How to make my Ubuntu detect more than 4GB memory

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.

The solution?

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.

6 Replies to “How to make my Ubuntu detect more than 4GB memory”

  1. I was going to say the same thing, FWIK part of whatever memory you buy is also reserved (in equal measure) to the gpu or graphic chipset you have.

    I read this in some technical journal somewhere. Can’t cite it atm, sorry.

  2. I did install the 64 bit and I still only see 3 gig of ram. Is there something in the kernel that need to set?

  3. To JP: I’m running 64bit and have no problems with 32bit appz running. You have to install the 32bit libraries which some god awful reason they’re not pre-installed.

  4. The problem with your “best” solution (re: p/s) is that you won’t enjoy all of your desktop applications with a 64 bit system. Lot’s of apps are still stuck needing 32bit libraries. A lot of Adobe Air apps, Google Gears and countless other applications still want 32 bits and fail to work properly.

    64 bit is great for servers…not so great for desktops..yet.

  5. Good Tip!

    I bought a machine advertised as having 4 GB memory. Ubuntu was only showing 3.5 GB. I was a bit puzzled until reading this article.

    Thanks for the memory!

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