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head disk assembly

Early IBM disk storage

The invention of magnetic disk storage, pioneered by IBM in the 1950s, was a critical component of the computer revolution. This article surveys the major IBM computer disk drives introduced in the 1950s, 1960s and early 1970s.

The basic mechanical arrangement of hard disk drives hasn't changed since the IBM 1301. Disk drive performance and characteristics are measured by the same standards now as they were in the 1950s.

This survey concludes with a modern (2004) PC hard drive for comparison. Few products in history have enjoyed such a spectacular decline in cost and size with such a stellar improvement in capacity.

IBM 350

The IBM 350 was part of the IBM RAMAC 305, the computer that introduced disk storage technology to the world. IBM introduced the IBM 350 storage unit on September 4, 1956 before unveiling the entire RAMAC 305 computer nine days later on September 13. RAMAC stood for "Random Access Method of Accounting and Control."

Its design was motivated by the need for real time accounting in business. The 350 stored 5 million 7-bit (6-bits plus 1 odd parity bit) characters (about 4.4 megabytes). It had fifty diameter disks with 100 recording surfaces. Each surface had 100 tracks. The disks spun at 1200 RPM. Data transfer rate was 8,800 characters per second. Two independent access arms moved up and down to select a disk and in and out to select a recording track, all under servo control. A third arm was added as an option. Several improved models were added in the 1950s. The IBM RAMAC 305 system with 350 disk storage leased for $3,200 per month. The 350 was officially withdrawn in 1969.

The 350's cabinet was 60 inches (approx. 1.52 meters) long, 68 inches (approx. 1.72 meters) high and 29 inches (approx. 74 centimeters) deep. IBM had a strict rule that all its products must pass through a standard 29.5 inch (approx. 75 centimeters) doorway. Since the 350's platters were mounted horizontally, this rule presumably dictated the maximum diameter of the disks.

As of 2006, the Computer History Museum in Mountain View, California has a RAMAC disk drive mechanism (without original control circuitry) which is in the process of being restored.

IBM 353

The IBM 353 used on the IBM 7030, was similar to the IBM 1301, but with a faster transfer rate. It had a capacity of 2,097,152 (221) 72-bit words (64 data bits and 8 ECC bits) and transferred 125,000 words per second.

IBM 355

The IBM 355 was announced on September 14, 1956 as an addition to the popular IBM 650. It used the same mechanism as the IBM 350 and stored 6 million 7-bit decimal digits. Data was transferred to and from the IBM 653 magnetic core memory, an IBM 650 option that stored just sixty 10-digit words, enough for a single sector of disk or tape data.

IBM 1405

The IBM 1405 Disk Storage Unit was announced by 1961 and was designed for use with the IBM 1401 series, medium scale business computers. The 1405 stored 10 million characters on a single module. Each module had 25 large disks, yielding 50 recording surfaces. The disks spun at 1200 rpm. The Model 1 had one module, the Model 2 had two modules, stacked vertically. Each recording surface had 200 tracks and 5 sectors per track. Data was read or recorded at 22,500 characters per second. A single arm moved in and out and up and down. Access time ranged from 100 to 800 milliseconds (Model 2).

IBM 1301

The IBM 1301 Disk Storage Unit was announced on June 2, 1961. It was designed for use with the IBM 7000 series mainframe computers and the IBM 1410. The 1301 stored 28 million characters on a single module (25 million characters with the 1410). Each module had 20 large disks and 40 recording surfaces, with 250 tracks per surface. The 1301 Model 1 had one module, the Model 2 had two modules, stacked vertically. The disks spun at 1800 rpm. Data was transferred at 90,000 characters per second.

A major advance over the IBM 350 and IBM 1405 was the use of a separate arm and head for each recording surface, with all the arms moving in and out together like a big comb. This eliminated the time needed for the arm to pull the head out of one disk and move up or down to a new disk. Seeking the desired track was also faster since, with the new design, the head would usually be somewhere in the middle of the disk, not starting on the outer edge. Maximum access time was reduced to 180 milliseconds.

The 1301 also featured heads that were aerodynamically designed to fly over the surface of the disk on a thin layer of air. This allowed them to be much closer to the recording surface, which greatly improved performance.

The 1301 was connected to the computer via the IBM 7631 File Control. Different models of the 7631 allowed the 1301 to be used with a 1410 or 7000 series computer or shared between a 7000 and a 1410 or between two 7000's.

