486 DX/2 66 - Switching speeds down to 33

[EverStaR]

Curious and need help!

What are my options for knocking a DX2 @ 66 down to 33 when needed? Are the CPU jumpers and a switch used for that typically or is there a program that can be run only when needed?

Thanks!
E

 

[TamaMan]

Not precisely a method for dropping to 33 MHz but so far I've tackled all my DX2@66 slowdown needs by just disengaging the turbo button and/or disabling Internal Cache from the BIOS (there should be a program the latter also).

 

[Timo W.]

Not possible. The DX2 has a fixed internal multiplier of 2x.

If the mainboard has a connector for a turbo button, use that. Disabling internal or external cache works as well, but gives unpredicted results in the speed you get (i.e. it is not equivalent to the CPU running at a certain lower clock speed).

 

[Eudimorphodon]

Just out of curiosity, what's the use case for trying to knock a DX/2-66 down to 33mhz? Most software from the 486 era should be reasonably tolerant of CPU speed variation of that magnitude.

 

[EverStaR]

Just out of curiosity, what's the use case for trying to knock a DX/2-66 down to 33mhz? Most software from the 486 era should be reasonably tolerant of CPU speed variation of that magnitude.

A sound card I managed to convince a collector to part with has a YAMAHA YMZ-263 "MMA" chip which is a speed-sensitive device and will not operate correctly on systems faster than a medium-range 486 potentially at or above 33mhz. Just curious what options I might have with my Gateway 2000 486 DX/2 to tackle the issues for the system timing. Apparently according to a user back in the day the official response from Adlib was that depending on hardware/software configuration, anything above a 486/33 can cause timing issues. I will have to look at the front panel it has a turbo button or not. I have had it off for a while now for cleaning the machine up. I may have forgot about that.

 

[Eudimorphodon]

Googling around it looks like this problem was associated with the Adlib Gold and a few clone cards? There's a thread about it that suggests it's not so much CPU speed that's the problem as bus timing issues. (IE, there's a person who claimed they got it to work fine on a 440BX motherboard, which of course would be a Pentium II or better CPU.)

Some 486 motherboards had BIOS-adjustable ISA speed dividers. (IE, 486 CPUs came in speeds anywhere from the rare 16mhz 486SX all the way up to the 50mhz non-doubled 486DX.) The "standard" for ISA is usually specified as 8.33mhz, so a 33mhz bus 486 typically has a 1/4th divider. It's probably something you'd be more likely to find on a generic clone than your gateway, but it's *possible* you might have the option of selecting a 1/5th or 1/6th divider for ~6mhz or ~5mhz respectively. Of course this will slow *everything* down, including video and hard disk performance, but it in theory might let the card work if it doesn't like the default setting.

(On the flip side, on my 486 that had this option I overclocked the bus to 11mhz using the 1/3rd divider. It's a great way to make an IDE hard disk with a cache run faster, or at least look a lot faster on dumb benchmarks.)

 

[EverStaR]

Thanks, yes, I'm getting ahold of an Adlib Gold Clone, the collector has a few and became willing to part with one. Was a really luck opportunity, sometimes when you ask you might receive!