When it was announced by MS that the xbox360 will have 10 MB of EDRAM at 256 GO/s, and this will allow it to do free AA at HDTV resolutions, anyone even with little knowledge about hardware, knew that 10 MB is just insufficient to do this. So everyone wondered about the truth . Fortunately the beyond3d article by Dave BAUMANN about xbox360 graphics clarified all this and revealed the truth : There is 10 MB of eDRAM on xbox360 which is not sufficient to do 4X AA at 720P and 1080i resolutions. So the solution was tile rendering, (as the article of Dave Baumann said : the solution is to divide the screen into multiple portions that fit within the eDRAM render buffer space) as you can see requiring a tile rendering technique to do anti aliasing, doesent make it free anti aliasing . Because rendering consume power, so there is no real HDTV free AA on xbox 360. Furthermore in the article of dave we have the following (ATI have been quoted as suggesting that 720p resolutions with 4x FSAA, which would require three tiles, has about 95% of the performance of 2x FSAA.) Do you know what does this mean ?!!
This means that if what they are saying is true, so passing from 2x AA at 720P to 4x AA at the same resolution will hit the performance of xbox 360 by 5% ! and if we suggest this same rate, than going from no AA at 720P ( no tiling required) to 2x AA ( 2 tiles required ) will hit the performance of xbox 360 by at least 5 % or more !!! meaning that at a minimum passing from no AA at 720P to 4x AA at 720P will hit the performance of xbox360 by at least 10 % !!! Now where is the free AA here ?!!
Do the same analysis for 4x AA at 1080i and you will conclude that at least to pass from no AA at 1080i ( no tiling needed ) to 4x AA at 1080i ( 4 tiles needed ) you will get at least 15 % hit in performance !!!
And if Microsoft consider this as free AA than even PS3 has almost free AA with its RSX ( almost 20-30 % real hit in performance when using 4x AA at 1080i resolutions in today actual games, ( officially its even less than 10 % ! like the official Microsoft numbers for the hit of performance on xenos when using AA ! Ironic…) and this wont change a lot in future games, because they will be more shader intensive rather than polygons intensive or even texture intensive )
So please don’t be fooled by the advantage of doing free AA, due to the using of an eDRAM of 10 MB. Because as you have seen this is not true. And there is no free AA at HDTV resolutions on xbox360.
So please stop believing anything, before you are sure of it.
Now lets look at the second main advantage of having eDRAM on xbox 360 : Economize bandwidth, by using the bandwidth of edram to do AA, and Z-buffer, and stencil. so the bandwidth of the GDDR3 ram will be used for shaders, and textures . But even this relative advantage against PS3, was simply killed due to memory bandwidth sharing between XENOS and XeCPU ( 22.6 GB/S ) so if we assume the CPU will need 50% of bandwidth 11.3 GB ( when running complicated physics, AI and animation engines ) than only 11.3 GB/s will be available for the GPU which is not sufficient, and will limit the power of the xbox 360 GPU.
NOTE : With the SATURN-3DO-PS1-N64 generation ( saying it’s the 32 bit generation its not accurate as you know), the trend (or the concentration of developers) was to create more polygons. With the DC-PS2-XBOX-GC generation the concentration of developers was to create better textures ( Sony failed to anticipate this fact, thus leading them to not include a S3TC texture compression technology, and to choose bandwidth over quantity of memory, which was a wrong choice for the GPU, but a great choice for the CPU ) but with next generation games the concentration will be to create better more complex shaders. So this will minimize the requirement for more bandwidth and more memory quantity ( I am not saying bandwidth and memory quantity aren’t a bottleneck on PS3, but I am saying that this Is less of a problem than it was in the previous generation ). So in the next generation we will return to the case of first 3D generation consoles : The CPU will be more important ( complex animations, physics, AI and simulations ), and the limits will be more of a processing power ( to do longer complicated shaders ) than bandwidth or memory quantity. ( thanks GOD for this because as you know its easier for manufacturers to improve processing power than to improve bandwidth )
Disadvantages of 10 MB of eDRAM :
We have just seen that the advantages of having eDRAM are just killed. Now lets look to the disadvantages : there is 332 million transistors on XENOS, but only 252 million transistors are used for LOGIC and calculations ( processing ) ( 232 million transistors for the mother die ( pipelines ) and 20 million transistors used on the back buffer, daughter die, for AA, z buffer, and stencil )
So if there was no eDRAM, ATI could use all 332 million transistors for logic and processing power ! ( like the 300( or a little more ) million transistors for the RSX ) this does mean that the RSX has 300 million transistors dedicated to processing, and xenos only 252 million transistors )
So could we say that the xbox360 is an unbalanced system ?!!
