NVidia's Strange Memory Sizes

[Lmeow]

I'm just wondering, why do some nVidia cards have what seems to be 'strange' memory sizes?
I.e., why don't they follow the regular 256, 512, 1024, 2048 etc. megabytes of RAM?

For example, the 9600 GSO has 384 MB of memory, the 8800 GTS G80 had either 320 MB or 640 MB, the 8800 GTX and 8800 Ultra had 768 MB (512 MB + 256 MB I suppose), the GTX 260 & GTX 275 had 896 MB, the GTX 470 1280 MB and the GTX 480 1536 MB.

Is it just part of their architecture? Or do they just want to be different?

With regards to memory sizes, here's what I've figured out:

320 = 256 + 64
384 = 256 + 128
640 = 512 + 128
768 = 512 + 256
896 = 512 + 256 + 128
1280 = 1024 + 256
1536 = 1024 + 512

Is there some meaning to the 'additional' memory on top of what I suppose I would call the standard memory sizes?

 

[Rustyy117]

If you look at some nvidia cards you'll notice that their core, shader and memory speeds are all alittle random aswell, take the GTX285 for example

Core speed: 648Mhz
Memory speed (effective): 2484Mhz
Shader speed: 1476Mhz

I guess their tying to get the absolute most from their cards.

 

[gamerk316]

...*quietly hides his QX9650*