On the weekend I decided to examine my old PowerPC 604 system. The case is from a RS/6000 type 7248, but the actual system board is from a Power Series 830. This is the famous Carolina board (or “planar” in IBM-speak), which was shared by RS/6000 43P (7248) workstations and Personal Power Series 830/850 desktops (type 6050/6070). The only significant difference was that the RS/6000 boards included a SCSI controller and the Power Series boards did not.
The differences between the Power Series 830 and 850 models were again small. The 850 system case was larger (with more slots and bays, 5/5 vs. 3/3), and the 830 was only sold as a 100MHz version while the 850 was additionally available in 120 and 133MHz variants. The system board was in all cases essentially the same except for the CPU (which is soldered to the board) and L2 cache (256K on 100/120MHz models, 512K on 133MHz models, always separate module in its own socket).
Anyway, my Frankensystem has a board FRU 12H0818. According to the EPRM, that’s a type 6070 (Power Series 850) system board. Except for the part number, it’s not apparent what differences there might possibly be between the 830 system board and a 100MHz 850 board. At any rate, the real surprise was waiting under the heatsink:
That’s right—a 133MHz PowerPC 604 processor. It’s worth noting that the 100/120/133MHz boards were separate part numbers. The CPU frequency does not appear to be user modifiable which would explain the need for separate boards (even if all of them actually used the same CPU model).
A better question is why IBM sold high-end 133MHz processors as 100MHz. I have no explanation for that, although it is not an uncommon practice within the industry. Sometimes the yields are good and there’s a shortage of cheaper/slower chips, so faster chips are sold as slower ones. However, the CPUs are then typically labeled as the slower parts and nowadays also multiplier locked. In this case, IBM may not have bothered since the CPU is soldered and effectively locked.
Unfortunately that means I’m stuck with a nice 133MHz PowerPC 604 that’s been officially crippled by IBM to only run at 100MHz…