Operating System - Memory Management - Notes, Study notes of Operating Systems

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MEMORY MANAGEMENT

OUTLINE

• (^) Basic memory management
• (^) Protection Hardware
• (^) Swapping
• (^) Memory Partition
• (^) Paging
• (^) Segmentation

Memory Management issues

• (^) Basic Hardware issue.
• (^) Binding of symbolic memory address to actual physical address.
• (^) Difference between logical address and physical address
• (^) Memory allocation & Deallocation

A typical instruction execution

cycle

• (^) First instruction is fetched from memory.
• (^) Then it is decoded and as per requirement operands are also fetched from memory.
• (^) Operation is performed on the operands.
• (^) Results are stored back to the memory.

Memory Management Task

• (^) Operating system must manage sharing

of physical memory between many

processes

Basic Memory Hardware.

• (^) Main Memory and registers are directly accessible to the processor.
• (^) There are memory instruction that takes memory addresses as an argument, none of them take disk address.
• (^) So every Data and instructions are required to loaded in to these direct access storage devices.

MEMORY PROTECTION

• (^) Each Process needs separate memory space.
• (^) The overlapping is not allowed.
• (^) For separation we need to have
  • (^) Base Register
  • (^) Limit Register For any access to the main memory.

A base and a limit register define

a logical address space

Address Binding

• (^) Two type of Addresses
  • (^) Symbolic Address (Generated by the program for example requirements like 5 memory blocks etc)
  • (^) Relocatable address (actual physical position of the memory block)
• (^) Address Binding is required for any execution.

Address Binding

• (^) Compile time :
• (^) Load time :
• (^) Execution time

Memory-Management Unit (MMU)

• (^) Hardware device that maps virtual to physical address In MMU scheme, the value in the relocation register is added to every address generated by a user process at the time it is sent to memory The user program deals with logical addresses; it never sees the real physical addresses

Dynamic relocation using a

relocation register

How to get good performance.

• (^) With High Degree of Multi programmability.
• (^) More program should be there into main memory.
• (^) So memory Swapping is required.

How to get good performance.

• (^) Programs spend much of their time accessing memory, so performance is important!
• (^) Programmers want unlimited fast memory, but
  • (^) Memory (hardware) has a cost
  • (^) Faster memory is more expensive
• (^) The solution is to put a fast memory (Cache) Between Processor and main memory.