A CDE Definition
(1) A group of disk or tape records that is stored and transferred as a single unit. On a CD, a block consists of 98 frames of 33 bytes for a total of 3,234 bytes, or 1/75th of a second. See block level.
(2) A group of bits or bytes that is transmitted or processed as a single unit.
(3) A group of text characters that has been marked for moving, copying, saving or other operation.
(4) A rectangular group of pixels that are processed as a unit.
(5) A group of program statements that are treated as a unit based on the results of a comparison.
Reading and writing a disk at the physical level. The disk controller in every computer and server reads and writes the disks at the block level. In storage area networks (SANs), where the disks are in cabinets external to the server, read/write access is also at the block level.
Block Level Vs. File Level
An application accesses data by file name (logical), which is translated into block level (physical) for reading and writing by the operating system's file system.
Users always deal with data at the file level; however, database and network administrators may get involved at the block level, because they can stipulate where data are physically stored for performance issues.
NAS vs. SAN
Although a stand-alone unit with its own disks, a network attached storage (NAS) device has its own file system for file level access. Because a SAN uses block level access and has no file system with its associated overhead, a SAN is much faster than a NAS. See SAN, NAS and file system.
Remote Block Level Access
With IP storage, block level access can be extended via the IP protocol to remote locations. See SAN and IP storage.
Blocks Are Also Logical
Modern drives maintain their own tables of good and bad sectors and remap requests on the fly. As a result, the physical block reads and writes are translated by the drive into actual sector reads and writes, making the block access somewhat like a logical request, rather than 100% physical.
Before/After Your Search Term
|blind drop||block access|
|blind spot monitoring||block addressable|
|BLOB||block level storage|
Terms By Topic
Click any of the following categories for a list of fundamental terms.