18 and 36-bit memory bus?

[dknguyen]

I was looking memories and I noticed a bunch of them have strange bus sizes that 18 , 36, or 72 bits wide rather than the standard 8, 16, and 32 bit sizes. Is there a reason these sizes exist? They aren't the standard word sizes.

THanks.

 

[3v0]

While we expect to see memory widths in powers of 2 there are applications that require otherwise. The one example that comes to mind in graphics. For example graphics with 12 bit memories, RBG 4 bits per color sort of thing. I am sure there are current examples but I do not know any offhand.

3v0

 

[Nigel Goodwin]

Isn't the extra bit a partity bit?.

 

[Hero999]

While we expect to see memory widths in powers of 2 there are applications that require otherwise. The one example that comes to mind in graphics. For example graphics with 12 bit memories, RBG 4 bits per color sort of thing. I am sure there are current examples but I do not know any offhand.

I thought planar modes were used if the number of bits per pixel aren't a power of 2?

So for 12-bit colour, you'd have 12 bit planes.

**broken link removed**)
Bit plane - Wikipedia, the free encyclopedia

 

[dknguyen]

Isn't the extra bit a partity bit?.

Don't think so...it is counted as part of the SRAM's memory and is used like normal memory. UNless you mean it's there so the user can manually implement as a parity bit.

 

[Nigel Goodwin]

Don't think so...it is counted as part of the SRAM's memory and is used like normal memory. UNless you mean it's there so the user can manually implement as a parity bit.

A quick google thinks so

Non-Parity, Parity and ECC Memory