I know this thread is old but I just wanted to address (pun not intended) the comments on 2^32 addressable BITS or 0.5GB addressable memory.
PC memory is BYTE-addressable, so 32-bits is 2^32 addressable BYTES or 4GB, no “unsound math” involved.
I see alot of negative comments about 64bits XP here, and I want to counter them.
I’ve run 64bits xp for 6 months no without any trouble what so ever. The only problem I could see happening is that you can’t find drivers for obscure hardware, but for everything else it’s just great 
so if you want to use more than 3-3,5gb ram, get 64bits xp
I’ve used it with 6gb and it’s no problem 
A 64-bit PC running a 64-bit OS has a truly vast basic memory address space. The 4Gb 32-bit address space was 4096 times the size of the 1Mb 20-bit space, but the 64-bit address space is 4,294,967,296 times the size of the 32-bit one.
(Actual 64-bit PCs so far aren’t actually able to address anything like that much memory, for reasons analogous to the restricted addressing of the old 8086; essentially, fewer memory address lines make for a cheaper computer. But even the most restrictive current x86-64 computer and operating system combinations can still address at least 2 to the power of 44 bits, which is 16,384 gigabytes. That ought to be enough for quite a while.)
By default, an all-64-bit PC will still have the standard big holes in its memory from three to four gigabytes. This is the lowest-hassle way to deal with the problem - just install more than 4Gb of memory, and live with the fact that your 8Gb PC with a 768Mb graphics card only actually has seven-point-not-much gigabytes of visible RAM.
One advantage of this is that you can still boot a 32-bit OS, if you want to. Another is that this vanilla configuration is most likely to actually work. Cleverer memory configurations aren’t necessarily properly supported by hardware, operating systems and device drivers yet.
If you don’t care about these factors, though, there are two ways to get the lost memory back.
Some 64-bit motherboards these days give you an option for “memory hole remapping”. That moves the fourth-gigabyte MMIO memory holes higher into the 64-bit address space, probably way above the maximum RAM you can physically install.
Many other 64-bit boards, though, are even smarter, and can leave the memory holes where they are and remap (at least some of) the physical RAM out from under the holes and up past 4Gb. This process is often entertainingly referred to as “memory hoisting”, and it used to be the preserve of server motherboards. It’s been showing up in more and more desktop mobos, though. And on some of them, the memory-hoisting BIOS setting even works, and doesn’t horribly crash the system as soon as something tries to use the remapped RAM.
You may only be able to “hoist” the last 512Mb of the 4Gb address space, but that’s better than nothing. If it works.
I should add a note about the /3GB, /4GT and /PAE Windows boot.ini switches, too, because they often come up when people are talking about 4Gb-plus Windows PCs.
They are all useless to you. You do not want them.
/3GB and /4GT are config settings for different versions of Windows that tell the operating system to change the partitioning of the 4Gb 32-bit address space so that applications can use 3Gb and the OS kernel only 1Gb, as opposed to the standard 2Gb-each arrangement. They don’t help at all with the 3Gb barrier, and most applications don’t even notice them, so desktop users lose kernel memory space (and system performance) for no actual gain at all.
The /PAE boot.ini switch, on NT-descended Windows flavours, activates the Physical Address Extension mode that’s existed in every PC CPU since the Pentium Pro. That mode cranks the address space up to 64 gigabytes (two to the power of 36), and the computer can then give a 4Gb addressing block within that space - or even more, with extra tricks - to each of several applications.
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.
Oh, and just in case you for some reason still wanted to try PAE: It eats CPU time, too.
First great discussion! But couldn`t find any comment about this:
My friend told me that i need more than 4 GB RAM to use a 64-bit system at full speed. If I had less it would cut down my performance. Is that true? (He says that the 64 bit key would not fit completely into the ram???)
AMD Turion64 X2
2 GB RAM
Linux 2.6.22.17-0.1-default
Sorry for my bad english but i am from germany
2 much …
Quote:
My friend told me that i need more than 4 GB RAM to use a 64-bit
system at full speed. If I had less it would cut down my
performance. Is that true? (He says that the 64 bit key would not
fit completely into the ram???)
He’s talking nonsense - or does he sell memory?
I run Vista x64 on an Intel Q6600 with 4GB ram. It’s fast and responsive, despite running Visual Studio 2008 and MS SQL Server on the same box. 4GB is fine for most x64 users.
I just built a gaming computer, its got the XP 32bit(didnt want vista atm) and 4 gbs of ram, and it only reads three, but then my wife’s computer is a year or two old Dell and I bought 4 gigs of ram for it as an upgrade and it reads it all 4gb of ram, it also is 32 bit XP, what’s the deal?
“In any 32-bit operating system, the virtual address space is limited”
The virtual address space has nothing to do with it. Windows is operating in paging mode, and thus there is no direct relation between the virtual and physical address space. True, the virtual address space is fixed at 4GB, but the physical address space can grow way larger.
