NVIDIA's Curse: Memory Bandwidth

While the chip itself probably supports much more, the GeForce2 MX will be available in 16MB or 32MB SDRAM board configurations.  Since this is a “value” part don’t expect to see any 64MB GeForce2 MX boards floating around. 

According to NVIDIA, the GeForce2 MX supports 64-bit SDR/DDR SDRAM or 128-bit SDR SDRAM.  This raised a pretty big flag for us as it made no sense that the chip could only support 128-bit SDR SDRAM and not DDR SDRAM since supporting DDR SDRAM does not change the pinout of the chip itself. 

This seems to be inherently crippling the GeForce2 MX’s performance.  Can you imagine how limited a GeForce2 GTS would be if it could only use SDR memory?  That’s pretty much the situation the GeForce2 MX is being placed in most likely to keep it from competing with the GeForce DDR and the GeForce2 GTS. 

At launch only 128-bit SDR boards will be available although later on we may see a version of the GeForce2 MX with a 64-bit memory bus. 

To make matters even worse, the GeForce2 MX’s memory clock will be placed at 166MHz which gives it the exact same memory bandwidth as a SDR GeForce 256.  So even before the GeForce2 MX can come close to hitting its fill rate limitation, it will bump into the memory bandwidth limitation that plagued SDR GeForce 256 owners not too long ago because it has the same amount of memory bandwidth as that card that was released last October. 

Video Card Specification Comparison
 
NVIDIA GeForce 256
NVIDIA GeForce2 MX
NVIDIA GeForce2 GTS
3dfx Voodoo5 5500
Core
NV10
NV11
NV15
Napalm (VSA-100)

Clock Speed

120MHz
175MHz
200MHz
166MHz
Number of Chips
1
1
1
2
Rendering Pipelines
4
2
4
2
Texels/Clock
1
2
2
1
Texels/Second
480 Million
700 Million
1600 Million
667 Million
Memory Bus
128-bit SDR/DDR
128-bit SDR or 64-bit SDR/DDR
128-bit SDR/DDR
128-bit SDR
Memory Clock
166MHz SDR/300MHz DDR
166MHz SDR
333MHz DDR
166MHz SDR
Memory Bandwidth
2.7/4.8 GB/s
2.7 GB/s
5.3 GB/s
5.3 GB/s
Manufacturing Process
0.22-micron
0.18-micron
0.25-micron (Enhanced)

At 166MHz, with a 128-bit memory bus, the GeForce2 MX has about 2.7GB/s of available memory bandwidth.  This is exactly half of the memory bandwidth that the GeForce2 GTS has and goes along perfectly with the fact that it also has pretty much half the fill rate of its bigger brother as well.  The only problem with this is that the GeForce2 GTS is already memory bandwidth limited with 5.3GB/s of memory bandwidth.  This then translates into the fact that the GeForce2 MX is already memory bandwidth limited out of the box, making its incredible fill rate for a value card not that useful of a feature. 

To summarize this all, the GeForce2 MX has a 45% greater fill rate than the original GeForce SDR yet it has the exact same amount of memory bandwidth.

The Chip The Card, Cost, NSR & T&L

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