Operating System Swapping and Dynamic Linking

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the view of a program represented in the diagram?

User's View (correct)

Physical View

Logical View

Segmentation View

What is the purpose of a Segment Table?

To store information about the segments of a process (correct)

To manage I/O operations

To handle interrupts

To allocate memory to processes

What is the term for the area of memory that is accessible by a program?

User Space (correct)

Logical Memory Space

Physical Memory Space

Virtual Memory Space

What is the relationship between a segment and the physical memory space?

A segment is a logical division of the physical memory space Signup and view all the answers

What is the term for a self-contained block of code that performs a specific task?

All of the above Signup and view all the answers

What is an example of a data structure used to store and organize variables?

Array Signup and view all the answers

What is the primary advantage of using dynamic linking?

It is useful for libraries Signup and view all the answers

What is the main purpose of a backing store in swapping?

To accommodate copies of all memory images for all users Signup and view all the answers

What is the term for storing the context or state of a process so that it can be reloaded when execution is resumed?

Context saving Signup and view all the answers

What is the average swap time if the transfer rate of the 10MB file to and from the memory is 40MB/sec and the average latency is 8ms?

516ms Signup and view all the answers

What is the purpose of the 'roll out, roll in' variant in swapping policy?

To differentiate between high and low priority processes Signup and view all the answers

What is the primary benefit of using a fast disk as a backing store?

It reduces the time required for swapping Signup and view all the answers

What is a limitation of flash memory in mobile systems?

Limited number of write cycles Signup and view all the answers

How does iOS handle low memory situations?

Asks apps to voluntarily relinquish allocated memory Signup and view all the answers

What is the purpose of the base register in contiguous memory allocation?

Contains the value of the smallest physical address Signup and view all the answers

What is a characteristic of multiple-partition allocation?

Variable-partition sizes for efficiency Signup and view all the answers

What happens to free partitions in multiple-partition allocation?

Adjacent free partitions are combined Signup and view all the answers

What is an example of static memory allocation?

Declaring variables before runtime Signup and view all the answers

What is the purpose of the limit register in contiguous memory allocation?

Contains the range of logical addresses Signup and view all the answers

Why is swapping not typically used in mobile systems?

Flash memory has a limited number of write cycles Signup and view all the answers

What is the physical memory address of 'b' or logical address 1?

21 Signup and view all the answers

What is the purpose of the Translation Look-aside Buffers (TLB) in a paging system?

To reduce the time to access a user memory location Signup and view all the answers

In a paging system, what is the number of bits in the logical address and physical address respectively for a logical address space of 64 pages of 1024 words each, mapped onto a physical memory of 32 frames?

16, 15 Signup and view all the answers

What is internal fragmentation in the context of paging?

Unused space within a page Signup and view all the answers

What is the function of the Page-Table Base Register (PTBR)?

To point to the page table Signup and view all the answers

What is the page number and offset for the logical address 9467, given a page size of 1KB?

9, 251 Signup and view all the answers

In a paging system, how many memory accesses are required to access data or instructions?

Two Signup and view all the answers

What is the number of pages and excess bytes required for a process of size 58,800 bytes, given a page size of 2,048 bytes?

28, 1,456 Signup and view all the answers

What is the purpose of the paging memory-management scheme?

To permit the physical address space of a process to be noncontiguous Signup and view all the answers

What is the size of each frame in paging?

Fixed size, between 512 bytes and 16 Mbytes Signup and view all the answers

How is the physical memory address determined in a paging system?

By combining the base address with the page offset Signup and view all the answers

What is the page table used for in a paging system?

To store the base address of each page in physical memory Signup and view all the answers

What is the purpose of breaking physical memory into frames?

To allow for the allocation of noncontiguous memory Signup and view all the answers

What is the size of the page table in the given example?

2n, where n=2 Signup and view all the answers

What is the logical address space in the given example?

2m, where m=4 Signup and view all the answers

What is the purpose of the page offset in a paging system?

To combine with the base address to define the physical memory address Signup and view all the answers

Study Notes

Dynamic Linking

Uses shared libraries when compiling programs
Useful for libraries

Swapping

Mechanism where a process is swapped out of memory to a backing store
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: variant in swapping policy
Implemented in higher priority and low priority processes

Context Switch Time

Involves storing the context or state of a process so that it can be reloaded when execution is resumed
Example: transfer rate of a 10MB file to and from memory is 1/4 sec or 250 milliseconds
Swap time: 258ms, swapping in and out: 516ms

Swapping on Mobile Systems

Not typically supported due to:
- Flash memory based
- Small amount of space
- Limited number of write cycles
- Poor throughput between flash memory and CPU on mobile platform
Instead, use other methods to free memory:
- iOS asks apps to voluntarily relinquish allocated memory
- Android terminates apps if low free memory, but first writes application state to flash for fast restart

Contiguous Memory Allocation

Memory must accommodate user processes and the operating system
2 partitions of contiguous memory: resident OS and user process
Lower memory: where the operating system is located
High memory: for user processes
Relocation registers used to protect user processes from each other and from changing operating-system code and data
Base register contains value of smallest physical address
Limit register contains range of logical addresses
MMU maps logical address dynamically

Memory Mapping and Protection

Hardware support for relocation and limit registers

Multiple Partition Allocation

Multiple-partition allocation
Degree of multiprogramming is limited by the number of partitions
Variable-partition sizes for efficiency (sized to a given process’ needs)
Hole: block of available memory; holes of various size are scattered throughout memory
When a process arrives, it is allocated memory from a hole large enough to accommodate it
Process exiting frees its partition, adjacent free partitions combined
Operating system maintains information about:
- Allocated partitions
- Free partitions (hole)

Static and Dynamic Memory Allocation

Static Memory Allocation: declaring variables before runtime
Examples:
- Main program, procedure, function, method
- Object, local variables, global variables
- Common block, stack, symbol table, arrays

Segmentation

Logical View of Segmentation:
- User space
- Physical memory space
Segmentation:
- Main process
- Segment table
- Memory
- Segment size and address

Paging

Memory-management scheme that permits the physical address space of a process to be noncontiguous
Avoids external fragmentation
Uses frames and pages
Breaking physical memory into fixed-sized blocks called frames (size is a power of 2, between 512 bytes and 16 Mbytes)
Breaking logical memory into blocks of the same size called pages
Keeps track of all free frames

Paging: Address Translation Scheme

Division of an address from the CPU:
- Page number (p) – used as an index into a page table which contains base address of each page in the physical memory
- Page offset (d) – combined with base address to define the physical memory address that is sent to the memory unit

Paging Hardware

Hardware support for Paging

Paging Model of Logical and Physical Memory

Example: logical memory has 4-byte page size and physical memory has 32 bytes (8 pages)

Free Frames

Implementation of free frames before and after allocation

Page Table - Implementation

PTBR (Page-Table Base Register) – points to the page table
PTLR (Page Table Length Register) – specifies the size of the page table
TLB (Translation Look-aside Buffers) - memory cache used to lessen the time to access a user memory location
Also called Associative Memory
Two Memory Accesses for data / instructions:
- Page table
- Data / instruction

Internal Fragmentation on Paging

Example: page size = 2,048 (size = 2n), size of process = 58,800 bytes, no. of pages = 28 and excess bytes = 1,456

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

Learn about swapping mechanism in operating systems, including swapping policies and backing store. Also, understand dynamic linking and its application in shared libraries.