Motorola 68451
The MC68451 was a Memory Management Unit (MMU) from Motorola (now Freescale ), which was mainly used in conjunction with the Motorola 68010 processor .
With the MMU, the 16 MB address space of the MC68000 or MC68010 could be managed and protected against unauthorized access. The block had a variable block size, which was mostly used for segment-based memory management. Up to 96 memory segments or pages of variable size could be mapped from logical to physical addresses. In order to allow more segments or pages, operation was officially possible with up to 3 MMUs .
In combination with the MC68010 which enabled MC68451 the realization of virtual memory . With the predecessor MC68000 , this was not possible due to an error in the handling of memory access errors. Due to the limitation to 96 table entries, systems with 68010 and 68451 had speed problems, as table entries often had to be reloaded due to the small table size. Some companies (e.g. H. Berthold AG ) therefore interconnected up to twelve 68451 MMUs, others (e.g. Sun Microsystems ) used a self-made so-called Berkeley MMU instead of the 68451 .