32bit 4Gb Memory Limit Explained

Corpsecrank · 11 Oct 2009

I found an interesting article that I thought was worth sharing. I have always been bugged when reading that 32bit operating systems were limited to 4Gb of memory because of the way memory is addressed. It never made any sense to me because when I took Windows XP classes it had a nice little table covering different versions of Windows in the back which showed certain 32bit versions allowing up to 128Gb of memory to be recognized.

The book was written for taking Microsoft exams to earn a certification in XP and I also had another book of the same type for Server 03 again with the same table in the back. So if Microsoft is saying that 32bit is not limited to 4Gb why are people trying to say that the limit is because 32bit is not capable of addressing it?

Because the standard 32bit home desktop versions of Windows are not licensed to allow more than 4Gb. The only reason you are limited is because Microsoft wrote the OS to limit you not because 32bit cannot address memory above 4Gb.

If you want to read more about this in full detail with some images where the guy actually removed the limitation by altering the license file you can do so here:

Geoff Chappell, Software Analyst - Viewer

Dinesh · 11 Oct 2009

Nice find +rep. BTW, the hack is very ugly.

Corpsecrank · 11 Oct 2009

Dinesh said:

Nice find +rep. BTW, the hack is very ugly.

Thanks :) Yeah I love it when he says PAE is an ugly hack lol.

I think this article is great because it finally answers one of the biggest most misunderstood questions about 32bit windows and memory addressing. The only problem is that now since I understand it when I run into articles where people do not it is even more irritating to read all the misleading information they believe is correct.

One guy even tried to say that 32bit processors were the cause and that the reason PAE could allow more memory to be addressed is because 32bit processors were actually designed as 36bit and limited to 32bit however the entire thing is easily dispelled because he failed to explain why a 64bit processor still had the same limitations.

Dinesh · 11 Oct 2009

I liked the way he has honestly written this article. Microsoft has been lying all these times.

Corpsecrank · 11 Oct 2009

Dinesh said:

I liked the way he has honestly written this article. Microsoft has been lying all these times.

Well not so much lying they just didn't mention the way memory was handled.

It has been my experience that any type of limitation set by Microsoft is nicely labeled as a license so that it sounds better.

The problem with this case is that they never mentioned that memory usage was something they licensed.

QuackPot · 11 Oct 2009

Good read OP. Must be a marketing ploy or rake in more revenue.

+rep (I gave you another pip in your rep

)

logicearth · 11 Oct 2009

The 4 GB limit for 32 bit is a technical limitation. There is just not enough addressing space in 32 bit integer lengths. To get around this issue you must increase the bit length, either by using 64 bit or with PAE. Now PAE must be supported not only by the hardware but also the OS and its core services (aka drivers). So why does Microsoft limit the 32 bit OS to 4 GBs of RAM? Well simple really, most of the hardware and drivers out there bulk with more then 4 GBs of RAM.

When you have an OS installed on billions of computers each with a unique set of hardware, why take the risky path? Limit to 4 GBs is the wisest choice to make. And honestly, Microsoft doesn't have to tell us jack about it (Microsoft artificially limits RAM all the time, Home Premium 64 bit is limited to 16 GB). That does not make it a marketing ploy or to rake in more revenue. Jeeze the 64 bit version cost the same as the 32 bit and they even come in the same box! Or you can get the 64 bit if you need it and use your 32 bit CD key.

Wild and silly speculation...meh.

whs · 11 Oct 2009

An interesting article indeed. The way I read it is that 32bit and 64bit OS are essentially the same code and both are present when you buy 32bit. With some hacks and tweaks you can disable the 32bit blockage and make it run as 64bit. That's like taking the muffler out of the exhaust pipe of a mofa in order to make it run faster - and that is not legal either.

Corpsecrank · 11 Oct 2009

The need for more than 4Gb of ram in a 32bit environment for a home user no matter what type of applications are being used is non existent really. Which is my guess why allowing more than 4Gb as a standard was never an option from the start.

The only time you really need more than 4Gb is if your running a server and if that were the case you would want to run a server version of windows which would support up to 128Gb depending on the version used.

I have done some pretty heavy operation with my current setup and never came close to touching the 4Gb of installed ram. I always have around 1200Mb of free ram even when running multiple apps that require a large amount of ram.

The reason it is so hard to fill the ram up though is mainly due to the speed at which it can pass off data.

H2SO4 · 11 Oct 2009

logicearth said:

The 4 GB limit for 32 bit is a technical limitation. There is just not enough addressing space in 32 bit integer lengths. To get around this issue you must increase the bit length, either by using 64 bit or with PAE. Now PAE must be supported not only by the hardware but also the OS and its core services (aka drivers). So why does Microsoft limit the 32 bit OS to 4 GBs of RAM? Well simple really, most of the hardware and drivers out there bulk with more then 4 GBs of RAM.
...
Wild and silly speculation...meh.

Completely agree. That article is entirely misguided. I think the conspiratorial tone was meant to raise his profile, as opposed to actually explaining the issue properly. A few other points...

The PAE requirement for 36-bit addressing was/is not met by all consumer-level processors. You need the motherboard and processor to provide a 36-bit address bus before anything else can happen.

"Client" Windows versions used to have this functionality. It was deactivated in XP SP2 and all subsequent versions because it was inducing BSODs in buggy drivers which did not deal well with the remapping. The dilemma faced by MS came down to two choices:

1) Work with every driver provider in the desktop space to teach them how to properly deal with PAE-remapped memory and hence not BSOD machines and corrupt data.

2) Deactivate the remapping for non-server versions of Windows since most 32-bit home/small-office users don't tend to sport in excess of 4GB RAM anyway.

The first one is obviously somewhat utopian, so they chose the latter - no remapping on "client" Windows as of XPSP2 and later. If you want to run more than 4GB, go with 64-bit.

There's no conspiracy. The guy's a ranter.