Graphic Aperture

[b4u]

Always thought about it, now I'm posting to find a definite answer

What is Graphic Aperture which can be set at BIOSes? What effect does it make?

(I do believe it may have some impact on performance, but don't know what it really is)


Thanks

 

[Peter]

In simple terms, the setting limits how much system memory the graphics card may borrow as an extension to its own local memory. The actual amount borrowed is entirely dynamic, and it's happening only when the graphics card's own memory is too small for a very complicated scene.

You should make it as large as you can, like half of the total system memory you have. You lose nothing.

 

[SpideyCU]

Yup. I like to view it as almost a sort of "virtual memory" for the video card. Much like your memory uses physical RAM and then dips into the swap space on a hard drive when it has to, the video card will use its own memory and dip into your system RAM when it needs to.

It's not really the same situation, but similar enough.

 

[Jeff7]

Of course, you'd probably be best to hope that you don't have to use system memory instead of the videocard's own RAM. I'll elaborate on SpideyCU's example of the hard drive serving as virtual RAM: RAM, being solid state is thousands of times faster than the hard drive. RAM accesses data in nanoseconds; HD's do it in milliseconds. RAM deals in GB/sec. HD's deal in MB/sec. So anyway, here, virtual memory is slow.
It's the same way with a videocard; it can use its own local RAM at high speed, but if it runs out there, it has to go over the system bus, and access the system RAM. Not only does that have an effect on latencies, but it also has do endure those latencies at the slower speed of the chipset and RAM. This will really kill framerates - it would quickly go from there being SO much data in the videocard RAM readily available to the video processor that it would slow down, to a situation where there's lots of data present, but the video processor can't get it from the system RAM fast enough to put out a good framerate.
In short, sufficient local video memory is a good thing.
Also, in case you're wondering what the point of this sharing is, it's in part because back when AGP was made available, high-speed RAM was pretty expensive. So, why not just make the big pool of system RAM easily available to the videocard? But RAM prices came down quick, and videocards pushed ahead, to speeds much faster than an AGP would be able to handle. AGP 8x is spec'd to run at 2.1GB/sec. New videocards can handle over 20GB/sec using the RAM on the card. Going over the system bus to the main RAM would utterly kill performance.
The AGP does still do an ok job; it provides a dedicated Port, not a bus, for the videocard to do its thing. But its days are numbered; PCI Express is coming.

Peter, feel free to check this through for technical accuracy. I wrote it out of my experience and understanding of current technology; yours seems to be far greater though.

 

[Peter]

Well explained, Jeff. In fact, when AGP was invented, graphics card RAM wasn't any faster than system RAM at all, and the speed bump in borrowing system RAM was next to nothing - but prices for RAM were outrageous, so the idea of putting the money into universal system RAM and letting the gfx card borrow some as needed made sense.

As we all know, RAM prices plummeted soon after, which in turn made graphics cards makers put much more and much faster RAM on the gfx cards - which made AGP both redundant and useless at the same time. You got enough RAM on the gfx card to hardly let an AGP transfer ever happen; and if it does, performance will STINK.

 

[Jeff7]

Originally posted by: Peter
Well explained, Jeff. In fact, when AGP was invented, graphics card RAM wasn't any faster than system RAM at all, and the speed bump in borrowing system RAM was next to nothing - but prices for RAM were outrageous, so the idea of putting the money into universal system RAM and letting the gfx card borrow some as needed made sense.

As we all know, RAM prices plummeted soon after, which in turn made graphics cards makers put much more and much faster RAM on the gfx cards - which made AGP both redundant and useless at the same time. You got enough RAM on the gfx card to hardly let an AGP transfer ever happen; and if it does, performance will STINK.

Plus, nowadays with 64, 128, and even 256MB of RAM on videocards, the GPU would be bogged down with that many textures already; dealing with even more would likely overwhelm it anyway.

 

[b4u]

Thanks for the replyes very good info, very good explanation

Peter: You should make it as large as you can, like half of the total system memory you have. You lose nothing.

I understand all the explanations, but as a conclusion, if I have (not yet, maybe soon ) a 9600 Pro 128Mb DDR card, would it be better so set something like 128Mb Aperture (on a 1Gb DDR400 main system RAM), or would I be better to reduce the Aperture so that the system use the minimum (or none) of the system RAM, avoiding the kind performance hit we all tend to avoid?

By other words, would the performance hit of accessing main memory be worse than the one I would have by not giving the graphic card enough mem space?

 

[Barnaby W. Füi]

It seems some people are confusing virtual memory with swap space. Virtual memory refers to all memory that apps can use; physical ram, and swap -- it is as the name implies, it is "virtualized", the apps themselves do not deal with the trouble of distinguishing one from the other, they just have one big memory space that's available to them, and the operating system deals with swap/physical memory intricacies. That was on hell of a run on sentence

 

[Peter]

We're not about any of that AT ALL.

b4u, the Aperture size just states an upper limit - how much system memory actually will be lent out to the graphics card depends on whether the current scenery fits into the graphics card's own memory or not.
So making the aperture large doesn't make you lose anything at all.

 

[SpideyCU]

Originally posted by: BingBongWongFooey
It seems some people are confusing virtual memory with swap space. Virtual memory refers to all memory that apps can use; physical ram, and swap -- it is as the name implies, it is "virtualized", the apps themselves do not deal with the trouble of distinguishing one from the other, they just have one big memory space that's available to them, and the operating system deals with swap/physical memory intricacies. That was on hell of a run on sentence

That's why I said the system dips into the swap space, not virtual memory. It's semantics at best, technical inconsistency at worst...personally I get more alerted at little things like "LCD displays". :Q