The reality of the PS3 frame-rate "issues" versus Xbox 360

[Game_boy]

There have been many topics n this forum where PS3 owners who bought a console advertised on raw performance see Xbox 360 versions of their games at a higher frame-rate with arguably better graphics. Here I shall explain what is causing this and why the numbers tell us very little. The Playstation 3 is undoubtedly the most powerful console in terms of floating point operations per second ever created, with theoretical performance of 2 TFLOPs according to Sony. Its CPU is based on the Cell Broadband Engine Architecture (CBEA), which derives from IBM's POWER architecture. It consists of nine cores: one general-purpose core and eight Synergistic Processing Elements (SPEs), floating-point operation specialised cores that are connected to it. Two of these are disabled in the PS3 CBE; one to increase yield (number of working processors coming off of production line), and the other for the operating system. To take advantage of this performance, developers would always have to find nine largely independent simultaneous tasks, eight of them primarily floating-point. This is very hard in games, because everything a game does is usually interlinked and branching (if statements), and to add to the difficulty a programmer must deal with asymmetric cores, i.e. SPE instructions are different from general-purpose ones so they can't shuffle tasks automatically between cores and expect similar results. Rather than spending potentially months optimising and separating the code for speed, many big-budget studios opt to just use the single general-purpose core for most of the game. This cuts out all of the advantages the CBEA in the PS3 had because it also stresses the small amount of RAM in the PS3 and forces graphics work to be offloaded to the GPU. The CBEA is great for iterative floating point tasks like prime number searching or protein folding but games primarily require generic, branching CPU tasks which unfortunately only one core of the CBE is designed for. The PS3 GPU is an older core design than the Xbox 360: it does not have unified shaders or many improvements modern PC GPUs have because it was not expected to do most of the floating-point work. Also, CPU-GPU bandwidth is lower than expected because the PS3 is designed for fast communication between processor cores: the CBEA's internal data transfer rate is very high. All of these factors make the PS3 function like a "normal" console, which is easy for the developers but ignores all of the PS3's potential. In contrast, though Xbox 360 uses the POWER architecture too, it's "Xenon" CPU has three general-purpose symmetric cores. It is easier for programmers to think of three general purpose tasks and so a lot more of the CPU's potential is used. Due to the general-purpose design of "Xenon", Microsoft expected all graphics work to go on the GPU and used a very advanced design which was only even available for PCs in April this year. It has high memory bandwidth and unified shaders which make it a very powerful GPU. Finally, because the Xbox 360 was the only seventh-generation console on the market for a year, developers have had much more exclusive time with it to understand how best to use it. The PS3 on the other hand has a much smaller userbase and it came out much later, so there is little financial incentive to get familiar with the PS3 when a studio could make better games with the Xbox 360 now. What all of this means is that while in theory the PS3's power exceeds the Xbox 360, the Xbox 360's layout was easier for developers and to use, it is suited more to game-like tasks, and they are more familiar with it due to historical context and a year's exclusive attention. The PS3 is not lacking potential, and we can expect great games for it in the future, but for now a lot of games on the Xbox 360 will appear to be faster, smoother and more graphically impressive than their PS3 counterparts. A warning: Do not judge ANY console by its "numbers" alone. The 3.2GHz number means very little when comparing consoles to consoles or PCs. The Wii is more powerful than its 729Mhz number suggests. 256MB of memory can be a lot or a little in different contexts. These numbers imply operating speed or operating capacity, not both or the speeds which connect the components together. I can have one transistor running at 100GHz and it'll be less powerful than a "3.2GHz" CPU.