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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.^[3]

Features[edit]

The Hard Disk 20 (or HD20, as it was known colloquially) contained a 20 MB 3.5' Rodimehard 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.

The drive had a rotational speed of 45.73 rotations/second (2744 rpm) and access time of 85 ms.^[2]

While other hard drives were available on the market, Apple's HD 20 was generally preferred mainly because Apple broke their own development rules when they offered it. Originally the Macintosh was designed with two serial ports which were to meet all the expansion needs of the user. It also included a dedicated floppy disk port for one external floppy disk. Most of the hard drives which were available on the market used the slower serial port to transfer data per Apple's specifications. Apple instead engineered the HD 20 to use the faster floppy disk port, enabling the user to daisy-chain an external floppy disk drive as well as an additional HD 20. With few exceptions, this along with complete compatibility with the new Hierarchical File System, gave Apple an instant edge over the competition. In addition, the HD 20 had a convenient 'zero-footprint' design which fit precisely underneath the Macintosh, merely elevating it 3 inches, but otherwise taking up no more desk-space.^[4]

History[edit]

In 1985, the HD 20 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 first SCSI drive they manufactured, the HD 20 was the only Apple-manufactured hard drive available for any Macintosh except the Macintosh XL. The HD20 was not compatible with any other Apple computer or other platforms.

However, the HD 20's unique design and position in the marketplace was quickly outmoded by the advancement of the significantly faster SCSI standard which also debuted with the Macintosh Plus in January 1986. Some third party companies offered a SCSI conversion kit which replaced the controller board thus preserving the user's investment in the expensive but proprietary Rodime drive.^[5] Apple officially dropped support for the HD 20 with System 6 as well as omitting the necessary ROM code beginning with the Macintosh II.^[6] Sales of the HD 20 continued to support the Macintosh 512Ke which had no other hard drive options until it was discontinued in late 1987. Apple quickly dropped support for the HD 20 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, were able to continue to use the older slower technology.

1. Choose Apple menu About This Mac, then click Storage. Each segment of the bar is an estimate of the storage space used by a category of files. Move your pointer over each segment for more detail. Click the Manage button to open the Storage Management window, pictured below.
2. Apple 16' MacBook Pro with Touch Bar, 9th-Gen 6-Core Intel Core i7 2.6GHz, 32GB RAM, 1TB SSD, AMD Radeon Pro 5300M 4GB, Space Gray, Late 2019 Z0XZ004QV 3.8 out of 5 stars 5 $2,799.94 $ 2,799.

Manufactured in significant numbers for almost two years, the HD 20 remains as one of the few surviving hard drives a stock Macintosh 512K or 512Ke can use.

See also[edit]

Since the Apple IIGS was the first Apple product to debut in the new gray color they called Platinum, the 20SC had to both match it and the beige color of the Macintosh Plus, which it is designed to sit perfectly beneath. In 1987, all Apple products would change to Platinum, which would remain in use for the next 10 years. 301 Moved Permanently. Listen to music by Disque Dur on Apple Music. Find top songs and albums by Disque Dur including Paris Night (Skyline Mix), Paris Night (Skyline Mix) and more. Apple mac malware scanner.

References[edit]

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1. ^'The Mac Plus 30 Years On'. January 24, 2016. Retrieved April 20, 2016.
2. ^ ^ab'Apple brand HD20, HD20 SC Info'. 2010. Retrieved April 20, 2016.
3. ^Macintosh 128K and 512K: SCSI Hard Drives
4. ^Lewis, Peter H (October 8, 1985). 'Peripherals; Apple gives its Macintosh a hard disk'. New York Times. Retrieved December 30, 2007.
5. ^Apple HD-20: How To Convert It Into A SCSI Device
6. ^System 6.0.3: Incompatible with Macintosh 512Ke and HD20

External links[edit]

