Windows 3GB of ram or 4GB. Which does windows see?

cpemma · 10 Dec 2008

GoodBytes said: ↑

No he means what the task manager is saying.
In reality I know why it says that but I don't know how to explain this in a easy, simple and quick fashion. Just take it as its normal, and it's correct, Windows does not lie, and everything works perfectly.
Click to expand...

How about this explanation? Not quick, but fairly thorough. But remember we're talking 32-bit systems here.

Ars said:

The processor has essentially two ways of talking to devices. The first are called I/O ports. These are limited in number, they're traditionally slow (you can only read or write a word at a time (or maybe even a byte at a time, I forget), and require special instructions to use, and so they're generally unpopular these days. If you need to send a data structure of some kind through an I/O port you have to stream it through one word at a time, so it's kind of sucky.

The upside to this approach is that the I/O ports have their own kind of "namespace". Each port has a number, and these numbers are used solely for I/O ports. There's no other resource using I/O port numbers.

The other way of talking to devices is through mapped memory. In this, the device takes up a portion of the processor's address space and any reads or writes to those addresses are redirected (by the memory controller) to the device instead of to RAM. This makes bulk transfers much easier; no streaming or anything like that. This mapping happens in the memory controller; the processor actually doesn't know what's going on. It just performs reads and writes to the memory locations, and the Right Thing happens behind the scenes.

The downside to this second, mapped memory approach is that the address space isn't dedicated to devices. It's used for everything addressable--including physical RAM. The processor can access 4 GiB of "stuff". That is to say, it has memory addresses starting at 0 and continuing all the way up to (2^32 - 1). And that's all it can access (with one exception that I'll get to later). With no devices (or devices that all use I/O ports instead of mapped memory), all of those addresses can correspond to physical RAM (actually, I think this isn't technically true; if memory serves, the Intel memory controller must allocate at least 128 MiB to devices, whether you want to or not, but it's still virtually all of the memory).

When you don't have that much physical RAM, and when your devices don't map much memory, that's not a big problem. There are enough addresses for all of the physical RAM and all of the devices, so you don't lose any addressable memory, so everything is hunky dory.

The problems crop up when you have lots of physical RAM, and devices that like to map lots of memory. For example, many video cards like to map their video memory to physical RAM, and that's a problem. If I have a video card with 1 GiB memory on it, and it wants to map all of that memory, then of the precious 4 GiB of address space I have, 1 GiB of that is used up by the video card. That 1 GiB thus can't be used to refer to physical memory. If I only had 2 GiB of physical memory, I'd be OK, but once you start getting to 3 or 4 GiB the BIOS has to start making choices; does it give physical addresses to RAM or to devices (and it picks the latter every time).

This is why you end up losing physical RAM when you have lots of it and some big video cards.

All is not lost, however. Although I said that the processor could only access 4 GiB of addresses, that's not strictly true. Current x86 processors offer two modes to allow the use of longer physical addresses; up to 36 bit from the normal 32-bit. There are some restrictions on this; the only thing that can readily be mapped to "high" (above 4 GiB) physical addresses is physical RAM; devices are still stuck below 4 GiB (there are mechanisms which mean this need not be so, but it all too often is).
Click to expand...

With my 4Gb RAM and 32-bit Vista, I apparently have 3581Mb available. (The GPU only has 256Mb).
Code:
Physical Memory	
Total	3581 MB
Used	1459 MB
Free	2121 MB
Utilization	41 %
	
Swap Space	
Total	9649 MB
Used	1375 MB
Free	8273 MB
Utilization	14 %
	
Virtual Memory	
Total	13230 MB
Used	2835 MB
Free	10395 MB
Utilization	21 %
	
Paging File	
Paging File	C:\pagefile.sys
Initial / Maximum Size	3067 MB / 6400 MB
Current Size	3067 MB
Current / Peak Usage	66 MB / 71 MB
Utilization	2 %
	
Paging File	
Paging File	F:\pagefile.sys
Initial / Maximum Size	3067 MB / 8400 MB
Current Size	3067 MB
Current / Peak Usage	65 MB / 73 MB
Utilization	2 %
	
Physical Address Extension (PAE)	
Supported by Operating System	Yes
Supported by CPU	Yes
Active	Yes

mm vr · 11 Dec 2008

That's a good explanation, cpemma. However, the OP has a 64-bit OS so that doesn't apply to his system (or does it?).

GoodBytes · 11 Dec 2008

Wow, something is definitely strange.
I have just received my new laptop from Dell (Latitude E6400), which replaces the exact same one (old one has a little dent)

In Everest, my old laptop shows 3751MB, same in the Task Manager. However the system properties shows 4GB of RAM. It has Samsung RAM.

On my new laptop, exactly the same configuration, it shows 4082MB in the Task Manager, same in Everest, is has Elpida brand RAM (never heard of them).

Both feature Vista 64-bit, they are right now side by side, and can't find any differences. Both have the Nvidia Quadro NVS 160M with 256MB of RAM, both with the same BIOS and same driver versions from Dell.

GoodBytes · 12 Dec 2008

OK I investigated further by switching the RAM, and the HDD, and realized it has nothing to do with the RAM, nor the BIOS, nor the motherboard (broken or new revision).

It's a Windows configuration!!!
You probably did a system tweak that did this.
Open msconfig, go to the "Boot" tab, then click on the "Advanced options" button. A panel will open, on it it will say how many CPU you want to set and the memory.
If the memory check box is enabled (no mater what the value is in the box), uncheck it. This should fix the problem after reboot. In my case, it was checked and had the value 0 (on the machine that had the same issue as you). If this does not fix the problem, then it must be a tweak you performed. I know for my case with the laptop, I installed a tweak UI tool at some point to see, but I didn't touch anything in it, and for some reason it played with Windows configuration despite me never clicking on anything. You might have fallen to the same crap.

teamtd11 · 11 Dec 2008

That could just be it GoodBytes, mine was ticked so i will see what happens on reboot later.

cpemma · 11 Dec 2008

mm vr said: ↑

That's a good explanation, cpemma. However, the OP has a 64-bit OS so that doesn't apply to his system (or does it?).
Click to expand...

Good point, it shouldn't, you'd be moaning "I've fitted 18.45 exabytes of RAM, how come Win only shows 18.449 exabytes?

teamtd11 · 12 Dec 2008

Fixed. Thanks GoodBytes.

Cupboard · 12 Dec 2008

Its weird that your graphics card is being allocated some of the RAM, mine managed to steal some at one point which annoyed me, but I couldn't find any way to stop it

That was when I had my 7950GT

Log in or Sign up

Windows 3GB of ram or 4GB. Which does windows see?

cpemma Ecky thump

mm vr The cheesecake is a lie

GoodBytes How many wifi's does it have?

GoodBytes How many wifi's does it have?

teamtd11 Custom User Title

cpemma Ecky thump

teamtd11 Custom User Title

Cupboard I'm not a modder.

Share This Page

Log in or Sign up

Windows 3GB of ram or 4GB. Which does windows see?

cpemma Ecky thump

mm vr The cheesecake is a lie

GoodBytes How many wifi's does it have?

GoodBytes How many wifi's does it have?

teamtd11 *Custom User Title*

cpemma Ecky thump

teamtd11 *Custom User Title*

Cupboard I'm not a modder.

Share This Page

Useful Searches

teamtd11 Custom User Title

teamtd11 Custom User Title