UNISERVO I - The First Tape Drive (Metal)


During the late 1940s computer design engineers recognized that "magnetic audio tape" technology could be adapted for computer data recording. The digital tape would replace punched cards vastly increasing the transfer rate of data into and out of the central computer system. The Eckert-Mauchly Computer Corporation (EMCC) developed a tape drive that was introduced in 1951. By then EMCC had been acquired by Remington Rand.

The UNISERVO tape drive was the primary input/output device on the UNIVAC I computer. It was the first tape drive for a commercially sold computer. The UNISERVO used "metal" tape which was a half inch wide thin strip of magnetic material (nickel plated phosphor bronze called Vicalloy). The metal tape reels were 1200 feet long and were "very heavy". The nickel-plated phosphor bronze tape was very abrasive so the UNISERVO tape drive had a moving film of plastic buffered tape between the tape and the tape head to prevent head wear.

The picture to the left is a UNISERVO with its cover off. It shows the levers, strings and pulleys that were used in the tape handlers for the UNISERVO. (To keep them working, one had to have a large supply of good fishing line on hand.)

There were six tracks for the data, one for parity, and one for timing. The data was recorded at 128 bits per inch resulting in a capacity of about 1.5 megabytes per tape. The drive could move the tape at 100 inches per second, resulting in a transfer rate of 12,800 characters per second. The data was recorded in a fixed size block of 60 words of 12 characters each.

The UNISERVO drive supported both reading and writing in both forward and backward directions. (DEC tape drives offered by Digital Equipment about 10 years later had the same forward/backward capability.) Data transfers to/from the UNIVAC I processor were fully buffered into a one block dedicated memory. This allowed the processor to execute instructions at the same time data was being transferred to/from the UNISERVO.

UNIVAC continued to use the name UNISERVO for later models of tape drives (e.g., UNISERVO II, UNISERVO IIIC, UNISERVO VIII-C) for later computers in their product line. The UNISERVO II could read metal tapes from the UNIVAC I as well as the higher density magnetic tape, similsr to music recording tape from 3M, that had become the industry standard by the late 1950s.  Top

IBM 726 - The First Magnetic Tape Drive


In 1949, IBM began to plan for a new storage and input/output medium to take the place of punched cards. The new medium would be more compact, faster, cheaper, and reusable. Magnetic tape technology had been used for audio recording and playback since World War II. It was initially adapted for computer usage in an internal IBM prototype called the Tape Processing Machine (TPM) during 1950-51.

Computer data storage and retrieval is very different from audio recording and playback, requiring very accurate positioning (both forwards and backwards) to arbitrary spots on the tape. This required much more accurate and expensive motors. There also was stress on the tape itself that was alleviated by the invention of the dual vacuum columns by IBM. New digital recording techniques were developed that allowed direct mapping of computer memory to tape with added error detection.

The first magnetic tape drives were successfully demonstrated on the TPM and were then adapted to the 701 computer system (IBM's first commercial computer) which could accommodate four tape drives. Two tape units were combined into one overall mechanical unit. See the two 726s pictured to the left with their covers removed.

The first IBM commercial tape drives were delivered to IBM Headquarters in New York in March, 1953 as part of the first 701 System. The 701 System was operating as a Technical Computing Bureau (now called a Service Bureau) for organizations that were solving problems involving large mathematical computations.

The 726 operated at 7,500 characters per second - 56 times faster than the punch card rate. The tapes for the machine were 1,200 feet long and had a capacity in excess of 2 million digits. The tapes had a magnetic surface on top of a plastic substrate which was very unique at the time. IBM said a reel of tape from the 701 replaced 12,500 punched cards.

