Question

Difference between 8237 and 8257 dma controller

Answer 1

The 8237 works in four different modes – single, block, cascade and demand – based on the number of ICs used and the number of bytes transferred in a cycle. Data transfer takes place from one memory device to another at the rate of 1.6 MBps.

The 8257 works in two different modes – master and slave. Data transfer takes place between an I/O device and memory without the CPU intervention at high speeds.

Answer 2

DMA ( Direct Memory Assess) controller, a technique for transferring data from main memory to a device without passing it through the CPU.

Computers that have DMA channel can transfer data to and from devices much more quickly than computers without DMA channel.

The difference between 8237 and 8257 is that, 8237 provides better performance than 8257.

8237 provides many programmable control and dynamic reconfiguration features which enhances the data transfer rate of the system remarkably.  It is a direct memory access controller

8257 is a four channel device that can be expanded to include any number of DMA channel input, the four peripheral devices can request data transfer at any instant, the request priorities are decided internally and each channel has two signals.