Term
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Definition
| Issue generic commands to the appropriate disk driver to read and write physical blocks on the disk. |
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Term
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Definition
| A translator from high-level commands to low-level, hardware-specific instructions that are used by the hardware controller. |
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Term
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Definition
| A block that contains volume details such as the number of blocks in a partition, size of the blocks, free blocks count and free-block pointers. |
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Term
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Definition
| Contains information about each mounted volume. |
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Term
| System-Wide Open-File Table |
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Definition
| Contains the FCB of each open file as well as other information. |
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Term
| Per-Process Open-File Table |
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Definition
| Contains a pointer to the appropriate entry in the system-wide open-file table. |
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Term
| File Handle/ File Description |
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Definition
| A pointer to the appropriate entry in the per-process file-system table. |
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Term
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Definition
| Dividing a disk into multiple parts that may be used separately from each other. |
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Term
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Definition
| Contains the operating system kernel and sometimes other system files. Mounted at boot time. |
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Term
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Definition
| Separates file-system-generic operations from their implementation by defining a clean VFS interface. Sever implementations for the VFS interface may coexist on the same machine, allowing transparent access to different types of file systems mounted locally. Provides a mechanism for uniquely represent a file throughout a network. |
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Term
| Linear List (Directory Implementation) |
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Definition
| A list of file names with pointer to the data blocks. Simple to implement but slow to execute. Biggest disadvantage is that to create a new file, a linear search must be done every time. |
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Term
| Hash Table (Directory Implementation) |
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Definition
| A linear list stores the directory entries but a hash table takes a value computed from the file name and returns a pointer to the file name in the linear list. Decreases directory search time. |
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Term
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Definition
| The way that we allocate space on a disk for files. |
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Term
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Definition
| Each file occupies a set of contiguous blocks on the disk. Biggest downside is the fact that finding space for a new file is difficult. |
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Term
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Definition
| Solves all problems of contiguous allocation. Each file is a linked list of disk blocks, and the block may be scattered all over the disk. Directory contains a pointer to the first and last block of the file. Only effective for sequential-access files. If we need a block in the middle of the file we need to go through the file until we reach it. |
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Term
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Definition
| A group of blocks that are placed close together. Reduces wasted space and increases read and write time. |
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Term
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Definition
| A section of disk at the beginning of each volume is set aside to contain the table. The table has one entry for each disk block and is indexed by block number. The FAT is used in much the same way as a linked list. The directory entry contains the block number of the first block of the file. The table entry indexed by that block number contains the block number of the next block in the file. |
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Term
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Definition
| Without FAT linked allocation does not support efficient direct access since the pointer to the blocks are scattered with the blocks themselves all over the disk and must be retrieved in order. Indexed allocation solves this by bringing all pointers into one location, the index block. Each file has its own index block which is an array of the disk-block addresses. |
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Term
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Definition
| Each file has one of these. Contains an array of the disk-block addresses for the file. |
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Term
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Definition
| The index block points to a set of second-level index blocks, which point to the file blocks. The access a block, the operating system uses the first-level index block to find a second-level index block and then uses this block to find the desired block of the file. |
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Term
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Definition
| A list that keeps track of all free disk space. This speeds up the time it takes to find space for a new file. |
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Term
| Bit Vector Free-Space Implementation |
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Definition
| A bitmap is used to represent all blocks. Each bit is a block and is the bit is one then it is free, if it is zero then it is allocated. |
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Term
| Linked List Free-Space Implementation |
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Definition
| Links together all the free blocks by putting a pointer to the next free block in the free block and having the pointer to the first one in the super block. |
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Term
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Definition
| Refers to writing files. Removes a page from the buffer as soon as the next page is request since previous pages are not likely to be used again and thus they waste buffer space. For read-ahead a requested page and several pages after it are read and cached. |
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Term
| File System Consistency Check |
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Definition
| A program that runs at reboot time to check for and correct disk inconsistencies. Disk inconsistencies can arise when the computer crashes and the cache doesn't have time to be written to the disk. |
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Term
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Definition
| An entry into a log is made every time a file is modified. If the system crashes the log file will contain zero or more transactions. Any transactions it contains were not completed to the file system even though they were committed by the operating system. The transactions can be executed from the pointer until the work is complete so that the file-system structure remain consistent. |
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Term
| Transaction (In a Log-Based File System) |
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Definition
| Each set of operations for performing a specific task. |
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Term
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Definition
| Whenever a file is changed in some way or its metadata is changed, a transaction occurs. |
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