• Shared memory
• Segmentation

• (a) One address space. (b) Separate I and D spaces.

• Two processes sharing the same program sharing its page table.

• A shared library being used by two processes.

A compiler has many tables that are built up as compilation proceeds, possibly including:

• The source text being saved for the printed listing (on batch systems).
• The symbol table – the names and attributes of variables.
• The table containing integer, floating-point constants used.
• The parse tree, the syntactic analysis of the program.
• The stack used for procedure calls within the compiler.

• In a one-dimensional address space with growing tables, one table may bump into another.

• A segmented memory allows each table to grow or shrink independently of the other tables.

• Comparison of paging and segmentation.

• (a)-(d) Development of checkerboarding. (e) Removal of the checkerboarding by compaction.

• Shared memory
• Segmentation

• Segmentation with Paging
• Summary of variable memory management methods

• The descriptor segment points to the page tables.

• A segment descriptor. The numbers are the field lengths.

When a memory reference occurs, the following algorithm is carried out:

• The segment number used to find segment descriptor.
• Check is made to see if the segment’s page table is in memory.
• If not, segment fault occurs.
• If there is a protection violation, a fault (trap) occurs.
• Page table entry for the requested virtual page examined.
• If the page itself is not in memory, a page fault is triggered.
• If it is in memory, the main memory address of the start of the page is extracted from the page table entry
• The offset is added to the page origin to give the main memory address where the word is located.
• The read or store finally takes place.

• A 34-bit virtual address.
• Conversion of a two-part address into a main memory address.

• A simplified version of the TLB. The existence of two page sizes makes the actual TLB more complicated.

• Summary of variable memory management methods

• Segmentation with Paging
• Summary of variable memory management methods

• logical address
• linear address
• physical address
• Address translation

• logical address (48-bit)
• linear address (32-bit)
• physical address (32-bit)

• Address translation has two steps. It is NOT segmentation with paging.

• A segment selector is the segment register (16-bit).
• Segment selector is the index of segment descriptor table.
• Global Descriptor Table (up to 8192 entry)
• Local Descriptor Table (up to 8192 entry)

• A segment descriptor is 64bit.

• Conversion of a (selector, offset) pair to a linear address.

• Mapping of a linear address onto a physical address.

• logical address
• linear address
• physical address
• Address translation

• Chapter 3: Memory management, Modern Operating Systems . Forth Edition, Andrew S. Tanenbaum