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.