Direct Memory Access

What is Direct Memory Access (DMA)?

Definition and meaning of Direct Memory Access

Direct reminiscence get admission to (DMA) is a way that permits an enter/Output (I/O) tool to send or get hold of Data imMediately to or from the main Memory, bypassing the CPU to hurry up reminiscence operations.

The sySTEM is conTrolled with the aid of a Chip known as a DMA Controller (DMAC).

What Does Direct Memory Access Mean?

A defined portion of memory is used to send Records at once from a Peripheral to the Motherboard without involving the Microprocessor, in order that the technique does not intervene with usual Laptop operation.

In older Computer Systems, four DMA channels were numbered 0, 1, 2 and three. When the sixteen-bit industry general structure (ISA) enlargement Bus become brought, channels 5, 6 and 7 had been delivered.

ISA was a Computer bus fashionable for IBM-well matched Computer systems, allowing a Device to provoke Transactions (bus getting to know) at a quicker pace. The ISA DMA controller has eight DMA channels, every one of which related to a sixteen-bit cope with and matter registers.

ISA has due to the fact that been cHanged through extended photographs port (AGP) and peripheral factor Interconnect (PCI) growth cards, which might be lots faster. Each DMA transfers about 2 MB of inFormation per second.

A computer’s machine aid equipment are used for communique among Hardware and Software Program. The four types of system resources are:

• I/O addresses.

• Memory Addresses.

• Interrupt Request numbers (IRQ).

• Direct memory get admission to (DMA) channels.

DMA channels are used to speak information between the Peripheral Device and the device reminiscence. All four gadget resources rely on positive lines on a bus. Some strains at the bus are used for IRQs, some for addresses (the I/O addresses and the reminiscence deal with) and some for DMA channels.

A DMA channel permits a tool to transfer information with out exposing the CPU to a work overload. Without the DMA channels, the CPU copies every piece of facts using a peripheral bus from the I/O device. Using a peripheral bus occupies the CPU at some point of the examine/write technique and does now not allow other work to be done until the operation is finished.

With DMA, the CPU can system other duties while facts Switch is being achieved. The transfer of records is first iNitiated through the CPU. The data Block may be transferred to and from memory via the DMAC in 3 approaches.

In Burst Mode, the System Bus is launched simplest after the information transfer is finished. In cycle stealing Mode, at some stage in the transfer of facts between the DMA channel and I/O device, the machine bus is relinquished for some Clock Cycles in order that the CPU can perform different obligations. When the Data Transfer is entire, the CPU receives an Interrupt request from the DMA controller. In obvious mode, the DMAC can take Charge of the machine bus best while it isn't required by the Processor.

However, using a DMA controller might purpose Cache coherency troubles. The facts saved in RAM Accessed by the DMA controller may not be up to date with the precise cache facts if the CPU is the use of external memory.

Solutions consist of FLUSHing cache strains before beginning outgoing DMA transfers, or performing a cache invalidation on incoming DMA transfers whilst outside writes are Signaled to the cache controller.

What does DMA stand for?

When we refer to DMA as an acronym of Direct Memory Access, we mean that DMA is formed by taking the initial letters of each significant word in Direct Memory Access. This process condenses the original phrase into a shorter, more manageable form while retaining its essential meaning. According to this definition, DMA stands for Direct Memory Access.

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