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[gofreak]

Posted and translated by one @ Beyond3D:

Source articles:
http://pcweb.mycom.co.jp/articles/2005/09/09/cedec1/
http://pc.watch.impress.co.jp/docs/2005/0909/kaigai210.htm

The event were NDAed, apparently, but somehow these guys got permission to report on it.

Summary of the "new" bits from the articles:

+ Among 3 cores in Xbox 360 CPU (codenamed "PX"), Core 0 is primary and Core 1/2 are secondary. Core 0 is fully usable by a game program. Core 1 and Core 2 are shared by a game program and the Xbox 360 system. Network stacks, services, drivers such as a USB driver run on those secondary cores. 5% computation usage of both core 1 and core 2 are reserved by the system.

+ The XMA (modified WMAPro) decoder in the southbridge chip can decode 256 XMA channels at the same time. Though the compression rate is variable, 1/8 is just enough for typical usage. After decoding, all software sound processing (multi-channel mixing, 3D surround sound, Dolby Pro Logic II/Dolby Digital 5.1 encoding) are done on CPU Core 2. When it processes 256 channels at the same time it costs 25% load of Core 2.

+ A hardware-assisted tile-rendering method called 'Predicated Tiling' is supplied as a library for Xbox 360 for the case when 10MB eDRAM is not sufficient, for example 64bit (FP16 * RGBA) HDR rendering + Z buffer + MRT in 720p. While it affects geometry processing with 1.2 - 1.3 times load, it doesn't affect pixel processing as there's no overlapping unlike geometry. As the result, it doesn't affect the total performance as pixel processing load is inherently larger than that of geometry.

+ The hardware tesselator in Xenos supports both adaptive and sequential, and adaptive tesselation requires 2-pass. If the tesselator is used the vertex output from it is limited to 1 vertex per clock though the performance impact can be mitigated as output vertices from the tesselator have higher locality for better caching.

+ In a double-layer DVD for Xbox 360, 7GB is usable by a game. The transfer rate of the DVD drive is 15MB/sec max, 10-12MB/sec average. The seek time is 115ms, switching layers takes 75ms. Loading 512MB data takes 34 seconds.

+ 2GB in the HDD is used for a temporary cache area for games. Its average transfer rate is 17MB/sec and the average seek time is 13ms.

+ Game data is managed per user account and saved in HDD, but 64MB Memory Unit is also usable for checkout/backup. The Memory Unit slot is 2.5MB/sec write, 8MB/sec read.

+ In its 512MB RAM, 32MB is allocated for the system. The RAM is GDDR3 SDRAM @ 700MHz (22.4GB/sec).

Some pics:

Interesting stuff!

 

[Striek]

Thanks, its all interesting, especially the Xenos information.

Loading 512MB data takes 34 seconds.

Thats good news. Significantly less than that 70seconds that was reported.

Core 1 and Core 2 are shared by a game program and the Xbox 360 system.

Is there any reason they would have two cores handling the OS instead of 1? Surely thats less efficient.

 

[kaching]

Cool. I was curious to know how much system resources they needed to put aside for persistent OS services - 5% on Core 1 and Core 2 + 32 meg of RAM doesn't seem too bad.

And that'll cut down the time to fill memory by like 2 seconds

 

[Spider_Jerusalem]

Is there any reason they would have two cores handling the OS instead of 1? Surely thats less efficient.

Probably they wanted to add more parallelization and independency to some processes.

And interesting data about streaming from disk, too: it seems that it won't be a big difference from HD, as long as the developers can avoid seeks in the process.

 

[xexex]

complex, but interesting still.