User’s View of a Program

Segmentation

• Memory-management scheme that supports user view of memory.
• A program is a collection of segments.  A segment is a logical unit such as:

                    main program,

                    procedure,

                    function,

                    method,

                    object,

                    local variables, global variables,

                    common block,

                    stack,

                    symbol table, arrays

Shared Pages

• Shared code

1. One copy of read-only (reentrant) code shared among processes (i.e., text editors, compilers, window systems).
2. Shared code must appear in same location in the logical address space of all processes.

• Private code and data

1. Each process keeps a separate copy of the code and data.
2. The pages for the private code and data can appear anywhere in the logical address space.

Inverted Page Table

• One entry for each real page of memory.
• Entry consists of the virtual address of the page stored in that real memory location, with information about the process that owns that page.
• Decreases memory needed to store each page table, but increases time needed to search the table when a page reference occurs.
• Use hash table to limit the search to one — or at most a few — page-table entries.

Hashed Page Tables

• Common in address spaces > 32 bits.
• The virtual page number is hashed into a page table. This page table contains a chain of elements hashing to the same location.
• Virtual page numbers are compared in this chain searching for a match. If a match is found, the corresponding physical frame is extracted.

Address-Translation Scheme

• Address-translation scheme for a two-level 32-bit paging architecture
• 
  
• 
• 
  
• 
  

Two-Level Page-Table Scheme