ubuntu 64 or 32 bit for macbook/vps?

i've got macbook pro and wonder if i should use 64 or 32 bits ubuntu server?

and then i've got a vps not hosted by med. how do i know what version to choose?

how do you check how many bits your cpu i working with?

can i use 64 on 32 and vice versa?

If you have a new macbook or any other that has "Intel Core 2 Duo" processor, your macbook has 64 bits processor.(See "System Profiler" > Hardware > Processor Name)

You can install any 32 bits OS(also Ubuntu 64) on any 64 bits Macbook's processor(not shore about others).

You CAN'T install any 64 bits OS on any 32 bits processor.

If your mac is core2 Duo Based, you have a 64 bit processor. (to find out Apple Menu->About this mac-> Processor info) So, you could use a 64 bit Ubuntu.

You can't use a 64 bit OS on a 32 bit architecture. But the reverse would work. 32 Bit OS on a 64 bit architecture.

If you need to know the version of the macbook, type in command line, in Ubuntu: less /proc/cpuinfo

see more details here

I understand that on a VPS, you're likely better off with a 32 bit OS as 64 bits have memory implications. Commonly, one will get a VPS with less memory to save money and hence you want a smaller memory foot print.

The problem is that this particular architecture (x86_64) uses more memory than plain old x86. Significantly more.

The other answers about your MacBook Pro and 64 bits are right. I have nothing to contribute to them.

The additional question I have is are you trying to replace Mac OS X or are you wanting to Run Ubuntu in a virtual environment? If this is the case, you needn't worry so much about 32 vs. 64 bits unless you are trying to do something specific.

If you need to pick one, I'd likely pick the 64 bit for a virtual environment but for such usages, I doubt it'd ultimately matter to me.