I found this interesting read on the PVC Board. Huge credit goes to TRAGIC from PVC for typing this up. I personally found it interesting because how can a game that takes the highest grade PC available be on Xbox which is relatively less powerful to some PCs today and have the same graphical look and run perfectly fine? Once again, credit goes to TRAGIC from the PVC Boards.
Want to know why DOOM3 and games like it can run on xbox? This may seem like a long post but if you read it will probably clear up alot of questions on the power of your xbox and the potential for incredible looking games that you may not have thought could run on it. But it's up to developer's to use it. And show this to the next person who say's: "The xbox is just a downgraded PC". That is such a false statement.
NOTE: I don't post this to "slam" PC tech, or to kick off a heated debate - flame responses will be ignored. I post this for informational purposes only, as it's a subject that I personally find interesting.
A while back I posed the question in the title to this forum, to see if any of the professionals who post here could let me know how the XBox could render Doom 3, and I quote Carmack here, "just fine". Recently, it's been noted that Carmack said that the XBox should be able to run Doom 3 with no graphical downgrade from the PC version. I was struck by how remarkable a claim that was. How could a box with a 733 MHz Pentium 3, an NV2A (Geforce 3 plus one vertex shader), and a total of 64 MB of ram under the hood possibly run Doom 3, when I knew that my PC, with specs that blow the XBox away, would in all likelihood render Doom 3 like a slide show at medium details? (A presumption, maybe, but come ON...)
I got a few responses, but the only one that seemed to make any sense at all was "bloated code". Basically, that since game developers had to code for such a variety of hardware on the PC, that the code could not be as efficient as it was for a fixed hardware platform like the XBox. As someone who works in a technical field, this made a degree of sense, but it didn't sit very well with me - weren't APIs and device drivers supposed to eliminate that sort of "hardware specific" code problem on the PC? Even if they didn't solve it altogether, why would it make THAT much difference to performance? I mean, my PC has got, between the system RAM and video RAM, TEN TIMES the memory of the XBox, and a CPU more than TWICE as fast. There had to be a better explanation, right?
I found one in a magazine sold here called "CPU - Computer Power User". They employ a number of PC hardware and software dudes/dudettes to write regular columns for them - people like Alex "Sharky" Ross, Anand Lal Shimpi, Kyle Bennet, and others. One of their regular columnists, Alex St. John - who the magazine lists as "one of the founding creators of Microsoft's DirectX technology", wrote a column in the Feb 2003 issue of CPU titled "XBox vs. PC: Fight!" in which he compares the XBox's capabilities with that of the latest high-end PCs in terms of 3D processing (it's worth noting that the guy no longer works for Microsoft). Turns out, it's more than just about screen resolution. Here are some excerpts:
He goes on to talk about how PC games must be coded to be capable of running on low-end graphics processors, which keeps the PC gaming market skewed to the low end. He also makes mention of some games utilizing a method of real-time shadowing that demands video data to be swapped back and forth over the AGP bus three times, resulting in a huge performance hit. Then he summarizes:How much video bandwidth does an XBox need to play Halo on your TV vs. on a PC?
PC: 60fps X 1024 X 768 X 32-bit color = 180 MBps
XBox: 30fps X 640 X 480 X 16-bit color = 18MBps
WHOA! The PC needs to generate 10 times as much video data as a console just to properly drive the display. Unfortunately, the calculation I just did doesn't tell the whole story. We haven't touched the really thorny issue of video bus bandwidth.....
...The internal memory bandwidth needed to generate 180MBps of 3D video for modern video games is on the order of 2 to 4 GBps. To drive a dual-monitor system at 1200 X 1600 X 32 requires around 10 to 20 GBps of internal video bandwidth. By contrast, an 8x AGP bus on a PC has a PEAK bandwidth of 2.1 GBps.
This is where the PC architecture breaks down and $200 children's toys (consoles) really kick its butt. The PCs CPU has its own local RAM and system bus. The PC's GPU sits across the AGP bus from the CPU with a redundant cache of its own local high-performance RAM. This duplication of memory and buses adds unnecessary expense to the PC design. PC RAM on the CPU side is single-access memory; it can't be accessed in parallel like console video RAM can. The RAM on the video chip, on the other hand, is dual-ported; it can be read by the GPU while the AGP is accessing it. The AGP bus, in effect, creates a huge gulf between the CPU and GPU: They are essentially separate computers. Sending data from CPU RAM to GPU RAM is fast, but pulling data back across the AGP bus can force the GPU to stall, causing a noticeable frame rate drop. Thus, once the CPU has shipped data off to the GPU, it can rarely help out with processing again.
Contrast this with the XBox, in which the CPU and GPU share the same pool of dual-ported RAM on the same bus. Both the CPU and GPU can hammer on video data in parallel. The XBox memory architecture is actually broken into two parallel banks, each operating at system bus speeds, independently allowing a total peak bandwidth of around 6.4 GBps. There is no OS or virtual memory management slowing things down. The result is that the XBox probably sustains 75% of its peak bandwidth continuously. The CPU can augment the GPU and add features to it in software that may not be hardwired in. All of the XBox's 64 MB of RAM is video RAM shared by the CPU. The PS2, by contrast, has 32 MB of RAM, 4 MB of which is dual-ported RAM shared by the CPU. The XBox and the PS2, to a lesser degree, can also store some large 3D data types, such as textures in compressed formats that the GPU can decompress on the fly, thus increasing effective video memory bandwidth another 3-5x...
So..quite interesting. Sure there is alot of technical things in it and it's long but most people should understand what he was talking about....So why does a two-year-old console architecture like the XBox sold for $200 in KB Toys kick a modern PC's butt for gaming?
1. The PC starts off with huge bandwidth disadvantage because of the demands of its display technology.
2. The XBox has an incredibly powerful video architecture.
3. The XBox CPU is not burdened with the baggage of running a giant memory and CPU consuming OS.
4. Every XBox comes with a great standard video chip, but most consumer PCs are sold with a crippled video chip, which drags down the whole PC game market.
5. A shared memory architecture between the CPU and GPU lets both processors help with graphics performance, while even the fastest AGP bus on the PC is a bottleneck. The next time somebody tells you an XBox is just a chopped-down PC, show them this column. They couldn't be more wrong.