ISA DMA: Difference between revisions
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* Transfers must be physically contiguous, and can only target the lowest 16 MB of physical memory; |
* Transfers must be physically contiguous, and can only target the lowest 16 MB of physical memory; |
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* ISA DMA is slow - theoretically 4.77 MB/second, but more like 400 KB/second due to ISA bus protocols; |
* ISA DMA is slow - theoretically 4.77 MB/second, but more like 400 KB/second due to ISA bus protocols; |
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* ISA DMA frees up CPU resources, but |
* ISA DMA frees up CPU resources, but adds an extremely heavy load to the memory bus; |
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* Very few devices currently use ISA DMA -- only internal floppies, some embedded sound chips, some parallel ports, and some serial ports. |
* Very few devices currently use ISA DMA -- only internal floppies, some embedded sound chips, some parallel ports, and some serial ports. |
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