Question

Course: Computer Architecture
Theme: Internal Memory

What is parity bitHow do the following work: flash memory, STT-RAM, PCRAM, ReRAM?? What is Hamming code? Give examples.

Answer 1

What is parity bit :-

• Parity bit is check bit which is used to add in block of data for error detection purposes and validate integrity of data.
• The value of parity bit is 0 or 1. parity bit is checks for message block either it is eve or odd.
• There are two tyeps of parity bits - Even parity and odd parity.
• Even parity -- The total number of bits in message is made even.
• Odd parity -- The total number of bits in message is made odd.
• Error detection by adding parity bit --
• Even parity bit-- if the number of 1s is even then the value of parity bit is 0 and if number of 1s is odd then value of parity bit is 1.
• Odd parity bit -- If number of 1s is odd then the value of parity bit is 0 and if the number of 1s is even then value of parity bit is 1

Flash Mamory :-

• When any bit information data is written to flash memory, the encoder circuits generates the parity bits and then add these parity bits to the k-bit information data and then create n-bit codeword.
• After this process the code word is written in and stored o page of memory array.
• In reading operation, the decoder circuits search errors in codeword and correct the bit if it has error.

STT-RAM :-

• STT-RAM stands for Spin transfer torque access memory.
• it is a nonvolatile memory known for its fast speed., small footprints and zero standby powers.

PCRAM :-

• PCRAM stands for Phase change random access memory.  
• It sotres the data by altering the state of matter from which the device is fabricated.
• PCRAM has fast read access time and good data retention and high data density.
• It has two state which include -- amorphous and crystalline.

ReRAM :-

• RERAM stands for Resistive random access memory. and it is next generation memory under development.
• ReRAM has lower read latency and faster write performance.
• In reram, voltage is applied to material stack and change in the resistance that records data which is 0s and 1s in the memory .

Hamming code with example :-

• Hamming code is used for error detection up to two bit immediate error and hamming code is a linear code and it is capable of single bit errors.
• The source encode the message by adding redudant bits in the message in hamming code
• The application of hamming code include -- Satellite, Computer memory, modems, open connectors and embedded processor.
• Process of encoding a message using hamming code --
• Hamming code calculate the total number of redundant bits.
• then chec position of the redundant bits.
• And after all calculate value of these redundant bits.
• For example --  1,4,5,7,8
• The above example is reffered as P1 at position 1 , p2 at position 2, and p3 at position 3.
• The p1 is a parity bit for each data bits in position whose binary representation include 1 in less important position which do not include 1.like (4,5,7,8).