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mem=80M ??

Posted on 2000-02-04
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I am using Linux Mandrake 6.1 .  The Compaq machine that it is running on contains 80 meg ram.  THe machine seems really slow though.  I have read that you need to specify any amount of ram over 16m??

How exactly do I let Linux know about the extra ram now that the system is allready installed???


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Question by:iowa1
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by:jlevie
ID: 2490748
If the bios sees the memory, so should Linux. If you want to check how much memory Linux knows about and how much is in use, you can do so from KDE's Settings->Information->Memory. The same information can be seen by examining the contents of /proc/meminfo.

Now, if Linux isn't seeing all of the installed memory, it could be that not all of it is actually usable, i.e., a bad chip or a hole in the address space. I don't have a url handy, but there are memory checkers for PC platforms that will do a pretty exhaustive test of a machine's memory.

BTW, 80Mb isn't that much memory, especially if the system is very heavily loaded. I'm on a laptop with 128Mb and as the only user I have no problem at all using up all available physical memory. When that happens the system slows down as it has to start swapping/paging.
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by:iowa1
ID: 2490986
I  opened the /proc directory and it listed meminfo in the directory, yet I did not know how to open it.  I tried usings emacs, but nothing was showing in the window.

I don't have KDE because I set this up as a server install.

If Linux should automaticly see the memory then, why do they recommend setting it with mem = 80m??

Thanks for the help, yet I need some more.
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by:jlevie
ID: 2491089
I just did "more /proc/meminfo". Who is "they" and where do you see the reference to setting "mem = 80m"?
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bernardh earned 0 total points
ID: 2491100
There are a couple of things that could be causing Linux to not see all your memory. On some 386's you need to compile your kernel with Limit memory to 16M? enabled.

On most systems, the reason is that the BIOS has a limit of how much memory it will tell the OS is present in the machine, even though the board can have more. Common limits seen with this promel are 16M, 32M, 64M, and 128M. To get around this, we need to explicitly specify the amount of memory to the kernel at boot time via the mem=memory goes
here> flag.

In the following example, we have a 32M machine but only 16M are being seen by Linux. At the LILO prompt, we type

     LILO: linux mem=32M

After the machine boots, we use the free command to see if the larger amount of memory was recognized by the kernel. If so, we can add an append line to the /etc/lilo.conf file and rerun lilo to make it happen permanently. The example from above could look like the following:

         boot=/dev/sda
         map=/boot/map
         install=/boot/boot.b
         prompt
         timeout=50
         image=/boot/vmlinuz-2.0.32
         label=linux
         root=/dev/sda1
         initrd=/boot/initrd-2.0.32.img
         read-only
         append="mem=32M"

Do not forget to run lilo after editing the file for the changes to be made to your Master Boot Record (MBR).
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by:j2
ID: 2491583
just type "free" and get over it ;) It is the ram >64 you _needed_ to specify in the 2.0.x kernels.
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by:iowa1
ID: 2491765
Good answer!  Thanks for the help.
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