The IBM 1301 Model 1 leased for $2,100 per month or could be purchased for $115,500. Prices for the Model 2 were $3,500 per month or $185,000 to purchase. The IBM 7631 controller cost an additional $1,185 per month or $56,000 to purchase. All models were withdrawn in 1970.

IBM 1302

The IBM 1302 Disk Storage Unit was introduced in September 1963. Improved recording quadrupled its capacity over that of the 1301, to 117 million 6-bit characters per module. Average access time was 165 ms and data could be transferred at 180 K characters/second, more than double the speed of the 1301. A second arm accessed a separate group of 250 tracks. As with the 1301, there was a Model 2 with twice the capacity. The IBM 1302 Model 1 leased for $5,600 per month or could be purchased for $252,000. Prices for the Model 2 were $7,900 per month or $355,500 to purchase. The IBM 7631 controller cost an additional $1,185 per month or $56,000 to purchase. The 1302 was withdrawn in February 1965.

IBM 1311

The IBM 1311 Disk Storage Drive was announced on October 11, 1962 and was designed for use with several medium-scale business and scientific computers. The 1311 was about the size and shape of a top-loading washing machine and stored 2 million characters on a removable IBM 1316 disk pack. Each disk pack was high, weighed 10 pounds (4.5 kg) and contained six diameter disks, yielding 10 recording surfaces (the outer surfaces were not used). The 10 individual R/W heads were mounted on a common actuator which was moved in and out hydraulically and mechanically detented at the desired track before reading or writing occurred. The disks spun at 1500 rpm. Each recording surface had 100 tracks with 20 sectors per track. Each sector stored 100 characters. Seven models of the 1311 were introduced during the 1960s. They were withdrawn during the early 1970s.

Models of the 1311 disk drive

  1. Must be drive 1 on an IBM 1440, IBM 1460, or IBM 1240 system. Contains the controller and can control up to 4 – Model 2 drives. Introduced October 11, 1962. Withdrawn February 8, 1971.
  2. Slave drive. Could have any special feature incorporated that the master drive (drive 1) had incorporated. Introduced October 11, 1962. Withdrawn January 6, 1975.
  3. Must be drive 1 on an IBM 1620 or IBM 1710 system. Contains the controller and can control up to 3 – Model 2 drives. Did not support any special features. Introduced October 11, 1962. Withdrawn May 12, 1971.
  4. Must be drive 1 on an IBM 1401 system. Contains the controller and can control up to 4 – Model 2 drives. Introduced October 11, 1962. Withdrawn February 8, 1971.
  5. Must be drive 1 on an IBM 1410, IBM 7010, or IBM 7740 system. Contains the controller and can control up to 4 – Model 2 drives. Direct Seek comes standard on this model. Introduced January 7 1963. Withdrawn May 12, 1971.
  6. No information available, probably a master drive (drive 1). Introduced March 5 1968. Withdrawn February 2, 1971.
  7. No information available, probably a master drive (drive 1). Introduced March 5, 1968. Withdrawn February 2, 1971.

The optional special features were

  • Direct Seek: Without this option every seek returned to track zero first.
  • Scan Disk: Automatic rapid search for identifier or condition.
  • Seek Overlap: Allowed a seek to overlap ONE read or write and any number of other seeks.
  • Track Record: Increased the capacity of the disk by writing ONE large record per track instead of using sectors.

Drive 1 (the master drive: models 1, 3, 4, and 5) was about a foot wider than the other drives (the slave drives: model 2), to contain extra power supplies and the control logic.

The IBM 1316 Disk Packs were covered with a clear plastic shell and a bottom cover when not in use. A lifting handle in the top center of the cover was rotated to release the bottom cover. Then the top of the 1311 drive was opened and the plastic shell was lowered into the disk drive opening (assuming it was empty). The handle was turned again to lock the disks in place and release the plastic shell, which was then removed and the drive cover closed. The process was reversed to remove a disk pack.

IBM 2311

The IBM 2311 Direct Access Storage Facility was introduced in 1964 for use throughout the System/360 series. It was also available on the IBM 1130. The 2311 mechanism was largely identical to the 1311, but recording improvements allowed higher data density. The 2311 stored 7.25 million bytes on a single removable IBM 1316 disk pack (the same type used on the IBM 1311) consisting of six platters that rotated as a single unit. Each recording surface had 200 tracks plus 3 optional tracks which could be used as alternatives in case faulty tracks were discovered. Average seek time was 85 ms. Data transfer rate was 156 kB/s.

