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The biggest problem with the DX/50 was the bus. AMD was already struggling to run the VLB at 40MHz with their DX-40 parts. A lot of video cards couldn't handle

The biggest problem with the DX/50 was the bus. AMD was already struggling to run the VLB at 40MHz with their DX-40 parts. A lot of video cards couldn't handle it and running certain hard drives controllers on that speed sometimes ran the risk of corrupting disks. I can imagine that the DX/50 was a hellscape of I/O trying to find cards that could run at the 50MHz bus clock or being stuck at EISA's 33MB/sec.

danbruc 4y ago
My first PC was a 486DX/50 and until today I was totally unaware of the potential bus timing issues but I can not remember ever having had issues. But this might finally explain why it came with a turbo button - even though it should probably be called an anti-turbo button - that allowed changing the clock to 10 MHz. But now I wonder why they would have made it that slow instead of say 25 MHz or 33 MHz? I vaguely remember using the slower clock to make games playable that were running way to fast, so maybe that also factored into it.
- elzbardico 4y ago
  If I am recalling correctly the turbo button was a workaround for software that had problems running at the high speeds. But I may be mistaken.
  - Koshkin 4y ago
    You remember correctly. (Remarkably, GORILLA.BAS did not have that problem.)
- AdrianB1 4y ago
  The Turbo button did exist on processors that ran over 4.77 MHz of the original 8086. I had a Turbo button on the 9.54 MHz 8088, also on the 386 DX/40 (lowering the frequency to 8 MHz IIRC), it was not specific to 486. Actually the 486 was the last CPU that had that button, I think.
myself248 4y ago
I had one of those AMD 486DX40's and it was a screamer. Yes, very picky about VLB card choice and even placement; we had a big multi-IO card (possibly made by DFI?) and a Trident SVGA card, and it took a few days of shuffling and benchmarking and stability testing to find the optimum arrangement. ISTR that if the IO card was closest to the CPU, it simply wouldn't boot about half the time, and it was unstable if it did. Putting the IO in the third VLB slot and the video card in the second, leaving the first empty, seemed to be the best arrangement. And it left the IDE cables reasonably close to the drives, so that was a win. But once we got all the drivers loaded for that IO card and stuff, it absolutely flew. Ran rings around a lot of Pentium/90 systems because their 33MHz bus just couldn't keep up, and in the days before GPUs, pushing pixels into video RAM was a contest of raw bus bandwidth and very little else. We eventually had quite a lot of drives on that machine, so UDMA/33 moved a lot of bytes while still leaving spare bus cycles for overhead. I tried overclocking it to 50MHz a few times, and the IO and VGA cards were both capable, it was the RAM that shat itself. The upper 3MB of RAM would just vanish, leaving only 1MB, which was honestly a fair tradeoff for some things -- I'd boot in that config if I had a lot of PKZIP to do, or for rendering fractal graphics, which didn't use a lot of RAM but really appreciated the extra clock speed. Then clock it back down and reboot to use the results of those operations. Underclocking was also nice, and something I did frequently, so I could unplug the CPU fan and enjoy some quietude during a long BBS file transfer, which certainly didn't need much CPU grunt. The mobo clock generator didn't mind being re-jumpered while the system was on, and going from 40MHz to 16MHz (I think) was a simple matter of adding or removing one jumper cap, as I recall. I could reach through the floppy-drive opening in the front of the case and do this after a download started. Then switch off the monitor, and listen to the quiet tick-hiss of interference on my FM radio, which picked up just enough of WHYT 96.3 in the basement that I could listen to some alt-rock while also being aware of the UART ISR being hit. When the ticking stopped, the modem was idle, turn the monitor back on, jumper the CPU back up to speed and plug the CPU fan back in while the CRT warmed up, and get on with unpacking the file.
- Zardoz84 4y ago
  My first PC was an AMD 386DX40 with a OAK SVGA 1MiB , a SB 2 clone card, a 200MiB hd and X2 Sony CDROM drive... I remember that worked very nice and stable. And that I could play Doom 2 and Sim City 2000 without issues.
saltcured 4y ago
I remember having a 486DX4/100 (a clock-tripled 33 MHz bus and 99 MHz core). I downloaded the reference manuals from Intel and found the pins I could jumper to change the clock multipler from x3 to x2, and then I increased the bus speed to 50 MHz to effectively have a 486 DX2/100. I don't remember all the hardware details anymore, but I think I tested system stability by recompiling XFree86 on Linux. This was something I already knew how to do as a beta tester for 2D accelerator drivers, and it took many hours and so seemed like a good test...
- xenospn 4y ago
  First thing I would do when I got a new CPU was FreeBSD make world or re-compiling wine from source.
deleted 4y ago
[deleted]

