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Thread ID: 90272 2008-05-28 12:38:00 Hi guys Zheng (13803) Press F1
Post ID Timestamp Content User
673485 2008-05-29 22:04:00 Why is that? why is it not 4gb - what ever the graphics card has?
So if you had a 32mb onboard graphics, why isnt the maximum 4064mb?Read here (www.dansdata.com). 		Greg (193)
673486 2008-05-29 23:29:00 Google 32 vs. 64 bit memory addressing. Or put 2x^32 into a calculator and see how many bytes you get.

2^32 is 4gb 		utopian201 (6245)
673487 2008-05-29 23:41:00 2^32 is 4gb

:horrified

It's not like that was my point or anything.

Actually, 2x^32 is 4billion bytes (or bits?), not 4GB... can't be bothered working out the difference

That's the reason a 32bit OS can only reference ~4GB.

Now 2x^64 and you see why 64bit is the future... exabytes of RAM anyone? 		Thebananamonkey (7741)
673488 2008-05-30 01:17:00 Actually, 2x^32 is 4billion bytes (or bits?), not 4GB... can't be bothered working out the difference.Sorry, using the standard method of counting GB (not the drive-manufacturers' method), 2^32 is *exactly* 4GB.

2^32 = 4294967296
1KB = 1024B
1MB = 1024KB (1048576B)
1GB = 1024MB (1073741824B)
4GB = 4096MB (4294967296B)


Thanks for that link Greg - explains perfectly why PAE under Windows XP (32bit) does absolutely nothing on my system :)
...PAE's no good to the everyday 3Gb-problem-afflicted user, though, for two reasons.

First, it presents 64-bit addresses to drivers, and thus causes exactly the same compatibility problems as a proper 64-bit operating system, except worse, because now you need PAE-aware drivers for 32-bit Windows, instead of just plain 64-bit drivers for a 64-bit OS. From a normal user's point of view, PAE gives you the incompatibility of a 64-bit operating system when you're still running a 32-bit OS.

For this reason, Microsoft changed the behaviour of the /PAE option in almost all versions of WinXP as of Service Pack 2. They fixed the endless driver problems by, essentially, making /PAE in XP not do anything. All versions of WinXP except for the x64 Edition now have a hard 4Gb addressing limit, no matter what hardware you use them on and what configuration you choose.

This isn't a big problem, of course, since XP is not meant to be a server operating system. But it's still mystifying to people who try the /PAE flag and can't figure out why it doesn't work. 		Erayd (23)
673489 2008-05-30 02:15:00 :horrified
That's the reason a 32bit OS can only reference ~4GB.


Thats my point; a 32bit OS CANT reference ~4gb, and my question is why :)

The video card's memory uses the same address space, so say you had a 32mb graphics card, I thought the maximum amount of usable ram would be 4096-32 = 4064.

I haven't look at that link in detail yet, but I'm guess it explains everything. Anyone with an understand want to summarise on why its not 4096-video + other driver uses? My understanding is that the extra is used by driver allocations... but it seems a bit much... 		utopian201 (6245)
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