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PSI 030 Bus Adaptor with 64KB Cache It! IIsi module
Posted by: David Cook on 2024-05-19 11:56:10
I recently purchased a IIsi from eBay without photos of the inside. Risky, I know. However, the rear expansion slot had a video connector, so I figured there was at least a video card and PDS adapter inside.

I was pleasantly surprised by an unusual PDS adapter with a cache SIMM. PSI 030 BUS ADAPTOR REV B P/N E-0K-0-51C 1990/1991. The adapter has the FPU installed. (There was also a video card, but that isn't the focus of this post.)

PSI 030 Bus Adaptor front.jpgPSI 030 Bus Adaptor back.jpg

There's a PAL on the adapter. I assume this is for the FPU.
PAL16L8BCN.jpg

I don't like the look of that ceramic capacitor.
Not a big fan of that ceramic capacitor.jpg

Nice bend on electrolytic C1! When I recapped C2, I made the mistake of installing a taller capacitor. It barely fits -- rubbing against the power connector for the hard drive. C2 really needs to be small like the original designer installed.
Interesting capacitor bend.jpg

The cache module is labeled PSI CACHE-It!-IIsi REV B. P/N EA-64K-20-rb 1990/1991. Based on the 64K part number (and tests presented later), this is a 64KB cache.
PSI CACHE-It!-IIsi.jpg

A cache simm is a pretty cool concept for 1990. It would be cool to swap in a larger cache, but I assume this is a proprietary pinout.

PSI Cache It module front.jpgPSI Cache It module back.jpg

I could only find one mention on the Internet. https://archive.org/details/TNM_030_Bus_Adapter_Card_for_Macintosh_IIsi_-_PSI_20170827_0383

Brochure.GIF
Notice they say the cache is rated for 25 MHz. Conspiracy theorists can point to this as further evidence that the IIsi was intended to be 25 MHz. I suppose this means that this will work in an 'overclocked' IIsi, although sadly the FPU installed in my adapter is only marked for 20 MHz.

Are you jealous of my really cool unique cache card? Well, read on...

I ran Norton System Info speed tests on System 7.1 on the IIsi. I compared the DayStar FastCache (with the control panel software and without) vs the PSI vs the stock IIsi. The PSI cache did not compare favorably.

IIsi PSI CPU.GIF
Notice that BlockMove is particularly bad (below stock) on the PSI cache, but not on the DayStar cache. I wonder why?

Video performance is generally better with a CPU cache. Still DayStar constantly beats PSI.
IIsi PSI Video.GIF

Just to be sure Norton isn't wrong, I ran my cache tester program. Results were consistent with Norton.

1716144502541.png

In conclusion, the IIsi receives a moderate performance boost from a CPU cache. DayStar is better than PSI.

- David
Posted by: Fizzbinn on 2024-05-29 18:20:31
I just bought one of these off eBay recently! (did I buy it from you/did you sell yours?). Did you need any Extension/software to enable it?
Posted by: David Cook on 2024-05-30 08:43:35
I just bought one of these off eBay recently! (did I buy it from you/did you sell yours?). Did you need any Extension/software to enable it?

I did not find any software for it. Perhaps adding software would further improve performance. If you locate anything, would you let me know?
Posted by: Fizzbinn on 2024-05-30 10:17:18
I did not find any software for it. Perhaps adding software would further improve performance. If you locate anything, would you let me know?

Sure. No luck so far. I don't think "PSI Integration Inc" made it to the web era to have a possibly archived website/downloads. :-/

Did find a somewhat interesting product/pricing list in Mac User Feb 92:

Untitled 2.png
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