DayStar PowerCache

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PowerCache 50/IIci

Provides cache and faster Motorola 68030 processor for the Macintosh IIci. See DayStar PowerCache 030 for this card.


PowerCache Performance in LC

Date: Fri, 1 May 92 13:57:05 MDT 
From: [email protected] (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 something faster (especially
when you can pretend like you're doing it but actually using far less memory!),
you have an advantage.

"Altho I shy away from standard benchmarks, as we prefer real world benchmarks,
here are the numbers comparing a 50MHz LC to a 50MHz IIci in Speedo 3.06. I
have given the summary numbers for each category here. Both were running on 8
bit internal video (the CI gets an additional 15% boost if you use a video
card), 50MHz 882 FPUs, the CI had 8MB, & the LC 10MB RAM. They ran off the same
Quantum 105 hard disk, running Sys 7.0.1 w/ TuneUp, in 32 bit mode, and had
After Dark and QuickMail running init-wise.

           PowerCache 50 LC    PowerCache 50 IIci    % Faster Than LC
           ----------------    ------------------    ----------------
P.R. Rating:     11.88               12.91                   9
  Bench Avg:     20.82               18.22                 *14 (LC is faster)
    FPU Avg:      4.05                4.05                   0
  Color Avg:      2.30                3.96                 *72

* The LC was faster on cpu intensive activities because the CI has to dedicate
more cpu activity to video than the LC when running on internal video.
Conversely, it blows the LC away in the video category because it is handled in
this manner (vs the LC having to work thru 16 bit data paths). If you add a
video card, the P.R. & bench ratings improve, but video comes down to about 21%
better than an LC.

"Hope this answers some of the questions out there. If you still doubt that it
can be true, give your local dealer a call, get an LC PowerCache and test it
for yourself. If you are not completely satisfied, return it within 30 days for
a full refund (thru participating dealers).

"As I have said before on CIS, I had an LC running at SF MW with a 50MHz
PowerCache running 50MB of VM and doing full renderings in Infini-D, and it was
just screaming along! You will not believe it's running on an LC. It's _that_

Steve Tuttle
DayStar Digital
voice: 404-967-2077
 fax: 404-967-3018
 CIS: 75300,1544

Steve can be reached in the CompuServe Macintosh Vendor Forum A (go macaven). 
DayStar Digital messages are in Section 6 of that forum.

As a new PowerCache owner (40 MHz, no FPU), I am impressed with the 
acceleration. Applications load faster, and games like MS Flight Simulator and 
Vette that depend on animation are much more playable. The acceleration doesn't 
make the vehicles run faster (that would be undesirable); the framing rate of 
the animations goes up noticeably. Before, response to control input was jerky 
and so I tended to overcontrol. Now I can control the plane or car much more 
smoothly. I can even do a power-induced oversteer in the Vette without crashing, 
impossible before the PowerCache because of the lower framing rate.

Steve Harmony    internet: [email protected]  CIS: 71101,404

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