Video memory

[nobond]

kind of basical question. Normally the 3d graphcis card we bought have some on-board video memory. My question is
a. How generally these piece of memory is allocated? Is the frame buffer being mapped to here as well? (highly doubt so though).
b. The data like texture surely should go into these memory I would imagine. But what if it is not enough? The driver would go for the main memory?
c. Any chance is the OS is managing these on-board memory? I mena general applicaion is using this piece of memory?

 

[Albuquerque]

a. How generally these piece of memory is allocated? Is the frame buffer being mapped to here as well? (highly doubt so though).

It's "flat" storage; framebuffer, render targets, textures, you name it, it all goes here.

b. The data like texture surely should go into these memory I would imagine. But what if it is not enough? The driver would go for the main memory?

Yes. If the local video memory is overflowed, it pages to system memory.

c. Any chance is the OS is managing these on-board memory? I mena general applicaion is using this piece of memory?

The OS manages it to the extent of paging behavior and eviction, but not to the level you're thinking of. General application usage of this memory would be ill-advised. You're bottlenecked by the PCI-E interface, and adding main system memory (DDR2 / DDR3) will ultimately be a cheaper solution than borrowing GDDR5 from your video card.

 

[nobond]

This is really done by the driver of graphics chips? If it runs out of video memory, then has to go for the OS for more memory. Otherwise, it keeps the memory allocaion to itself?

It's "flat" storage; framebuffer, render targets, textures, you name it, it all goes here.

Yes. If the local video memory is overflowed, it pages to system memory.

]

 

[eastmen]

I got a question and I hope you don't mind me asking in this thread

Why don't video cards have a secondary pool of slower memory for cache ?

Like 4 gigs of flash ram. While it wont be as fast main system ram you wont have to leave the board to get models and textures and should help increase performance ? I would think doubly so when you'd have to hit the hardrive ?

 

[AlNom]

hrm... Cost?

 

[hkultala]

I got a question and I hope you don't mind me asking in this thread

Why don't video cards have a secondary pool of slower memory for cache ?

Like 4 gigs of flash ram. While it wont be as fast main system ram you wont have to leave the board to get models and textures and should help increase performance ? I would think doubly so when you'd have to hit the hardrive ?

Using system ram over PCI Express 16x bus is MUCH faster than using any flash memory; flash is terribly slow to write.

Also, that separate flash memory would need separate wires on the PCB, making the graphics board more expensive.

DRAM has become so cheap, that the sensible thing(best price-performance-ratio) is to have enough fast video DRAM on the board, AND have enough system DRAM that paging the hard disk is never needed.

 

[Mendel]

I'd still really like to see Xenos type EDRAM solutions for framebuffer too

 

[erick]

Using system ram over PCI Express 16x bus is MUCH faster than using any flash memory; flash is terribly slow to write.

Also, that separate flash memory would need separate wires on the PCB, making the graphics board more expensive.

DRAM has become so cheap, that the sensible thing(best price-performance-ratio) is to have enough fast video DRAM on the board, AND have enough system DRAM that paging the hard disk is never needed.

Correct me if I'm wrong, but if your videocard ever runs out of video memory, aren't you f*cked anyway? Epic levels of fps drop. Sure, it won't crash, but whatever you're running will be slow as hell if it has to go to the system RAM.

 

[rpg.314]

I'd still really like to see Xenos type EDRAM solutions for framebuffer too

Xenos is lucky. It only needs to run stuff at one resolution for ~6 years.