IBM pioneered not only the tape drives, but also the half inch tape itself. Vic Witt played a large part in that program. "I started with the program in 1951," recalled Witt. "There were no tape experts at that time. They handed me a piece of tape and said, 'You have to know everything there is to know about this stuff.' It was a quarter-inch, and we were going to use half-inch, but this was all we had then. We worked with 3M to find a way to produce a tape to our specifications. IBM said, "We need tape so flawless that if it were a highway stretching the 60-plus miles from Poughkeepsie to Manhattan, any defect would be the size of a marble". 3M came through for IBM and made a fortune selling magnetic tape to customers.  Top

IBM 750 - The First Hard Drive

IBM 350 Drive

In 1952, with computer excitement in the air, IBM sent Reynold Johnson to San Jose to start a new research lab. When the Air Force requested a random access inventory system, Johnson set his 50-person lab in motion, trying everything: strips, rods, tapes, flat plates, you name it. In the early 1950s, no one had any idea how to make a fast, reliable random access memory machine.

The technical obstacles were enormous. The lab soon settled on using spinning, horizontal disks coated with magnetic material. Magnetic spots on the disk would represent a character of data. Since the spots would have a magnetic field, a magnetic arm like a record needle, could hover over the spots and read them as the disks rotated at high speed.

But the first challenge was finding material for the disks. The disks had to be perfectly flat, strong and light enough to be spun by a reasonable-size electric motor. A single aluminum disk warped at high speeds. After much trial-and-error, the researchers tried gluing two aluminum disks together. It worked.

Even more problematic was the arm. It could never touch the disk or it would wipe out the data. Two researchers, William Goddard and John Lynott, came up with an arm that fired compressed air to hover the head just above the disk. “When we concluded we could do that, we could see a fairly clear road to building a practical random access memory,” said Louis Stevens, a senior engineer at the San Jose lab.

350 Disks

Since a single disk could not store enough data to be useful, the researchers built a research machine that held 16 disks stacked horizontally with a tiny space between each disk. “We called it a meat cutter and a lot of other things,” Reynold Johnson said. To disbelieving executives at headquarters, it was known as the baloney slicer.

IBM introduced the 305 RAMAC (the name stands for Random Access Method of Accounting and Control) computer in September 1956, which was the first computer to include a hard disk drive - the IBM 350 Disk Drive, pictured above. The 350 disk assembly consisted of a stack of fifty 24 inch discs, pictured to the left. The 350 Drive was 16 square feet, weighed over a ton, and had to be transported by plane. (See the plane umloading a 350 at the very top of this page.) The RAMAC was the first commercial computer to use a moving head hard disk drive, storing five million characters of accounting data (the equivalent of 64,000 punched cards).

The magnetic disks were accessed by two arms, controlled by vacuum-tubes, that were protected by compressed air. The 50 disks inside spun at 1200 revolutions per minute, while the arm dashed in and out, accessing the data at about 100,000 bits per second. To put it in today's terminology, the 350 held about 5MB of data. This is about the same capacity as the first personal computer hard drives that appeared in the early 1980's, but was an enormous capacity in 1956.

The RAMAC introduced the concept of instantly accessible information. Before the 350, information had to be entered into a computer by running a stack of cards through a punched card machine or mounting and running a magnetic tape which took a bunch of minutes or even hours (in the case of punched cards). By the time production ended in 1961, IBM had manufactured over 1,000 RAMAC Systems. For those RAMAC companies, the amount of data they could store, and the speed with which they could access it, was increasingly important to their bottom lines.  Top

Removable Disks And Disk Drives

IBM 1316 Pack

The IBM 1316 Disk Pack. The IBM 1316 removable pack was used on the the 1311 and 2311 Disk Storage Drives. Each 1316 pack was 4 inches high, weighed 10 pounds and contained six 14-inch diameter disks, yielding 10 recording surfaces (the outer surfaces were not used). The 10 individual read/write heads on the storage drive were mounted on a common actuator within the drive which moved in and out hydraulically to 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. This resulted in about 2 million characters per pack.

The disk pack was 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 lowered into the disk drive opening. The handle was turned again to lock the disks in place and release the plastic shell. The shell was then removed and the drive cover closed. The process was reversed to remove a disk pack. The same shell cover methods were used on later disk packs.

