🚀 go-pugleaf

oldwanda (93gke@williams.edu) wrote:
: In article <1993Jan13.203244.6289@pacific.mps.ohio-state.edu> viznyuk@pacific.mps.ohio-state.edu (Sergei Viznyuk) writes:
: > If you have 70ns DRAM on 486-33 it makes sense to
: >try to run it at 40Mhz. It will reduce the memory access
: >time from 90ns to 75 ns. If you have 60ns DRAM
: >then 40Mhz may give you even worse performance
: >(75ns vs. 60ns).
: 
: This topic comes up frequently, but nobody explains why.
: Can someone please explain this in some detail? Also, how does this
: relate to wait state selection?
: (Please reply publicly)

i think i see some confusion here - the speed raing of ram indicates the
fastest speed that it will operate. a DX33 requires at least 70nS dram -
60nS will work equally well, but possibly at a cost penalty. (faster ram
costs more). 80nS ram _may_ work - no guarantees ;-). a faster clock usually
requires faster ram (disregarding interleaving and the like). but the speed
that the processor and peripheral chips will operate is generally limited by
the ratings of those chips. running a DX33 at 40MHz bay be stretching things
a little, and certainly won't do anything to help your warrantee.

bottom line - use a DX33 @ 33MHz with 70 or 80 nS dram. a DX40 (say a 386)
should definitely use 70nS ram. there's absolutely _no_ advantage in using
faster ram. the overall performance is determined by clock speed. providing
that the ram can keep up, the speed rating of it is irrelevant.
		 	    	
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richard lindner                   ,-_|\            rjl@spectre.apana.org.au
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