I just upgraded my "Emachines e520" computer to 4 GB RAM (the maximum) today. But Slackware only sees 3 GB (according to KInfoCenter) I checked my BIOS, and it sees all 4 GB of RAM in the machine. So it seems to be a problem with Linux. I've read that this is fairly common with some Linux users, and that the kernel's usually part of the problem. Now, I just need the knowledge to fix the problem

Anybody have any ideas?

Machine specs:
Emachines e520
4GB RAM
Slackware Linux 13.0 (KDE 4.2.4)

Type in terminal:

You have to build a new kernel. The stock kernels with Slackware are not enabled to support >4GB.

Try here for specific information.

Actually, it is not enabled to support =>4GB....

The '=' part is important (the reason why it only sees 3GB)

And in that thread this post is particularly relevant. If the existing memory usage pattern isn't causing swapping with the existing kernel, enabling HIGHMEM64G will probably slow the system.

As milkycow mentioned, enabling HIGHMEM64G results in a 3 to 6% time penalty on memory access. The only memory usage pattern which would gain would be if the system is actually using > ~3.5 GB and thus swapping. Even then, depending on specific usage, the time penalty might be more significant than avoiding swapping. Different story if the system is swapping > 2 GB and 6 GB RAM are fitted but with only 4 GB RAM fitted it is questionable whether enabling HIGHMEM64G would improve performance.

The best solution is a 64-bit kernel.

Okay, I've read the topic and the wiki page. I'm obviously gonna have to compile/build/whatever a new kernel. I'd prefer to have someone guide me through that, because I'm a complete newbie to most of that >.>

Google a bit for Alien Bob's Kernel compile guide. You can also search this forum as the link has been posted many times.

download the kernel sources
extract
cd to the directory
type make menuconfig at the terminal
look at evrey option and check it or uncheck to your desires
make sure to enable large ram support (under processor and features i think) (ether 16 or 64 GB)
save / exit
type make
...WAIT...
setup your kernel for bootloading

Some important notes before you begin!

1. Ensure your lilo.conf has a proper entry directly to the current kernel and not just a symlink! (huge is always a good option as a failsafe)

2. IF you don't know how to use an initrd image, LEARN NOW. read /usr/doc/mkinitrd-1.3.4/README.initrd and know why you are making one for the "general" labeled kernel

3. Configure your kernel using your current configure script in /boot
configure two options (or more if you need to)
General setup > Local Version - ad something like "-mine" or anything you want. This way your pre installed modules will not be overwritten.

Toggle the Ram=>4gig option

4. Install the modules and kernel. Make sure the file names in /boot are something that mark it as yours
vmlinuz-<your build version>-2.6.29.6<Local Version Tag>

5. Make an initrd image using -k 2.6.29.6<Local Version Tag>

6. Make a new entry in lilo.conf and run lilo

7. Reboot and pray.

8. Rebuild external kernel modules for things like nvidia and virtual box

http://blog.tpa.me.uk/slackware-kernel-compile-guide/

This guide will not only who you how to set HIGHMEM64G, but also will show you how to have a nice slim kernel with no initrd..

..and it's only 10 steps!