The Power 100 is based on a PowerPC 601+ processor rated at 100MHz. The Bus runs at 33.3MHz giving a Bus to Processor ratio of 1:3. This is the same as the Apple PM8100/100 and 110 machines. The signal is generated by a Motorola clock generator/PLL part # PC955 located at U12 on the motherboard. This part is "set" by the presence/absence of resistors on 8 sets of resistor pads on the board. These pads are located on the top side of the mother board on the left, front side. I will refer to the pads as 1 2 3 4 and A B C D since they are not all labeled.
|My Notation||Board Notation|
These resistors can be changed to give 75, 90, 100, and 112.5MHz machines, and the Bus to Processor ratio can be set to 1:2, 1:3, or 1:4 in many cases. The potential for 50 and 60MHz machines exists, but I've been unable to tweak the System 7.1.2 or 7.5 software to allow me to get the machine up at these speeds.
The table below tabulates all of the possible resistor configurations. The resistors used are surface mount 0805 5% resistors. Pads 1, 2, 3, and 4 take 10K Ohm resistors; they are marked (103). Pads A, B, C, and D take 1K Ohm resistors; they are marked (102). 1 and A are matched sets, so a resistor need only be on pads 1 or A. The same follows for 2, 3, 4 and B, C, D respectively. The gestalt is a number reported by the computer that signifies the type of computer it thinks it is. (see the table just below this one)
|1||2||3||4||A||B||C||D||Gestalt||Bus (MHz)||Processor (MHz)||Bus:Processor||Note|
|Gestalt||Apple Computer Notation||PowerComputing Notation|
|12||Power Macintosh 8100/120||Power 120|
|55||Power Macintosh 8100/100||Power 100|
|65||Power Macintosh 8100/80||Power Macintosh 8100/80|