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Present By:- aBhay Panchal What is Operating System
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| bet | 5/6 | | Sana | 01.02.2024 | | Hajmi | 0,7 Mb. | | #150097 |
Bog'liq Unix - The kernel must gather the page addresses of data at primary memory to be swapped out
- Kernel copies the physical memory assigned to a process to the allocated space on the swap device
- The mapping between physical memory and swap device is kept in page
table entry
Demand Paging - Not all page of process resides in memory Locality
- When a process accesses a page that is not part of its working set, it incurs a page fault.
- The kernel suspends the execution of the process until it reads the page
into memory and makes it accessible to the process
Data Structure for Demand Paging File Management in UNIX
In UNIX there are three basic types of files:
- Ordinary Files: An ordinary file is a file on the system that contains data, text, or program instructions. In this tutorial, you look at working with ordinary files.
- Directories: Directories store both special and ordinary files. For users familiar with Windows or Mac OS, UNIX directories are equivalent to folders.
- Special Files: Some special files provide access to hardware such as hard drives, CD-ROM drives, modems, and Ethernet adapters. Other special files are similar to aliases or shortcuts and enable you to access a single file using different names.
File Management in UNIX
File Access Modes:
- Read: Grants the capability to read ie. view the contents of
the file.
- Write:Grants the capability to modify, or remove the content of the file.
- Execute:User with execute permissions can run a file as a program.
File Management in UNIX
Directory Access Modes:
- Read: Access to a directory means that the user can read the contents. The user can look at the filenames inside the directory.
- Write: Access means that the user can add or delete files to the contents of the directory.
- Execute: Executing a directory doesn't really make a lot of sense so think of this as a traverse permission.
A user must have execute access to the bin directory in order to execute or command.
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