Upgrading a Power Mac 6100 with a 1MB cache memory

It was seven years ago (today) that I published a post about my Power Macintosh 6100, which I had upgraded with a 512 KB cache memory module and a few RAM modules. At the end, I mentioned that I was looking for a 1 MB module, which I finally found.

Well, I stumbled upon it somewhat accidentally, and it still cost me around fifteen euros. While browsing eBay, I came across a listing for a cache memory without any markings. After researching the chip references, I found a thread on the 68KMLA forums with a module containing the same chips, so I decided to make the purchase (successfully). The module indeed contains 1 MB of level 2 cache memory, a substantial value for an early-’90s computer. On the Power Mac 6100, cache memory was often absent or limited to 256 KB, and 1 MB modules were (very) expensive.

The cache memory

I then took out my Power Mac 6100 and ran four series of benchmarks: without cache memory, with 256 KB, with 512 KB, and with 1,024 KB. The performance gains were quite significant.

The three modules

Mac OS shows (falsely) 128 KB

On the CPU side, there was a 27% performance increase in integers with the addition of a cache memory module, 51% with 512 KB (compared to a machine without cache), and 60% with 1 MB. In terms of FPU (Floating Point Unit), it was much lower: roughly around 10% in all cases. There were also considerable gains in the graphical section because it uses shared memory (approximately 640 KB), and the cache memory is faster. With 1 MB, the gain was 37% with MacBench. Speedometer even showed a 45% gain in the graphical section and ~20% overall (12% and 16% with 256 KB and 512 KB, respectively).

0 kB

1 MB

0 kB

1 MB

In all cases, it was quite visible, especially in the graphical section. Obviously, this isn’t a massive upgrade, especially in 2023. It’s far more effective to find a faster Mac initially than to search for a 1 MB module. However, if, for some reason, one needs to keep a Power Mac from the x100 family, this upgrade is interesting. On the other hand, if you have a machine of this type without cache memory, trying to find a 256 KB module (which is quite common) is a good idea.

One thing to note: I didn’t have any overheating issues with the 1 MB module, whereas I sometimes experienced that with the 512 KB one.