In
computing (specifically data transmission and
data storage), a
block, sometimes called a
physical record, is a sequence of
bytes or
bits, usually containing some whole number of
records, having a maximum length, a
block size. Data thus structured are said to be
blocked. The process of putting data into blocks is called
blocking, while
deblocking is the process of extracting data from blocks. Blocked data is normally stored in a
data buffer and read or written a whole block at a time. Blocking reduces the
overhead and speeds up the handling of the data-stream. For some devices such as magnetic tape and
CKD disk devices blocking reduces the amount of external storage required for the data. Blocking is almost universally employed when storing data to 9-track
magnetic tape, to NAND
flash memory, and to rotating media such as
floppy disks,
hard disks, and
optical discs.