherboard.

Does anyone know if a 286 is in any way capable of "telling" a computer (or in this case, an expansion board) what speed it should run at?

I used to have one of those. It uses a ribbon cable from the accelerator card that has an adapter on the end that plugs into the 8088 socket on the motherboard. If I recall you then take the removed 8088 and stick it in a socket on the accelerator board for backwards compatibility. Some boards had an additional socket for an 80287 math co-processor too. The accelerator board probably gets it's clock source over the ribbon cable from the CPU socket so it can operate synchronously with the rest of the motherboard.

Sadly, if you don't have that cable it's probably useless-although making your own wouldn't be too difficult if you're capable of soldering ribbon cable to the topside of a dip socket.

FesterBlatz wrote:

I used to have one of those. It uses a ribbon cable from the accelerator card that has an adapter on the end that plugs into the 8088 socket on the motherboard. If I recall you then take the removed 8088 and stick it in a socket on the accelerator board for backwards compatibility. Some boards had an additional socket for an 80287 math co-processor too. The accelerator board probably gets it's clock source over the ribbon cable from the CPU socket so it can operate synchronously with the rest of the motherboard.

Sadly, if you don't have that cable it's probably useless-although making your own wouldn't be too difficult if you're capable of soldering ribbon cable to the topside of a dip socket.

I guess I didn't make it real clear in the original post, but I have the card complete with cable and its been installed for a while in my 5150. It works great and benchmarks show it running like a 286. I just wanted to make it a little faster.

If it gets the clock source from the board, what makes the CPU run at 7.16Mhz? That's what is reported in most programs. This is waaay before my familiarity with motherboards and CPU clocks, so I genuinely have no idea how a CPU is told to run at a given clock speed on a system from this era.

Welp, that was easy... The only chip that stood out on the Tiny Turbo was the little AMD chip next to the CPU socket:

http://pdf1.alldatasheet.com/datasheet-pdf/vi … TEL/D82284.html

A Clock generator for 286 processors! It looks like they are made in either 8Mhz or 10Mhz versions. If there is no "10" designation, then it is likely 8Mhz.

I found an interesting post on VCF too:
http://www.vcfed.org/forum/archive/index.php/t-28758.html

I'll quote a poster there:
"The typical speed to accelerate an 8088 system is to 8MHz. Why 8MHz? Two reasons. First, the CPU accesses the ISA bus at full speed, which is OK at 4.77MHz. But XT boards do not have any capability to automatically insert wait states between bus accesses, so you are limited to accessing slots at no more than 8.33MHz to be safe. 10MHz accesses will lead to instability. Second, the RAM must be able to respond in 4 8088 bus cycles, and if you approach 10MHz slower RAM chips may not be able to respond in time. With 8MHz, even 250ns RAM chips will be able to respond in time for the 8088."

I'm not sure if this applies for CPUs on upgrade cards like mine, but it seems logical that it would. If the BUS can't keep up with a faster CPU and would actually become unstable, then there's no point in trying to push it any farther. So, aside from doing really crazy modifications to the card that would allow it to run as close to the threshold as possible, this is as fast as an IBM PC can get... and that's pretty cool! The thought of bumping the CPU speed up a bit was nice, but RAM and storage limitations are going to creep in before long anyway. I'm still contemplating whether I should bother trying to fit my CT1350B in this system or not... I doubt most games that could use Adlib or CMS music would be worth playing on such a slow computer. I'd probably be best off saving that for my first 386 or something. 😉

So, this is the fastest an IBM 5150 can get apparently. The jury is still out on whether there's any room for improvement with a different EGA card, but it seems like my EV-659 Deluxe is probably about as fast as its going to get. I can finally call this system nearly finished. I just need to repair the old Model F keyboard I have and it will be DONE. 😀

There are faster processor upgrades card that have RAM on the card to avoid slow ram on the PC motherboard becoming a bottleneck. I used to run an Intel inboard/386 in my 5160. A quick google suggests it will run in a 5150 if you can find one. 386DX-16 with 1MB onboard RAM (I never did find the optional RAM upgrade for it). Toyed with the idea of putting a 486DLC on it, but never actually got around to it. That machine is long gone now unfortunately. There's also the SOTA mothercard. 12Mhz 286 with 4 30 pin SIMM slots for up to 16MB onboard RAM. I've only ever seen one them in pictures though, so even harder to find than an inboard/386.

A few people have already done this. The best upgrade for your card is something like a make it 486, which would upgrade your 8MHz 286 to a 16MHz 486SLC (clock doubled).

If I found a dirt cheap 386 or 486 upgrade board I'd probably try it just for kicks, but I wouldn't put much into it. There are too many limitations for the 5150 to be of practical use for gaming beyond this point. Squeezing in a sound card and a faster CPU card would be interesting, but then I'd be limited by EGA and the monitor, so I might as well just save the more advanced games for another system. I'm hoping to put together a full 386 system next, since I have lots of hardware from that era and I'm itching to use it! As soon as I find a motherboard and CPU cheap\free, that will be the next project. I think I have everything else I'd need. Same for a 486... 😁