System Memory Lesson 005: ECC Memory

Non-Parity Memory

Standard memory that does not check for errors and allows data to be put in or taken out.

What is the most common type of parity memory and why?

Non-parity memory due to its affordability and speed.

Parity Memory

A legacy error checking method that ensures the memory contents are reliable and have integrity.

What type of memory is more expensive and slower?

Parity memory.

What is parity memory good for?

Systems used for tasks that require high reliability, like servers and some high-end workstations.

Can parity memory fix errors?

No, it can only catch them.

What does every parity byte have and how is it used?

A parity bit, which is set at write time and is calculated and compared when read from the memory.

What determines if parity data is correct?

If the calculated parity bit is the same when read from memory.

What is the limitation with parity bits and how they check errors?

Some parity bits aren't caught, due to two or more bits of data changing between write and read time, making it uncatchable.

Why can't parity checking work every time?

It operates on an older error checking method, involving whether or not the number of ones present is odd or even, basically using a TRUE/FALSE checking method.

What percentage of errors are single-bit type parity errors?

About 90% of errors.

Error Correcting Code (ECC)

A modern type of memory that detects and corrects an error in data.

What is the drawback of (ECC)?

It is slower than both non-parity and parity memory, due to the additional functionality of correcting errors.

What is the benefit of ECC?

It is more reliable than non-parity and parity memory, with higher integrity data and is capable of correcting errors.

Where would I see ECC in practice?

In high-end workstations and servers, due to the additional cost and high level of integrity needed for these functions.

Buffered/Registered Memory

A type of additional hardware between the memory and CPU, that is used for the functionality of ECC or parity memory.

What additional support is needed for parity memory and ECC?

The motherboard and CPU need to support this functionality.

Are ECC and non-ECC modules compatible with one another and why?

No, because having a mixture of both can cause errors in the system.

Which type of memory has some error checking capabilites, while not being considered ECC or parity memory?

DDR5 SDRAM.