MMFeb17 - MemoryManagement B.Ramamurthy Page1 10/16/10...

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10/16/10 Page 1  Memory Management B.Ramamurthy
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10/16/10 Page 2 Introduction Memory refers to storage needed by the  kernel, the other components of the operating  system and the user programs.  In a multi-processing, multi-user system, the  structure of the memory is quite complex.  Efficient memory management is very critical  for good performance of the entire system.  In this discussion we will study memory  management policies, techniques and their  implementations.
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10/16/10 Page 3 Topics for discussion Memory Abstraction and concept of address  space Memory management requirements Memory management techniques Memory operation of relocation Virtual memory  Principle of locality Demand Paging Page replacement policies
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10/16/10 Page 4 Memory (No abstraction) User program OS in RAM User program OS in ROM User program Device Drivers ROM OS in RAM
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10/16/10 Page 5 The notion of address space An address space is set of addresses that a  process can use to address memory. Each process has its own address space  defined by base register and limit register. Swapping is a simple method for managing  memory in the context of multiprogramming.
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10/16/10 Page 6 Swapping A process can be  swapped  temporarily out of  memory to a  backing store , and then brought back  into memory for continued execution. Backing store – fast disk large enough to  accommodate copies of all memory images for all  users; must provide direct access to these memory  images. Roll out, roll in  – swapping variant used for priority- based scheduling algorithms; lower-priority process is  swapped out so higher-priority process can be loaded  and executed.
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10/16/10 Page 7 Schematic View of Swapping
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10/16/10 Page 8 Contiguous Allocation Main memory usually into two partitions: Resident operating system, usually held in low  memory with interrupt vector. User processes then held in high memory. Single-partition allocation Relocation-register scheme used to protect user  processes from each other, and from changing  operating-system code and data. Relocation register contains value of smallest  physical address; limit register contains range of  logical addresses – each logical address must be  less than the limit register. 
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10/16/10 Page 9 Basic memory operation:  Relocation A process in the memory includes instructions plus  data. Instruction contain memory references:  Addresses of data items, addresses of instructions.  These are  logical addresses : relative addresses  are examples of this. These are addresses which  are expressed with reference to some known point,  usually the beginning of the program.
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MMFeb17 - MemoryManagement B.Ramamurthy Page1 10/16/10...

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