What do you think ?
This means that if what they are saying is true, so passing from 2x AA at 720P to 4x AA at the same resolution will hit the performance of xbox 360 by 5% ! and if we suggest this same rate, than going from no AA at 720P ( no tiling required) to 2x AA ( 2 tiles required ) will hit the performance of xbox 360 by at least 5 % or more !!! meaning that at a minimum passing from no AA at 720P to 4x AA at 720P will hit the performance of xbox360 by at least 10 % !!! Now where is the free AA here ?!!
Do the same analysis for 4x AA at 1080i and you will conclude that at least to pass from no AA at 1080i ( no tiling needed ) to 4x AA at 1080i ( 4 tiles needed ) you will get at least 15 % hit in performance !!!
And if Microsoft consider this as free AA than even PS3 has almost free AA with its RSX ( almost 20-30 % real hit in performance when using 4x AA at 1080i resolutions in today actual games, ( officially its even less than 10 % ! like the official Microsoft numbers for the hit of performance on xenos when using AA ! Ironic…) and this wont change a lot in future games, because they will be more shader intensive rather than polygons intensive or even texture intensive )
So please don’t be fooled by the advantage of doing free AA, due to the using of an eDRAM of 10 MB. Because as you have seen this is not true. And there is no free AA at HDTV resolutions on xbox360.
So please stop believing anything, before you are sure of it.
Now lets look at the second main advantage of having eDRAM on xbox 360 : Economize bandwidth, by using the bandwidth of edram to do AA, and Z-buffer, and stencil. so the bandwidth of the GDDR3 ram will be used for shaders, and textures . But even this relative advantage against PS3, was simply killed due to memory bandwidth sharing between XENOS and XeCPU ( 22.6 GB/S ) so if we assume the CPU will need 50% of bandwidth 11.3 GB ( when running complicated physics, AI and animation engines ) than only 11.3 GB/s will be available for the GPU which is not sufficient, and will limit the power of the xbox 360 GPU.
NOTE : With the SATURN-3DO-PS1-N64 generation ( saying it’s the 32 bit generation its not accurate as you know), the trend (or the concentration of developers) was to create more polygons. With the DC-PS2-XBOX-GC generation the concentration of developers was to create better textures ( Sony failed to anticipate this fact, thus leading them to not include a S3TC texture compression technology, and to choose bandwidth over quantity of memory, which was a wrong choice for the GPU, but a great choice for the CPU ) but with next generation games the concentration will be to create better more complex shaders. So this will minimize the requirement for more bandwidth and more memory quantity ( I am not saying bandwidth and memory quantity aren’t a bottleneck on PS3, but I am saying that this Is less of a problem than it was in the previous generation ). So in the next generation we will return to the case of first 3D generation consoles : The CPU will be more important ( complex animations, physics, AI and simulations ), and the limits will be more of a processing power ( to do longer complicated shaders ) than bandwidth or memory quantity. ( thanks GOD for this because as you know its easier for manufacturers to improve processing power than to improve bandwidth )
Disadvantages of 10 MB of eDRAM :
We have just seen that the advantages of having eDRAM are just killed. Now lets look to the disadvantages : there is 332 million transistors on XENOS, but only 252 million transistors are used for LOGIC and calculations ( processing ) ( 232 million transistors for the mother die ( pipelines ) and 20 million transistors used on the back buffer, daughter die, for AA, z buffer, and stencil )
So if there was no eDRAM, ATI could use all 332 million transistors for logic and processing power ! ( like the 300( or a little more ) million transistors for the RSX ) this does mean that the RSX has 300 million transistors dedicated to processing, and xenos only 252 million transistors )
So could we say that the xbox360 is an unbalanced system ?!!
What do you think ?
