Memory problem with Centos 5.2

Hi, I have a server running Centos 5.2 with 12 GB RAM Memory, but, when I execute the command "top" or "free -m" it just reports me 3.5 GB RAM, when I restart the server the hardware self test shows me 12 GB RAM, but when the Centros is running just reports me 3.5 GB RAM with those commands ("top" or "free - m") even I tried the system monitor and it's the same, just shows me 3.5 GB RAM.

Please, could someone give me a hand on this,

Thanks,

 

You'd need to install a 64bit kernel in order to use all that memory.

 

No No No you cannot install a 64bit kernel on a 32bit arch machine, what you need is the PAE kernel,

Code:

yum install kernel-PAE

 

And how can you tell that the OP has a 32bit CPU?
It's time to let go of 32bit OSs and move on!

 

Okay genius, if he is running a 32bit system the PAE kernel is the solution. NOT installing 64bit kernel.

 

The 64bit kernel can address 64 TB of physical memory, 64bit kernels manage memory a lot better than 32bit kernels. While PAE can only go up to 64GB, since the address space is just 32 bits a process can't grow above 4GB. So installing PAE is just a dirty hack with no considiration for the future upgrades and system integrity on the server, genius.
I've seen mysql using upto 8GB memory on busy clusters, imagine what kind of issues I'd be having if I had PAE in place instead of a 64bit kernel?

 

What does the merits and demerits of architectures have to do which the question that was posed ?

Am not gonna waste my time in a flame war with you people will not notice the difference if u get my drift genius

 

The question was about large chunk of unused memory, and architectures have a lot to do with memory management.
And my post was simply informational, not intended to start a flame war with "you people"

 

Well well, great troubleshooting skills, you got.

How on earth was anaconda going to install a 32bit kernel on a 64bit machine in the first place ? By basic deduction you should know that the machine in question is NOT a 64bit machine, the default centos installer on 32 bit installs the normal kernel that does not enable PAE extentions thus can not address more than 3.5 GB memory.

The solution to help a guy running a 32bit system with 12GB of memory is to advise him to install the PAE enabled kernel, not tell him how great 64 bit machines are now he must throw away his server and buy the 64bit one blah blah blah.

 

I bet $100 that the person has a 64bit system, since it's quite uncommon and silly to place 12GB RAM on an outdated 32bit system.
I'm not saying that PAE is not a solution to the guy's problem, but it's just bad planning, since when you run a system with that amount of RAM then you're planning to use quite resource hungry applications, and if/when those application(s) start to use more than 4GB per process, issues would arise and a lot of head scratching would occur.