I bought a cheap GT 520 of 65 euro’s which is passively cooled and has 35 watt or something, it goes up to 40 or 50 degrees.
Anyway I think I know what is going on… I guess I confused the shader frequency with the memory frequency… and I think I also now know how to calculate maximum random access performance without cache benefits:
The memory frequency of this card is: 810 megahurtz lol hurtz.
Anyway… the memory bus is 64 bit.
This means it can transfer 8 bytes per clock.
So the maximum number of bytes it can transfer is clock * bus.
However because of coalescing the ammount of memory transactions per second becomes: (clock * bus) / memory transaction size
So this is:
(810.000.000 * 8) / 128 = 50.625.000
Only 50 million memory transactions per second, which is really low.
So it’s a little bit surprising that I have been seeing 64 million and now even 92 million which almost seems beyond it’s spec.
This is probably because of lucky caching External Image :) (And also the memory test doesn’t do full random access but block-based random access which might get more cache-lucky).
Anyway I hope these formula’s/calculations are correct. This will allow me to figure out which card I might want to purchase in the future ! External Image
I am looking for “maximum memory transactions per second”.
Also turning of memory coalescing would make sense if it was possible.
Suppose it was possible to use the lanes in 4 byte memory transaction sizes then this would give:
(810.000.000 * 8 / 4) = 1.620.000.000
A hell lot more memory transactions !
I have seen some documents about ATI cards being able to do 32 bit memory transactions, so I am becoming a little bit curious about ATI cards ?!?
However the test program I wrote is perhaps a bit extreme, perhaps not… so in practice there might be some coalescing but that’s based on luck… I’d rather have garantueed performance than just luck.
Ok, my sharpness is declining as it gets bed time for me.
Apperently I got confused or didn’t look further then my nose was long.
The mentioned megahurtz is probably something else… what it is… I don’t know…
But the website mentions different timings:
According to this website the memory is actually 1200 MHZ. However the accuracy of the website might be in doubt, but usually it’s pretty close.
(I noticed this because the higher performing cards also has 800 MHZ I thought… ouch… is that really true… and then I noticed higher performing cards have 4000 MHZ for memory speed ?!External Image)
So I am gonna try my formula again (I am not sure which numbers to plug into my formula so I am just gonna try):
(1200 * 1000 * 100 * 8) / 128 = 75.000.000
That’s much closer to the number I saw: 64.000.000
The rest of the bytes maybe overhead ?!?
Anyway… now 92.000.000 doesn’t seem so far off anymore External Image
For now it would help if somebody else who knows a lot about DRAM could provide me with some formula to be able to calculate how many random access reads and writes it can do per second ?