4 replies to this topic

[MaLing]

I know this topic is now obsolete, but I can find a solid proof recently only, so this topic is extremely late.

Many people say that 32-bit Windows can utilise 4GB ram maximum, because 32 bits equal to 4GB (2^32=4G), if users want to utilise more than 4GB ram, 64-bit Windows must be used.

I always doubted this statement but there had been no proof.

I now just found a solid proof:
Physical Address Extension - PAE Memory and Windows

The best proof is:
Windows 2000 Advanced Server - 8 GB of physical RAM
Windows 2000 Datacenter Server - 32 GB of physical RAM
(There are only 32-bit versions but no 64-bit versions of Windows 2000.)

I am so happy now that my belief was true, so I just share my view and the proof here.

Edited by MaLing, 07 March 2010 - 02:44 PM.

[Charalambos]

Physical Adress Extension supports memory up to 64 GB (and in fact it can support much more), and is activated in all computers that their hardware supports DEP, but there are limitations according to the operating system that is being used. In fact it has to do with a 64-bit parameter of which the last 12 bits are used to flag some processor capabilities or by the OS (the 63rd one for DEP). That means that 52 bits are not used, if they are all used for the PAE then they can theoretically support 2^ 52 (4 petabytes) of memory! For more details have a look at the Wikipedia's related article:

http://en.wikipedia....dress_Extension

Of course there may be some practical problems in supporting so much memory but anyway 64 GBs are enougth for the 99,99% of the computer systems, aren't they? Yet the OS itself is the one that eliminates this aditional memory support capability.

[MaLing]

Right! Therefore whether the operating system is able to utilise more than 4GB ram, it all depends on the design of the operating system, but not on 32-bit or 64-bit.

Of course, there must be still with the proper equipment (eg DEP processor) in order for the operating system to utilise.

Edited by MaLing, 09 March 2010 - 04:04 PM.

[Charalambos]

DEP doesn't really has to do with it, yet it is the reason for the use of PAE when the memory is 4 GB or less. It is just that it is activated/deactivated by the 63rd, the NX (NoeXecute) bit of the mentioned 64-bit parameter. So, if you have PAE activated and you don't know why, this is the real reason.

As for the 64-bit OSes you can see in the mentioned Wikipedia article that in fact they use a similar way to PAE in order to utilize the increased memory.

Edited by Charalambos, 09 March 2010 - 09:33 PM.

[MaLing]

Oh yes, my carelessness--It should be PAE instead of DEP, thanks!