4GB RAM Limit

[Nate Shoffner]

I am just wondering if, when you have 4GB of RAM installed on your computer and the limit for 32-bit is about 3GB, does that mean it only shows up as 3GB but still uses that extra GB of memory or what? Sorry if this sounds kind of stupid.

[Revolutionary101]

I am just wondering if, when you have 4GB of RAM installed on your computer and the limit for 32-bit is about 3GB, does that mean it only shows up as 3GB but still uses that extra GB of memory or what? Sorry if this sounds kind of stupid.

32 bit computers can address 4 GB. It will show and use all of the 4 GB of RAM. The 3 GB limit is just something Windows has.

[Nate Shoffner]

Well I currently have 4GB of RAM installed. BIOS detects 4GB, but Ubuntu only detects 3.3GB. :confused:

[Revolutionary101]

Well I currently have 4GB of RAM installed. BIOS detects 4GB, but Ubuntu only detects 3.3GB. :confused:
That is weird because I did the math and 32 bit computers can support up to 4 GB. Here is the math.

2(this is the 0 and 1)^32(bits of address space)/1024(converts it to kilobytes)/1024(coverts to megabytes)/1024(converts to gigabytes)= 4 GB

I also compiled my own Linux kernel and it said that the Linux kernel supports up to 4 GB of RAM on 32 bit systems. Maybe it has something to do with your BIOS, even though it may show 4 GB of RAM it may only allow the computer to use 3.3 GB.

[Nate Shoffner]

Hmm...any way I can possibly figure out how much my computer allows?

I ran free -m and these were the results:



total used free shared buffers cached
Mem: 3402 1308 2093 0 47 757
-/+ buffers/cache: 503 2898
Swap: 478 0 478

[DownTown22]

Nope...as far as I know, you're only going to be able to use 3.3GB of that 4GB.

[Revolutionary101]

I think you are going to have to check your computer manufacter's manual. If you built your own computer search for your motherboard model online and look for it's limit.

[Revolutionary101]

Nope...as far as I know, you're only going to be able to use 3.3GB of that 4GB.

Then explain this:
http://www.spack.org/wiki/LinuxRamLimits

[Yellow Pasque]

The BIOS will reserve some of the address space for hardware, so 3.4GB sounds right.

Possible ways around this:
1) Use 64-bit OS and enable memory-remapping in your BIOS if it supports it
2) Use a kernel with PAE
3) Monitor your RAM usage and see if you can actually use 3.4GB of RAM under your normal workload before you get concerned with addressing more :)

[Nate Shoffner]

The BIOS will reserve some of the address space for hardware, so 3.4GB sounds right.

Possible ways around this:
1) Use 64-bit OS and enable memory-remapping in your BIOS if it supports it
2) Use a kernel with PAE
3) Monitor your RAM usage and see if you can actually use 3.4GB of RAM under your normal workload before you get concerned with addressing more :)

It's not that I necessarily need it. I was just curious because I Know Windows will not read all 4GB of RAM, but I wasn't completely sure about Linux. I haven't really looked into 64-bit but from what I've heard, is that some applications aren't fully compatible with it. Now, if I did what you said and used a kernel with PAE, will that impact anything else on the system in a negative way?