LinuxQuestions.org
Share your knowledge at the LQ Wiki.
Go Back   LinuxQuestions.org > Forums > Linux Forums > Linux - Newbie
User Name
Password
Linux - Newbie This Linux forum is for members that are new to Linux.
Just starting out and have a question? If it is not in the man pages or the how-to's this is the place!

Notices


Reply
  Search this Thread
Old 04-26-2013, 06:16 AM   #16
shivaa
Senior Member
 
Registered: Jul 2012
Location: Grenoble, Fr.
Distribution: Sun Solaris, RHEL, Ubuntu, Debian 6.0
Posts: 1,800
Blog Entries: 4

Rep: Reputation: 286Reputation: 286Reputation: 286

Quote:
Originally Posted by TobiSGD View Post
According to your explanation I would have about 25GB of RAM and that is definitely not the case.
MemTotal shows the total amount of memory available to the system.
I do not wish to argue, but the original question is still unanswered and unexplained... If there is 4GB of RAM, then why MemTotal is showing 2.8GB? A good explaination could show a way to not only the OP but others too.
 
Old 04-26-2013, 07:16 AM   #17
johnsfine
LQ Guru
 
Registered: Dec 2007
Distribution: Centos
Posts: 5,286

Rep: Reputation: 1181Reputation: 1181Reputation: 1181Reputation: 1181Reputation: 1181Reputation: 1181Reputation: 1181Reputation: 1181Reputation: 1181
Quote:
Originally Posted by shivaa View Post
If there is 4GB of RAM, then why MemTotal is showing 2.8GB? A good explaination could show a way to not only the OP but others too.
You need to start by understanding there is a difference between physical ram and physical address space.

Several big chunks in the first 4GB of the physical address space are reserved for things other than ram. The total of those is typically 5/8 of a GB, but it may be significantly more or less than that typical amount. The actual amount depends on details of the design of both the motherboard and the BIOS.

There is a memory controller (inside the CPU package on most newer designs, but inside some other major chip on the motherboard in older designs).

Ram is not directly accessed by physical addresses. Ram is accessed by a complicated system of strobe and select signals generated by the memory controller. The memory controller is programmed (on each power up) with mapping information that translates ranges of physical address into the signals needed to access ranges of actual ram.

Because big chunks are used for other things, you can't map 4GB of ram into 4GB of physical addresses. You need to use addresses above the 4GB boundary.

1) In some older designs, there are only 32 physical address signals going from the CPU package to the memory controller, so even with PAE there is no way to access physical addresses over 4GB.

2) Some BIOSs aren't set up to map any ram above the 4GB boundary.

3) Some BIOS's have a special option (in BIOS setup) to allow them to map over the 4GB boundary.

4) A 32bit OS without PAE cannot use physical addresses over 4GB.

5) Most 32bit Windows versions, even with PAE,cannot use physical addresses over 4GB. But 32bit Linux with PAE can use physical addresses over 4GB.

In this thread (4) and (5) are irrelevant, because the OS is 64 bit. But 1 to 3 apply regardless of whether the CPU and OS are 64 bit.

If the problem is 3, the OP can fix it fairly easily. If it is 2, a new BIOS version might exist that fixes it. If the problem is 1, it can't be fixed.
 
Old 04-26-2013, 08:24 PM   #18
jefro
Moderator
 
Registered: Mar 2008
Posts: 15,658

Rep: Reputation: 2257Reputation: 2257Reputation: 2257Reputation: 2257Reputation: 2257Reputation: 2257Reputation: 2257Reputation: 2257Reputation: 2257Reputation: 2257Reputation: 2257
I put in a vote to run memtest. See what it says.

If what the OP posted is correct, I tend to think that what was said before. That the chipset is not supporting that amount of ram. Kind of an odd thing, looks more like a 32 bit OS issue.

Doesn't really seem likely that bios was set to reserve such a large amount for video.

Last edited by jefro; 04-26-2013 at 08:28 PM.
 
Old 04-26-2013, 09:22 PM   #19
o-madsen
LQ Newbie
 
Registered: Apr 2013
Location: Denmark
Distribution: Ubuntu / Manjaro
Posts: 17

Original Poster
Rep: Reputation: Disabled
Quote:
Originally Posted by jefro View Post
I put in a vote to run memtest. See what it says.

If what the OP posted is correct, I tend to think that what was said before. That the chipset is not supporting that amount of ram. Kind of an odd thing, looks more like a 32 bit OS issue.

Doesn't really seem likely that bios was set to reserve such a large amount for video.
the machine is 64 bit all the way through, I have made it print out how many bits before and it showed 64 bit

Ole
 
  


Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is Off
HTML code is Off



Similar Threads
Thread Thread Starter Forum Replies Last Post
Reparing filesystem vasthan Red Hat 2 05-05-2011 03:48 PM
Reparing Windows XP on a dual boot setup Fried Egg Linux - Software 20 01-20-2010 09:20 AM
Reparing MBR from linux for Windows XP n1nja56 Linux - Newbie 1 06-09-2008 03:10 PM
Difference between resident memory,shared memory and virtual memory in system monitor mathimca05 Linux - Newbie 1 11-11-2007 05:05 AM
Help!?! RH 8 Memory Mapping -High Memory-Virtural Memory issues.. Merlin53 Linux - Hardware 2 06-18-2003 05:48 PM


All times are GMT -5. The time now is 08:07 PM.

Main Menu
Advertisement
My LQ
Write for LQ
LinuxQuestions.org is looking for people interested in writing Editorials, Articles, Reviews, and more. If you'd like to contribute content, let us know.
Main Menu
Syndicate
RSS1  Latest Threads
RSS1  LQ News
Twitter: @linuxquestions
Facebook: linuxquestions Google+: linuxquestions
Open Source Consulting | Domain Registration