IBM 1311 Drive

1962 - The IBM 1311 Disk Storage Drive. By October of 1962, the issue of the physical space needed for a hard disk drive was pressing and IBM responded by introducing the 1311. The IBM 1311 looked similar to a top loading washing machine. The IBM 1311 was designed for use with several medium-scale business and scientific computers. It saved a lot of space and also had better components than its predecessors. This was the first hard disk drive to introduce removable disk packs. The space between the head and the disk was reduced by a factor of two fom the previous disk drive version. This resulted in a doubling of the disk recording density.

1964 – IBM 2311 Disk Storage Drive. This model was similar to the 1311 version, but was slightly smaller and had a lot more capacity and better performance than the 1311. The disk drive stored about 7.25 megabytes of data in a single pack, and offered a good data transfer rate of about 156 kilobytes per second. The average seek time was 85 milliseconds. Each recording surface had 200 tracks plus three optional tracks which could be used as alternatives in case faulty tracks were discovered.

1965 – IBM 2314 Disk Storage Drive. The IBM 2314, part of the IBM/360 System, looked very different from previous models. See the large image below. The 2314 had the capacity to store 29 megabytes of data in a single pack, and of course the disk packs could be removed and stored. The data rate was about doubled the 2311, 310 kilobytes per second. (The fun fact about this hard drive was that because of its appearance it was called a “Pizza Oven”.)

The 2314 used a disk pack, the 2316 Disk Pack, that was different from the 1311 and 2311. The 2316 pack contained eleven 14-inch diameter disks which yielded 20 recording surfaces, each with 200 tracks. The 2316 pack stored 29,176,000 characters (20×200×7,294 bytes per track). The 2316 pack was similar in design to the 1316, but was taller as a result of increasing the number of disks from six to eleven.

IBM 2314 Subsystem


1970 – IBM 3330 Disk Storage Drive. The IBM 3330 Drive was introduced in June 1970 for use with the IBM System/370 and the IBM System 360/195. Its removable disk packs held 100 megabytes. The 3330 achieved 100 MB by increasing both tracks per inch and the number of bits per track (19x404×13,030 bytes). Access time was 30 ms and data transfered at 806 kilobytes per second. A major advance introduced with the 3330 was the use of error correction. Error correction 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 through the use of codes called Fire Codes. The drive packaging was similar to the 2314 style pictured above.

IBM 3340 Drive

1973 – IBM 3340 Disk Storage Drive. As the number of tracks per inch increased, the vertical alignment of 20 disk surfaces became more and more challenging to achieve interchangeable removable disks. So, 3340 development focused on a drive with a fixed head and disk combination. Also the overall drive packaging was much smaller than the 2314 style to minimize space. See the IBM 3340 photo to the left.

The disks, spindle and bearings, head-positioning carriage and head-arm assemblies were all incorporated into a removable sealed cartridge called the IBM 3348 Data Module. The IBM 3348 was a removable module similar to a disk pack, but the head and arm assembly was also inside the pack. An access door of the data module opened or closed during a mechanical load/unload process to connect the data module to the drive. Unlike previous disk packs there was no cover to remove during the insertion process. A track density of 300 tracks per inch and an access time of 25 milliseconds were achieved. Data was transfered at 885 kilobytes per second.

The most significant aspect of this product, and the reason that disk drive technology in general became known as "Winchester Technology", was that (as mentioned above) this was IBM's first disk drive to dedicate all heads to a specific set of media. Winchester Technology enabled the head to land and take off from right on the lubricated disk media surface as the disks spun up and down. This resulted in a very significant savings and a large reduction to the complexity of the head and arm actuating mechanism. With a load of less than 20 grams, the ferrite read/write head started and stopped in contact with the disk on a dedicated landing zone but flew over the disk on an air bearing 18 microinches thick between the magnetic head and spinning disk. This technology approach rapidly became a standard design within the entire disk manufacturing community.

