A transaction is
a series of changes that must either all be successful, or none be successful.
For example, if one moves a file from one location to another (cut and paste), the new file directory entry
must be written and the old file directory entry must be erased. Both actions must occur, or neither must occur.
A journaling file system first writes any intended changes to a ???write-ahead??? log file. Then it makes the
required changes to the file system. If the changes to the file system fail for some reason (e.g., a total system
failure at just the wrong moment), the file system can either recover the changes by redoing the transaction, or
roll back the changes to the original state.
The Windows NT File System (NTFS) incorporates journaling features, and so does Sun??™s UFS and Apple??™s
Mac OS X. There are also several journaling file systems available for Linux.
SUMMARY
Operating systems are programs designed to make the use of the computer hardware easier, more efficient,
and more secure. They manage the scheduling of processes, the allocation of memory and other resources to
processes, and all input and output of data. In addition, operating systems provide a file system for managing
programs and data, and various system software utilities for facilitating program development and execution.
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