Re: How much RAM do I need?
On 11 Nov 1998, Gary L. Hennigan wrote:
> "Henry Kingman" <hkingman@best.com> writes:
> | > On the other hand, if your chipset can't cache more than 64MB, going to
> | > 80MB might actually make some things slower. I'm not sure if telling the
> | > kernel "mem=64M" on an 80MB machine would be enough to fix that problem
> | > or not.
Should be. in that case Linux won't ever address that memory, so it
should have zero effect. Fortunately, we can do better - see below.
> | Pasted below is an article from the ZDNet Web site about this. It seems to
> | suggest that the L2 cache is somehow the limiting factor on RAM addressing
> | capability (Is that right?).
>
> That's partially correct. All the Pentium processors will address
> quite a bit more than 64MB of RAM, the question is whether or not your
> motherboard can cache more than 64MB. It's a pretty complex issue, but
> it's becoming less important now that the PII has it's cache packaged
> in the CPU module. I believe the PII's cacheable limit is in the GB
> range.
Yeah, Intel crippled a few of its Pentium motherboard chipsets so they
could only cache 64MB of RAM. If you touch RAM above 64MB, it's much
slower.
However...
...there are some tricks. Somewhere I saw an announcement for a set of
patches to the kernel that allows it to treat memory above 64MB as a swap
disk. Sure, it's slower than cached RAM, but *much* *much* *much* faster
than an actual disk. ;->
Or, you can just use it as a plain ol' ramdisk. Put your source code and
compiler on a ramdisk and you won't believe how fast you can compile code.
:-> And on a laptop, RAM takes less power than a spinning disk.
Anyway, as other have noted, to see how much RAM you need, try doing
typical things with your system, and worst-case things, and use vmstat and
free. I have 64MB in my desktop, and I've never used more than a meg or
two of swap, even when compiling a kernel, running several xterms, emacs,
and Netscape (which is an enourmous resource pig) and Apache. (I'll never
go back to 16MB, beleive me.)
Sincerely,
Ray Ingles (248) 377-7735 ray.ingles@fanucrobotics.com
The above opinions are probably not those of FANUC Robotics. Yet.
Reply to: