I decided I needed a laptop, so I picked up a relatively cheap Toshiba. It has 3GB of ram and an AMD Turion X2 dual-core processor. I don't really know much about the difference between 32-bit vs. 64-bit systems. I know the laptop supports 64-bit os. I want to put Ubuntu on it and so I was wondering if I should put the 32-bit Ubuntu on it or the 64-bit. Thanks in advance.

I'm still working on 32bit myself, but I understand the following:
- 32bit is limited in the amount of RAM (4G) it can access.
- 32bit is very stable, but 64bit has been around long enough to fix most of the major hiccups.
- There is only nominal improvement in performance with 64bit over 32bit.

There is a HUGE improvement in performance on SOME applications. Anything that has a lot of large number calculations or moves a lot of memory will show improvements(picture and movie editing/conversion are in this category). However for things like browsing, email, word processing, you will not see much (if any) difference.

And there is moderate reduction in performance (I've seen up to 30%) in other applications.

I think it is having a lot of very systematic floating point computations that tends to cause the huge improvement. I'm pretty sure the huge improvement comes from having twice as many XMM registers, not directly from using 64 bit addresses.

As for moving a lot of memory. I'm pretty sure that wouldn't have any performance difference.

I think you're right, but I think it is because the various re sampling algorithms make good use of the extra XMM registers.

For such things, you wouldn't normally even know if there was a CPU speed performance difference. In those tasks, the CPU is almost always waiting for you or for the network or for the hard drive. It waits at the same speed in 32bit mode as in 64bit mode.

Even for many cpu intensive tasks there is no significant performance difference between 32 bit mode and 64 bit mode.

An application that internally uses a LOT of pointers (something the programmer would know about but an end user couldn't predict) will run slower in 64 bit mode because there will be a lot more L2 cache misses (I've seen 30% slower).

An application that makes good use of the XMM registers (for a large amount of systematic floating point computation) can run much faster in 64 bit mode.

An application that works with several GB of data at once might use dynamic file mapping of chunks of the data in a 32 bit version, but use simple file mapping of the whole data in a 64 bit version (and let the virtual memory system do the dynamic part). That can run MUCH faster in 64 bit mode. I've seen some such programs (again in picture editing). I expect such programs will gradually get more common. But right now such programs, that run faster because of the fundamental advantage of 64bit mode, are very rare.