Dma in computer architecture

By • Technical Writer and Editor What is direct memory access (DMA)? Direct Memory Access (DMA) is a capability provided by some computer bus architectures that enables data to be sent directly from an attached device, such as a disk drive, to the main memory on the computer's DMA enables devices -- such as disk drives, external memory, graphics cards, network cards and sound cards -- to share and receive data from the main memory in a computer. It does this while still allowing the CPU to perform other tasks. Without a process such as DMA, the computer's CPU becomes preoccupied with data requests from an attached device and is unable to perform other operations during that time. With DMA, a CPU initiates a data transfer with an attached device and can still perform other operations while the data transfer is in progress. DMA enables a computer to transfer data to and from devices with less CPU overhead. An alternative to DMA is Ultra DMA, which provides a burst The CPU gets the DMA controller to begin data transfers, and the DMA controller then sets the memory addresses and read/write lines to the system memory. How does DMA work? Usually, a specified portion of memory is designated as an area to be used for direct memory access. For example, in the DMA channels send data between an attached peripheral device and the system memory. System resources such as the CPU, memory, attached I/O devices and a DMA controller are connected through a The CPU gets the DMA controller to...

The method that is used to transfer information between internal storage and external I/O devices is known as I/O interface. The CPU is interfaced using special communication links by the peripherals connected to any computer system. These communication links are used to resolve the differences between CPU and peripheral. There exists special hardware components between CPU and peripherals to supervise and synchronize all the input and output transfers that are called interface units. Mode of Transfer: The binary information that is received from an external device is usually stored in the memory unit. The information that is transferred from the CPU to the external device is originated from the memory unit. CPU merely processes the information but the source and target is always the memory unit. Data transfer between CPU and the I/O devices may be done in different modes. Data transfer to and from the peripherals may be done in any of the three possible ways • Programmed I/O. • Interrupt- initiated I/O. • Direct memory access( DMA). Now let’s discuss each mode one by one. • Programmed I/O: It is due to the result of the I/O instructions that are written in the computer program. Each data item transfer is initiated by an instruction in the program. Usually the transfer is from a CPU register and memory. In this case it requires constant monitoring by the CPU of the peripheral devices. Example of Programmed I/O: In this case, the I/O device does not have direct access to th...

Page 3 : Drawbacks of Programmed and InterruptDriven I/O, ▪Interrupt-driven I/O, though more efficient than simple programmed I/O, still, requires the active intervention of the processor to transfer data between, memory and an I/O module, and any data transfer must traverse a path, through the processor., ▪ Thus, both these forms of I/O suffer from two inherent drawbacks:, , 1. The I/O transfer rate is limited by the speed with which the processor can, test and, service a device., 1. The processor is tied up in managing an I/O transfer; a number of, , instructions must be executed for each I/O transfer, When large volumes of data are to be moved, a more efficient technique is, required: direct memory access (DMA). Page 4 : DMA Function, ▪The DMA module is capable of mimicking the processor and,, indeed, of taking over control of the system from the processor., , ▪It transfer data to and from memory over the system bus., ▪For this purpose, the DMA module must use the bus only when, the processor does not need it, or it must force the processor to, suspend operation temporarily., , ▪The latter technique is more common and is referred to as cycle, stealing, because the DMA module in effect steals a bus cycle. Page 5 : i te a block of data, it issues a, ▪When the processor wDsiMheAstoFrueandcotriworn, command to the DMA module, by sending to the DMA module the, following information:, • Whether a read or write is requested, using the read or write, control line, between the proce...

Stands for "Direct Memory Access." DMA is a method of transferring data from the computer's For example, a sound card may need to access data stored in the computer's RAM, but since it can process the data itself, it may use DMA to bypass the CPU. Video cards that support DMA can also access the system memory and process graphics without needing the CPU. In order for devices to use direct memory access, they must be assigned to a DMA channel. Each type of port on a computer has a set of DMA channels that can be assigned to each connected device. For example, a Definitions by TechTerms.com The definition of DMA on this page is an original TechTerms.com definition. If you would like to reference this page or cite this definition, you can use the green citation links above. The goal of TechTerms.com is to explain computer terminology in a way that is easy to understand. We strive for simplicity and accuracy with every definition we publish. If you have feedback about the DMA definition or would like to suggest a new technical term, please Want to learn more tech terms? Subscribe to the daily or weekly newsletter and get featured terms and quizzes delivered to your inbox. Subscribe

What is a DMA Controller? The term DMA stands for direct memory access. The hardware device used for direct memory access is called the DMA controller. DMA DMA Controller Diagram in Computer Architecture DMA controller provides an interface between the bus and the input-output devices. Although it transfers data without intervention of processor, it is controlled by the processor. The processor initiates the DMA controller by sending the starting address, Number of words in the data block and direction of transfer of data .i.e. from I/O devices to the memory or from main memory to I/O devices. More than one external device can be connected to the DMA controller. DMA in Computer Architecture DMA controller contains an address unit, for generating addresses and selecting I/O device for transfer. It also contains the control unit and data count for keeping counts of the number of blocks transferred and indicating the direction of transfer of data. When the transfer is completed, DMA informs the processor by raising an interrupt. The typical block diagram of the DMA controller is shown in the figure below. Typical Block Diagram of DMA Controller Working of DMA Controller DMA controller has to share the bus with the processor to make the data transfer. The device that holds the bus at a given time is called bus master. When a transfer from I/O device to the memory or vice verse has to be made, the processor stops the execution of the current program, increments If the DMA contr...