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, of which 500 kilobytes were accessible with fixed heads for faster access. Due to the relatively high cost of the Data Module and its low capacity, the 3340 was not a high volume product relative to other disk drive products.  Top

Control Data Disk Drives - An Alternative To IBM

Control Data SMD

The Control Data Corporation (CDC) Normandale disk drive operation in Edina, Minnesota departed from IBM standards and technology in a project launched in 1972 for a new removable media product to compete with the rumored IBM “Winchester” system. CDC was already a leading supplier of disk drives for its own computers, as well as to other original equipment manufacturers (OEMs). In the past, the company had generally followed IBM’s lead in media and technology. In this case, CDC did not have access to IBM’s new contact start-stop head approach and wished to avoid the complex and expensive removable head disk assembly of the 3340 configuration.

Therefore CDC developed the first of a family of Storage Module Drive (SMD) products that they announced at the National Computer Conference in New York City in 1973. The CDC 9760 was a disk drive with a non-IBM compatible removable 40 megabyte 5-disk pack, but at a higher level of recording density and performance (6000 bits per inch and 10 megabytes per second). This was achieved with a unique head that flew at less than 30 microinches above the disk spinning at 3,600 revolutions per minute. After an 80 megabyte (9762) version was announced in 1974, 150 megabyte (9764) and 300 megabyte (9766) drives followed.. The CDC drives had the largest capacity removable packs on the market. The SMD drives were sold to OEMs and also plug compatible drives were sold directly to IBM customers.

With the easy to attach SMD interface employed on a broad family of fixed and removable media drives, CDC shipped over 100,000 units by 1981 to become the world’s largest disk drive supplier outside of IBM. After adoption of SMD as an ANSI disk standard in 1982, more than 20 other manufacturers offered SMD compatible products. (PS: The author spent four years from 1964 to 1968 at the Normandale CDC facility and then 14 more years at other CDC facilities.)  Top

The IBM 3350 - First Of The Big Disk Drives

IBM 3350 Hard Drive

In 1976 IBM introduced a "hard disk drive" (HDD) for the System/370 with a non-removable disk - the 3350. See a picture of a dual 3350 unit to the left. The non-removable head disk assembly (HDA) was sealed and included the head and arm assembly. The disk drive had the capacity to hold 317.5 megabytes of data on each drive, bringing the total to 635 megabytes for the dual unit, which was standard on the 370. Sealed HDAs became the standard practice on all IBM disk storage drives thereafter.

Each 3350 head disk assembly had a total of 8 disks and 16 recording surfaces (data was recorded on both sides of the disk). Fifteen surfaces were used for data and one for servo control. There were two data heads for each data surface, making a total of 30 data heads. In summary - there were 555 cylinders (plus 5 alternatives), times 19,069 bytes per cylinder track, times 30 heads which gave each HDA a storage capacity of 317.5 megabytes. The data transfer rate was about 1.2 megabytes per second.

The A2 Disk Models also contained a disk controller for a string of up to 8 HDAs. B2 Models did not contain a controller. C2 Models (optionable on the opposite string end of the A2) contained a second controller. If the A2 controller was not available, a switch on the C2 controller could be activated making all the data on the string available to the central processor and the user.

The A2F, B2F and C2F Models had a fixed head area over the first five cylinders. The fixed heads on the 2F Models provided up to 1.14 million bytes of zero seek time storage per HDA. The fixed head area was popular with customers who used the Time Sharing Option (TSO) to quickly swap key information back and forth between two or more programs. The fixed head storage capacity took the place of an equal amount of storage under the moving heads.

More Recent IBM Drives.  In January 1979 IBM introduced the IBM 3370 Storage Drive for midrange computers. It had seven fixed 14-inch disks, and each unit has a capacity of 571 MB. It was the first hard disk drive (HDD) to use thin film head technology. In 1980, they produced another hard drive innovation - the IBM 3380, the world’s first gigabyte HHD. At the time, it was the most powerful disk drive on the planet. The drive had the capacity to store 2.5 gigabytes of data and offered a data transfer rate of 3 megabytes per second. The IBM 3390 Storage Drive series was introduced in November 1989 with a maximum storage of 22 gigabytes. The 3390 Model 9 was IBM's last large disk of its own manufacture. IBM manufactured magnetic disk storage devices from 1956 to 2003, and then 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 most of the innovations in those technologies.  Top

The IBM 3590 Magstar Tape Family

IBM 3590 Cartrige

The Tape Cartridge. In 1995 IBM unveiled a revolutionary new type of tape storage - a very small tape cartridge and a new type of drive. The new type of tape drive, the IBM 3590, was nicknamed Magstar. The name stuck for the entire life of the product and cartridge family. The tape was a half inch metal particle tape spooled into a four-by-five-by-one inch data cartridge containing a single reel. A takeup reel was embedded inside the tape drive. See the front and back tape cartridge photos to the left.

