Now the 360’s GPU is one impressive piece of work and I’ll say from the get go it’s much more advanced than the PS3’s GPU so I’m not sure where to begin, but I’ll start with what Microsoft said about it. Microsoft said Xenos was clocked at 500MHZ and that it had 48-way parallel floating-point dynamically-scheduled shader pipelines (48 unified shader units or pipelines) along with a polygon performance of 500 Million triangles a second.

Before going any further I’ll clarify this 500 Million Triangles a second claim. Can the 360’s GPU actually achieve this? Yes it can, BUT there would be no pixels or color at all. It’s the triangle setup rate for the GPU and it isn’t surprising it has such a higher triangle setup rate due to it having 48 shaders units capable of performing vertex operations whereas all other released GPUs can only dedicate 8 shader units to vertex operations. The PS3 GPU’s triangle setup rate at 550MHZ is 275 million a second and if its 500MHZ will have 250 million a second. This is just the setup rate do NOT expect to see games with such an excessive number of polygons because it wont happen.

Microsoft also says it can also achieve a pixel-fillrate of 16Gigasamples per second. This GPU here inside the Xbox 360 is literally an early ATI R600, which when released by ATI for the pc will be a Directx 10 GPU. Xenos in a lot of areas manages to meet many of the requirements that would qualify it as a Directx 10 GPU, but falls short of the requirements in others. What I found interesting was Microsoft said the 360’s GPU could perform 48 billion shader operations per second back in 2005. However Bob Feldstein, VP of engineering for ATI, made it very clear that the 360’s GPU can perform 2 of those shaders per cycle so the 360’s GPU is actually capable of 96 billion shader operations per second.

To quote ATI on the 360’s GPU they say.
“On chip, the shaders are organized in three SIMD engines with 16 processors per unit, for a total of 48 shaders. Each of these shaders is comprised of four ALUs that can execute a single operation per cycle, so that each shader unit can execute four floating-point ops per cycle.”
# 48 shader units * 4 ops per cycle = 192 shader ops per clock
# Xenos is clocked at 500MHZ *192 shader ops per clock = 96 billion shader ops per second.

(Did anyone notice that each shader unit on the 360’s GPU doesn’t perform as many ops per pipe as the rsx? The 360 GPU makes up for it by having superior architecture, having many more pipes which operate more efficiently and along with more bandwidth.)

Did Microsoft just make a mistake or did they purposely misrepresent their GPU to lead Sony on? The 360’s GPU is revolutionary in the sense that it’s the first GPU to use a Unified Shader architecture. According to developers this is as big a change as when the vertex shader was first introduced and even then the inclusion of the vertex shader was merely an add-on not a major change like this. The 360’s GPU also has a daughter die right there on the chip containing 10MB of EDRAM. This EDRAM has a framebuffer bandwidth of 256GB/s which is more than 5 times what the RSX or any GPU for the pc has for its framebuffer (even higher than G80’s framebuffer).

Thanks to the efficiency of the 360 GPU’s unified shader architecture and this 10MB of EDRAM the GPU is able to achieve 4XFSAA at no performance cost. ATI and Microsoft’s goal was to eliminate memory bandwidth as a bottleneck and they seem to have succeeded. If there are any pc gamers out there they notice that when they turn on things such as AA or HDR the performance goes down that’s because those features eat bandwidth hence the efficiency of the GPU’s operation decreases as they are turned on. With the 360 HDR+4XAA simultaneously are like nothing to the GPU with proper use of the EDRAM. The EDRAM contains a 3D logic unit which has 192 Floating Point Unit processors inside. The logic unit will be able to exchange data with the 10MB of RAM at 2 Terabits a second. Things such as antialiasing, computing z depths or occlusion culling can happen on the EDRAM without impacting the GPU’s workload.

Xenos writes to this EDRAM for its framebuffer and it’s connected to it via a 32GB/sec connection (this number is extremely close to the theoretical because the EDRAM is right there on the 360 GPU’s daughter die.) Don’t forget the EDRAM has a bandwidth of 256GB/s and its only by dividing this 256GB/s by the initial 32GB/s that we get from the connection of Xenos to the EDRAM we find out that Xenos is capable of multiplying its effective bandwidth to the frame buffer by a factor of 8 when processing pixels that make use of the EDRAM, which includes HDR or AA and other things. This leads to a maximum of 32*8=256GB/s which, to say the least, is a very effective way of dealing with bandwidth intensive tasks.

In order for this to be possible developers would need to setup their rendering engine to take advantage of both the EDRAM and the available onboard 3D logic. If anyone is confused why the 32GB/s is being multiplied by 8 its because once data travels over the 32GB/s bus it is able to be processed 8 times by the EDRAM logic to the EDRAM memory at a rate of 256GB/s so for every 32GB/s you send over 256GB/s gets processed. This results in RSX being at a bandwidth disadvantage in comparison to Xenos. Needless to say the 360 not only has an overabundance of video memory bandwidth, but it also has amazing memory saving features. For example to get 720P with 4XFSAA on traditional architecture would require 28MB worth of memory. On the 360 only 16MB is required. There are also features in the 360′s Direct3D API where developers are able to fit 2 128×128 textures into the same space required for one, for example. So even with all the memory and all the memory bandwidth, they are still very mindful of how it’s used.

