TUGASAN 1

Memory Management

Paging

§  Logical address space of a process can be noncontiguous process is allocated physical memory whenever the latter is available

§  Divide physical memory into fixed-sized blocks called frames(size is power of 2, between 512 bytes and 8,192 bytes)

§   Divide logical memory into blocks of same size called pages

§  Keep track of all free frames

§  To run a program of size n pages, need to find n free frames and load program

§  Set up a page table to translate logical to physical addresses

§  Internal fragmentation

Paging Hardware

Paging Example

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

Segmentation Architecture

§  Logical address consists of a two tuple:

<segment-number, offset>,

§  Segment table – maps two-dimensional physical addresses;

each table entry has:          

§  base – contains the starting physical address where the

segments reside in memory

§  limit – specifies the length of the segment

§  Segment-table base register (STBR)points to the segment

table’s location in memory

§  Segment-table length register (STLR)indicates number of

segments used by a program;

segment number s is legal if s< STLR

Protection

§  With each entry in segment table associate:

®     validation bit = 0 Þ illegal segment

®     read/write/execute privileges

§  Protection bits associated with segments code sharing occurs at segment level

§  Since segments vary in length, memory allocation is a dynamic storage-allocation problem

§   A segmentation example is shown in the following diagram

Segmentation Hardware