The innermost zone has 8 sectors per track, the next zone 9 sectors per track, and so on the outermost zone has 12 sectors per track. This is called the 'Zoned CAV' system there are five zones of 16 tracks each.

The disk speeds up when accessing the inner tracks and slows down when accessing the outer ones. However, Apple's custom interface uses Group Coded Recording (GCR) and a unique format which puts fewer sectors on the smaller inner tracks and more sectors on the wider outer tracks of the disk. The standard on all of these was MFM with 80 tracks and 9 sectors per track, giving 360 KB per disk. Apple's Hard Disk 20 could accommodate an additional daisy-chained hard drive as well as an external floppy disk.ģ.5-inch single-sided floppies had been used on several microcomputers and synthesizers in the early 1980s, including the Hewlett Packard 150 and various MSX computers. The Macintosh could only support one external drive, limiting the number of floppy disks mounted at once to two, but both Apple and third party manufacturers developed external hard drives that connected to the Mac's floppy disk port, which had pass-through ports to accommodate daisy-chaining the external disk drive. However, confusingly all of these drives were labelled identically. Although very similar to the 400-kilobyte drive which newly replaced Apple's ill-fated Twiggy drive in the Lisa, there were subtle differences relating mainly to the eject mechanism. The drive case was designed to match the Macintosh and included the same 400-kilobyte drive (a Sony-made 3 + 1⁄ 2-inch single-sided mechanism) installed inside the Macintosh. Bill Fernandez was the project manager who oversaw the design and production of the drive. However, it did not actually ship until May 4, 1984, sixty days after Apple had promised it to dealers. The original Macintosh External Disk Drive (M0130) was introduced with the Macintosh on January 24, 1984.

Apple produced only one external 3 + 1⁄ 2-inch drive exclusively for use with the Apple II series called the Apple UniDisk 3.5. The Macintosh external drives were the first to widely introduce Sony's new 3 + 1⁄ 2-inch rigid disk standard commercially and throughout their product line. Though Apple had been producing external floppy disk drives prior to 1984, they were exclusively developed for the Apple II, III and Lisa computers using the industry standard 5 + 1⁄ 4-inch flexible disk format. Later, Apple would unify their external drives to work cross-platform between the Macintosh and Apple II product lines, dropping the name 'Macintosh' from the drives. The Macintosh External Disk Drive is the original model in a series of external 3 + 1⁄ 2-inch floppy disk drives manufactured and sold by Apple Computer exclusively for the Macintosh series of computers introduced in January 1984.

Macbook support external hard disk