The DMA adapter frees the processor from having to move data between an adapter and system memory. The DMA slave adapter arbitrates for control of the MCA. Once control is given, the DMA controller uses the DMA channel allocated to the DMA slave adapter to transfer the data.
The Micro Channel supports up to 15 DMA units, which may use the burst mode data transfer capability of the Micro Channel. The DMA controller implemented in current PS/2 machines supports transfers of up to 64KB segments of contiguous data and is able to address 16MB of memory. In the case of systems that have more than 16MB of memory, DMA transfers can only take place to memory locations below the 16MB line.
The major limitation is that the data must be contiguous. For a system using paged memory (with 4KB pages) this introduces an overhead through the need to reserve contiguous blocks of memory. This makes the system DMA controller best suited for records shorter than or equal to the page size.