Subject: Re: 486DX/40 or 486DX2/66?
To: None <>
From: Mark P. Gooderum <>
List: current-users
Date: 04/08/1994 15:09:25
> Okay, here is a question for ya...
> I've always been under the impression that a 486DX/40 would be overall faster
> than a 486DX2/66 since with VLB, you can get 40Mhz throughput across the bus
> with the 40, vs. 33Mhz with the 66.  After speaking with a friend though, he
> claims that the 66 has MUCH better overall performance than the 40's...
> Which is the case in real life?  We have several 40's running as servers
> here now, is it worth upgrading them to 66's??  Should we buy 66's in the
> future?  Is it better to get EISA, ISA, VLB, or PCI motherboards??

Well, comments like on which PC bus are better left to others.

But on clock speed versus memory speed, remember that a 486 still isn't
any where close to a RISC chip in cycles per instruction ratio.

Plus the 486 has it's internal cache which gives a good hit rate on most
non I/O code and many systems still have large external caches.

Finally, when doing raw byte stuffing, the 486 has a hard time keeping the
pipeline full once it runs out its internal data cache.  

So in general a DX2/66 will be better able to fill the 33MHz "pipe" and use
it than a straight DX/40 (and DX/50's begin to suffer more from wait states
since many PC's just don't have memory quite fast enough unless they have big
external caches).
> Ah... This damn flu, I can't think straight.. ;)

BTW...some testing I saw showed a DX2/66 run faster than a even DX/50 even in
high memory I/O situations unless you had a motherboard with a large
external cache (128k in this case, true 0 wait state).

I saw similar results with a DX2/50 versus a DX/33