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1. Memory Management

2. What is Memory Management in an Operating System?
Memory management in OS is a technique of controlling and managing the functionality of Random access
memory (primary memory).
It is used for achieving better concurrency, system performance, and memory utilization.
Memory management moves processes from primary memory to secondary memory and vice versa. It also
keeps track of available memory, memory allocation, and unallocated.
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3. Why Memory Management is Required?
● Allocate and de-allocate memory before and after process execution.
● To keep track of used memory space by processes.
● To minimize fragmentation issues.
● To proper utilization of main memory.
● To maintain data integrity while executing of process.
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4. Logical and Physical Address Space
● Logical Address Space: An address generated by the CPU is known as a “Logical Address”. It is also
known as a Virtual address. Logical address space can be defined as the size of the process. A logical
address can be changed.
● Physical Address Space: An address seen by the memory unit (i.e the one loaded into the memory
address register of the memory) is commonly known as a “Physical Address”.
● A Physical address is also known as a Real address. The set of all physical addresses corresponding to
these logical addresses is known as Physical address space. A physical address is computed by MMU.
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5. Static and Dynamic Loading
Static Loading : Involves loading all the necessary program components into the main memory
before the program's execution begins.
This means that both the executable code and data are loaded into predetermined memory
locations.
Dynamic Loading: The entire program and all data of a process must be in physical memory
for the process to execute.
So, the size of a process is limited to the size of physical memory. To gain proper memory utilization,
dynamic loading is used.
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6. Static and Dynamic Linking
To perform a linking task a linker is used. A linker is a program that takes one or more object files generated
by a compiler and combines them into a single executable file.
Static Linking: In static linking, the linker combines all necessary program modules into a single executable
program. So there is no runtime dependency.
Some operating systems support only static linking, in which system language libraries are treated like any
other object module.
Dynamic Linking: on the other hand, takes a more dynamic approach. In this method, the
necessary libraries are not included in the final executable.
Instead, the program dynamically links to the required libraries at runtime. This means that
multiple programs can share a single copy of a library, reducing redundancy and conserving
memory.
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7. Swapping
Swapping is a technique used in an operating system
for efficient management of the memory of the
computer system.
Swapping includes two tasks, swapping in, and
swapping out. Swapping in means placing the blocks or
pages of data from the secondary memory to the
primary memory.
Swapping out is removing blocks/pages of data from
the main memory to the Read-Only Memory (R.O.M.).
Swapping is useful when a large program has to be
executed or some operation has to be performed on a
large file
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8. Contiguous Memory Allocation
Contiguous memory allocation is a memory management technique that involves
allocating a process to the entire contiguous block of the main memory it requires to
execute.
First Fit is a memory allocation algorithm that allocates the first available block of memory that is large
enough to accommodate a process.
The Best Fit algorithm searches the entire memory space to find the smallest block that can accommodate a
process. This helps in minimizing wastage of memory, as it selects the smallest available block that fits.
However, it may lead to more fragmented memory spaces compared to other allocation strategies.
Worst Fit, as the name implies, allocates the largest available block of memory to a process. This approach
can result in more fragmentation compared to First Fit or Best Fit strategies.
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9. Fragmentation
When processes are moved to and from the main memory, the available free space in primary memory is broken into
smaller pieces.
1. External Fragmentation:
The total amount of free available primary is sufficient to reside a process, but can not be used because it is non-contiguous.
External fragmentation can be decreased by compaction or shuffling of data in memory to arrange all free memory blocks together and thus form one
larger free memory block.
2. Internal Fragmentation:
Internal fragmentation occurs when the memory block assigned to the process is larger than the amount of memory required by the process.
In such a situation a part of memory is left unutilized because it will not be used by any other process. I
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10. Segmentation
Segmentation is a memory management technique in which each job is divided into several segments of
different sizes, one for each module that contains pieces that perform related functions. Each segment is
actually a different logical address space of the program.
When a process is to be executed, its corresponding segmentation are loaded into non-contiguous memory
though every segment is loaded into a contiguous block of available memory.
The operating system maintains a segment map table for every process and a list of free memory blocks
along with segment numbers, their size and corresponding memory locations in main memory.
For each segment, the table stores the starting address of the segment and the length of the segment.
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