“Addressing more than 4 GB of memory is possible in a 32-bit operating system, but it takes nasty hardware hacks like 36-bit PAE extensions in the CPU, together with nasty software hacks like the AWE API”
PAE is not a “hack”. It is just a way to extend the page table. Most people today uses PAE in XP and Vista, because they want DEP. By the way, check out the structure of the page table in 64bit mode.
“OK, so we’re limited to 4,096 megabytes of virtual address space on a 32-bit operating system”
As I stated above, the virtual address space has nothing to do with how much physical memory (RAM and MMIO) a 32bit x86 OS can address.
“To be perfectly clear, this isn’t a Windows problem-- it’s an x86 hardware problem.”
On modern hardware that is not true. It is a hardcoded limitation in the memory manager in 32bit Windows XP/SP2 and Vista.
Oh, and a note on AWE. AWE is NOT PAE. You can use the AWE API if your application needs to access more physical ram that can be expressed in the 2/3GB “user space” portion of the virtual address space.
AWE can also be used without PAE.
i am givving this up to long to read
Well, I installed 64bit XP after upgrading to 4gig of ram (and needing to reinstall windows anyway)… It lasted a week.
I am a designer and Adobe’s PDF Creater wouldnt work because its a 32bit printer driver, and to top that the printer service constantly crashed.
What mainly annoyed me was WinXP 64bit wasnt supported by Windows Live Messenger, the latest installer from messenger.msn.com wouldnt install it… Another great FAIL by Microsoft… “We will release an OS and not have any of our free software support it”… Fantastic!
Back to WinXP 32bit with 3gig of ram - The only Viable OS at this moment in time.
And Vista? Vista is the Captain of the Failboat
erm… shouldn’t that be 16 exabytes of addressable memory using 64-bit. The division by 8 is unnecessary, since all memory since basically the beginning of time has been byte-addressable, not bit-addressable.
/pedant
Geez, this gets more confusing the more I read about it. I thought the 4GB limit was a Windows problem. According to wikipedia, the PAE is enabled in XP Pro SP2. It has to be enabled so XP can use DAP. So if PAE is enabled, why doesn’t XP have access to more than 4GB? According to wikipedia, the limit is set to 4GB because of driver compatibility issues. Now I see people blaming it on the chipset?
I use my system for gaming. I was going to install 2x2GB for my XP Pro SP2 system when I found out about this problem. Should I get X64, Linux, or use PAE? I don’t know how to use PAE and I can’t find instructions with Google. Thanks.
Locutus;
Your first impulse is correct. For gameing you
need XP. The added ram will work without doing
anything; Do not trouble your head.
Cheers
EDIT 4 gig works fine.
I rue the day when I am forced to deal with Vista in any x version divisible by 2. Regardless of how much it may have progressed in reliability,stability,dependability, …*ibility… I still dispise it… All those nice colors and inviting graphics… It’s evil!!! When that M$ Storm comes a-blowing full force, I’ll be hugging my XP box in tears.
Don’t think I’ll have to worry too much about that Fedora 8 bastard in the corner though. I prefer to just let him think that 512 is all the memory in the world. Keep him humble for his own good.
My other computer is a Beowulf cluster
Want to be a great man? Do something great.
Want to be a great man remembered? Do something great and pick your nose on national television.
Vista sucks big time. I went to Fry’s to get 4 gigs of RAM. And the support guy advised against it. He said the 3.4 gig limit thing is real and with 32 bit OS it’s no use putting in more than 3 gigs. I guess, bottom line is with current state of technology and M$ wisdom, we are stuck with 4GB at most and curse M$ while we are at it. I just don’t understand what M$ thinks about its customers. They are the biggest con artist on the planet. Vista Sucks!
I have just bought a HP Pavillion notebook, Intel core 2 duo 2.1, Vista. On the box it is written very clearly - 4GB RAM. I went to check the System if it prints also the same amount, umm 3020MB RAM. Could be better a MacBook, at least would show exact RAM.
I have a Core 2 Processor 3 GHz, 4 gb of ram, a video card Geforce 8400gs, the Motherboard suports processes up to 4 gb, two sata hard disk and two dvd-rom rw, i’m a Graphic Designer (AutoCad, Adobe Illustrator CS3, etc) and a passionate gamer. I want to use as much as possible the RAM, i’ve read all the discussion and still wondering which OS i should use. Please, Vita 32 bits? or xp 32 bits?.. The RAM not used, will affect the PC in a negative way? and if so how?Thanks.
P. D: Sorry, my english is rusty. I’m from South America
I have a Core 2 Quad with 2x2GB of RAM (4GB Total). I’m using Windows Vista Ultimate (32-bit). When I go to Computer Properties, It says “Memory (RAM): 4.00 GB” – so it’s recognizing all of the RAM there. However, when I go to Task Manager Performance tab, it says I have 1533 MB of Physical Memory (less than 1/2)!!!
I also have Windows Virtual Server 2005 on this machine, and when I go to server properties it is also reporting only 1533 MB of RAM!
I’m inclined to believe that Vista is only using 1533 MB of my 4GB of RAM because Task Manager constantly shows my Physical Memory usage at 85% and higher.
Anyone seen this or have any idea how I can get Vista to recognize/use all of my 4GB of RAM?!?