1999 – KSJ writes: I was wondering if you could help me figure something out. I have a Power Mac 5400/120 that I bought a couple of years ago. I am looking into a PCI-based G3 upgrade, but no one seems to acknowledge the fact that my machine has a PCI slot (as evidenced by my computer’s documentation and Apple’s spec database).

The only upgrade company that offers a G3 upgrade for my machine uses the L2 cache slot. Is there something that I am missing? Is there something peculiar about the PCI slot in this machine? Or are the upgrade companies off-base?

Mac Daniel writes: To my knowledge, no accelerators for any Macintosh actually use the PCI slot. [Update: Sonnet later introduced an accelerator for the Power Mac 7200, the Crescendo/7200, that occupies a PCI slot. This is the only accelerator I have ever heard of to sit in a PCI slot.]

There are four places that a processor upgrade can go:

1. in the CPU socket (e.g., Power Mac G3, SuperMac C500, Sonnet QuadDoubler)
2. in a CPU card socket (e.g., Power Mac 7300–7600, SuperMac J700, many Power Computing models)
3. in a processor direct slot or PDS (PowerPC upgrades for some Quadras)
4. in the L2 cache slot (5400, 5500, 6360, 6400, 6500)

The last one is a relatively recent discovery. I don’t know the technical details but speculate that the cache slot and processor direct slot are similar. By putting in a card that “hijacks” data that would normally go to the main CPU, these accelerators let a G3 take over as the brains of the computer.

With a 40 MHz system bus, the 5400 can support a G3 as fast a 320 MHz (eight times bus speed). For best performance, you want a 1 MB backside cache (512 KB will do in a pinch).

At this point, both Vimage and MacCPU are making G3 cards for the 5400. The Vpower PF 54xx/64xx G3 runs at 240 MHz and has a 512 KB 2:1 cache. The MacCPU Vpower G3 has the same specs.

Keywords: #powermac5400 #performa5400 #g3upgrade

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