Hi. I am using Linux Slackware 13.37 with the new self-compiled kernel on Acer Aspire 5750G.

But it sees only 2.3 Gb of my 4 Gb RAM.
I suppose it's because for some reason Slackware has installed 32 bit Linux. Though, my machine has 64 bit processor. Here are the specs:

http://www.techradar.com/reviews/pc-.../specification

And another thing, that I don't understand, is the cpuinfo:

It says, that the core speed is 800 MHz. While Intel says, it's 2.4 GHz. Maybe, it has decreased the speed of kernels to save the energy?

http://ark.intel.com/search/advanced...Threading=true

What is wrong? How to fix?

You might not have PAE enabled in your kernel, recheck your kernel settings. Another thing is to reboot into the stock SMP kernel and check cpuinfo again and compare the results.

If it hasn't been super long since the system was booted, you can get important ram info using the command
Post the output of that and someone will explain the meaning. It tells you what ram can be used by a non PAE 32-bit kernel and it tells you what additional ram can be used by PAE or 64-bit.

If significant memory is unusable even via PAE, it may give some insight into why.

Probably you need to switch either to a PAE kernel or a complete 64 bit distribution. But the command I gave above is a useful look before you leap so you know what you can expect to gain from a change of kernel.

High memory support is set to 4 Gb.

gives nothing

If I understand you correctly, that means you do not have PAE.

It is a confusing feature. 4GB used that way means 4GB of physical address space, not 4GB of ram. To use 4GB of ram, you need more than 4GB of physical address space.

No, it seems, that I have PAE enabled. Look here:

http://www.larmeir.com/2009/07/enabl...g-up-to-64-gb/

I did exactly the same as on the screenshots, only I chose 4 Gb instead of 64 Gb, which must fit.

Adding something from my Linux machine.

So, the RAM is there. But the kernel doesn't use it.

Slackware does not decide which version to install, the only one that can decide that is the user. If you have the 32 bit version this is because you downloaded and installed the 32 bit version.

Nope. It was the kernel that decreased the speed of the CPU to save energy and increase the lifetime of the CPU. If more computing power is needed the kernel will automatically increase the speed. There is no need to fix that. You can do that with setting the powersaving options to performance, but this will bring nothing more than the CPU waiting faster for work.

Again no, PAE will NOT be enabled if you choose 4 GB instead of 64 GB. To enable PAE for usage of more RAM you HAVE to choose 64 GB. This is for a simple reason: Due to technical reasons an area of the memory below 4GB (usually about 500MB to 1GB, can be more, like in your case) is not usable, because it is mapped to peripheral devices. To make this memory available to the system it is remapped to an area above 4GB. So if you choose 4GB instead of 64GB this remapped area will simply not be used.

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As TobiSGD explained above (and I explained earlier) selecting 4GB is selecting no PAE and does NOT enable support for 4GB of ram.

Dmidecode and most BIOS reports of ram size tell you about all the ram that is physically plugged into the motherboard. The amount of ram that can be used is smaller, maybe much smaller. The motherboard or BIOS or some BIOS menu setting might be limiting the amount of ram that can be used. Your non PAE 32 bit kernel is also limiting the amount of ram that can be used. I was hoping that dmesg command would tell you how much a PAE kernel could use. Maybe it would if given soon enough after a reboot (before the dmesg log overflows), or maybe Slackware wrecks that dmesg command in some other way I haven't seen. Switching to a PAE kernel might be the easiest way to find out how much ram your BIOS actually enables.

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I rebuilt and installed the new kernel. RAM is ok now. Thx!