32 bit Computing + 4 GB RAM?

haduken

Australia8267 Posts

May 12 2008 12:44 GMT

This has being bugging me a lot and i need some definite answers and explanations from ppl like BILL, R1CH or headbugger.

Ok, the problem is simple. 32 bit computers using Windows XP and Vista can not utilize full 4 GB of RAM. I understand that while you can get at least 3 GB of RAM and the rest can be used for devices, but answers from people are inconsistent.

A general philosophy on whirlpool.net.au (Australian IT community) is that the BIOS set restrictions on how much RAM that can be used for OS and the rest are just there...

To use more than 4 GB, you need a 64 bit computing OS and sometimes with the right mobo and with the right firmware you can remap the memory allocations etc...

But that doesn't explain the fact that Linux 32 bit systems can use as much as 32 GB of RAM while still subject to BIOS.

What's the answer here? :/

gusbear

333 Posts

May 12 2008 13:27 GMT

nobody tells it better than dan: http://www.dansdata.com/askdan00015.htm

LazarusSpeaks

100 Posts

May 12 2008 13:44 GMT

Dan didn't answer this part, and I'm still wondering:

But that doesn't explain the fact that Linux 32 bit systems can use as much as 32 GB of RAM while still subject to BIOS.

chiflutz

Romania1025 Posts

May 12 2008 13:44 GMT

That's both comprehensive AND a trip down memory lane. I'll make it shorter.

32-bit Windows uses a memory mapping model called Physical Address Extension, which maps a total of 4 GB system-wide. This encompasses the RAM, CPU caches and registers, GPU VRAM, basically everything. The BIOS detects and makes the devices' memory available for use, the OS has to actually read/write it.

ToKoreaWithLove

Norway10161 Posts

May 12 2008 13:47 GMT

Use linux! Its better anyway

haduken

Australia8267 Posts

May 12 2008 13:48 GMT

so BIOS actually restrict OS RAM allocation because the system need to reserve memory that grow from the top (e.g. 4GB) and down for devices? is that the reason? but that doesn't explain linux memory allocation. unless Linux allocate memory very differently which i have a sneaking suspicion that it actually does ( can't remember exactly how linux works internally).

gusbear

333 Posts

May 12 2008 13:53 GMT

On May 12 2008 22:44 LazarusSpeaks wrote:
Dan didn't answer this part, and I'm still wondering:

Show nested quote +

http://en.wikipedia.org/wiki/Physical_Address_Extension

haduken

Australia8267 Posts

May 12 2008 14:16 GMT

i get it now. so PAE actually works but the only reason it's not popular on MS platforms is because of the potential driver compatibilities associated with 64 bit / 32 bit.

linux overcomes this problem by having better designs.
ah thx so much gusbear

FreeZEternal

Korea (South)3396 Posts

May 12 2008 14:28 GMT

The problem is that programs do not use main memory directly. The OS has something called Virtual Memory which maps directly to Main Memory. What applications in your OS see is Virtual Memory which maps nicely to main memory or RAM. This is done because main memory gets fragmented and you would need apps to map to different location in main memory instead of mapping the whole thing in a nice chunk of contiguous space. Some of this Virtual Memory is reserved to devices in your machine. The rest is mapped to RAM. Since you only have a 32-bit (~4GB) Virtual Address Space and some of this space is reserved for devices, your applications can only use what is remaining. When you click on System from the Control Panel, you are actually seeing the total Virtual Memory available and not the actual physical memory available.

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