dividebyzero
Posts: 4,840 +1,271
can someone explain me why nvidia's GTX 480 GDDR5 memory works at 1848MHz... and ATI's GDDR5 is 4x the clock speed of the memory, say HD5850 has a memory of 1000MHz for and effective clock of 4000MHz... or the HD5870 with 1200MHz for the memory for an effective clock of 4800MHz... so.... anyone?
Matthew quoted the GTX 480 memory as 1848MHz- which is it's DDR (Dual Data Rate). Doubling this will give you it's "effective" rate (i.e. 3696MHz). Which is lower than the HD5xxx series but on a wider memory bus, so peak bandwidth is actually fairly similar.
A basic equation for the GTX 480 would be:
924MHz clock x 4 (DDR doubled) x 384 bit bus / 8 bits (1 byte) = 177408 Mb/sec
177408Mb / 1024 (Mb per Gb) = 173.25Gb/sec (173.4 if you round the effective rate to an even 3800MHz)
and for the HD 5870...
1200MHz clock x 4 x 256 bit bus / 8 = 153600 Mb/sec / 1024 = 150Gb/sec