Memory Management Using Paging: A Comprehensive Guide
As a computer engineer, one of the most important concepts to understand is memory management. Memory management is the process of controlling and coordinating computer memory, assigning portions called blocks to various running programs to optimize overall system performance.
One way to manage memory is through a technique called paging. Paging is a method of memory management that allows the physical memory of a computer to be used more efficiently by breaking it up into smaller pieces called pages.
When a program needs to access data in memory, the operating system checks to see if the data is already stored in a page in physical memory. If it is, the operating system can quickly retrieve the data for the program. If the data is not already in memory, the operating system will bring it into memory by loading it from secondary storage (such as a hard drive) into an available page.
Paging helps to make the most of the available physical memory by allowing multiple programs to share it. This means that even if there isn’t enough physical memory to store all of the data for all of the programs running on a computer at once, the operating system can still keep everything running smoothly by swapping pages in and out of memory as needed.
Paging also helps to protect programs from one another. Each program is given its own set of pages in memory, so one program cannot accidentally overwrite the data of another program.
In order to use paging effectively, it’s important to understand some key concepts and formulas. Here are some important formulas related to paging:
- Page size = Physical memory size / Number of pages
- Number of frames = Physical memory size / Page size
- Number of pages = Virtual memory size / Page size
- Page number = Virtual address / Page size
- Offset = Virtual address % Page size
- Physical address = (Frame number * Page size) + Offset
Virtual memory is a technique that allows a computer to use more memory than it physically has available by using secondary storage (such as a hard drive) to store data that isn’t currently being used. When a program needs to access data that isn’t currently stored in physical memory, the operating system will bring it into memory by loading it from secondary storage into an available page.
A virtual address is an address used by a program to access data in virtual memory. The operating system translates virtual addresses into physical addresses using a page table, which maps virtual page numbers to physical frame numbers.
In addition to these basic concepts and formulas, there are many other factors and techniques involved in effective paging. For example, when there isn’t enough physical memory to store all of the pages needed by all of the programs running on a computer, the operating system must decide which pages to keep in memory and which to swap out to secondary storage. This process is known as page replacement, and there are many different algorithms and strategies that can be used to make these decisions.
Another important factor to consider when using paging is the size of the pages. The page size can have a big impact on the performance of the system, as it determines how much data can be stored in each page and how many pages are needed to store all of the data for a program. Choosing the right page size requires balancing several trade-offs, such as the overhead of managing many small pages versus the waste of space when using fewer large pages.
Solved example:
Consider a machine with 64 MB physical memory and a 32 bit virtual address space. If the page size is 4 KB, what is the approximate size of the page table?
1. 16 MB
2. 8 MB
3. 2 MB
4. 24 MB
Solution-
Given-
· Size of main memory = 64 MB
· Number of bits in virtual address space = 32 bits
· Page size = 4 KB
We will consider that the memory is byte addressable.
Number of Bits in Physical Address-
Size of main memory
= 64 MB
= 226 B
Thus, Number of bits in physical address = 26 bits
Number of Frames in Main Memory-
Number of frames in main memory
= Size of main memory / Frame size
= 64 MB / 4 KB
= 226 B / 212 B
= 214
Thus, Number of bits in frame number = 14 bits
Number of Bits in Page Offset-
We have,
Page size
= 4 KB
= 212 B
Thus, Number of bits in page offset = 12 bits
So, Physical address is-
Process Size-
Number of bits in virtual address space = 32 bits
Thus,
Process size
= 232 B
= 4 GB
Number of Entries in Page Table-
Number of pages the process is divided
= Process size / Page size
= 4 GB / 4 KB
= 220 pages
Thus, Number of entries in page table = 220 entries
Page Table Size-
Page table size
= Number of entries in page table x Page table entry size
= Number of entries in page table x Number of bits in frame number
= 220 x 14 bits
= 220 x 16 bits (Approximating 14 bits ≈ 16 bits)
= 220 x 2 bytes
= 2 MB
Thus, Option © is correct.
