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1. MODES OF TRANSFER -J.MOWLIDHARAN
DHAKSHANAMOORTHY
K.M.RADHU DHARSAN
M.SHRISANJAY

2. MODES OF TRANSFER
Data transfer between the central computer and I/0 devices may be handled in
a variety of modes. Some modes use the CPU as an intermediate path; others
transfer the data directly to and from the memory unit. Data transfer to and
from peripherals may be handled in one of three possible modes:
1. Programmed I/0
2. Interrupt-initiated I/0
3. Direct memory access (DMA)

3. PROGRAMMED I/O
Programmed I/0 operations are the result of I/0 instructions written in a
computer program. Data transfer is initiated by an instruction in the program,
usually from a CPU register and peripheral. The CPU must monitor the
interface to see when a transfer can be made. It is up to the programmed
instructions executed in the CPU to keep close tabs on the interface unit and
the I/0 device.

6. INTERRUPT INITIATED I/O
In the programmed 1/0 method, the CPU stays in a program loop until the 110
unit indicates it is ready for data transfer. This time-consuming process keeps
the processor busy and can be avoided by using anan interrupt facility and
special commands to inform the interface to issue an interrupt request signal
when the data are available from the device. The interface watches the device
while the CPU pauses the task it is processing and branches to a service
program to process the 110 transfer, and then returns to normal.

7. PRIORITY INTERRUPT
Priority interrupt is a mechanism in computer architecture that allows high-
priority devices to interrupt the CPU and take control of the system when they
need immediate attention. The CPU suspends its current operation and
services the interrupt from the high-priority device
The daisy-chaining method involves connecting all the devices that can
request an interrupt in a serial manner. This configuration is governed by the
priority of the devices. The device with the highest priority is placed first
followed by the second highest priority device and so on.

9. DIRECT MEMORY ACCESS
Direct memory access (DMA) is a method that allows an input/output (I/O)
device to send or receive data directly to or from the main memory, bypassing
the CPU to speed up memory operations.

11. THANK YOU
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