The original cartridge tape was 1,050 feet long and could hold 10 megabytes of uncompressed data. If the data was compressed it could hold 30 megabytes. The "Extended" Magstar cartridge could hold 20 megabytes uncompressed and 60 megabytes compressed. The extended cartridges had tape that was twice as long as the original cartridge, but the cartridge was the same physical size. The initial tape cartridge had 128 total tracks - 8 sets of 16 tracks. The IBM 3590 marked the introduction of a track-following head servo that leveraged the proven technology of IBM disk storage devices.


The IBM 3590. The IBM 3590 was a series of tape drives and corresponding magnetic tape cartridges in Magstar format. To the far left is a stand alone 3590 drive that included a tape controller. Next to it is a 3590 Model A14 Tape Facility that is designed for mounting internally up to four 3590 B11 Tape Drives, plus up to two 3590 Controllers for connection to channels on IBM mainframes. The 3590 B11 type tape drives were rack mounted. B1A drives could became part of an automated tape library system (see the next section below).

On the front of the 3590 A14 are four "Automatic Cartridge Facilities".The Magstar 3590 10-cartridge Automatic Cartridge Facility (ACF) functioned as a low-cost mini-library. Inside the A14 Tape Facility can be up to four 3500 B11 magnetic tape drives that can retreive and replace tape cartridges to and from any of the four ACFs.

With the four ACFs, each loaded with 10 cartridges, the A14 Magstar tape drives could automtically access up to 1,200 (40 times 30) gigabytes of compacted data (not bad for such a small size).

A hallmark of the product line was interchangeability: Tapes recorded on one tape drive were readable on another drive, even if the tape drives were built by different manufacturers. Magstar tapes and drives eventually existed in 128 (B), 256 (E) and 384 (H) track versions. Therefore, a tape that was written at a specific drive's upper density could only be read by a drive of the same model type or a higher version model. For example, a tape written on an H drive (60 megabytes max) could only be read by an H drive. A tape written on an E drive (40 megabytes max) could be read by an E drive or an H drive. A tape written on a B drive (20 megabytes max) could be read by a B, E or H drive. The 3590 B drives had a data transfer rate of 9 megabytes per second, the E and H drives had a transfer rate of 14 megabytes per second.

Because of their speed, reliability, durability and low media cost, the 3590 tape drives were very popular.

IBM Tape Library

The IBM Automated Tape Library. The IBM TotalStorage Enterprise 3494 Tape Library consisted of individual frames that could be configured to address a variety of client requirements (see the example to the left). The 3494 flexible design enabled organizations to install a solution that addressed not only their current capacity requirements, but the ability to add additional capacity as required.

Configurations included a library base frame, 3350 drive frames, storage only frames, and up to two IBM TotalStorage Virtual Tape Servers. The 3494 was a backup for hard drive storage in case of an unusual system failure or storage for seldom accessed but important data.

The 3494 library supported multiple generations of tape drives, tape controllers, and Virtual Tape Servers. The versatility of its design supported the increasing demands of storage growth.

The 3494 Tape Library had a small footprint, starting at 2.5 feet wide by 5 feet deep. That size allowed the 3494 Library to fit in many environments and made it suitable even for vaults. The 3494 Library could also provide significant savings in total floor space.

The Magstar 3590 had doubled the capacity of the enterprise-level tape solution by introducing extended-length media cartridges. The performance and reliability of both the initial 10 gigabyte media and then the extended-length media were attained through an intensive co-development with leaders in the magnetic media industry.