Dispelling Some of the Hype

Now there are people that look at the 360 having a triple core processor and the PS3 with the much publicized Cell Processor and start to wonder…
# #1 How in God’s name can the 360 ship with a 3 core processor in November 2005 while there isn’t an available purchase for 3 or 4 core CPUs for desktop computers?
# #2 Why didn’t Intel or AMD manufacture and start selling such a processor at the same time or before the Xbox 360 shipped?
# #3 How can the cell have 1 Power PC core and, in addition to that, have 7 SPE, which are basically seven extra processors?
# #4 Everyone knows processors aren’t cheap and when you factor in everything else you need, it’s even more expensive. How can Microsoft get away with charging as low as $299 for the Xbox 360? How can Sony get away with charging as low as $500 for the PS3, when the processors themselves cost 90% of the PS3’s price or cost more than $500?

Marketing talk from Microsoft and Sony: The processors inside these machines are extremely powerful and cutting edge you literally have a supercomputer in your home as the Xbox 360 has 1 Teraflop worth of computing power and the PS3 has 2 Teraflops worth of computing power.

TRUTH: Both the 360 and PS3’s CPUs are heavily stripped down compared to what most of us are probably using on our desktop computers to view this article. Both consoles are labeled as 3.2GHZ, but they don’t offer performance comparable to that of a typical Athlon 64 3200+ or better than even an Athlon XP 2800+ CPU. The CPUs inside the Xbox 360 and PS3 are “In-Order Execution” CPUs with narrow execution cores, whereas what we use on our computers are classified as “Out-of-Order Execution” CPUs with wider execution cores.

The reason they can sell for so cheap is because they are not as robust or complex as what we have inside our computers. The execution theme in both the 360 and PS3’s CPUs is similar to that of what you would see in the original Intel Pentium Processor. (Not referring to the Pentium 2 3 or 4, but the original) This is because they’ve stripped out hardware designed to optimize the scheduling of instructions at runtime. As a result, neither the 360 nor PS3’s CPU contain an instruction window. Instead, instructions pass through the processor in the order in which they were fetched; hence both are “In-Order Execution” CPUs.

Marketing talk from Microsoft and Sony: Thanks to these multi-core processors developers will be able to multi-thread their games and get significant performance improvements and achieve Artificial Intelligence in games that people previously thought impossible for a videogame. It’ll be as if you’re playing with another living breathing human being.

TRUTH: “What is the big deal? How exactly does the fact that both processors being “In-Order Execution” CPUs hurt them? Well, see the 3.2GHZ clock speed for both CPUs? The type of nasty game code, full of branches, loops etc… that would’ve been greatly improved speedwise, thanks to out-of-order execution and a wider execution core is not there to help, so that 3.2GHZ actually performs slower than out-of-order execution CPUs available to desktop computer users.

This brings us to the very reason why both the PS3 and Xbox 360 are using multiple processors in an effort to combat the lack of an instruction window and the fact that they have a narrow execution core. It gets even better, because this very same code that they hope to speed up using parallelism on multiple cores isn’t by any means parallel programming friendly.

On the other hand, Graphics-related code is great on both these processors, as graphics code is nice and parallelism friendly. There is a reason people consider graphics accelerators to be the poster child for parallelism. As a matter of fact, it’s the most successful form of parallelism the field of computer science has ever witnessed. GPUs are able to get all transistors firing that actually produce a significant real world benefit to the people using the product.

For the CPU to become more like the GPU is the ultimate goal for many and AMD together with ATI seem to be going for it. The cell processor is actually one such attempt to do so, but it’s not yet at the level everyone had hoped. (Perhaps a bit early as a cell like CPU isn’t on Intel’s to do list until about 2015) Long story short, both Microsoft and Sony have given developers more than enough on the graphics side of things, but at the same time, are asking developers to do more with less on the aspects of the game unrelated to graphics.

i just think the ps3 is getting even for when the ps2 power was crap compare to the xbox but if u remenber even tho the xbox had better grahpic the ps2 had more of better games but not to say that xbox dont have any good ones but instead of putting all this power in the system they should be like the wii something fun and new and cheaper the xbox did get there with the price tho (only 50$ more then the wii) infact i dont even think i get a ps3 till it around 300 to 250 cause i cant aford no 400-650$ for a system i see if it was coming with some games like the wii bundle pack but it not and i no why it cost so much because of the blueray but nether of them is going to last long if the prices keep going up in a bad government *cough* bush *cough* *cough*

Anyone hasn’t said this yet but has anyone else noticed the RSX is on a 128 bit memory bus. If that isn’t one hell of a bottleneck for that fast GPU then I dunno what is.

The problem for the PS3 is a bit like the problem the Xbox1 had,the time devolopers make use of any PS3 advantage the next round of consoles will be here,,the 360 has all the BIG games “NOW”(look at the 360 March AAA titles) and also whereeas before Nintendo were not a feature they certainly are now.