Re: The Linear Address Space
From: Jonathan Bartlett (johnnyb_at_eskimo.com)
Date: 04/28/04
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Date: Wed, 28 Apr 2004 04:19:55 +0000 (UTC)
> Physical address space has nothing to do with the hard drive. The IDE
> controller (or SCSI if you prefer) is part of the physical address space.
> Some of its registers are accessible as memory. When for some reason data
> must be read off the hard drive, the OS sends a command to the IDE or SCSI
> controller to read the data into physical memory (RAM).
Your post is correct, but I thought I'd point something interesting
out for everyone. In the HURD, the ext2 filesystem driver is actually
built by mmap()ing in the whole partition into the driver's address
space, and then just dealing with it as a big block of memory. Of
course, this limitted the HURD to only 2GB partitions, but it was a
pretty nifty idea from a programming perspective, and one of the
benefits of being able to have operating system pieces running in
userspace. They may have changed the implementation since I last
looked at the HURD, but it was really interesting.
Jon
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