It has been known that the X86 64bit architecture outperform 32bit architecture. However, little is known whether 64-bit Ubuntu installation outperforms its 32-bit counterpart significantly as the latter is marked as recommended download from Ubuntu website.
Luckily [Phoronix] had answered these questions for us. In its latest article, [Phoronix] compares the performance between 64-bit Ubuntu installation and 32-bit Ubuntu installation on a Intel Core i5 2520 (4 cores) with 4GB RAM.
Audio File Encoding Performance (less is better)
Server Workload Performance (more is better)
The result concludes that Ubuntu 12.10 64-bit performs better on overall compared to 32-bit, especially on video/audio encoding/decoding tasks. Ubuntu 12.10 also performs better with server workloads.
Although Canonical still marks Ubuntu 12.10 32-bit as the recommended download. It seems that 64-bit installation offers greater performance even without the advantage of having greater memory. Some might argue that PAE still allows 32-bit Ubuntu to access more than 4GB RAM, PAE access on 32-bit is still significantly slower when compared to 64-bit memory access. Personally, I use Ubuntu 64bit for my development machine as all of my hardware has opensource drivers.
There were a couple of people that I met recently complained to me that their Ubuntu only detects 3 gigs of RAM after they upgraded their machine to 4 GB RAM.
Actually the problem does not lie with Ubuntu or any operating system in particular, rather the problem is related to 32bit operating system which only can address maximum of 232 bytes of memory.
Some might argue that 32-bit should be enough to address 4GB RAM, but in reality some of those memory location are reserved for computer and application operation that only a fraction of it are addressable when you installed 4GB RAM on a 32bit operating system. Thus you would see that your computer would only have around 3.5 GB only.
There are two solutions to remedy this problem :
i) Install a 64-bit (Ubuntu) operating system
ii) Compile/Install kernel with PAE features enabled
The (i) solution is obvious, just install a 64bit edition of Ubuntu to your computer, and your problem will be automatically solved! The downside is, you probably does not want to use a 64bit edition of Ubuntu yet for some obscure reason (the evil binary only drivers and blobs)
The (ii) solution requires you to install a kernel with Physical Address Extension (PAE) support enabled.
For you information, Ubuntu comes with pre-compiled linux kernel that has PAE enabled. What you need to do is to apt-get these 3 packages “linux-headers-server, linux-image-server and linux-server” and reboot your computer. This will enable you operating system to recognize the extra RAM installed inside your computer.
p/s : The best solution is to get a system that does not depend on binary blogs (hardware drivers, etc) and move to 64-bit operating system in order to enjoy the full potential of your computer.