FPU for my Performa 460 (LCIII)

[highlandcattle]

Hi ,

My Performa 460 didn't come with a CPU but I know it has a slot for an FPU and I plan to buy one. But two weeks ago I obtained an LCII with an fpu card in its pds slot. I plugged this in the Performa 460 and it seems to work. Even Norton system info recognized it. Now I have a few questions:

Is this safe?

Will the 16Mhz FPU overclock itself to match the 33mhz speed of my 460 ?

Well that are all the questions I have. :b&w:

 

[beachycove]

Is it safe? I don't think any fires are going to break out, if that's what you mean, though I might want to make sure that the fan was working, and one strategy might be to turn it over so that it sucks cold air up into the case rather than pushing warm air out. "Danamania," one of the old admins around here, used to use this strategy when overclocking Quadra 605s with much hotter full 68040 processors installed, and found it cooled more effectively that way.

Will your 68882 work at 33MHz? You need to find out if it is really working at the moment, since mostly it is ignored. So, run a program that uses the FPU and see what the results are (benchmarking utilities are some of the very few Macintosh programs that actually use the FPU, along with high-end CAD, graphics applications, spreadsheets and screensavers like After Dark, seemingly).

Certainly some LCIIIs (25MHz) shipped with a 68030 marked at only 16MHz. The Performa 460 (or LCIII+) is just a speed-bumped LCIII, and I would not be the slightest surprised if everything in it with the exception of the oscillator controlling the speed were not identical to what is in the average LCIII; in general, 68030s seem to be willing to be overclocked fairly generously. In general, the speeds Apple set its hardware at in the early 90s were controlled as much by marketing criteria and the associated profit lines of the company than they were by the hardware's inherent capacity (e.g., a IIsi can run as fast as a IIci, except that it can't because it was deliberately hobbled so as not to compete with the much more expensive IIci).

The 68882 is most likely much the same animal as the 68030, but YMMV. The proof of the pudding will be in the eating.

 

[Bunsen]

Will the 16Mhz FPU overclock itself to match the 33mhz speed of my 460 ?

It is driven directly by the clock on the motherboard, so in one sense, yes. In the sense of "how long will it run without burning out" - who knows? FPUs are not ordinarily fitted with heatsinks, but as you are overclocking this one by 2x, I would advise adding one.

 

[highlandcattle]

Thanks for all the info!

What type of heatsink do you recommend ? A small one that you glue on top?

I know it works. I got this pinball game that only works with an FPU and The norton benchmarks notices it. However norton rates it as slower as the fpu in the IIci that makes me think it might run slower the 33mhz