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GeForce7: New Graphics Architecture?

The new graphics architecture was quite expectedly named GeForce 7, and the graphics processor which is its embodiment is called G70. NVIDIA seems to imply that this is a perfectly new architecture rather than an improved GeForce 6. Is it really so? Let’s delve deeper into the matter.

First, the new graphics processor from NVIDIA is the most complex GPU for personal computers today, consisting of as many as 302 million transistors. For note: the NV40 consists of 222 million transistors, and the ATI R480 of only 160 million. This complexity is quite natural since the new GPU contains 24 pixel pipelines and 8 vertex processors against 16 and 6, respectively, in GPUs of the previous generation. Moreover, the G70 is not just an overgrown NV40. NVIDIA has considerably revised the architecture of pixel and vertex processors to improve their performance. More about that shortly, but now let’s have a look at the technical specification of the new GPU in comparison with previous-generation models:

NVIDIA GeForce 7800 GTX

NVIDIA GeForce 6800 Ultra

ATI RADEON X850 XT Platinum Edition

Manufacturing technology

0.11 micron

0.13 micron

0.13 micron low-k

Number of transistors

302 mln.

222 mln.

160 mln.

Clock frequency

430MHz

400MHz

520MHz

Graphics memory controller

256bit GDDR3 SDRAM

256bit GDDR3 SDRAM

256bit GDDR3 SDRAM

Graphics memory clock frequency

1200 MHz

1100 MHz

1180 MHz

Memory bus peak bandwidth

34GB/s

32.8GB/s

33.4GB/s

Maximum graphics memory size

512MB

512MB

512MB

Interface

PCI Express x16

PCI Express x16

PCI Express x16

Pixel processors, pixel shaders

Shader model

3

3

2.x

Static loops and branching

yes

yes

yes

Dynamic loops and branching

yes

yes

no

Multiple Render Targets

yes

yes

yes

Floating-Point Render Target

yes

yes

yes

Maximum number of pixels per clock cycle

24

16

16

Maximum number of Z values per clock cycle

32

32

16

Number of texturing samples

16

16

16

Texture filtering algorithms

Bi-linear

Bi-linear

Bi-linear

tri-linear

tri-linear

tri-linear

anisotropic

anisotropic

anisotropic

tri-linear + anisotropic

tri-linear + anisotropic

tri-linear + anisotropic

Maximum level of anisotropy

16x

16x

16x

Vertex processors, vertex shaders

Shader model

3

3

2.x

Number of vertex processors

8

6

6

Static loops and branching

yes

yes

yes

Dynamic loops and branching

yes

yes

no

Reading textures from the vertex shader

yes

yes

no

Tesselation

no

no

no

Full-Screen Anti-Aliasing

FSAA algorithms

Ordered-grid super-sampling

Ordered-grid super-sampling

Rotated-grid multi-sampling

Rotated-grid multi-sampling

Rotated-grid multi-sampling

temporal anti-aliasing

super-sampling + multi-sampling

super-sampling + multi-sampling

transparent supersampling

Number of samples

2..8

2..8

2,4,6

Technologies increasing the efficiency of the memory bus bandwidth

Hidden Surface Removal (HSR)

yes

yes

yes

Texture, Z-buffer, frame buffer compression

yes

yes

yes

Fast Z-buffer clear

yes

yes

yes

Additional technologies

OpenEXR (HDR)

yes

yes

no

Videoprocessor

yes

yes

no

So, the G70-based graphics card is called GeForce 7800 GTX. This new device looks quite imposing, being technologically head above the GeForce 6800 Ultra, not to mention the RADEON X850 XT Platinum Edition. There’s only one parameter the ATI card is superior in – the clock rate of the G70 is lower, having increased by only 30MHz above the previous-generation NV40 chip. This is of course the consequence of the high complexity of the chip, but there seem to be no problems with production. NVIDIA says graphics cards on the new GPU will be available at the day of the announcement. That’s good, recalling that the last-year announcement of the NV40 was in fact just a marketing event, the actual silicon being unavailable in shops.

The table above does not reveal the distinguishing features of the G70 which make it a truly new-gen solution. We will dwell on these features individually. At first sight, the G70 is similar to the NV40, save for the number of pixel and vertex processors:

The number of Raster Operation (ROP) units has remained the same. There 16 of them in the chip, and the number of texture samples per pass is still 16 or 32 when only Z values are sampled. In other words, the number 24 refers to the number of pixel processors only. So, the GeForce 7800 architecture generally resembles the GeForce 6800, but there are some considerable differences, too.

 
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