Real and availible RAM

Kyle Rollin knr at
Mon May 5 11:08:04 PDT 2003

On Mon, 5 May 2003 09:30:30 -0400 (EDT), agent dero wrote
> I have been looking through the kernel boot messages in /var/log 
> while working on some custom kernel compile work, and I came across 
> that I think is very interesting, but doesn't make sense.
> real memory  = 100663296 (98304K bytes)
> avail memory = 94580736 (92364K bytes)
> This tells me that FreeBSD recognizes my 98MB of RAM, but it only 
> uses 92MB? Are the 6MB of RAM that are left getting shafted, and 
> just using power, but not being addressed by FreeBSD? Does this slow 
> down my machine at all, I mean, is there a percentage to this? Where 
> only x% of 100% RAM is availible or usable?


If you look at the way x86 architecture is designed (and somebody else can 
feel free to correct me if I'm wrong), but system memory is often used in 
the caching/shadowing of BIOS. This is where a lot of system memory often 
goes before the OS is loaded - also, as Rob said, the kernel itself will 
take up memory before the rest of the OS is booted. 

If you're concerned that you might run out of memory, RAM is cheap - adding 
a stick of 128MB will greatly reduce that risk :)

-Kyle Rollin

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