Hard Disk 20 M0135

The HD20 connects to the DB-19 external floppy disk drive port of a Macintosh 512K, Macintosh 512Ke, Macintosh Plus or Macintosh SE, but it uses an entirely different communication protocol from a floppy drive. It cannot be used with Macintosh 128K.

Since the Macintosh 512K with 64K ROMs does not support HFS a floppy disk is required for system startup. The Macintosh Plus, or other computers that have been upgraded with the 128K ROMS, can boot directly from the HD20.

3.5" HH Rodime 552 hard disk.
Formatted capacity 20,769,280 bytes.
2744 rpm, average seek time 85 ms.
Drive startup time 15 seconds.
Drive spin-down time 25 seconds.
4 data surfaces, 1 head per surface.
305 tracks per surface, spacing 600 tracks per inch.
32 sectors per track, 9760 per surface.
Transfer rate from disk 7.5 Mbits/second.
Transfer rate to the computer 500 Kbits/second.
Expansion port for additional floppy or hard disk drive.
AC mains power input 100 - 240v, later 85 - 270v, 35W.

A test utility was provided that can perform a non-destructive test of the disk in about 15 minutes, and an extended diagnostic was available that exercises the disk for 24 hours.

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