Control computer is often used for large channel mode . Channel mode, i.e., according to a program capable of controlling a plurality of external devices, and provide shared DMA function, and only a fixed DMA data transfer operations. The data transfer mode, the channel can be divided into multiple byte-channel, and select the channel array of three types of multi-channels
DMA dedicated channel
The processor device (mainframe computers), via channel communication , the processor device, the processor and the communication channel, the same meaning. Communication devices and apparatus , without going through the processor core, communicates directly through the DMA controller . Thus, the communication single-core processor computer, with a processor device, the device and equipment can be run in parallel .
In the microcomputer, the host and exchange data suitable for high-speed disk direct memory access (DMA) mode.
DMA is the main memory and peripheral a passage between the racks, to reduce the number of CPU during the data transfer being intervention.
In the DMA mode, the I / O devices to obtain control of the bus, the data transfer will be managed by the DMA interface, when the word counter overflows, an interrupt request is made, indicating the end of the batch transfer to the CPU.
DMA is in dedicated hardware, control, automatic exchange of data in batches to minimize CPU intervention input / output operation between the high-speed peripherals and main memory.
There are generally three ways: stopping the CPU access, cycle stealing mode, the DMA access to the CPU alternately .
