B

Block Device
A special device file that represents a disk, disk partition, virtual disk, or other random-access storage area for bytes. Although it usually represents a huge number of bytes, the special device file itself takes up little or no actual space on the volume it is found in, much like a symlink. Block devices are usually found in /dev and its subdirectories.

For instance, on a Linux system, /dev/hda represents the first IDE disk, if any, and /dev/sda represents the first SCSI disk, if any. If you are the superuser, you can read and write these as if they were really large files, although writing will probably cause big trouble, unless you know exactly what you are doing. /dev/hda5 represents the 5th partition on the disk /dev/hda, and it is also a block device, although it represents just a part of hda, and it might not even exist, depending on how hda is partitioned.

OFten there is a volume (filesystem) mounted on a block device. That is, the file system software in the operating system keeps the data in a block device organized into files and directories. You can then run your programs on your files. You can see which volumes live on which block devices in your particular computer system by displaying the Host Window in Interrogator.


See also man sd, man mkfs, man mount, man format, man scsi, man fdisk (86 cpu and Sparc cpu systems), man pdisk (PowerPC systems), man dkio (Solaris),

byte
A number in the computer composed of 8 bits. A byte can assume 256 different values.

An Ascii text file uses one byte per character. Storing more complicated numbers or kinds of data requires more bytes; for instance, a number in a spreadsheet program typically uses 8 bytes, and a directory file might use 512 or 4096 bytes.


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