The 2311 had 10 individual R/W heads mounted on a common actuator which was moved in and out hydraulically and mechanically detented at the desired track before reading or writing occurred. The 2311 was organized into cylinders, tracks, and records. (A cylinder referred to all surfaces the same track on each of the 5 platters.) Record 0 was reserved for timing.

Because the 2311 was to be used with a wide variety of computers within the 360 product line, its electrical interconnection was standardized. This created an opportunity for other manufacturers to sell plug compatible disk drives for use with IBM computers and an entire industry was born.

IBM 2314/2319

The IBM 2314 Disk Access Storage Facility was introduced on April 22, 1965, one year later after the System/360 introduction. It was used with the System/360 and the System/370 lines. With Two Channel Switch feature it could interface with two 360/370 channels. The 2314 Disk access mechanism was similar to the 2311, but further recording improvements allowed higher data density. The 2314 stored 29,176,000 characters (200×20×7294 bytes per track) on a single removable IBM 2316 disk pack which was similar in design to the 1316 but was taller as a result of increasing the number of disks from six to eleven. The 2316 disk pack containing the eleven diameter disks yielded 20 recording surfaces. The drive access consisted of 20 individual R/W heads mounted on a common actuator which was moved in and out hydraulically and mechanically detented at the desired track before reading or writing occurred. Each recording surface had 200 tracks. Access time was initially the same as the 2311, but later models were faster as a result of improvements made in the hydraulic actuator. Data transfer rate was doubled to 310 kB/s.

The original Model 1 consisted of the 2314 control unit, a 2312 single drive module, and two 2313 four drive modules for a total of 9 disk drives. Only eight drives of the nine were available to the user at any one time. The ninth drive was there for a spare for the user and could also be worked on 'offline' by a Field Engineer while the other drives were in use by the customer. Each of the nine drives were mounted in individual drawers that were unlatched and pulled out to access the Disk Pack. Because of their appearance they picked up the nickname of 'Pizza Ovens'

Other 2314 Models came later: 2314 Model A with combinations of one to nine drives. 2314 Model B with 2319 disk drives were available in three, six and nine drive models. A 2844 Control Unit could be added to the 2314 Control Unit which allowed two S/360 Channels simultaneous access to two separate disk drives in the Storage Facility.

IBM 2310

The IBM 2310 Removable Cartridge Drive was introduced with the IBM 1130 in 1965. It could store 512,000 words (1,024,000 bytes) on an IBM 2315 cartridge. A single oxide-coated aluminum disk spun in a plastic shell with openings for the read/write arm and two heads.

IBM 2321

The IBM 2321 Data Cell (the "Noodle Picker") was introduced in the early 1960s. A development based on NCR's CRAM (Card Random Access Memory) technology, it was designed by IBM's Alan F. Shugart, who also designed the first modern hard disk drive and pioneered the floppy diskette. The 2321 housed up to ten removable and interchangeable data cells. Each data cell contained 200 magnetic strips, which were the basic recording media. The total storage capacity was 400 million bytes or 800 million decimal digits. Up to eight 2321s could be attached to the IBM 2841 control unit, allowing an overall capacity of over 3 GB. Reportedly the Data Cell required 23 liters of motor oil. It was a less than successful device -- there were too many mechanical movement, wear and tear, and reliability problems with the reinsertion of tape strips into their clips in the Data Cell cartridge after use.

IBM operating systems address rotating direct access storage devices with a 5-byte CCHHR address. The CCHHR refers to the addressed Cylinder, Head, and Record numbers. With the introduction of the 2321 this format was extended to the 8-byte MBBCCHHR format. The M field is the 2321 Module number and the BB field is the 2321 Bin number.

IBM 3330

The IBM 3330 Direct Access Storage Facility, code-named Merlin, was introduced in June 1970 for use with the IBM System/370 and the IBM System 360/195. Its removable disk packs held 100 MB (404x19x13,030 bytes) (the 1973 Model 11 featured IBM 3336 Disk Packs that held 200 MB (808x19x13,030 bytes)). Access time was 30 ms and data transferred at 806 kB/s. A major advance introduced with3330 was the use of error correction, which made the drives more reliable and reduced costs because small imperfections in the disk surface could be tolerated. The circuitry could correct error bursts up to 11 bits long. The 3330 was withdrawn in 1983.

