Re: about /proc/meminfo and mmap

From: Zhixu Liu (liuzx@bnl.gov)
Date: Sat Oct 21 2000 - 10:03:13 EST


On Sat, 21 Oct 2000, Cefiar wrote:

> At 08:24 PM 20/10/00 -0400, Zhixu Liu wrote:
> >My PC have 128M RAM, but in /proc/meminfo, it display 122424K, not
> >128*1024K = 131072K, what does this mean?
>
> Sounds like something is stealing your ram.
>
> Usual suspects are..
>
> Shadow RAM is enabled.
> - This steals a TINY (usually 64k for BIOS, and 32k each for each extra
> memory address enabled) of ram. Nothing major though.
>
> Local memory accessing devices.
> - Embedded video cards (and possibly embedded sound devices) on boards
> using the Intel 815E chipset (and others) use local RAM for memory, instead
> of their own special memory - to reduce cost. Apart from weird memory
> sizes, this also can lead to latency and slow-down issues when accessing
> the memory normally. Many of these machines have AGP slots, and almost
> always have a PCI slot, so throwing in a cheap video (audio?) card can
> remove such issues, and frees up that memory again. Maximum I've seen a
> board allow for local video ram is 8 Meg, which is pretty much the amount
> you are missing. The board in question was a Socket 7 board with embedded
> video.

My PC is intel i810 chipset, so perhaps you are right. But now, question
is if I want to reserve some RAM for program use, how can I do? Thanks for
your help.

Zhixu

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