4 ms·
Before CPU throttling or fan speed control, I wanted my 486 to be quieter when it wasn't doing much. My siblings and I had built a 486DX/40. Intel's chips topp
by myself248 3y ago
Before CPU throttling or fan speed control, I wanted my 486 to be quieter when it wasn't doing much.
My siblings and I had built a 486DX/40. Intel's chips topped out at 33MHz until you got into the clock-doubled DX2/50 (which ran its bus at 25 MHz) or the DX2/66 (33). But AMD's DX/40 wasn't clock-doubled, the core and the bus both ran at 40MHz. In the days before accelerated graphics, all pixel-pushing went through the CPU, so this was a very big deal for games.
It also ran hot enough that a CPU fan, optional-but-a-good-idea on slower chips, was an absolute necessity here. But the fan (a little 40mm Crystal Cooler™) would never be described as silent.
So when I wasn't gaming, I'd remove the 3.5" floppy drive from the case (it was in a modular sled, and the cables had enough slack that I could just unplug it), then reach in through the resulting opening, and re-jumper the clock-generator IC on the motherboard. Live, and blind. I knew that moving the jumper-cap one position towards me would go from 40MHz to 8, and that was enough to seriously drop the heat. The first time I did this I was flabbergasted that the machine didn't crash, but evidently it was fine? The no-jumper state was something like 12MHz or whatever, so presumably it was just blipping through that speed as I moved the jumper.
Then I'd unplug the CPU fan and enjoy the silence. This was particularly nice during a long download, where servicing the UART ISR didn't exactly take much processor time.
Even better, the computer room was in the basement, and the FM radio signal from my favorite station was pretty weak. So weak that, if I tuned just a smidge off to the side of the station, my radio receiver would pick up little ticks of interference from the computer, while still being able to hear the music. This meant I could turn off the monitor too, and just listen to music while downloading whatever file.
When the ticks stopped, the UART buffer was no longer triggering an interrupt, meaning the download was done, so I could turn the monitor back on and resume my BBS session, clock the CPU back up and plug the fan back in to unzip the file in a reasonable amount of time, and otherwise get on with my day.