The Macintosh Hard Disk 20 was the first

hard drive A hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electro-mechanical data storage device that stores and retrieves digital data using magnetic storage with one or more rigid rapidly rotating platters coated with magnet ...

developed by

Apple Computer Apple Inc. is an American multinational technology company headquartered in Cupertino, California, United States. Apple is the largest technology company by revenue (totaling in 2021) and, as of June 2022, is the world's biggest company b ...

specifically for use with the

Macintosh 512K The Macintosh 512K is a personal computer that was designed, manufactured and sold by Apple Computer from September 1984 to April 1986. It is the first update to the original Macintosh 128K. It was virtually identical to the previous Macint ...

. Introduced on September 17, 1985, it was part of Apple's long-awaited solution toward completing the

Macintosh Office The Macintosh Office was an effort by Apple Computer to design an office-wide computing environment consisting of Macintosh computers, a local area networking system, a file server, and a networked laser printer. Apple announced 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 Small Computer System Interface (SCSI, ) is a set of standards for physically connecting and transferring data between computers and peripheral devices. The SCSI standards define commands, protocols, electrical, optical and logical interface ...

interface introduced on the

Macintosh Plus The Macintosh Plus computer is the third model in the Macintosh line, introduced on January 16, 1986, two years after the original Macintosh and a little more than a year after the Macintosh 512K, with a price tag of US$2,599. As an evolutiona ...

in January 1986, would accommodate far faster and more efficient hard drives, rendering the Hard Disk 20 virtually obsolete.

Features

The Hard Disk 20 (or ''HD20'', as it was known colloquially) contains a 20 MB 3.5"

Rodime Rodime was an electronics company specialising in hard disks, based in Glenrothes, Scotland. It was founded in 1979 by several Scottish and American former employees of Burroughs Corporation and listed on the London Stock Exchange in 1986, bec ...

hard disk A hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electro-mechanical data storage device that stores and retrieves digital data using magnetic storage with one or more rigid rapidly rotating platters coated with magnet ...

which provides 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 HD20 can contain, Apple's original

Macintosh File System Macintosh File System (MFS) is a volume format (or disk file system) created by Apple Computer for storing files on 400K floppy disks. MFS was introduced with the original Apple Macintosh computer in January 1984. MFS is notable both for ...

, which does not allow for directories, made organizing those files unwieldy. Therefore, Apple introduced it with a new

System A system is a group of Interaction, interacting or interrelated elements that act according to a set of rules to form a unified whole. A system, surrounded and influenced by its environment (systems), environment, is described by its boundaries, ...

and Finder update which include the

Hierarchical File System Hierarchical File System (HFS) is a proprietary file system developed by Apple Inc. for use in computer systems running Mac OS. Originally designed for use on floppy and hard disks, it can also be found on read-only media such as CD-ROMs. HFS ...

allowing the user to better organize files on such a large volume. As a result, only the

can access it; the original

Macintosh 128K The Apple Macintosh—later rebranded as the Macintosh 128K—is the original Apple Inc., Apple Macintosh personal computer. It played a pivotal role in establishing desktop publishing as a general office function. The motherboard, a CRT monit ...

does not have enough

RAM Ram, ram, or RAM may refer to: Animals * A male sheep * Ram cichlid, a freshwater tropical fish People * Ram (given name) * Ram (surname) * Ram (director) (Ramsubramaniam), an Indian Tamil film director * RAM (musician) (born 1974), Dutch * ...

to load the new file system. In fact, even for the Macintosh 512K to use the drive, it requires an additional file in the System Folder on a special startup disk which adds additional code into memory during startup. A startup routine also allows the Mac to check for the presence of a System file on the Hard Disk, switch over to it and eject the startup disk. The HD20 cannot be used as a startup disk directly without first loading the code from the floppy disk drive. With the release of the

and the

Macintosh 512Ke The Macintosh 512K ''enhanced'' (512Ke) was introduced in April 1986 as a cheaper alternative to the top-of-the-line Macintosh Plus, which had debuted three months previously. It is the same as the Macintosh 512K but with the 800K disk drive a ...

