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The Disk II Floppy Disk Subsystem, often rendered as Disk ][, is a 5¼-inch floppy disk drive designed by Steve Wozniak. It went on sale in June 1978 at a retail price of US$495 for pre-order; it was later sold for $595 including the controller card (which can control up to two drives) and cable. The Disk II was designed specifically for use with the Apple II personal computer family to replace the slower cassette tape storage. The original controller formatted disks at 13 sectors per track, yielding a capacity of 113KB per diskette. An controller upgrade introduced in 1980 increased this to 16 sectors and 140KB total capacity.
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