danbruc 4y ago

My first PC was a 486DX/50 and until today I was totally unaware of the potential bus timing issues but I can not remember ever having had issues. But this might finally explain why it came with a turbo button - even though it should probably be called an anti-turbo button - that allowed changing the clock to 10 MHz. But now I wonder why they would have made it that slow instead of say 25 MHz or 33 MHz? I vaguely remember using the slower clock to make games playable that were running way to fast, so maybe that also factored into it.

elzbardico 4y ago
If I am recalling correctly the turbo button was a workaround for software that had problems running at the high speeds. But I may be mistaken.
- Koshkin 4y ago
  You remember correctly. (Remarkably, GORILLA.BAS did not have that problem.)
AdrianB1 4y ago
The Turbo button did exist on processors that ran over 4.77 MHz of the original 8086. I had a Turbo button on the 9.54 MHz 8088, also on the 386 DX/40 (lowering the frequency to 8 MHz IIRC), it was not specific to 486. Actually the 486 was the last CPU that had that button, I think.

myself248 4y ago

I had one of those AMD 486DX40's and it was a screamer. Yes, very picky about VLB card choice and even placement; we had a big multi-IO card (possibly made by DFI?) and a Trident SVGA card, and it took a few days of shuffling and benchmarking and stability testing to find the optimum arrangement. ISTR that if the IO card was closest to the CPU, it simply wouldn't boot about half the time, and it was unstable if it did. Putting the IO in the third VLB slot and the video card in the second, leaving the first empty, seemed to be the best arrangement. And it left the IDE cables reasonably close to the drives, so that was a win. But once we got all the drivers loaded for that IO card and stuff, it absolutely flew. Ran rings around a lot of Pentium/90 systems because their 33MHz bus just couldn't keep up, and in the days before GPUs, pushing pixels into video RAM was a contest of raw bus bandwidth and very little else. We eventually had quite a lot of drives on that machine, so UDMA/33 moved a lot of bytes while still leaving spare bus cycles for overhead. I tried overclocking it to 50MHz a few times, and the IO and VGA cards were both capable, it was the RAM that shat itself. The upper 3MB of RAM would just vanish, leaving only 1MB, which was honestly a fair tradeoff for some things -- I'd boot in that config if I had a lot of PKZIP to do, or for rendering fractal graphics, which didn't use a lot of RAM but really appreciated the extra clock speed. Then clock it back down and reboot to use the results of those operations. Underclocking was also nice, and something I did frequently, so I could unplug the CPU fan and enjoy some quietude during a long BBS file transfer, which certainly didn't need much CPU grunt. The mobo clock generator didn't mind being re-jumpered while the system was on, and going from 40MHz to 16MHz (I think) was a simple matter of adding or removing one jumper cap, as I recall. I could reach through the floppy-drive opening in the front of the case and do this after a download started. Then switch off the monitor, and listen to the quiet tick-hiss of interference on my FM radio, which picked up just enough of WHYT 96.3 in the basement that I could listen to some alt-rock while also being aware of the UART ISR being hit. When the ticking stopped, the modem was idle, turn the monitor back on, jumper the CPU back up to speed and plug the CPU fan back in while the CRT warmed up, and get on with unpacking the file.

Zardoz84 4y ago
My first PC was an AMD 386DX40 with a OAK SVGA 1MiB , a SB 2 clone card, a 200MiB hd and X2 Sony CDROM drive... I remember that worked very nice and stable. And that I could play Doom 2 and Sim City 2000 without issues.

saltcured 4y ago

I remember having a 486DX4/100 (a clock-tripled 33 MHz bus and 99 MHz core). I downloaded the reference manuals from Intel and found the pins I could jumper to change the clock multipler from x3 to x2, and then I increased the bus speed to 50 MHz to effectively have a 486 DX2/100. I don't remember all the hardware details anymore, but I think I tested system stability by recompiling XFree86 on Linux. This was something I already knew how to do as a beta tester for 2D accelerator drivers, and it took many hours and so seemed like a good test...

xenospn 4y ago
First thing I would do when I got a new CPU was FreeBSD make world or re-compiling wine from source.

deleted 4y ago

[deleted]