History
A "block", a contiguous number of bytes, is the minimum unit of memory that is read from and written to a disk by a disk driver. The earliest disk drives had fixed block sizes (e.g. the IBM 350 disk storage unit (of the late 1950s) block size was 100 6 bit characters) but starting with the 1301 IBM marketed subsystems that featured variable block sizes: a particular track could have blocks of different sizes. The disk subsystems on the IBM System/360 expanded this concept in the form of Count Key Data (CKD) and later Extended Count Key Data (ECKD); however the use of variable block size in HDDs fell out of use in the 1990s; one of the last HDDs to support variable block size was the IBM 3390 Model 9, announced May 1993
Modern hard disk drives such as Serial attached SCSI (SAS) and Serial ATA (SATA) drives, appear at their interfaces as a contiguous set of fixed-size blocks; for many years 512 bytes long but beginning in 2009 and accelerating through 2011, all major hard disk drive manufacturers began releasing hard disk drive platforms using the Advanced Format of 4096 byte logical blocks.
Floppy disks generally only used fixed block sizes but these sizes were a function of the host's OS and its interaction with its controller so that a particular type of media (e.g., 5ΒΌ-inch DSDD) would have different block sizes depending upon the host OS and controller.
Optical disks generally only use fixed block sizes.
Read more about this topic: Disk Formatting
Famous quotes containing the word history:
“To care for the quarrels of the past, to identify oneself passionately with a cause that became, politically speaking, a losing cause with the birth of the modern world, is to experience a kind of straining against reality, a rebellious nonconformity that, again, is rare in America, where children are instructed in the virtues of the system they live under, as though history had achieved a happy ending in American civics.”
—Mary McCarthy (1912–1989)
“History is more or less bunk. It’s tradition. We don’t want tradition. We want to live in the present and the only history that is worth a tinker’s damn is the history we make today.”
—Henry Ford (1863–1947)
“Free from public debt, at peace with all the world, and with no complicated interests to consult in our intercourse with foreign powers, the present may be hailed as the epoch in our history the most favorable for the settlement of those principles in our domestic policy which shall be best calculated to give stability to our Republic and secure the blessings of freedom to our citizens.”
—Andrew Jackson (1767–1845)