Leonard Tramiel once told me that the "world's record" for a production 6502 was around 25Mhz before the smoke came out. This was in a lab at Commodore, and beer was probably involved (and may have been used to cool the chip).
One day I was working at a different branch filling in for someone on sick leave, and I spent an hour trying to get a PC I just built to boot reliably. Every time it crashed after an minute or so. I didn't get it, everything seemed fine.
Eventually it turned out the "cheat sheet" they had of the jumpers was upside down over there. Someone had copy/pasted the pictures so it was matching the orientation of how they usually had the PC on the desk, rather than upside-down as I was used to. But the text was the right way up. So the total thing looked the same as in our branch except it wasn't.
It was a square block so I hadn't noticed the orientation was different. Turned out I had the 100Mhz pentium configured for 180Mhz. Oops. That wasn't even an officially supported speed of the motherboard but the BIOS messages indicated this (which I only noticed afterwards)
As we didn't want to sell this CPU after the torture I had put it through we decided to use it for a display box instead, and we tried to keep it running as long as possible by using compressed air cans upside down to blow dry ice :D It actually ran reliably until the can ran out. Only later I found out that liquid nitrogen extremeclocking was actually a thing :D
I loved modifying CONFIG.SYS with a hex editor to translate MS-DOS 6.2 (?) boot menu.
Just for fun, I loaded Red Hat 5.2 on to the machine and it ran just fine. The syslog was full of bizzare errors, chattering the whole time too.
See http://www.benchtest.com/rain.html
Reasoning by MS was low quality of the countless low-end power supplies, and maybe voltage regulator modules on mainboards, being 'unreasonably' stressed by load changes that fast.
[1]: 豪杰超级解霸2000 [2]: https://www.wendangwang.com/doc/e6d559d6f2cd9ba7007939d7/3
So during a long download, I didn't need all 40 MHz screaming along (and heating up the chip to the point that it needed a cooling fan -- a COOLING FAN, can you imagine a CPU running so fast it couldn't cool itself on ambient air?), so I decided to see if the clock generator jumpers were hot-pluggable.
Lo and behold, they were! I could reach in and seamlessly downclock the CPU to 8MHz (which was just one jumper-cap different than the 40MHz setting), which was still plenty to service the UART FIFO interrupt. Unplug the CPU fan too, which made the machine silent. Turn the monitor off, kick back in my chair, and take a catnap. The Telemate terminal software would play a little tune when a download finished, which would wake me up, I'd turn the monitor back on, open a DOS prompt, start unzipping the file, and then reach in and clock the CPU back up so the pkunzip process would finish in a timely manner.
It would do 50MHz but the upper half of RAM would disappear, so there weren't a lot of workloads appropriate for that configuration....
The game was intended to be on a 7Mhz stock machine pre-1990. And it was perfectly timed to that speed.
Sidebar: Ultima games are great. Did you see Nox Archaist?
They originated with "Turbo XT" class machines which ran an 8088 but at 8, 10 or 12 MHz -- faster than a real IBM PC/XT. Turbo on meant a faster machine, and turbo off meant 4.77 MHz -- fully compatible with timing-sensitive PC software.
Later, in the 386/486 whitebox PC era, some machines had the buttons wired wrong and now it's a meme that turbo made the computer go slower, but that was never true for systems built correctly.
The speed on my Apple FastChip is adjustable in real time too. It's neat to just dial a speed appropriate for the application at hand.
for other interested parties:
http://www.a2heaven.com/webshop/index.php?rt=product/product...
If you are interested in programming your Apple in assembly, you can ask nicely for your FastChip to include a 65816 processor. It's going to act like a 65802, due to hardware limitations, but otherwise yeah. You get the 16 bit instructions to use.
I've not had any compatibility trouble with mine, which is a 65816.
It was fun to turn it on for games that used timing-loops for frame rendering to make games twice as fast :)
This feels super nitpicky but I'm curious about your setup and if you're either remembering the clock speed wrong or if the fan was actually completely extraneous, because in fact neither of the common 40 MHz 486 parts, the Cyrix Cx486DX40 or the AMD Am486DX40, required a fan. The Cyrix one came with a heatsink, which was a rarity at the time.
The first 486-class CPU that pretty much always ran with active cooling was the DX4/100. Even the DX2/66 could run fanless if you had half decent airflow.
But consensus among everyone _but_ the manufacturers was that additional cooling couldn't hurt. (A representative opinion can be found in Upgrading And Repairing PCs, whatever edition was current at the time.) Running right at the top of Tcasemax wasn't good for longevity in terms of electromigration within the chip itself, nor for the capacitors and other components in the neighborhood. Thermal goop wasn't commonplace yet, but the little heatsinks and fans sold like hotcakes (har!) at the local computer shows. Plain aluminum heatsink, clear (polystyrene?) fan, with a holographic "CRYSTAL COOLER" sticker on top. I still see the fans around, but without the shiny sticker.
The Am486DX-40 was my favorite chip. With a VLB video card (Trident 9400CXi) that worked well on the 40MHz bus, its pure pixel-pushing power ran rings around 33MHz-bus systems regardless of their core clock, and that included the P-75. I later got the impression that I lucked out with that Trident card, as almost everyone else with a 40 or 50MHz VLB machine had tales of woe and flakiness.
If you're not already familiar with it, you'll likely enjoy this trip down memory lane: https://redhill.net.au/ig.html
Yes, running a 40 or 50 MHz bus made a huge difference, especially if you could get VLB graphics running reliably on it. I'm into collecting and tinkering with 486-era machines for nostalgia's sake and often i see things like DX2 or DX4 systems with plain cheapo 16-bit ISA graphics cards and think such wasted potential...
Luckily I did not fry it and after adding a cooler it worked just fine.
I don't remember if AMD or Cyrix CPUs were worse though.
https://en.wikipedia.org/wiki/Turbo_button
> With the introduction of CPUs which ran faster than the original 4.77 MHz Intel 8088 used in the IBM Personal Computer, programs which relied on the CPU's frequency for timing were executing faster than intended. Games in particular were often rendered unplayable. To provide some compatibility, the "turbo" button was added. Engaging turbo mode slows the system down to a state compatible with original 8086/8088 chips.
I never had such a button in my PCs (first one was a 386SX) but I did see it on other PCs and always wondered what it did... => today I finally found that out :P
Why? What you did is basically a burnintest. All manufacturers torture their hardware by locking it in a hot room for several days at max speed to see if it fails. The basic theory is that if it's able to survive the torture test, then it's less likely to fail once it's been sold to the customer. Parts for things like space missions go through even more severe torture tests, where they're bombarded by radiation and every horrible thing you can imagine and that actually makes the price go up!