PARITY BIT

Parity:

Checks whether data has lost or written over when it is moved from one place storage to another.

Bit:

Adds to bit that number of bits in the string is even or odd.

History:

Present on magnetic tape data storage in 1951.

Parity bit also called as:

Check bit.

In computers:

Called as Vertical redundancy check.

Purpose:

Simple way to check for errors.

Uncommon for bits to flip.

Working:

Parity is an extra bit send through bit stream.

It cannot correct error only it can detect.

What parity can detect:

Detect a single bit error (or) Extra bit.

Extra bit:

Total number of 1's in transmitted signal.

How parity bit works:

Parity bit adds check sums to data.

Checksum:

Redundancy check used to detect errors in data.

Types:

Even parity bit:
Even number of ones are present.

Odd parity bit:

The total number of ones is odd number. 

Differences between Even and Odd parity bit:

Even parity bit	Odd parity bit
Even number of ones.	Odd number of ones.
value is 1010101.	value is 1010101.
Parity bit will be adding zero.	parity bit will be adding one.
Result will be even parity.	Result will be odd parity.

Example:

Parity generator:

Logic circuit that generate parity bits in the transmitter.

Parity generator also called as:

Parity checker.

Parity checking:

Data has transmitted correctly or not.

How parity checker works:

Numbers of ones are odd it will add one.

Number of ones are even it will add zero.

With receiver it will add extra bits to parity bit.

Any error checks by parity checker based on parity bit.

Error detection:
Errors caused by noise or other impairments during transmission from transmitter to receiver.

Odd number of bits transmitted incorrectly.

Cannot correct errors, no way to determine which bit is corrupted.

RAID:
Redundant Array Of Independent Disks.
Storing data in different places on hard disk.

Advantages:

Locate on erroneous portion of data.

On communication links.

Noise link will be identified fast.

Disadvantages:

Not suitable for multiple errors.

Not capable of finding all errors.
Not able to correct the data so data has to be re-transmitted.
Not capable of finding all errors only odd number of bits to flip will be detected.