DMA isn't something you access. Direct Memory Access means that an external device can issue reads and writes to main system memory (you call such a transaction

DMA isn't something you access. Direct Memory Access means that an external device can issue reads and writes to main system memory (you call such a transaction a "DMA transfer"). What you access is entirely normal memory. A DMA transfer is done entirely by the external device, without any intervention by you or the CPU (apart from potentially a cache invalidation before/after, depending on platform). From the point of view of the CPU (and therefore you), data just magically appears. You don't need to memcpy anything anywhere, unless you need to make sure the external device doesn't accidentally overwrite things (who knows, it might be stupid). You can read and write directly to wherever it appeared as if it was any other memory. Caching still applies, although a fresh DMA transfer will of course be a cache miss. There is a little bit of magic related to memory regions used for DMA transfers, but that is invisible to the end-user. 'memcpy' does not discriminate, and unless you're copying a single byte, memcpy will never operate on byte-sized chunks. Source: I do driver development for devices that DMA at extremely high rates (we're desperately waiting for PCIe 4.0 to become normal—PCIe3.0x16's 126Gb/s is way too slow for us).