Skip to main content

Direct memory access in operating system-computer world

                             Direct memory access 

Direct memory access : DMA stands for  direct memory access and it is another mechanism where input output device is given full transfer block of data to from memory without going through the CPU. In other word we can say that it is a method of transferring data from the computers RAM to another part of computer. The DMA controller operate the memory bus directly without the help of main CPU so DMA controller improves the system performance.

Whenever a device uses DMA , it has to specify a DMA channel . Ultra DMA hard drive uses DMA to transfer at high speed. Whereas earlier hard drives were the first to transfer data from CPU which took more time. 

In older computers , the four DMA channel were 0, 1, 2 and 3 were used , when the 16 bit ISA bus was introduced, the channels 5, 6 and 7 were also added to it.

DMA transfer modes

1. Burst mode : Burst mode is the fastest DMA mode in which two or more bytes can be continuously transferred.

2. Cycle steal mode : Cycle steal mode is slower than burst mode. In this mode only one byte is transferred at a time.

3. Transparent mode : This is the slowest data transfer mode in which the processor executes some status that makes it different from the system bus.

Comments

Popular posts from this blog

Single partition allocation, Multiple-partition allocation and Fixed Equal-size partitions in operating system-computer world

  Single partition allocation, Multiple-partition allocation and Fixed Equal-size partitions in operating system Single partition allocation In this scheme operating system is residing in law memory and user process are executing in higher memory. Advantages It is simple  It is easy to understand and use Disadvantages User job is limited to the size of available memory. It leads to poor Utilization of processor and memory. Multiple-partition allocation  It is the simplest method for allocating  memory is divided memory into several fixed size partitions. Fixed Equal-size partitions It divides the main memory Into equal number of fixed sized partitions, operating system occupies some fixed portion and remaining portion of main memory is available for user processes. Advantages It supports multi programming. A process whose size is less then or equal to the partitions size can be loaded into any available partition. Disadvantages If a program is big to fit in...

Deadlock in operating system-computer world

  Deadlock in operating system-computer world Deadlock :  In a multi-programming environment, many process may complete for a minute number of resources. A process make a request for a resource and if the resource is not available at that time, the process enter In a waiting state. A waiting state process is never again-able to change state because the resource it has requested is held by other waiting process. This situation is called deadlock. So we can say that a process is said to be deadlock when it is waiting for an event or resources which will never occurs.   so we can say that in this situation none of the process gets executed  since the resource it needs, is held by some other process which is also waits for some other resource to be released.  Let's assume that there are three process P1, P2, p3 and three different resources R1, R2 and R3. R1 is assigned to p1, R2 is assigned to P2 and R3 is assigned to P3.   After somet...

What is computer and its characteristics-computer world

  What is computer and its characteristics  Computer  :  Computer is an electronic data processing device, which accept and store data input, process the data and generates the output in a required format. computer is made up of integrated  parts (input, control, ALU, storage and output unit) All the part work together to process data so, we can say that a computer is a programmable electronic device accept row data as input and process it with  set of instruction to produce the result as output. Meaning of computer The word "computer" comes from the word "compute" which means to "calculate". The word computer is derived from the Latin word compute which means to calculate. Characteristics of computer Automatic : It is a automatic machine work by itself without human instruction. Speed :  A computer is a very fast devices. It can perform in a few second, the amount of work that a human being can do in an entire year.  Accuracy : In addition t...