• Hard Disk 20 technical specifications at apple.com at the Wayback Machine (archived May 16, 2011)
• Mac Systems Compatible with Hard Disk 20 at apple.com
• Hard Disk 20 tutorial at VintageMacWorld.com
• Hard Disk 20 Info at Mac512.com's Classic Macintosh Preservation area at the Wayback Machine (archived February 20, 2007)
• The M0001 Registry Owners of Vintage Macintosh

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[edit]

Released in September 1986 along with the Apple IIGS (which required an optional SCSI interface card to use it), it debuted over 9 months after the introduction of the Macintosh Plus, the first to include Apple's SCSI interface. Apple clear computer. It was a welcome addition, delivering considerably faster data transfer rates (up to 1.25 megabytes per second)^[4] than its predecessors, the Hard Disk 20 (62.5 Kilobytes per second)^[5] and ProFile.^[6]

Hardware[edit]

The 20SC originally contained a half height 5.25' Seagate ST-225N 20MB SCSI hard drive, but was later manufactured with a full-height 3.5' MiniScribe 8425SA 20MB SCSI hard drive. The latter drive was the same size as the drive inside the Macintosh Hard Disk 20, but 10 to 15 MB over what had previously been offered by Apple for the II family. The same drive mechanism would also be offered 6 months later as a built-in drive option on the Macintosh II and SE. It had two standard Centronics 50-pin connectors, one for the System and one for daisy-chaining additional SCSI devices and a SCSI ID selection switch. An external terminator was required if it was the only SCSI device connected. The case itself could accommodate a 3.5' or 5.25' full-height hard drive mechanism. Indeed, the case design would be reused unchanged (in Platinum only) for 3 more models introduced the following year: 40SC, 80SC & 160SC (offering respective Megabytes of storage). While the transfer rates were significantly higher due to the faster SCSI bus technology, the actual transfer rate varied from computer to computer thanks to different SCSI implementation based on developing industry standards.^[7]

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Design[edit]

In addition to being the first cross-platform drive offered by Apple it was the first hard drive to use the Snow White design language. Notably, it was the only Snow White product to use the Macintosh beige color and one of the few Apple products to be introduced in two different colors at the same time. Since the Apple IIGS was the first Apple product to debut in the new gray color they called Platinum, the 20SC had to both match it and the beige color of the Macintosh Plus, which it is designed to sit perfectly beneath. In 1987, all Apple products would change to Platinum, which would remain in use for the next 10 years.

See also[edit]

References[edit]

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1. ^Industry News, U-M Computing News, Volume 1, 1986, Page 14, ..Apple announced the Hard Disk 20SC. The 20 megabyte hard disk drive features a small computer system interface (SCSI) for connection to the Macintosh Plus or the APPle II with a SCSI adapter card. The University price for the HD20SC will be $927, with delivery expected in November. The price does not include the required SCSI cable and terminator..
2. ^Ehman Offers 2 SCSI Hard Drives for the Mac Plus, By Lisa L. Spiegelman, InfoWorld, 3 Nov 1986, Page 15, ..Other recently introduced SCSI drives include the Apple Hard Disk 20SC. Price at $1,299, it has a 65-millisecond access speed, the company said..
3. ^Spiegelman, Lisa. 'Ehman Offers 2 SCSI Hard Drives for Mac Plus.' InfoWorld. 3 Nov. 1986: p. 15. Print.
4. ^'Apple Hard Disk 20SC: Specifications (Discontinued)'. Archived from the original on May 16, 2011. Retrieved January 29, 2008.
5. ^'Hard Disk 20: Specification (Discontinued)'. Archived from the original on May 16, 2011. Retrieved May 16, 2011.
6. ^'ProFile Hard Drive: Specifications (Discontinued)'. Archived from the original on June 6, 2012. Retrieved May 29, 2011.
7. ^'Apple HD SC: Specifications (Discontinued)'. Archived from the original on May 16, 2011. Retrieved January 29, 2008.

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