讲座3文件系统.pdfVIP

File Systems Haibo Chen Slides of “Afile is a NOT file” from the papers authors. Parts of File-related slides form CS- 4513 D-term 2008 of WPI. 1 File File Systems A (potentially) large amount of information or data that lives a (potentially) very long time Often much larger than the memory of the computer Often much longer than any computation Sometimes longer than life of machine itself (Usually) organized as a linear array of bytes or blocks Internal structure is imposed by application (Occasionally) blocks may be variable length (Often) requiring concurrent access by multiple processes Even by processes on different machines! 2 File Systems and Disks User view File is a named, persistent collection of data OS file system view File is collection of disk blocks — i.e., a container File System maps file names and offsets to disk blocks Introduction to File Systems CS-4513 D-term 2008 3 Fundamental ambiguity Is the file the “container of the information”or the “information”itself? Almost all systems confuse the two. Almost all people confuse the two. Introduction to File Systems CS-4513 D-term 2008 4 Example –Suppose that you me a • Later, how do either of us know that we are using the same version of the ? • Windows/Outlook/Exchange/MacOS: • Time-stamp is a pretty good indication that they are • Time-stamps p on copy, drag and drop, transmission via , etc. • Unix/Linux • By default, time-stamps not p