Daystar Powercache

Date: Fri, 1 May 92 13:57:05 MDT From: sharmony@nova.ta52.lanl.gov (Stephen C. Harmony) Subject: [*] PowerCache performance in LC Dear Moderators: I think the following report on the DayStar PowerCache performance in LC's would be a useful addition to the info-mac/reports directory. The following explanation of how the PowerCache minimizes the effect of the LC's 16-bit data path was written by Steve Tuttle, the Online Resources Mgr for DayStar Digital. I will submit an expanded report to the info-mac archives as soon as Steve forwards the results of the benchmark tests on the unenhanced LC and IIci, but the results as presented give a good indication of the performance difference between a PowerCache-enhanced LC and IIci. "Altho it would appear intuitive that due to the 16 bit path on the LC you are going to be forced to run slower, it is not necessarily the case. You see, all Macs have some sort of delays inherent in their design: The II,IIx,IIcx, & SE/30 all have 120ns RAM and require 2 wait states to be added to the memory cycle in order to ensure the memory is stable enough before the processor accesses it. On the IIci they go to 80ns RAM & 1 wait state. So all we're really talking about here is just another built in delay in the Mac's architecture that keeps the processor from running as fast as it would normally be able to run. "Our solution? Static RAM Cache. What we do is take a 32K cache of 25ns static RAM and build it into our accelerator boards. What happens is that all cacheable data and instructions that are normally read out of memory and loaded into the processor are now intercepted and loaded into cache - the processor always works from our cache. What this means is that the processor can run at almost zero wait states because for all intents and purposes, it is running with 25ns memory. "Is it effective? Extremely so. We are able to maintain a cache hit rate of 80-90%, meaning that only 1 time in 5 to 1 time in 10 do we have to go out and make a slow memory cycle. Over 80% of the time we are working out of cache. You can see the dramatic difference caching makes by turning the cache off on a PowerCache - the performance boost, even of a 50MHz board, drops off to about a 30% increase. Why, simply because the added processor speed means nothing if it has to sit there idly waiting on memory to give it more information to process. "This method works on any sort of bottleneck to the processor. We are sold on caching as being a fundamental method of performance enhancement - look at our entire product line! We have our FastCaches & ComboCache, simple cache boards for roughly 20% boosts, our line of PowerCaches that add cpu acceleration to caching for boosts up to over 300%, our SCSI PowerCard, which uses caching in addition to increased thruput to speed hard disks, and our RAM PowerCard, which is a large RAM Disk for caching of your hard disk & VM scratch files. Simply put, whenever you can replace something slow with so…