<Tr> <Th> Weight </Th> <Td> 7 lbs (3.2 kg) </Td> </Tr> <Tr> <Th> </Th> <Td> 3.1 x 9.7 x 10.5 inches (7.9 x 25 x 27 cm) </Td> </Tr> <P> The Macintosh Hard Disk 20 was the first hard drive developed by Apple Computer specifically for use with the Macintosh 512K . Introduced on September 17, 1985, it was part of Apple's long awaited solution toward completing the Macintosh Office (a suite of integrated business hardware & software) announced in January 1985 . It would be over a year more before Apple would release the file server software AppleShare that would link all of the hardware together . By that time the SCSI interface introduced on the Macintosh Plus in January 1986, would accommodate far faster and more efficient hard drives, rendering the Hard Disk 20 virtually obsolete . </P> <P> The Hard Disk 20 (or HD20, as it was known colloquially) contained a 20 MB 3.5" Rodime hard disk which provided over 50 times the data storage of the stock 400 kB disk drive . At the time when the average file size was around 10 - 20 kB and due to the vast number of those files the HD 20 could contain, Apple's original Macintosh File System, which did not allow for directories, would have made organizing those files unwieldy . Therefore, Apple introduced it with a new System and Finder update which included the brand new Hierarchical File System allowing the user to better organize files on such a large volume . As a result, only the Macintosh 512K could access it; the original Macintosh 128K did not have enough RAM to load the new file system . In fact, even for the Macintosh 512K to use the drive, it required an additional file in the System Folder on a special startup disk which added additional code into memory during startup . An ingenious startup routine also allowed the Mac to check for the presence of a System file on the Hard Disk, switch over to it and eject the startup disk . Unfortunately, the HD 20 could not be used as a startup disk directly without first loading the code from the floppy disk drive . With the release of the Macintosh Plus and the Macintosh 512Ke, both containing the upgraded 128 kB ROM which contained the additional code, the HD 20 could finally be used alone as a startup disk . </P>

When was the first hard disk is made available for macintosh computers