I'm going to run CentOS 6 on Dell PowerEdge R210 II with Xeon E3-1220 CPU and 4 GB RAM.

I'm going to run several virtual machines on it, running various setups of websites. VMs most certainly be 32 bits, to conserve memory and memory bandwidth; nothing inside of them can be that large.

Now I'm inclined to have the host OS be 32-bit too, but I'm thinking whether or not I might be better off installing 64-bit "just in case". I may or may not upgrade the RAM over the lifetime of this server (my previous server had 1 GB over its whole lifetime), but I know Linux supports PAE well and up to 64 GB of RAM should be accessible over PAE. I'm running 32-bit Ubuntu on my 64-bit laptop with 8 GB just fine (it uses less RAM and I think boots faster). And I know the individual processes and VMs won't get too big as to run into a limit of 32-bit system.

What do you think: should I run 64-bit host "just in case"?

  • 5
    Just use 64-bit.
    – ewwhite
    Mar 26, 2014 at 13:12

3 Answers 3


The only time you should care about whether your OS is 32-bit or 64-bit is when you have an application that specifically needs one of the two.

If you do not have such an application requirement, and/or you have more than 3.2 GB of memory, you may as well just use 64-bit.

  • Where does 3.2 GB figure come from? I know it's true for 32-bit Windows, but in CentOS - I think that's not a limit. I know for a fact that 32-bit Ubuntu installs PAE by default and utilizes my 8 GB RAM just fine. According to this article, Linux should be able to utilize 64 GB. Mar 26, 2014 at 13:15
  • @NickolaiLeschov The limit everywhere is 4gb - MOST LIKELY minus some memory for hardware. This is totally bios / chipset dependent. And on older machines.... well... there is a limit way below 4gb. On most machines these days this stuff is mapped so all 4gb can be used. Unless one has a cheap shared memory graphics card / chip. PAE is a LOT slower than linear memory access, so on your latptop you give up speed - may or may not be an issue, depending on application, but no real gain to run the OS on 32 bit.
    – TomTom
    Mar 26, 2014 at 13:33
  • Many 32bit OSes can use more than 2^32 byte of RAM in total, but still only 2^32 byte per process.
    – Philipp
    Mar 26, 2014 at 15:23

Use 64-bit to preserve an upgrade path. RHEL 7 will only be available in 64-bit, so if you use 32-bit, you will not be able to upgrade and will have to do a fresh installation when you want to move to the new version of the distro.


According to this page, both CentOS 5 and 6 x86 support up to 16GB of RAM. It all depends on whether or not you plan to upgrade beyond this at any point during the host's lifetime.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.