• Page Memory Organization
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    Segmentation Implementation In IA-32




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    Segmentation Implementation In IA-32
    Architecture
    In the IA-32 architecture, logical addresses in the program are formed using
    segmentation and look like a "shift selector". The values of the selector are
    loaded into a special register of the processor (segment register) and used as
    an index in the table of descriptors of the segment, which is in memory and
    is an analog of the table of segments, described earlier. Six segment
    registers are supported in IA-32 architecture. This means that the executable
    code at the same time can address these six independent d cops.
    The selector contains a descriptor index in the table, bits of the local or
    global table indicator, and the required privilege level.
    For system set common global descriptor table ( Global D e scriptor Table,
    GDT ), and for each task - local descriptor table ( L o cal Descriptor Table,
    LDT ). The descriptors in IA-32 are 64 bits long. They define the properties
    of software objects (for example, memory segments or descriptor tables).
    Handle contains the value base ( base ), which corresponds to the address of
    the object (for example, the beginning segment); limit value ( limit ); object
    type (segment, descriptor table, etc.); protection characteristics.
    Access to tables of descriptors is supported by hardware. If the security
    characteristics specified in the handle do not correspond to the privilege
    level specified by the selector, it will not be possible to access the memory
    using it. They provide memory protection. However, it has never been
    mentioned that a physical address is stored in the handle. The fact is that for
    the IA-32 architecture, due to the conversion of the logical address, they
    receive not another physical address, but another type of address, which is
    called a linear address.
    Page Memory Organization

    The main technologies of virtual memory implementation other than
    segmentation owned -page memory organization  ( paging ). Its main idea
    is the allocation of memory blocks of fixed length. These blocks are
    called pages and so are we . This technology is the most common approach
    to virtual memory implementation in modern operating systems.

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