In computing (specifically data transmission and data storage), block is a sequence of bytes or bits, having a nominal length (a block size). Data thus structured is said to be blocked. The process of putting data into blocks is called blocking. Blocking is used to facilitate the handling of the data-stream by the computer program receiving the data. Blocked data is normally read a whole block at a time. Blocking is almost universally employed when storing data to 9-track magnetic tape, to rotating media such as floppy disks, hard disks, optical discs and to NAND flash memory.
Most file systems are based on a block device, which is a level of abstraction for the hardware responsible for storing and retrieving specified blocks of data, though the block size in file systems block may be multiple of the physical block size. In classical file systems, a single block may only contain a part of a single file. This leads to space inefficiency due to internal fragmentation, since file lengths are often not multiples of block size, and thus the last block of files will remain partially empty. This will create slack space, which averages half a block per file. Some newer file systems attempt to solve this through techniques called block suballocation and tail merging.
Block storage is normally abstracted by a file system or database management system for use by applications and end users. The physical or logical volumes accessed via block I/O may be devices internal to a server, direct attached via SCSI or Fibre Channel, or distant devices accessed via a storage area network (SAN) using a protocol such as iSCSI, or AoE. Database management systems often use their own block I/O for improved performance and recoverability as compared to layering the DBMS on top of a file system.On the internet, a block is a technical measure intended to restrict access to information or resources.
Blocks should not be confused with bans, although they are often used to enforce a ban.
A blocked user may have certain privileges revoked, such as the ability to publish content or communicate with other users, or they may be completely unable to access the service in question. Blocks can apply to individual user accounts or ranges of IP addresses. In most cases, individual services and websites set their own blocking policies, and a block issued by one will not apply on any others.
Most online communication tools, including chat software and social networking sites, allow users to block other users from contacting them. Such a block normally has no effect on the subject's access to any other part of the service.
Wikis block editors who edit unacceptably. There may sometimes be genuine uncertainty as to what is a misguided attempt to improve a wiki and what is deliberate vandalism though usually vandalism is clear. Those who have power to block are called sysops. Different wikis have different criteria to decide what is acceptable. For example an editor who edited Wikipedia the way Uncyclopedia is edited and refused to stop after warnings would certainly face steadily increasing blocks. Reactions to Wiki blocks vary. Being blocked from a wiki is a bit like being banned from a Social club. Some blocked users are not concerned and go off to have fun somewhere else on the Web. Other blocked users can be quite upset. There are frequent complaints about alleged unfairness of blocks. Sysops who want to be fair may find this difficult because the Block Dialogue Box they use shows only the case for the prosecution and not the case for the defence.
Answered by
Kaushal
, an ibibo Advisor,
at
3:19 PM on April 14, 2008
