Re: The Linear Address Space

From: Ivan Korotkov (koroNOSPAMtkov2_at_ztelDOT.ru)
Date: 04/27/04

  • Next message: Matt Taylor: "Re: Detecting total RAM size via BIOS" 
    Date: Tue, 27 Apr 2004 17:56:46 +0000 (UTC)

    > The problem is that in a computer there is Hard Drive storage, RAM storage
    > and a heap of other devices and the like that all require byte addresses.
    > Say for example you had a 180GByte HDD in your system, even with the 36
    bit
    > address extension mechanisms which bring the Physical Address Space up to
    > 64GBytes, there are still just not enough Logical Addresses to reference
    the
    > whole of the addresses on a system.

    Hard drive storage has nothing to do with RAM. The former one is dealt with
    via IDE/SCSI bus and the latter one - directly via system bus. Disk space is
    addressed by sectors which are usually 512b or 1kb in size (at the level of
    a logical disk) and by clusters (at the level of filesystem) of size about
    4kb. This makes it possible to address the whole disk with 32-bit addresses.

    >>From all this I have come to think that the Linear Address Space is simply
    > an abstraction or a virtualization of the true state of all of the
    addresses
    > within a computer so what I need to know is how are these abstractions
    that
    > are used in a program "mapped" to the real addresses of the computer?
    > How does this work?

    Virtual memory addresses are mapped to physical. A program never knows
    (unless it's a driver) where actually its data and code resides, it deals
    with virtual addresses.

    > Also, I think that paging has something to do with RAM management and the
    > "checking in" and "checking out" of data to and from RAM but frankly I can
    > neither confirm nor deny this and hence I just cannot figure out what is
    > actually going on with paging.

    Of course it has. It is used to organize swap memory on disk, for memory
    protection and (in some OSs) to make each process have its own address
    space.

    Ivan

  • Next message: Matt Taylor: "Re: Detecting total RAM size via BIOS"