Direct Memory Access (DMA) Seminar and PPT with pdf report: In many input/output interfacing applications and surely in the information acquisition systems, it is often required to send data to an interface or receive data from an interface at data rates higher than those possible by using simple programmed input/output loops.

Microprocessor controlled alienates with the personal computer need a significant amount of CPU time, while the avail of interrupts might permit the CPU to do some concurrent tasks and two such applications are by alienating the screen data to the video card adapter on the board memory and by alienating information from a remote I/O machine to the personal computer’s memory. You can download Direct Memory Access (DMA) Seminar and PPT with pdf report and this is totally free.

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Direct Memory Access DMA Seminar PPT with pdf report

The abbreviation of the direct access memory is the DMA and it makes the task easy about the maximum information alienate rate. In the program or interrupt controlled I/O, the information is alienated through the microprocessor and its internal register but the direct memory access alienates the information directly between an I/O machine and memory. A separate DMA controller is needed to perform the direct access memory I/O operations.

What is the direct memory access?    

The transfer of information between a speed storage machine like magnetic disk and memory are often limited by the speed of CPU. To enhance the speed of transfer, it is required to remove the CPU from the path and permit the peripheral machines and manage the memory buses directly and this transfer mechanism is called as direct memory access. The controller of the direct memory access takes over the buses to manage the alienate directly between the input and output machine and memory, at the time of DMA transfer the CPU will have no power on the memory buses and will be idle. The direct access memory chip was as Intel 8237 machine and there are three ways in which the 8237 devices can transfer the information and they are following:

  • Input/output to memory
  • Memory to input/output
  • Memory to memory

History of direct memory access:

An IBM i.e. International Business Machines, the consistent computer system of IBM has two Intel 8237 consistent DMA controllers. Intel Corporation published datasheet called 8237A high-performance programmable DMA controller and it has the total description or explanation of the 8237 DMA controller.

Why we need DMA?

The assumption about the I/O machines like keyboards, mouse, and printer etc. are genuinely very slow when compared with the central processing unit (CPU). To overcome this issue an interrupt handler was used and the I/O machine produces all the signals that the CPU produce, then the I/O machine can bypass the information alienates to central processing unit and hence increases the speed.

What is actually DMA?

The direct memory access is a system where the samples are saved in the memory of the system while the processor does something else.

DMA channels:

The 8237 controllers furnished by the IBM is a peripheral interface circuit for permitting peripheral machines to directly alienate information to or from main memory. It has four independent channels and the number of channels can be increased by adding the controller chips. The architecture of IBM has two DMA controllers and in it, one DMA controller is used to transfer the byte and has four channels namely 0, 1, 2, 3; the other is used to transfer the word and has four channels namely 4, 5, 6, 7.

Different modes of DMA operation:

The DMA operation can be done by using three different modes and those are as follows:

  • Continuous mode DMA
  • Cycle stealing
  • Interleaved DMA

DMA operational modes and settings:

The 8237 DMA can be operated in many modes and the major modes are as follows:

  • Single
  • Block/demand
  • Cascade
  • Auto initialize

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DMA signals:

The signals that are required to understand the operation of DMA are as follows:

  • DREQ0-DREQ3-DMA Request
  • DACK0-DACK3-DMA Acknowledge
  • AEN and ADSTB—Additives Enable and Address Length
  • MEMR and MEWR—Memory Read and Memory Write
  • A3-A0 and A7-A4—Address
  • HRQ and HLDA—Hold Request and Hold Acknowledge


There are two types and those are as follows:

  • Bus- Master DMA devices
  • System DMA devices


The advantages of the DMA are as follows:

  • The DMA is quick because a piece of hardware alienates information from one computer location to another.
  • DMA is needed to get high information transfer speed.
  • It reduces latency in servicing a data acquisition machine.
  • The reduced latency decreases the amount of temporary memory needed on an I/O machine.
  • It off-loads the processor.


The disadvantages of the DMA are as follows:

  • The hardware of DMA is very costly.
  • DMA is the useful one and only for the commands of DATA.
  • The information has to be saved in continuous locations in the storage.
  • The complete error conditions have to read by the CPU analyze by the CPU.
  • All the existing limitations lead to the next mode of I/O and that is I/O channels.

Content of the Seminar and pdf report for DMA

  • Introduction
  • History
  • What is DMA?
  • What is actually DMA?
  • Application
  • DMA Channels
  • Different Modes of DMA operation\
  • DMA Operational Modes and Settings
  • Types
  • DMA Signals
  • Advantages
  • Disadvantages
  • Conclusion
  • References

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