History of IBM magnetic disk drives


manufactured magnetic disk storage devices from 1956 to 2003, when it sold its hard disk drive business to Hitachi. Both the hard disk drive and floppy disk drive were invented by IBM and as such IBM's employees were responsible for many of the innovations in these products and their technologies. The basic mechanical arrangement of hard disk drives has not changed since the IBM 1301. Disk drive performance and characteristics are measured by the same standards now as they were in the 1950s. Few products in history have enjoyed such spectacular declines in cost and physical size along with equally dramatic improvements in capacity and performance.
IBM manufactured 8-inch floppy disk drives from 1969 until the mid-1980s, but did not become a significant manufacturer of smaller-sized, 5.25- or 3.5-inch floppy disk drives. IBM always offered its magnetic disk drives for sale but did not offer them with original equipment manufacturer terms until 1981. By 1996, IBM had stopped making hard disk drives unique to its systems and was offering all its HDDs as an OEM.
IBM uses many terms to describe its various magnetic disk drives, such as direct-access storage device, disk file and diskette file. Here, the current industry standard terms, hard disk drive and floppy disk drive, are used.

Early IBM HDDs

IBM 350

The IBM 350 disk storage unit, the first disk drive, was announced by IBM as a component of the IBM 305 RAMAC computer system on September 14, 1956. Simultaneously a very similar product, the IBM 355, was announced for the IBM 650 RAMAC computer system. RAMAC stood for "Random Access Method of Accounting and Control". The first engineering prototype 350 disk storage shipped to Zellerbach Paper Company, San Francisco, in June 1956, with production shipment beginning in November 1957 with the shipment of a unit to United Airlines in Denver, Colorado.
Its design was motivated by the need for real time accounting in business. The 350 stores 5 million 6-bit characters. It has fifty-two diameter disks of which 100 recording surfaces are used, omitting the top surface of the top disk and the bottom surface of the bottom disk. Each surface has 100 tracks. The disks spin at 1200 rpm. Data transfer rate is 8,800 characters per second. An access mechanism moves a pair of heads up and down to select a disk pair and in and out to select a recording track of a surface pair. 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.
from the RAMAC program is generally considered to be the fundamental patent for disk drives. This first-ever disk drive was initially cancelled by the IBM Board of Directors because of its threat to the IBM punch card business but the IBM San Jose laboratory continued development until the project was approved by IBM's president.
The 350's cabinet is long, high and wide.
The RAMAC unit weighs about one ton, has to be moved around with forklifts, and was frequently transported via large cargo airplanes. According to Currie Munce, research vice president for Hitachi Global Storage Technologies, the storage capacity of the drive could have been increased beyond five million characters, but IBM's marketing department at that time was against a larger capacity drive, because they didn't know how to sell a product with more storage. Nonetheless, double capacity versions of the 350 were announced in January 1959 and shipped later the same year.
In 1984, the RAMAC 350 Disk File was designated an International Historic Landmark by The American Society of Mechanical Engineers. In 2002 at the Magnetic Disk Heritage Center, a team led by Al Hoagland began restoration of an IBM 350 RAMAC in collaboration with Santa Clara University. In 2005, the RAMAC restoration project relocated to the Computer History Museum, Mountain View, California and is now demonstrated to the public in the museum's Revolution exhibition.

IBM 353

The IBM 353, used on the IBM 7030, was similar to the IBM 1301, but with a faster transfer rate. It has a capacity of 2,097,152 64-bit words or 134,217,728 bits and transferred 125,000 words per second. A prototype unit shipped in late 1960 was the first disk drive to use one head per surface flying on a layer of compressed air as in the older head design of the IBM 350 disk storage. Production 353s used self-flying heads essentially the same as those of the 1301.

IBM 355

The IBM 355 was announced on September 14, 1956, as an addition to the popular IBM 650. It used the mechanism of the IBM 350 with up to three access arms and stored 6 million decimal digits and 600,000 signs. It transferred a full track to and from the magnetic core memory of the 653, an IBM 650 option that included just sixty signed 10-digit words, enough for a single track of disk or a tape record, along with two unrelated features.

IBM 1405

The IBM 1405 Disk Storage Unit was announced in 1961 and was designed for use with the IBM 1400 series, medium scale business computers. The 1405 Model 1 has a storage capacity of 10 million alphanumeric characters on 25 disks. Model 2 has a storage capacity of 20 million alphanumeric characters on 50 disks. In both models the disks are stacked vertically on a shaft rotating at 1200 rpm.
Each side of each disk has 200 tracks divided into five sectors. Sectors 0–4 are on the top surface and 5–9 are on the bottom surface. Each sector holds either 178 or 200 characters. One to three forked-shaped access arms each contains two read/write heads, one for the top of the disk and the other for the bottom of the same disk. The access arms are mounted on a carriage alongside the disk array. During a seek operation an access arm moved, under electronic control, vertically to seek a disk 0–49 and then horizontally to seek a track 0–199. Ten sectors are available at each track. It takes about 10 ms to read or write a sector.
The access time ranges from 100ms to a maximum access time for model 2 of 800ms and 700ms for model 1. The 1405 model 2 disk storage unit has 100,000 sectors containing either 200 characters in move mode or 178 characters in load mode, which adds a word mark bit to each character. The Model 1 contains 50,000 sectors.

