COP4600 - FINAL EXAM Exam Questions With Verified Solutions

COP4600 - FINAL EXAM Exam Questions With Verified Solutions What is a path? - answerA path is a sequence of directories used to reference a file. They can be relative or absolute. Why do we need file systems? - answer1. Locate free storage space 2. Store information in a persistent way (survives process termination) 3. Allow more than one process to access the information store concurrently 4. Find information by human-accessible identifiers 5. Protect data from unauthorized use 6. Identifying types of data stored and programs that can read the data How are directories implemented? - answerDirectories can be implemented in-line or via reference - Variable attribute/name size Why do we mount filesystems? - answerWe mount a file system to make it accessible to programs through the operating system. Challenges with mounting filesystem? - answerWhere will the root of the file system appear to the user? How should different devices be presented to the user? When accessing a file system on a device, we need to know? - answerboot block, Filesystem type/organization (super block), and where the root directory is What is in the filesystem superblock? - answerThe file system superblock holds information about its type, format, and organization What happens when you make a mounting call in Unix - answerCopies the Superblock from the disk being mounted to the superblock table in main memory. Sets pointers in the directory inode to FS mounted What are the approaches to file allocation? - answer1. Contiguous allocation (all-in-a-row) 2. Linked list allocation (block) 3. Chained table allocation (FAT) 4. Indexed allocation (index nodes) 5. Chained indexed allocation (index + linked list) 6. Multi-level indexed allocation (tree structure) Hardware is an abstraction that provides two main operations - answer1. Read block at index "k" 2. Write block at index "k" 3. Allocate and Deallocate Contiguous allocation - answerDEFINITION: A file's contents are stored purely in order on the drive CONS: suffers from external fragmentation, because it is a contiguous approach to system memory Linked List Allocation - answerDEFINITION: Each block holds a pointer to the next. Requires iteration through drive blocks (drive accesses) for random access CONS: Problematic in large files; App has to iterate through each node. Chained Table Allocation - answerDEFINITION: Chain store the linked list as a table in memory to minimize disk access. It is called a File Allocation Table (FAT) Indexed Allocation - answerDEFINITION: Indexed allocation stores locations of each block in an index block referenced by the file control block CONS: A pure index system limits file size Multi-level Indexed Allocation - answerUse direct and indirect blocks to increase maximum file size Chained Indexed Allocation - answerDirect blocks with an additional indirect pointer What are Inodes? - answer1. Index Nodes 2. Store file block information, along with some block pointers - but are usually smaller (128B or 256B (T/F) Does a bigger block size have a better data rate? - answerTrue (T/F) Does a bigger block size have a good disk space utilization? - answerFalse What happens with a worse disk space utilization? - answerInternal Fragmentation (T/F) Does a smaller block size have a better data rate? - answerFalse, lower data rate (T/F) Does a smaller block size have a good disk space utilization? - answerTrue MS-DOS File System - answer1. Maximum partition size for different block sizes. 2. The empty boxes represent forbidden combinations. How do you keep track of a free block? - answer(a) Storing the free list on a linked list (b) A bitmap What is the file control block (FCB)? - answerWhere the attributes and location information of a file are stored. It is often distributed across the file system, meaning that they are within directories or reachable from them Common file attributes in an FCB - answerOwner, group, permissions, length, file type, read-lock, write-lock, date created, date modified, data accessed True or False: In the process of creating a file, a link to the directory is created - answerTrue True of False: a deletion involves the unlinking of a file to a directory - answerTrue What is a file's link count? - answerA counter that tracks the number of links to that file A file's link count is __________ when a file is opened to prevent deletion mid-operation. - answerincremented True or False: In Linux, a file can be added to (shared by) exactly one directory via a file system link - answerFalse: It can be added to more than one directory Hard link vs soft link - answerA hard link holds the reference to the inode of the target file (only within same file system). A soft link holds the path of the target file (may span file systems, but can suffer from link rot, which is when a file is moved and the soft link becomes invalid). What are the two types of links? - answerRegular (hard) and symbolic (soft) When can linking/unlinking fail? - answerSometimes linking/unlinking can fail due to permissions, existence, and other issues (space) When is a file considered deleted? - answerWhen its link count reaches 0 What is a file directory? - answerA directory/folder is a special file type that holds (part of) the File Control Block about other files. A directory file is usually marked as such via an attribute in the FCB for the file Layouts of directories - answerSingle shared directory, one directory per user, freeform/nested