The Real Maximum Memory Limit on MPE/iX 6.5
A feature of Release 6.5 and above is an increase in maximum memory to 16GB over the previous maximum of 3.75GB. Most users inferred that all newer systems would be able to take advantage of this feature. Unfortunately this is not the case. The MPE operating system is not the only limiting factor in determining the largest memory configuration a system can have.
Older systems are physically limited by number of slots and the largest size memory boards and/or arrays that are available such as the 922/932/948/958 family and the 9×7 family of processors.
Of the newer systems only those which are based on PA-8000 or PA-8200 RISC processors are candidates for higher memory configurations. PA-8×00 processors are 32-bit RISC processors with 64-bit memory extensions. To address more than 3.75GB of memory requires 64 bits.To add to the confusion, not all of the systems in the Series 9×9 family carry the same processor. Earlier versions of the low-end 929, 939, and 969 systems use PA-7000 processors. The newer 9×9/030 systems are utilizing the PA-8000 processors. Furthermore, only the Series 997 systems can go up to the maximum 16GB limit. The 9×9 systems have a maximum of 8GB.
Here is a simplified list of the systems that will support more than 3.75GB:
All other systems (including Series 992, 995, and 996 systems) will not handle more than 3.75GB.