IBM 7300

The IBM 7300 Disk Storage Unit was designed for use with the IBM 7070; IBM announced a model 2 in 1959, but when IBM announced the 1301 on June 5, 1961, 7070 and 7074 customers found it to be more attractive than the 7300. The 7300 uses the same technology as the IBM 350, IBM 355 and IBM 1405

IBM 1301

The IBM 1301 Disk Storage Unit was announced on June 2, 1961 with two models. It was designed for use with the IBM 7000 series mainframe computers and the IBM 1410. The 1301 stores 28 million characters per module. Each module has 25 large disks and 40 user recording surfaces, with 250 tracks per surface. The 1301 Model 1 has one module, the Model 2 has two modules, stacked vertically. The disks spin at 1800 rpm. Data is transferred at 90,000 characters per second.
A major advance over the IBM 350 and IBM 1405 is 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 eliminates 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 is also faster since, with the new design, the head will usually be somewhere in the middle of the disk, not starting on the outer edge. Maximum access time is reduced to 180 milliseconds.
The 1301 is the first disk drive to use heads that are aerodynamically designed to fly over the surface of the disk on a thin layer of air. This allows them to be much closer to the recording surface, which greatly improves performance.
The 1301 connects to the computer via the IBM 7631 File Control. Different models of the 7631 allow the 1301 to be used with a 1410 or 7000 series computer, or shared between two such computers.
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 is 165 ms and data can be transferred at 180 K characters/second, more than double the speed of the 1301.
There are two access mechanisms per module, one for the inner 250 cylinders and the other for the outer 250 cylinders.
As with the 1301, there is a Model 2 which doubles the capacity by stacking two modules.
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 is about the size and shape of a top-loading washing machine and stores 2 million characters on a removable IBM 1316 disk pack. Seven models of the 1311 were introduced during the 1960s. They were withdrawn during the early 1970s.
Each IBM 1316 Disk Pack is high, weighs and contains six diameter disks, yielding 10 recording surfaces. The 10 individual read/write heads are mounted on a common actuator within the disk drive which moves in and out hydraulically and is mechanically detented at the desired track before reading or writing occurs. The disks spin at 1500 rpm. Each recording surface has 100 tracks with 20 sectors per track. Each sector stores 100 characters. The disk pack is covered with a clear plastic shell and a bottom cover when not in use. A lifting handle in the top center of the cover is rotated to release the bottom cover. Then the top of the 1311 drive is opened and the plastic shell lowered into the disk-drive opening. The handle is turned again to lock the disks in place and release the plastic shell, which is then removed and the drive cover closed. The process is reversed to remove a disk pack. The same methods are used for many later disk packs.
There are seven models of the 1311 disk drive. The first drive attached to a system is a "master drive" which contains the controller and can control a number of Model 2 "slave drives."
  1. Master drive on an IBM 1440, IBM 1460, or IBM 1240 system and can control up to four Model 2 drives. Introduced October 11, 1962. Withdrawn February 8, 1971.
  2. Slave drive to a master drive. Can have any special feature incorporated that the master drive has incorporated. Introduced October 11, 1962. Withdrawn January 6, 1975.
  3. Master drive on IBM 1620 or IBM 1710 system and can control up to three Model 2 drives. Does not support any special features. Introduced October 11, 1962. Withdrawn May 12, 1971.
  4. Master drive on an IBM 1401 system and can control up to four Model 2 drives. Introduced October 11, 1962. Withdrawn February 8, 1971.
  5. Master drive on an IBM 1410, IBM 7010, or IBM 7740 system and can control up to four Model 2 drives. Direct Seek comes as standard on this model. Introduced January 7, 1963. Withdrawn May 12, 1971.
  6. No information available, probably a master drive. Introduced March 5, 1968. Withdrawn February 2, 1971.
  7. No information available, probably a slave drive to Model 6. Introduced March 5, 1968. Withdrawn February 2, 1971.
The optional special features are:
  • Direct Seek: Without this option every seek returns to track zero first.
  • Scan Disk: Automatic rapid search for identifier or condition.
  • Seek Overlap: Allows a seek to overlap a single read or write, and any number of other seeks, when multiple drives are in use.
  • Track Record: Increases the capacity of the disk by writing a single large record per track instead of using 20 separate sectors. A track can hold 2,980 characters in 6-bit 'Move Mode", and 2,682 7-bit characters in "Load Mode", giving the drive a total capacity of 17,880,000 bits in 6-bit mode, and 18,774,000 bits in 7-bit mode.
The master drives, Models 1, 3, 4, and 5, which contain extra power supplies and the control logic, are about a foot wider than the Model 2 slave drive.