IBM 3340

The IBM 3340 Direct Access Storage Facility, code-named Winchester, was introduced in March 1973 for use with IBM System/370. Its removable disk packs were sealed and included the head and arm assembly. There was no cover to remove during the insertion process. Access time was 25 millisecond and data transferred at 885 kB/s. Three versions of the removable IBM 3348 Data Module were sold, one with 35 megabyte capacity, another with 70 megabytes, the third also had 70 megabytes, but with 500 kilobytes under separate fixed heads for faster access. The 3340 also used error correction. It was withdrawn in 1984.

The 3340 was developed in San Jose under the leadership of Ken Haughton. Early on the design was focused on two removable 30 megabyte modules. Because of this 30/30 configuration, the code name Winchester was selected after the famous Winchester 30-30 rifle; subsequently the capacities were increased, but the code name stuck.

The significance of this product, and the reason that disk drives in general became known as "Winchester technology" had nothing to do with the configuration of the product. This was IBM's first drive to not unload the heads from the media. The Winchester technology allowed the head to land and take off from the disk media as the disk spun up and down. This resulted in very significant savings and a large reduction of complexity of the head and arm actuating mechanism. This rapidly became a standard design within the disk manufacturing community.

IBM 3350

The IBM 3350 Direct Access Storage Facility, code-named Madrid, was introduced in 1975 for use with IBM System/370. Its non-removable disk packs were sealed and included the head and arm assembly. The 3350 disk geometry was 555 cylinders, 30 heads, and 19069 bytes per track which gave the Head Disk Assembly (HDA) a storage capacity of 317,498,850 bytes. Disk units were identified as A2, A2F, B2, B2F, C2, and C2F. Each unit contained two HDAs and they were installed in "strings" of units. An A2 or A2F unit was required and attached to a "control unit" such as the IBM 3880. After the A2 could be up to 3 B2 units or 2 B2s and a C2. The C2 unit could also be connected to a control unit and with it in place then two I/O operations could be executed on the string at the same time. The "x2F" unit was a normal x2 unit, but its two HDAs also had a "Fixed Head" area over the first 5 cylinders. This Fixed Head area was intended to be allocated to the HASP or JES2 checkpoint area and thus would greatly reduce head motion on the device. In the background of this photograph of a 3350 A2/B2/B2 string is an IBM 3066 console, used on the IBM 370/165 and 370/168 computers.

IBM 3370

IBM introduced the IBM 3370 Direct Access Storage Device in January 1979 for its for IBM 4331, 4341, and System/38 midrange computers. It has 7 fixed disks, and each unit has a capacity of 571 MB. It uses thin-film head technology; research on that technology started at T.J. Watson laboratory in the late 1960s.

IBM 3380

The IBM 3380 Direct Access Storage Device was introduced in June 1980. It used new film head technology and had a capacity of 2.52 gigabytes with a data transfer rate of 3 megabytes per second. Average access time was 16 ms. Purchase price at time of introduction ranged from $81,000 to $142,200. Due to problems encountered, the first units did not ship until October, 1981.

IBM 3390

The IBM 3390 Direct Access Storage Device series was introduced November 1989, offering a maximum storage of up to 22 gigabytes. Cost of a storage system varied by configuration and capacity, between $90,000 and $795,000.

The floppy disk

Another important IBM innovation was little noticed when it was introduced with the System/370 in 1971. IBM needed a way to load new microcode into the IBM System/370 Model 158 and developed the 23FD floppy disk for this purpose.

IBM's "first" floppies were in diameter and held 80 Kilobytes of data. They were extensively used starting in 1972 as a data entry media ideally suited to replace 80-column punched cards. Card readers were in turn replaced by diskette readers. By 1978 most of IBM's and other manufacturers' punched-card, or "unit record equipment" such as punch machines, punched card verifiers, sorters, collating machines, card readers, etc., had been discarded, replaced by floppy diskette units, and in the process, saved millions of tons of cardboard paper worldwide each year.

Floppy diskettes 5¼" and 3½" in diameter, having higher data densities and larger capacities, became important storage devices for the personal computer developed in the late 1970s and remained a standard component of computers until the early 2000s.

Disk storage in 2004

IBM sold its disk drive operation to Hitachi in 2002. For comparison purposes, the Hitachi Deskstar 7K250 PC hard drive stores 250,000,000,000 bytes (250 gigabytes) on three 3.5-inch (90 mm) diameter platters spinning at 7200 rpm. It has a sustained average transfer rate of 61,400,000 bytes per second over a serial ATA bus. The average seek time is 8.5 milliseconds. It weighs 640 grams (1.4 lb). Like all 3.5-inch hard drives, it is about as long as the carrying handle on an IBM 1316 disk pack. Retail price in April 2006 was about US$100.

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