what's the exact size of X360's eDRAM?

[Quaz51]

what's the exact size of X360's eDRAM? (10MB or 10.5MB?)

because if it's 10.5MB and not 10MB then they can to sustain a FB 1280x720 64bit HDR (no AA) without tile and in this case why use 32bit HDR (that certain X360 game or X360 engine use although without AA) if 64bit HDR have no tile penalty and FB is no bandwidth limited ? (it's also valid with MSAAx2, no tile penalty with 64bit HDR in this case)

 

[Carl B]

I think it's straight 10MB - but you know you could have asked this in one of several other Xenos threads going on right now...

 

[Quaz51]

I think it's straight 10MB - but you know you could have asked this in one of several other Xenos threads going on right now...

then why 10MB and not 7MB (1280x720 32bit) or 10.5MB (1280x720 64bit)
10MB it's an illogic choice? this number is not randomly selected by ingineer, it must correspond precisely has something? but what?

 

[j^aws]

then why 10MB and not 7MB (1280x720 32bit) or 10.5MB (1280x720 64bit)
10MB it's an illogic choice? this number is not randomly selected by ingineer, it must correspond precisely has something? but what?

Here's the Xenos eDRAM module patent I posted many months ago when many believed Xenos was a single chip solutions,

http://www.beyond3d.com/forum/showthread.php?t=19152

I believe the extra memory holds compression/pointer info etc...basically 'house keeping' stuff between the parent/daughter die...

 

[Quaz51]

Here's the Xenos eDRAM module patent I posted many months ago when many believed Xenos was a single chip solutions,

http://www.beyond3d.com/forum/showthread.php?t=19152

I believe the extra memory holds compression/pointer info etc...basically 'house keeping' stuff between the parent/daughter die...

but everyone says that there is no FB compression?
and if there is FB compression, what can contain eDRAM with compression? 1280x720 32bit AAx2 probably (otherwise the compression is inutile)? in this case then why lot game use no AA? all that is not very logic, why nobody speaks about these questions

 

[mckmas8808]

What's up with all the talk about EDRAM on this board all of a sudden.

 

[j^aws]

but everyone says that there is no FB compression?
and if there is FB compression, what can contain eDRAM with compression? 1280x720 32bit AAx2 probably (otherwise the compression is inutile)? in this case then why lot game use no AA? all that is not very logic, why nobody speaks about these questions

Well the parent-daughter B/W is not exactly 32 GB/sec but a 'little' more apparently. This B/W has the capacity for 8 pixels/cycle at 8 bytes/pixel and the 'extra' B/W can transfer this 'house keeping' info compressed. This would later be uncompressed at the eDRAM module...

 

[richardpfeil]

I don't think they considered 64 bit HDR a viable option for this generation of GPUs, instead focusing on their 32 bit, 10 bits per component implementation.

You bring up an excellent question. Where did the 10MB EDram size come from? Somebody had to select it. Maybe it's just to reduce the 720p 4xAA scenario down to 3 tiles instead of 4. Maybe it has something to do with limits in fabrication. Sure would have been nice to have at least 14MB, making 2xAA truely free. 16MB would open up 1080p, untiled.

Achille's heel:
XBox 360 - 10MB limit to frame buffer size.
PS3 - 128 bit bus to VRam.

 

[Jawed]

I think it's about time someone with a 7800GTX clocked it at 550/350 to simulate RSX and then we can see what kind of performance it gets in various games when its ROPs and texture units are so bandwidth-limited.

Jawed

 

[scooby_dooby]

Didn't Dave already do that??

 

[Teasy]

What kind of eDRAM does 360 use?

 

[j^aws]

What kind of eDRAM does 360 use?

From NEC's site,

http://www.necelam.com/edram90/index.php?Subject=edramoptions

 

[Rockster]

Doesn't 10MB fit 640x480 w/4xAA nicely?

 

[MechanizedDeath]

Doesn't 10MB fit 640x480 w/4xAA nicely?

Yup. I thought this was the original argument proposed on this board. That MS originally planned for a VGA buffer with 4xAA and then presented the tiling solution once they jumped into the HD era. PEACE.

 

[pipo]

Cost? Power? Heat?

Who knows...

 

[Shifty Geezer]

Yup. I thought this was the original argument proposed on this board. That MS originally planned for a VGA buffer with 4xAA and then presented the tiling solution once they jumped into the HD era. PEACE.

That makes sense if originally they were targetting SDTV output. Though when they decided to go with 720p there must have been a reason to think about changing the amount of eDRAM and deciding against it.

 

[SynapticSignal]

Yup. I thought this was the original argument proposed on this board. That MS originally planned for a VGA buffer with 4xAA and then presented the tiling solution once they jumped into the HD era. PEACE.

I hope that you'll realize that this is almost senseless

 

[Titanio]

Might you also be holding other buffers in there too, asides from the framebuffer/z-buffer? Other render targets perhaps, for RTT etc. etc.?

 

[Dave Baumann]

The eDRAM is a write buffer; when you are rendering it will write in the eDRAM, but if you are performing an RTT then the write will occur in the eDRAM, it is then written to system RAM and read from there when it needs to be sampled (again, this is in the article).