Turn Direct Memory Access (DMA) ON or OFF

Turn Direct Memory Access (DMA) on or off

You must be logged on as an administrator to perform these steps.

Direct Memory Access (DMA) is usually turned on by default for devices such as hard disks and CD or DVD drives that support DMA. However, you might need to turn on DMA manually if the device was improperly installed or if a system error occurred.

• (To open Device Manager first open RUN (Windows + R) then, on the RUN box type DEVMGMT.MSC and OK) If you are prompted for an administrator password or confirmation, type the password or provide confirmation.
• Double-click IDE ATA/ATAPI controllers.
• Under IDE ATA/ATAPI controllers, for each item that has the word Channel as part of its label, right-click the item, and then click Properties.
• Click the Advanced Settings tab. Under Device Properties, select or clear the Enable DMA check box, and then click OK.

What Direct Memory Access (DMA)?

Direct memory access (DMA) is a feature of computer systems that allows certain hardware subsystems to access main system memory (random-access memory), independent of the central processing unit (CPU).

Without DMA, when the CPU is using programmed input/output, it is typically fully occupied for the entire duration of the read or write operation, and is thus unavailable to perform other work. With DMA, the CPU first initiates the transfer, then it does other operations while the transfer is in progress, and it finally receives an interrupt from the DMA controller (DMAC) when the operation is done. This feature is useful at any time that the CPU cannot keep up with the rate of data transfer, or when the CPU needs to perform work while waiting for a relatively slow I/O data transfer. Many hardware systems use DMA, including disk drive controllers, graphics cards, network cards and sound cards. DMA is also used for intra-chip data transfer in multi-core processors. Computers that have DMA channels can transfer data to and from devices with much less CPU overhead than computers without DMA channels. Similarly, a processing element inside a multi-core processor can transfer data to and from its local memory without occupying its processor time, allowing computation and data transfer to proceed in parallel.

DMA can also be used for "memory to memory" copying or moving of data within memory. DMA can offload expensive memory operations, such as large copies or scatter-gather operations, from the CPU to a dedicated DMA engine. An implementation example is the I/O Acceleration Technology. DMA is of interest in network-on-chip and in-memory computing architectures.