Memory allocation (4)

 Memory is the processes by which
information is encoded, stored and
retrieved. Encoding allow information
that is from the outside world to reach
our senses in the forms of chemical
and physical stimuli.

 An alloation is something that you set
aside for use .for instance if you want to
set aside a certain amount of hard drive
space for an application,you can
allocate how much in the settings.

 The placement of blocks of information in a
memory system is called memory
allocation.
 To allocate memory it is necessary to keep
in information of available memory in the
system.If memory management system finds
sufficient free memory,it allocates only as
much memory as needed ,keeping the rest
available to satisfy future request .
 If sufficient memory is not available,
swapping of blocks is done.

 In static memory allocation, size of the
memory may be required for the
calculation that must be define before
loading and executing the program.

 Two methods are used for dynamic
memory allocation:
1-Nonpreemptive allocation
2-preemptive allocation

 Consider M1 as a main memory and M2
as a secondry memory and a block K of
n words is to be transferred from M2 to
M1.for such memory allocation it is
necessary to find or create an available
reason of n or more words to
accommodate K.This process is known
as nonpreemptive allocation.

 In this algorithm, searching is started
either at the beginning of the memory or
where the previous first fit search ended.

 In this algorithm, all free memory blocks
are searched and smallest free memory
block which is large enough to
accommodate desired block K is used to
allocate K.

 Nonpreemptive allocation can’t make
efficient use of memory in all situation.
Due scattered memory blocks larger free
memory blocks may not be available.
Much more efficient us of the available
memory space is possible if the
occupied space can be re allocated to
make room for incoming blocks by a
method called as compaction.

 Fixed memory
 Stack memory
 Heap memory

 Executable code
 Global variables
 Constant structures that don’t fit inside a
machine instruction. (constant arrays,
strings, floating points, long integers etc.)
 Static variables.
 Subroutine local variable in non-recursive
languages (e.g. early FORTRAN).

 Stores information in such a manner that the
item stored last is the first item retrieved.
 In digital computer, it is essentially a
memory unit with an address register that
can count only after an initial value is
loaded into it.
 Two operations of a stack are
1. Insertion
2. Deletion

 Structures whose size varies dynamically
(e.g. variable length arrays or strings).
 Structures that are allocated
dynamically (e.g. records in a linked list).
 Structures created by a function call that
must survive after the call returns.
Issues:
 Allocation and free space management
 Deallocation / garbage collection

Memory allocation (4)

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