Question Calculating Memory Bandwidth!?

meeshu

Member
Jun 9, 2003
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Calculating video card memory bandwidth is fairly straight forward, or so I thought!!

It is base memory clock frequency times multiplier to allow for multiple instructions per cycle times memory bus width.

MC x mf x mbw.

But since the memory bus width is noted in bits, and the memory bandwidth is usually shown as bytes per second, then the memory bus width has to be divided by 8 (to give memory bus width in bytes).

MC x mf x mbw/8

The multiplier (mf) for multiple instructions per cycle depends on how the card processes instructions per cycle. This multiplier varies depending on the type of memory being used on the card. For many cards the multiplier is 2, but for later memory such as GDDR5 and GDDR6, the multiplier is 4.

Now, I have this card with further specifications here.

This card has a base memory clock frequency of 1500 MHz. The memory used is GDDR6 so the multiplier is 4. And this card has a bus width of 128 bits.

Calculating the maximum bandwidth so - 1500 MHz x 4 x 128/8, I get 96000 MB/s, or 96GB/s.

However, the specifications for this card say the memory bandwidth is 192 GB/s!!

This doesn't make sense! Error in specification? Or did I calculate wrong!?

Comments?
 
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