Introduction To Direct Memory Access Within The Processor

Introduction To Direct Memory Access Within The Processor

In direct memory access method, the Hardware present inside the processor is allowed to access the main memory without the help of the processor. This means that the hardware components need not take permission or go via the processor to access the main memory. In DMA, there is no wastage of time. This is the main advantage of using a DMA method. 

Introduction To Direct Memory Access Within The Processor

DMA or Direct Memory Access is an ability offered by several computer bus architectures that permits sending of data directly from a connected device like the hard drive to the physical RAM or the memory on the computer’s motherboard. The data transfer excludes the processor therefore boosting the overall performance of the machine.

Normally, it assigns a particular part of the memory as an area to be used for direct memory access. In the ISA or Industry Standard Architecture bus standard, up to 16 MB of memory can be allocated for DMA. In the EISA or Extended Industry Standard Architecture and MCA or MicroChannel Architecture standards, it allows access to the full range of memory addresses.

PCI or Peripheral Component Interconnect achieves DMA by utilizing a bus master by which the processor assigns the input/output control to the PCI controller. The PIO or Programmed Input/Output interface is an alternative to direct memory access where all data transmitted among devices goes through the processor.

Ultra DMA is a newer protocol for the ATA/IDE interface which offers a burst data transfer rate of up to 33 MB per second. Hard drives that support UDMA/33 also support PIO modes 1, 3, and 4 and multi-word DMA mode 2 which is about 16.6 MB per second.