I just posted on this computer from Bulgaria here:
Pravetz-16ES from Bulgaria - I wanted it original, but it turned out better with upgrades
I have a 8087-1 successfully running on this motherboard with heat sinks attached to it. My question is has anyone else had success running an 8087-1 on these 12MHz Super Turbo XT motherboards given how hot the 8087-1 runs to begin with.
8087’s never overclocked AT ALL for me, not sure if it’s just me or if there might be an async solution for 8087’s just as there was for 287
rmay635703 wrote on 2023-07-31, 18:54:8087’s never overclocked AT ALL for me, not sure if it’s just me or if there might be an async solution for 8087’s just as there was for 287
I don't know of any async solution for 8087. The 287 was redesigned as a slave device to the 286 due to the complexities of protected mode. It could be these boards somehow run the 8087 at 10MHz vs 12MHz. I am not really sure if that is even possible. That is why I am asking.
jasa1063 wrote on 2023-07-31, 19:10:rmay635703 wrote on 2023-07-31, 18:54:8087’s never overclocked AT ALL for me, not sure if it’s just me or if there might be an async solution for 8087’s just as there was for 287
I don't know of any async solution for 8087. The 287 was redesigned as a slave device to the 286 due to the complexities of protected mode. It could be these boards somehow run the 8087 at 10MHz vs 12MHz. I am not really sure if that is even possible. That is why I am asking.
Most at/XT power supplies allow you to trim the 5v rail up and down .
If your board doesn’t further regulate the 5 volt rail you could try overclocking the old fashioned way.
Target 5.5 volts to start and see if your coprocessor passes the floating point tests, 10mhz 8087s run hot so a heatsync is likely needed.
Be forewarned at 10mhz there isn’t really any overhead so you might turn your 8087 into a brick.
rmay635703 wrote on 2023-07-31, 19:51:Most at/XT power supplies allow you to trim the 5v rail up and down . […]
jasa1063 wrote on 2023-07-31, 19:10:rmay635703 wrote on 2023-07-31, 18:54:8087’s never overclocked AT ALL for me, not sure if it’s just me or if there might be an async solution for 8087’s just as there was for 287
I don't know of any async solution for 8087. The 287 was redesigned as a slave device to the 286 due to the complexities of protected mode. It could be these boards somehow run the 8087 at 10MHz vs 12MHz. I am not really sure if that is even possible. That is why I am asking.
Most at/XT power supplies allow you to trim the 5v rail up and down .
If your board doesn’t further regulate the 5 volt rail you could try overclocking the old fashioned way.
Target 5.5 volts to start and see if your coprocessor passes the floating point tests, 10mhz 8087s run hot so a heatsync is likely needed.
Be forewarned at 10mhz there isn’t really any overhead so you might turn your 8087 into a brick.
Well so far with heat sinks attached mine passes the MCPDIAG 5 minute test with no issues as well as tests from CheckIt 3.0, so I am keeping my fingers crossed. I may just have gotten lucky in this instance with the 8087-1 I have.
jasa1063 wrote on 2023-07-31, 19:58:rmay635703 wrote on 2023-07-31, 19:51:Most at/XT power supplies allow you to trim the 5v rail up and down . […]
jasa1063 wrote on 2023-07-31, 19:10:I don't know of any async solution for 8087. The 287 was redesigned as a slave device to the 286 due to the complexities of protected mode. It could be these boards somehow run the 8087 at 10MHz vs 12MHz. I am not really sure if that is even possible. That is why I am asking.
Most at/XT power supplies allow you to trim the 5v rail up and down .
If your board doesn’t further regulate the 5 volt rail you could try overclocking the old fashioned way.
Target 5.5 volts to start and see if your coprocessor passes the floating point tests, 10mhz 8087s run hot so a heatsync is likely needed.
Be forewarned at 10mhz there isn’t really any overhead so you might turn your 8087 into a brick.
Well so far with heat sinks attached mine passes the MCPDIAG 5 minute test with no issues as well as tests from CheckIt 3.0, so I am keeping my fingers crossed. I may just have gotten lucky in this instance with the 8087-1 I have.
Maybe you have a really late example,
It’s a normal Intel and runs great at 12mhz?
