D686: Operating Systems for Computer Scientists (chapter 13)

block

A self-contained unit of work. The smallest physical storage device storage unit, typically 512B or 4KB. In the Grand Central Dispatch Apple OS scheduler, a language extension that allows designation of a section of code that can be submitted to dispatch queues.

file system

The system used to control data storage and retrieval; provides efficient and convenient access to storage devices by allowing data to be stored, located, and retrieved easily.

I/O control

A logical layer of the operating system responsible for controlling I/O, consisting of device drivers and interrupt handlers.

basic file system

A logical layer of the operating system responsible for issuing generic commands to the I/O control layer, such as "read block x," and also buffering and caching I/O.

file-organization module

A logical layer of the operating system responsible for files and for translation of logical blocks to physical blocks.

logical file system

A logical layer of the operating system responsible for file and file-system metadata management; maintains the FCBs.

file-control block (FCB)

A per-file block that contains all the metadata about a file, such as its access permissions, access dates, and block locations.

inode

In many file systems, a per-file data structure holding most of the metadata of the file. The FCB in most UNIX file systems.

UNIX file system (UFS)

An early UNIX file systems; uses inodes for FCB.

extended file system

The most common class of Linux file systems, with ext3 and ext4 being the most commonly used file system types.

boot control block

A storage block of data containing information needed by the system to boot from the volume containing the block.

boot block

A block of code stored in a specific location on disk with the instructions to boot the kernel stored on that disk. The UFS boot control block.

partition boot sector

The NTFS boot control block

volume control block

A per-volume storage block containing data describing the volume

superblock

The UFS volume control block.

master file table

The NTFS volume control block

mount table

An in-memory data structure containing information about each mounted volume. It tracks file systems and how they are accessed

system-wide open-file table

A kernel in-memory data structure containing a copy of the FCB of each open file, as well as other information.

per-process open-file table

A kernel in-memory per-process data structure containing pointers to the system-wide open-file table, as well as other information, for all files the process has open.

file descriptor (fd)

UNIX open-file pointer, created and returned to a process when it opens a file.

file handle

Windows name for the open-file file descriptor.

free-space list

In file-system block allocation, the data structure tracking all free blocks in the file system.

bitmap

A string of n binary digits that can be used to represent the status of n items. The availability of each item is indicated by the value of a binary digit: 0 means that the resource is available, while 1 indicates that it is unavailable (or vice-versa).

bit vector

A string of n binary digits that can be used to represent the status of n items. The availability of each item is indicated by the value of a binary digit: 0 means that the resource is available, while 1 indicates that it is unavailable (or vice-versa).

ZFS

Oracle file system, created by Sun Microsystems, with modern algorithms and features and few limits on file and device sizes.

metaslabs

Chunks of blocks. In ZFS, a pool of storage is split into metaslabs for easier management.

contiguous allocation

a method where all blocks of a file are stored next to each other on disk

external fragmentation

when free memory is scattered in small pieces, not enough to satisfy a large request even though the total free space is sufficient

extent

a continuous block of storage space added to already allocated space, linked by a pointer

linked allocation

a method where each file is a linked list of disk blocks, which may be scattered across the storage device

cluster

in Windows storage, a group of disk sectors combined for better I/O performance

file-allocation table (FAT)

a method used by MS-DOS where a table at the start of each volume keeps track of disk blocks

indexed allocation

storing all block pointers in one or more index blocks for efficient direct access

index block

in indexed allocation, a block that holds pointers to the file's data block

direct blocks

in UFS, blocks that contain pointers directly to data blocks

indirect block

in UFS, a block that points to direct blocks, which in turn point to data blocks

single indirect block

in UFS, a block that contains pointers to direct blocks, which point to data blocks

double indirect block

in UFS, a block with pointers to single indirect blocks, which then point to data blocks

triple indirect block

in UFS, a block containing pointers to double indirect blocks, which point to single indirect blocks, leading to data blocks