, both containing the upgraded 128 kB

ROM Rom, or ROM may refer to: Biomechanics and medicine * Risk of mortality, a medical classification to estimate the likelihood of death for a patient * Rupture of membranes, a term used during pregnancy to describe a rupture of the amniotic sac * R ...

which contains the additional code, the HD20 can finally be used alone as a startup disk. While other hard drives were available on the market, Apple's HD20 was generally preferred because it uses the high-speed floppy disk port, whereas third-party drives use the lower-speed

Serial Port In computing, a serial port is a serial communication interface through which information transfers in or out sequentially one bit at a time. This is in contrast to a parallel port, which communicates multiple bits simultaneously in parallel. ...

. While the floppy port was not initially supposed to be used this way, making creative use of the port allows the HD20 to achieve much higher transfer rates than products limited to the serial ports. With few exceptions, this along with complete compatibility with the new

, gave Apple an instant edge over the competition. In addition, the HD20 has a convenient "zero-footprint" design which fit precisely underneath the Macintosh, merely elevating it 3 inches, but otherwise taking up no more desk-space.

Specifications

* Recording Surfaces: 2 * Per Drive: 20.7 MB (formatted) * No. of Cylinders: 610 * Total No. of Tracks: 1220 * No. of Sector/Track: 32 * Bytes/Sector: 532 (formatted) * Total No. of Blocks (Data): 38,964 * Spare Blocks: 76 * Access Time: Track to Track 10 ms; Average 50 ms; Maximum 150 ms; Average Latency 10.9 ms * Rotational Speed: the drive has a rotational speed of 45.73 rotations/second (2744 rpm) and access time of 85 ms.

History

In 1985, the HD20 was an important step to solidifying the Macintosh as a true business computer and it was eagerly anticipated following its April announcement. Until Apple's introduction a year later of the

Hard Disk 20SC The Apple Hard Disk 20SC is Apple's first SCSI based hard drive for the Apple II family as well as the Macintosh and other third party computers using an industry standard SCSI interface. History Released in September 1986 along with the Apple ...

, the first SCSI drive they manufactured, the HD20 was the only Apple-manufactured hard drive available for any Macintosh except the

Macintosh XL Macintosh XL is a modified version of the Apple Lisa personal computer made by Apple Computer In the Macintosh XL configuration, the computer shipped with MacWorks XL, a Lisa program that allowed 64 K Macintosh ROM emulation. An identical ma ...

. The HD20 was not compatible with any other Apple computer or other platforms. However, the HD20's unique design and position in the marketplace was quickly outmoded by the advancement of the significantly faster

standard which debuted with the Macintosh Plus in January 1986. Some third party companies offered a

conversion kit which replaced the controller board thus preserving the user's investment in the expensive but proprietary Rodime drive. Apple officially dropped support for the HD20 with

System 6 System 6 (or System Software 6) is a graphical user interface-based operating system for Macintosh computers, made by Apple Computer It was released in 1988, and is part of the classic Mac OS series. It is a monolithic operating system, with coop ...

as well as omitting the necessary ROM code beginning with the

Macintosh II The Macintosh II is a personal computer designed, manufactured, and sold by Apple Computer from March 1987 to January 1990. Based on the Motorola 68020 32-bit CPU, it is the first Macintosh supporting color graphics. When introduced, a basic sys ...

. Sales of the HD20 continued to support the Macintosh 512Ke which has no other hard drive options, until it was discontinued in late 1987. Apple dropped support for the HD20 in all of its newer Macs, only to find many business users upgrading their older systems needed a way to transfer data from the unsupported drives to the newer Macs. Only Macs with legacy technology and floppy disk ports, which were eliminated entirely from Macintosh computers in 1991, are able to continue to use the older slower technology. Manufactured in significant numbers for almost two years, the HD20 remains as one of the few surviving hard drives usable by a stock Macintosh 512K or 512Ke.

Features

Specifications

History

See also

References

External links