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Technology Stocks : Advanced Micro Devices - Moderated (AMD)

AMD 214.18

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To: Tenchusatsu who wrote (69588)	1/31/2002 1:38:21 AM
From: dale_laroy	Read Replies (1) of 275872

>What does PMMU mean, anyway?< Well, without clearly defining what a page is, the term PMMU is relatively meaningless. For example, the Macintosh II used the 68851 PMMU while maintaining compatibility with the "segmented" memory management of the 68000 based Macintosh through the use of custom memory management hardware. I thought this was sort of rediculous because the 68851 PMMU supported five levels of programmable page sizes with early termination of table walk. Theoretically, the lowest two levels could have been set at the smallest page size of the DRAMs (allowing for up to two different DRAM page sizes), the next level up at the 32KB segment size that Apple handled in hardware, the next level up at the 16MB address space of a NuBus slot and the next level up at the 256MB address space of a NuBus Superslot. This would have allowed each memory structure from an active DRAM page to an entire NuBus Superslot to be handled using a single table entry terminated at the appropriate level. Now that was a PMMU! Directory based cache coherency is probably a reasonable description of what I was talking about.

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