 |
| 16. |
Re: Not a problem in Linux. |
Jun 4, 2007, 15:33 |
Zathrus |
|
|
But, if there needs to be so much of the system memory reserved for something like the video card, and it can use that 3-4gb range for that, then it is not a waste
What you're misunderstanding here is that there's no physical memory located at that point. If you have 128MB, 1GB, or 3 GB of memory it doesn't matter -- the video card is going to map from D000 0000 to FFFF FFFF (from 3.25GB up to 4GB) no matter what. It'll still do that if you have 4GB of memory -- but you won't ever be able to access the physical memory that's located in that address range because it's being "obscured" by the device driver.
That's what he means by >3GB of physical memory being a waste.
But if you have only say 3gb, and windows uses the 2-3gb range for system usage, that means that the 760mb of system memory starts coming from the usable 0-2gb range, no?
No. See above. MMIO does not take up real memory.
But then he says that only 64bit OSes can access that 3-4gb range. But I think he means for general application usage, not dedicated hardware usage?
What he says is that some motherboards can remap the memory that's physically located behind the MMIO area to someplace else (e.g. -- the memory that's physically at 3-4GB is mapped to 8-9GB if you have 8GB of memory), or the OS can have the MMIO located somewhere else (say, toward the end of the 48-bit address range of current 64-bit x86 CPUs; why no, they don't have a full 64-bit virtual address space... go see the Wikipedia article on AMD64 if you want details). Either way, the memory is no longer obscured and can be used.
So he implies that that the 3-4gb of memory is wasted, but really, depending on the system configuration, it is not wasted that much?
No, it is completely wasted. Much like on older PCs running DOS (and even your current PC, although you probably don't even notice or care) much of the 768K-1024K area was unusable due to MMIO. You could get small chunks of memory available via himem.sys, or QEMM, or similar, but a good bit of memory was simply unavailable for use in any manner whatsoever. Of course, now that we're playing with GB of memory, a few paltry KBs are irrelevant. When's the last time you saw options in your BIOS to disable Video BIOS or Video RAM shadowing? That's all part of the crap in that 384K that haunted us in the DOS and Win 3.x days.
It's the exact same thing now, but with bigger numbers.
|
|
|
|
|
|
  |
|
| |
| |
|
Date |
Subject |
Author |
| |
1. |
Jun 3, 20:34 |
3gb memory barrier |
Shok |
| |
2. |
Jun 3, 21:05 |
Re: 3gb memory barrier |
DrEvil |
| |
3. |
Jun 3, 22:08 |
Re: 3gb memory barrier |
Zathrus |
| |
10. |
Jun 4, 05:54 |
Re: 3gb memory barrier |
TorTorden |
| |
11. |
Jun 4, 07:24 |
Re: 3gb memory barrier |
HardCore |
| |
4. |
Jun 3, 23:46 |
Re: 3gb memory barrier |
Exe |
| |
7. |
Jun 4, 00:56 |
Re: 3gb memory barrier |
Smoove |
| |
8. |
Jun 4, 04:00 |
Re: 3gb memory barrier |
Cutter |
| |
9. |
Jun 4, 05:19 |
Re: 3gb memory barrier |
vacs |
| |
5. |
Jun 3, 23:57 |
Not a problem in Linux. |
Potato |
| |
6. |
Jun 4, 00:43 |
Re: Not a problem in Linux. |
Jono |
| |
12. |
Jun 4, 09:50 |
Re: Not a problem in Linux. |
Zathrus |
| |
13. |
Jun 4, 12:59 |
Re: Not a problem in Linux. |
Enahs |
| |
14. |
Jun 4, 13:52 |
Re: Not a problem in Linux. |
Zathrus |
| |
15. |
Jun 4, 14:16 |
Re: Not a problem in Linux. |
Enahs |
| >> |
16. |
Jun 4, 15:33 |
Re: Not a problem in Linux. |
Zathrus |
| |
17. |
Jun 4, 16:00 |
Re: Not a problem in Linux. |
Enahs |
|
|
Twitter 
