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I am wondering why are read/write operations on I/O devices much faster when we use DMA?I must be that when using DMA we have 1 less clock cycle to access the local buffer of a IO device since it is already part of the main memory.Am I correct?

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  • $\begingroup$ Some IO devices don't have local buffers. Other times, the local buffer is slow. $\endgroup$
    – user253751
    Oct 17, 2023 at 13:36

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DMA is expensive. It is used in more expensive devices. More expensive devices are faster. There is a correlation but not a causal relationship.

And in the 2020s you want nobody, not even a trusted external device, to have the ability to write directly to your RAM. Too much of a security risk.

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