How many ways to transfer the data between input/output devices and main memory?

Here I will discuss about the transferring data…………

How many ways to transfer the data between input/output devices and main memory?

There are different  ways to transfer data between i/o devices and main memory..

(1)    Using interrupt

(2)    Using DMA(Direct Memory Access)

Interrupts:

                                An interrupt are the signals that is sent to CPU by an i/o device and also sent to the i/o device by CPU. When CPU is interrupted in the execution of the program then it stop its current all activities such as execution of the program. After this, it transfer the control to interrupting device to check the interrupt.

                                Interrupt are one that is most commonly used scheme to handle i/o devices. In this scheme, the CPU normally called processer issues a command signals to the input/output devices for i/o operation. When the device is ready , it generate the interrupt signals to the processer(CPU). The processing exit all other operations when it receives the interrupt signals for that device. Then it perform the input/output operations.

Advantages of interrupt:

                                                The main advantages of the interrupt scheme is that there is no required of the additional hardware. It is easy to and implement.

Disadvantages of interrupt:

The disadvantages of this interrupt scheme is that it reduces the overall performance of the computer system.

DMA:

                DMA stands for Direct memory access. DMA scheme use a special hardware component to perform the task. This hardware is called the DMA controller. In this scheme the data transferring between input/output devices and main memory is takes place without the involvement of the CPU (processer). To complete this operation, the CPU send the request to the DMA controller to perform the input/output operation such as transferring the data from input/output devices. Then CPU (processer) continue to perform their other tasks. When the data transferring is complete with DMA, then the DMA controller send an interrupt signals to CPU. Thus, CPU is involved only at the beginning and the end of the data transferring.

Advantages of DMA:

                                                The main advantages of the DMA is that the processor does not have to wait the completion of the tasks of i/o operations. The performance of the computer system increased.

Disadvantages of the DMA:

 The main disadvantages of the DMA controller is that it is more complex and more hardware is require to needed to implement this scheme.

CPU Registers

The storage area that is used to store a small data is called register.  These are the high speed memories. These memories are use to store data and instruction during the program’s execution.  The CPU consist of many types of the registers. Each of the registers is use for special purposes. The size of these registers is 2, 4, 8, 16 or more. The large size of these registers increase the performance of the CPU (processer).

Types of Special Purpose Registers:

There are different special purpose registers that are used to perform different task during executions of the program. These registers are as follow:

1.       Program counter register

2.       Instruction register

3.       Memory address register

4.       Memory buffer register

5.       Stack register

Program counter register (PC):

                                                                The program counter register is use to control the sequence of the instruction that are comes or fetched from the memory. This register also store the address of the next instruction that will be fetched form the memory. when the instruction is fetched form the main memory then the value of PC is incremented. This register is also known as Instruction pointer register.

Instruction Register (IR):

                                                Those instructions are stored in the instruction register that are fetched from the main memory. The instruction that is in IR, the control unit take these instruction and decodes it and then executer these instruction one by one.

                “The next registers will be discuss in Next lecture”