CompuServe Messages

Donovan, MMU stands for Memory Management Unit. It is a chip, on in the case of your 3000….the chip's functionality has been moved inside the 68030 CPU…that allows the system to have multiple blocks of memory that all appear to have the same address. That is…it re-addresses memory as far as the rest of the machine is concerned. For example, the core operating system on the Amiga is in Read Only Memory (in most cases) and that ROM resides at a specific location in memory. You can copy the contents of that ROM into RAM (which also resides at a specific location or address) where the instructions would execute faster. The basic problem in doing that is, of course, the ROM and the RAM don't reside at the same address and the software is designed to look in the address designated for the ROM when it needs to execute an instruction that is in the ROM. So what an MMU does is "translate" all addresses that would go into the ROM, to addresses that are in RAM…thus things run faster. It can also prevent writes to those memory addresses…so the ROM image (in RAM) is stable…just as it would be if it were really working with the ROM. Kind of like when you move, and you give notice to the post office of your new address. Main sent to your old address gets forwarded to your new address. That's one of the main features of an MMU. It's "disabled" because nothing you are running requires its "services". If you ran a program such as SetCPU (or it's replacement CPU)…it would be enabled. Don