Tutorial :Ubuntu 32 bit maximum address space



Question:

Jeff covered this a while back on his blog in terms of 32 bit Vista.

Does the same 32 bit 4 GB memory cap that applies in 32 bit Vista apply to 32 bit Ubuntu? Are there any 32 bit operating systems that have creatively solved this problem?


Solution:1

Ubuntu server has PAE enabled in the kernel, the desktop version does not have this feature enabled by default.

This explains, by the way, why Ubuntu server does not work in some hardware emulators whereas the desktop edition does


Solution:2

Well, with windows, there's something called PAE, which means you can access up to 64 GB of memory on a windows machine. The downside is that most apps don't support actually using more than 4 GB of RAM. Only a small number of apps, like SQL Server are programmed to actually take advantage of all the extra memory.


Solution:3

Yes, 32 bit ubuntu has the same memory limitations.

There are exceptions to the 4GB limitation, but they are application specific... As in, Microsoft Sql Server can use 16 gigabytes with "Physical address Extensions" [PAE] configured and supported and... ugh http://forums.microsoft.com/TechNet/ShowPost.aspx?PostID=3703755&SiteID=17

Also drivers in ubuntu and windows both reduce the amount of memory available from the 4GB address space by mapping memory from that 4GB to devices. Graphics cards are particularly bad at this, your 256MB graphics card is using up at least 256MB of your address space...

If you can [your drivers support it, and cpu is new enough] install a 64 bit os. Your 32 bit applications and games will run fine.


Solution:4

In theory, all 32-bit OSes have that problem. You have 32 bits to do addressing. 2^32 bits / 2^10 (bits per kb) / 2^10 (kb per mb) / 2^10 (mb per gb) = 2^2 = 4gb.

Although there are some ways around it. (Look up the jump from 16-bit computing to 32-bit computing. They hit the same problem.)


Solution:5

There seems to be some confusion around PAE. PAE is "Page Address Extension", and is by no means a Windows feature. It is a hack Intel put in their Pentium II (and newer) chips to allow machines to access 64GB of memory. On Windows, applications need to support PAE explicitely, but in the open source world, packages can be compiled and optimized to your liking. The packages that could use more than 4GB of memory on Ubuntu (and other Linux distro's) are compiled with PAE support. This includes all server-specific software.


Solution:6

Linux supports a technology called PAE that lets you use more than 4GB of memory, however I don't know whether Ubuntu has it on by default. You may need to compile a new kernel.

Edit: Some threads on the Ubuntu forums suggest that the server kernel has PAE on by default, you could try installing that.


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