Each PP had 4096 words of 12 bits memory (see photo). This PP memory
was equivalent to one (1) core memory block.
Later 800-series systems had 8K words of 16 bit SECDED memory. The limited
instruction set allowed internal processing, read/write to Central Memory,
read/write to I/O channels and exchanging the CPU.
There was only one accumulator and there were direct cells (like in the PDP8) that allowed efficient and compact 12 bit instructions.
PP's were organized in groups of ten (in the 800-series systems in groups of 5) or barrels.
As said before, each PP was perceived as a single, separate processor in the system.
In reality, only one hardware processor serviced a complete barrel of PP's. Using
shift-registers, PP instructions were processed in either one, two or 5 minor (memory read/write)
cycles. For the CYBER 840 system that meant that each PP register moved through the barrel
at a 20 MHz rate, causing each PP tio run at four MHz.
Each PP barrel had a:
At a deadstart, all PP's were forced to do a loop for input available on their "own" channel. As the first bytes from the deadstart panel were forced into PP0, PP0 (MTR) was responsible to output the Standard Library (STL) to each PP on its own channel during the start-up phase of the system. Deadstarts could be initiated by using a hardware button between the two console "eyes" or under the single console screen in later systems. Another way was using the deadstart switch adjacent to the deadstart panel. After some time, system programmers and operators were very experienced in "toggling in" the deadstart program in the 16 or 20 rows with switches. It was always amazing that one could (warm)start from a deadstart tape (later a disk) using only seven to 12 PP words located in the deadstart panel.
01 1402 LDN 2 load 2 02 73ch OAM out,ch output 2 words from 17B on ch 03 0017 04 754ch DCN ch disconnect channel ch 05 77ch FNC 120B,ch function 120B on ch 06 0120 07 74ch ACN ch activate ch 10 71ch IAM 7301B,ch read (A) words from ch to 7301 11 7301 12 0710 MJN hang 17 0000 out 0000 20 7112 7112 21 0000 hangSample deadstart panel program