4GB RAM in 32-bit Slackware 13?
 

I have 4GB of RAM in my system, but only see 3.5GB using the default kernel-generic-smp-2.6.29.6. From /proc/config.gz it seems that highmem is already enabled in the kernel.

Did anyone else experience this? Is there supposed to be some setting in my BIOS (which I have so far been unable to find)?

HIGHMEM64G mustn't be enabled, you'll have to rebuild your kernel for that. Or switch to Slackware 64.

Unless your system has PAE, that is the maximum amount of RAM the OS can address, regardless of whatever your kernel settings are. If you have PAE, you will need to enable it in the BIOS.

I think you need to enable HUGEMEM for 4GB and up (not sure tho).

I have a laptop with 4GB of RAM and only 3.5GB used to be detected. I recompile the kernel with the option High memory (64GB) enabled and now 3.96 GB of RAM is detected. The High Memory (64GB) option is under “Processor type and features” -> “High Memory Support (64GB)".
PS: you can find a good tutorial about compiling your own kernel at http://alien.slackbook.org/dokuwiki/...kernelbuilding

By HUGEMEM (maybe they changed the name) I mean 64GB, I think HIGHMEM is 4GB. I use 64-bit, so it's hard for me to check if this still holds true.

It's HIGHMEM64G.

Thanks for the responses, I have compiled a kernel with CONFIG_HIGHMEM64G=y and that indeed enables PAE.

Although supposedly there's a 3-6% penalty on all memory accesses with this configuration, and for my motherboard which supports a maximum of 4GB RAM I wonder if that extra 500MB is really worth it...