It's a D8087-1 with a ceramic shell and no gold top. Looks exactly like the one pictured. It is currently running stable on this motherboard, which makes me wonder if it is really running at 12MHz or not.
CheckIt 3.0 reports 320.8K Whetstones for the 8087-1 in this system. For comparison my Juko Nest N3 NEC V30@10MHz w/8087-1@10MHz reports 331.6K Whetstones. I don't know if the 16-bit bus makes that much difference, but I would have thought that a 8087-1@12MHz would have the higher score.
Edit: see also PC Magazine, 1986 Sep 30 - Microway's ad mentions 8087-12.
Nie tylko, jak widzicie, w tym trudność, że nie zdołacie wejść na moją górę, lecz i w tym, że ja do was cały zejść nie mogę, gdyż schodząc, gubię po drodze to, co miałem donieść.
I agree the Intel 8087-1 was a 10Mhz max design (for Turbo XT's with 4.77/10mhz) and you are already OC your V20 a lot. Personally I do not know why you do not try to run it all at 10Mhz... that seems the logical choice.
Hate posting a reply and then have to edit it because it made no sense 😁 First computer was an IBM 3270 workstation with CGA monitor. Stuff: https://archive.org/details/@horun
Horun wrote on 2023-08-01, 02:58:I agree the Intel 8087-1 was a 10Mhz max design (for Turbo XT's with 4.77/10mhz) and you are already OC your V20 a lot. Personally I do not know why you do not try to run it all at 10Mhz... that seems the logical choice.
The board came with an 8MHz NEC V20 clocked at 12MHz. That is how it was packaged from the factory in Bulgaria. It has a jumper for 4.77MHz or 12MHz operation and that is it. Unless you mod the board those are your only supported speeds. I am just grateful the 8087-1 I am using has not had any issues so far.
rmay635703 wrote on 2023-07-31, 19:51:Most at/XT power supplies allow you to trim the 5v rail up and down .
If your board doesn’t further regulate the 5 volt rail you could try overclocking the old fashioned way.
I have several AT PSUs - none of them allows the user to adjust the 5V rail. Can you give an example for an AT-PSU with adjustable 5V output?
Also XT / AT mainboards for 8086 or 286 that have their own voltage regulator onboard must be extremely rare.
majestyk wrote on 2023-08-01, 04:47:rmay635703 wrote on 2023-07-31, 19:51:Most at/XT power supplies allow you to trim the 5v rail up and down .
If your board doesn’t further regulate the 5 volt rail you could try overclocking the old fashioned way.
I have several AT PSUs - none of them allows the user to adjust the 5V rail. Can you give an example for an AT-PSU with adjustable 5V output?
Also XT / AT mainboards for 8086 or 286 that have their own voltage regulator onboard must be extremely rare.
All the small Packard bell at PSUs I salvaged have a trim pot that bumps voltage up or down.
Same for the old At tower Omnitek systems I have.
every time I’ve had to adjust voltage (which is rare) I’ve found an adjustment Pot.
Maybe luck or maybe the brand.
majestyk wrote on 2023-08-01, 04:47:Also XT / AT mainboards for 8086 or 286 that have their own voltage regulator onboard must be extremely rare.
They are. I assume, that's because floppy drives and fixed-disks needed +12/+5v volts, anyway.
So it made sense to leave the task of generating multiple voltages up to an power supply.
I assume that certain embedded motherboards are an exception, though.
Motherboards used in laptops sometimes work with a single DC voltage and have their own voltage generators.
In the early days of 8080 systems, there used to be a lot of different voltages on the motherboard, too.
DRAM, EPROMs and the 8080 needed two, if not three operating voltages.
The Z80 made things much easier (8085, too). It had an integrated DRAM refresher and worked with a single voltage.
EPROMs also had evolved and could work with a single voltage (read mode).
Anyway, it just came to mind. The Z80 and XT systems had a lot in common, including the standard voltages used.
"Time, it seems, doesn't flow. For some it's fast, for some it's slow.
In what to one race is no time at all, another race can rise and fall..." - The Minstrel
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I have had the computer running now for a few weeks and I have yet to have any issues with the 8087-1 FPU. I have run over 1500 iterations of Intel's CHKCOP v2.2 utility with not 1 single error. I can now say even at 12MHz with proper cooling and the right 8087-1 everything should work just fine.
