I just bought 8GB of RAM for my old desktop which I'm using as an Ubuntu dev box and secondary workstation. Can I just install the RAM and go merrily on my way or do I need to run some commands for Linux to take recognize and take advantage of the extra memory?

You didn't say whether you use 32 bit or 64 bit Ubuntu, and if 32 bit whether it is PAE or not.

The output from the command uname -a would tell most of us whether your Ubuntu is 32 bit or 64 bit and would tell someone with some Ubuntu specific knowledge whether 32 bit is PAE or not. So post that output if you don't know what kernel you have.

There may also be many questions about whether your motherboard/BIOS really supports 8GB of ram and whether you need to change any BIOS settings to enable that support. A BIOS may easily recognize and report 8GB without actually supporting 8GB. But that is not at all the question you asked.

A 32-bit non PAE Linux kernel can only support 3 and a fraction GB of ram. A 32 bit PAE kernel can easily support 8GB (usually more). If you have a non PAE kernel, you can switch to a PAE kernel by simply installing the correct package with the package manager and (unlike most package changes) then reboot.

Some people will tell you switching to 64 bit is better (see lots of other threads debating that). But for sure switching from 32 bit to 64 bit is far harder than switching 32 bit non PAE to PAE.

It is reasonable to try the hardware upgrade of ram before any software change. Assuming you have a 32 bit non PAE kernel now, if the ram works then you will initially be able to use 3 and a fraction GB of it, and there is a way to tell whether the BIOS has enabled all 8GB even before you change to a kernel that can use it.

You can just pop it in and be happy. Just, if you are running a i386 architecture, (32bit) Ubuntu will not show the full RAM. it will utilize it but if you have conky or a screenlet set to show the RAM, you won't see the full 8GB....only 64bit does that....

Cheers!

EDIT: I stand corrected about the PAE....what he said...

Hi,

Here are couple commands you can check a new RAM installation. It will report current usage and total ram installed.

But if those methods give contradictory results, you won't know where the support was missed:

The dmidecode and lshw and related methods all give a very optimistic view, telling you about all the physical ram unless it is very seriously broken or fundamentally inaccessible. Even if the total ram is far above what the motherboard can support, dmidecode will still be able to see all the ram.

The free and top and meminfo and related methods all give (slight underestimates of) final usable ram.

If you see memory via dmidecode that is missing in meminfo, neither tells you whether it is bad memory vs. motherboard doesn't support that much vs. BIOS doesn't support that much vs. BIOS misconfigured vs. Linux kernel doesn't support that much vs. Linux misconfigured.

To start to divide up those possibilities, you can look at the BIOS memory map that is near the beginning of the output of the dmesg command.

That will tell you what ram the BIOS allows the OS to use. Ram not listed there can't be used by Linux no matter how you configure Linux nor which Linux kernel you have. Ram listed there can be used by Linux so if your current Linux kernel can't use it, you can change that.

Thanks so much for all the replies. My mobo specs say 8GB is the maximum supported. It's got 4 slots and I'm putting 2GB in each. Also, I've got 64-bit Ubuntu 10.10 so the OS should be able to work with the 8GB easily. I suppose I was wondering aout installed applications (e.g., Apache, PHP) and whether they have adaptive behavior or whether they check the RAM at install time and configure themselves accordingly.

In any case. I'm going to pop it in right now and see what happens.

There still might be a confusing option somewhere in BIOS setup that needs to be changed in order to actually enable 8GB of ram. Otherwise the BIOS would find and report 8GB but silently enable less.

So nothing to worry about there.

I'm only pretty sure there is nothing to worry about there either. For most applications I'm certain there is nothing to worry about. But I don't uses Apache nor PHP.

I agree. 64 bit shouldn't care but saying that there are ways to check the kernel usage and maybe correct it if needed as far as the kernel is concerned.

The problem is with any installer. Dunno how many times this sort of thing happens where some oddity of an installer made a choice and not generally known.

To be sure, install it as new. (no one ever likes to hear that) Since it is a dev box you should start with a known clean install.

Yikes! Unfortunately, this box has 4 different boots on it
* XP, set up for Protools recording
* XP, set up for dev
* Ubuntu 64, for dev
* Ubuntu 32, for dev

It was quite a nightmare to get them all running and playing nice.

I've put the RAM in and when I run 'free' it looks like it's all there.