COA- EXTERNAL DEVICE

1. By
Ms.V.VENNILA,MCA.,M.Phil.,
Assistant Professor,
Bon Secours College for Women, Thanjavur.

2.  An external device attaches to the
computer by a link to an Input Output
module.
 An external device linked to an I/O
module is called peripheral device or
peripheral.
 Human readable suitable for
communicating with computer user.

4.  A Human Readable medium or human
readable format is a representation
of data or information that can be
naturally read by Humans.
 In computing human readable data is
often encoded as ASCII or Unicode
text , rather than presented in a
binary representation.

5.  A machine readable document is a
document whose content can be
readily processed by computers.
 Such documents are distinguished
from machine readable data by
virtue of having sufficient structure
to provide the necessary context to
support the business process for
which they are created.

6.  Human Readable input is what it
says , a human could easily read and
understand it.
 Machine readable is convenient for
the machine and is raw binary in the
format the machine uses normally.

7.  I/O module stands for Input Output
module.
 Which is a device that acts as the
connective bridge between a
computer system at one end and an
input output or peripheral device of
some kind at the other, such as
printer, webcam or scanner

9.  Channel I/O Requires the use of
instruction that are specifically
designed to perform I/O operation.
 The I/O instruction address the
channel and device. The channel
asynchronously accesses all other
required addressing and control
information. This is similar to DMA ,
But more flexible.

11.  Input output does not inform CPU
directly Programmed I/O.
 Interrupt driven I/O.
 Direct Memory Access.
Programmed I/O :
 CPU requests input output operation.
 Input Output module performs
operation.

12.  Overcomes CPU waiting no repeated
CPU checking of device.
 CPU issues read command.
 I/O module get data from peripheral
while CPU does other work.

14.  DMA Function :
 Additional module hardware on bus.
 DMA controller takes over from CPU
for I/O.
o Read/write.
o Device address.
o Staring address of data.