Fixed block architecture

Fixed Block Architecture (FBA) is a disk layout in which each addressable record (block) on disk is of the same size. The term fell out of use, since nearly all modern disk drives use this principle, termed logical block addressing and usually having a constant addressable block size of 512 bytes.


Count Key Data

Main article: Count Key Data

IBM mainframe systems' disks, called DASD, had traditionally been addressable in a form MBBCCHHR (extent-Bin-Cylinder-Head-Record,[1] which was capable of storing records of varied size. Besides direct addressing, programmers were able to search by key, using the underlying count-key-data (CKD) structure.


In IBM's implementation, a disk drive that stores data in blocks of fixed size.[2]

Various IBM FBA devices featured block sizes of 270,[3]:62366,[4]:11 512, 1024, 2048, and 4096.

Hard Disk Drives

Main article: Hard disk drive

Modern HDD serial interfaces, i.e., Serial ATA (SATA) or Serial attached SCSI (SAS) use logical block addressing.


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