[Eug]

Just wundrin. On the current Macs, DDR is irrelevant for the CPU, and overall leads to just a mild increase in app speed.

However, would it speed up Quartz Extreme OS stuff significantly?

[MacGorilla]

Since QE is passed off to the graphics card, I would say DDR doesn't help. But in on the other hand, it probably doesn't hurt, either.

[Eug]

Originally posted by MacGorilla:
Since QE is passed off to the graphics card, I would say DDR doesn't help. But in on the other hand, it probably doesn't hurt, either.

Is AGP completely independent of the DDR bus, and already at full speed both on SDR and DDR machine?

Just wondering...

[Rickster]

One of the key features of Quartz Extreme is that it's based on DMA (direct memory access) capabilities of the motherboard and video hardware.

Rendering a window is a two-step operation: first, the application renders the window content into a buffer; then, the Window Server composites it onto the screen. Under Quartz Extreme, the latter step is handled entirely by the GPU. However, this presents a problem -- the initial rendering is done in main memory, and for the GPU to do the compositing, it has to have the data in its VRAM. The conventional approach to getting the data moved is to have the CPU do the work of reading it out of main memory and "pushing" it over the AGP bus to your graphics hardware. Instead of bogging down the CPU with all that data streaming, Quartz Extreme has the GPU do the work of "pulling" the data out of main memory into its own VRAM.

The upshot of all this is that, yes, it's theoretically possible that the DMA activity used by QuartzExtreme can benefit from DDR memory while the CPU cannot. But I don't know enough specifics on the current hardware to tell if if it actually does.

[Eug]

OK I've done a little digging. (I haven't verified this superficial research, so take this with a grain of salt.)

It seems that ASSUMING that Macs make good use of DDR via AGP, then DDR may help. While PC133 SDRAM speeds is similar to 4X AGP, 4X AGP is still limited by SDRAM because of bus utilization of bandwidth by other things on the system. Having DDR can alleviate some of the bandwidth bottleneck.

It's a different story with 2X AGP though, on a PC133 SDRAM bus. PC133 has nearly twice the bandwidth of 2X AGP, so the memory bus shouldn't be a bottleneck.

However, all the current PowerBooks support 4X.

In the case of the TiBook 1 GHz, the bus is PC133 SDRAM, and thus its 4X AGP bus MAY be somewhat bandwidth limited in certain situations. But my guess it should still be faster in most situations than the AluBook 12" overall since the AluBook's GPU is significantly slower. Furthermore, it only has 32 MB memory on the video card. (I wonder if this is one of the reasons besides marketing that the VGA output of the 12" AluBook is limited to 1600x1200.)

The AluBook 17" has an advantage however, in that it has not only a 167 MHz bus, it also utilizes DDR.

This all is in the context of Quartz Extreme 2D. For Macs, it will not apply so much for gaming, since Macs are too CPU limited in games anyway for the AGP bandwidth to be as important.

[Millennium]

Does DDR help for Quartz Extreme?

Um... if the people making Quartz Extreme are off dancing to bizarre Japanese pop songs mostly sung in English for no discernible reason, that probably doesn't help get anything done. I don't care how cool the game is.

[Eug]

Originally posted by Millennium:
Um... if the people making Quartz Extreme are off dancing to bizarre Japanese pop songs mostly sung in English for no discernible reason, that probably doesn't help get anything done. I don't care how cool the game is.

1) I'm not talking about gaming, but OS speed.

2) I dunno WTF you're talking about. ??????

[mattfong]

I could be wrong, but I believe DDR is in reference to "Dance Dance Revolution," the incredibly crazy game on PlayStation ...

Of course, it also mean "Double Data Rate"

mattfong

[Millennium]

Originally posted by mattfong:
I could be wrong, but I believe DDR is in reference to "Dance Dance Revolution," the incredibly crazy game on PlayStation ...

Of course, it also mean "Double Data Rate"

You caught my reference.

http://www.ddrfreak.com