Not recognize 4GB =? Not use 4GB?

OK it's said that Win XP can only recognize up to about 3GB memory. Does that mean it can only use that much memory? Or can it use 4GB instead of not recognizing it?

 

32bit operating systems can only address 3.5GB or so. You can have more mem just the computer wont see it or use it.

 

^^^
Yep.

If it doesnt recognise it, it cant use it either.

 

You can use the unaddressed memory as a RAMDisk of some sort, or go with XP 64-bit to have the whole 4GB addressed.

 

somtimes a 32bit OS can recognize all 4gig, but just cant use it all I think

 

A 32 bit OS can use up to 4GB address space, but those 4GB will need to be shared by RAM and all other components installed in your computer. Your graphics card, CPU, network card, USB controller, sound card and everything else needs address space too and they will use part of those 4GB. That's why you see less than 4GB available for the RAM.

For example: the following screen shot is a snap shot of address space being used by various components in my computer.


All those memory address you see (in hex) use part of the memory address space that is otherwise available for the RAM. Normally, this is not a problem if you have less than 3GB of RAM. But as you use more and more RAM, the RAM would start to have to compete with other components in your computer to share the address space.

 

Device Manager is reporting that I have 3620704k RAM available (32 bit Win XP on Dell E6400). My computer say 3.45GB.

But the computer also knows I have 2 x 2GB.

John

 

The common misconception is that if it's not being seen, it's not being used. It's true that the OS/programs can only use 3.5GB of RAM, but the other 500MB is used as cache for the rest of the computer.

 

The unaddressed RAM is not used by anything. You can only make use of it by using a 3rd party software that accesses the unaddressed memory and creates a RAMDisk of some sort.

That is because of the kilo- and kibi- byte thing.

 

Is that something you've told yourself that it is like that?

The rest is shared for the adressing as shown in a screenshot earlier in this thread.




And 3620704k = 3.45GB, the exact same amount.

 

The devices using the address space is fine, but a nerd who knows hexadecimal can actually read and pinpoint where the memory hole actually is.

I remember reading an article somewhere where the poster showed screenshots of the memory map and showed how the memory map changed, pin-pointing the aperture and the change in it by tweaking the AGP aperture from 32MB to 64MB and then 256MB, in the BIOS.

 

A 32-bit version of Windows counts, recongizes, and utilizes all 2^32 bytes (4GB) of memory. The memory not directly reported is utilized for memory-mapped I/O.

 

or you could go PAE with linux

 

Hey, that's a good idea, to use the unaddressed memory as a RAMdisk. One could create a batch file to copy some important files to the Ramdisk on bootup, which might speed up the system, reading them from RAM rather than the HDD. Never heard that before. If the system cannot see that memory, however, how can it make a Ramdisk out of it? Is that made in DOS, before Windows boots up?

Is anyone actually doing that? How do you make the Ramdisk?

 

Um, guys, the memory is not unaddressed. The OS uses it all the time to communicate with devices mapped to main memory (your video card, for example).

 

I use Gavotte's RAMDisk v1.0.4096.4 in this way to store temp files, page file and IE/FF cache. The RAMDisk bypasses Microsoft's software lock which restricts total usable memory to 3.12GB in Vista or Windows 7 x86.

This allows me to utilise all 4GB RAM on Windows 7 as all recent builds have only been x86 (roll on Beta 1 x64 ). Browsing the net is also incredibly quick now and doesn't cause unnecessary wear on my SSD.

 

Since the address is being used by the I/O of a device, it cannot be used to address RAM. So, basically the unused RAM has no address.

 

The OS directly uses this RAM to read and write to those devices, and yes, each byte of this RAM has an address.

Best explanation I've seen to date.

 

In which case RAMDisk software would not be able to use it, so something must be wrong here.

 

I had a desktop with vista 32bit home premium and it saw all 4gb of ram.

 

It will know what you have but addressing it is a diffrent story.

 

Your Vista SP1 reports the amount of RAM physically installed in your computer but not the amount of RAM available to the OS. If you want to know how much RAM actually available for the OS, press Ctrl-Alt-Del, Start Task Manager, click Performance tab and under "Physical Memory (MB) Total" will tell you that.

 

It is pretty straight forward. 4GB of address space, 4GB of RAM..Now RAM isn’t the only thing needing an address, there are other critical functions and devices as well. Not allocating address space to devices renders them inoperable. Not allocating addresses to RAM simply results in the unaddressed section not being used in an otherwise fully functional computer - All the CPU knows about is that it's reading and writing data to a certain address space.
(Sometimes that address space has RAM in it, other times it can be a device. Since more than 3GB of RAM will trespass into the "top" of the address space, the devices would either get superseded by the RAM, or the RAM gets superseded by the devices. Devices get a higher priority because they are more critical to the system.)

EDIT:

The RAMDisk tools use PAE as the basis for doing their stuff. If the hardware does not support PAE, then the RAMDisk thing won't work. The way this works is pretty similar to the way the pagefile works and the term used for it is I think "Page Frame Number", and I don't know more about it.

 

Yes I realise PAE is used but I was referring to rflcptr's comment.