The IBM 350 was the first disk storage unit produced by IBM. First shipped in 1956, it marked IBM’s entrance into disk storage technology and revolutionized data storage for computers at the time.
What was special about the IBM 350 disk storage unit?
The IBM 350 introduced several innovations in data storage technology. Here are some of its notable features:
- First commercial use of disk storage – The 350 was the first disk storage device sold commercially. It helped make disk storage viable for businesses.
- Random access – The 350 allowed random access to any data point on the disk, unlike sequential access media like tape drives. This made data retrieval much faster.
- Removable disks – The 350 used removable disk packs that contained 50 metal disks coated with magnetic iron oxide. These could be easily swapped out to expand storage.
- Stored 5 million characters – Each disk pack stored up to 5 million alphanumeric characters. This was an enormous capacity at the time.
- Air filtration system – The 350 had an advanced air filtration system to minimize contamination from dust particles which could damage disk surfaces.
These innovations made the 350 a revolutionary product for its time. The ability to randomly access data on removable disk packs paved the way for more practical business applications of computer technology.
What was the history behind the development of the IBM 350?
IBM had produced the first commercial computer – the IBM 701 – in 1953. The 701 used magnetic tape for data storage. However, tapes had their limitations for data access and storage capacity. IBM wanted to develop a better storage solution.
In 1953, IBM formed a task force to build a random access disk storage system for use with their computers. Engineers explored various technologies including wire matrices, drum memory, and disk stacks. They selected the disk stack concept due to its potential for high capacity storage and rapid random access.
The project was completed in about a year. In 1956, IBM released the IBM 350 Disk File which was the first disk storage system built for commercial business use. It had a capacity of 5 million characters and allowed data access within 600 milliseconds.
The IBM 350 was compatible with several IBM computer systems including the IBM 650, IBM 702, and IBM 305 RAMAC. It quickly became an indispensable storage technology for these early business computers.
What was included in the IBM 350 system?
The IBM 350 was not just a single disk drive unit. It was an integrated disk storage system that consisted of these key components:
- Disk File Unit – This contained the removable disk packs and access mechanism.
- Control Unit – The control unit contained the electronic circuits governing operation of the system.
- Power Supply Unit – Provided power to the entire system.
- Maintenance Panel – This housed monitoring meters and maintenance controls.
The Disk File Unit was designed for easy operator handling. It had a transparent plastic front cover allowing the operator to view the disk packs. The disk pack containing the disks was loaded onto a horizontal shaft inside. The control unit coordinated power and timing signals to access data on the spinning disks.
What was the physical design of the IBM 350?
The IBM 350 was designed as a large pedestal cabinet that housed all its components. Here are some key dimensions and weight figures:
- Height – 62.5 inches (159 cm)
- Width – 33.5 inches (85 cm)
- Depth – 26 inches (66 cm)
- Weight – 965 pounds (438 kg)
The exterior was painted in IBM’s trademark gray color. The Disk File Unit took up the top third of the cabinet. The lower section contained the other components.
Air vents on the front and back allowed cooling air to flow through the unit. The air filtration system trapped dust particles that could potentially contaminate the disk surfaces.
All maintenance work could be performed by opening the front panel. Cables for power and data connections were located at the rear.
How did the IBM 350 disk packs work?
The key innovation of the IBM 350 was its use of removable disk packs for data storage. Here are some details on how the disk packs functioned:
- Contains 50 metal disks coated in magnetic iron oxide.
- Disks are 24 inches (61 cm) in diameter.
- Spaced 0.4 inches (1 cm) apart in the disk pack.
- Rotated at 1200 rpm by the drive motor.
- Two read/write heads per disk surface for 100 recording surfaces.
- Data recorded in 100 concentric tracks on each surface.
- Tracks had 250 sectors giving 25,000 sectors per pack.
- Access time to any sector was 600 milliseconds.
The disk pack was easily removable from the drive for offline storage. Discount packs with a capacity of 2 million characters were also available.
What was the data transfer rate of the IBM 350?
The IBM 350 was able to transfer data to and from the computer at these approximate rates:
| Data Transfer Rate | 7,200 characters per second |
| Peak Transfer Rate | 8,800 characters per second |
The transfer rate depended on the compute system it was connected to. The rates above applied to the IBM 702 computer using the IBM 781 Data Synchronizer.
For comparison, tape drives at the time had transfer rates below 1,000 characters per second. So the 350 offered a significant speed advantage over tapes.
How reliable was the IBM 350 Disk File?
IBM highlighted the reliable design of the 350 Disk File for error-free operation:
- Disks made of high quality aluminum alloy for rigidity.
- Proprietary disk coatings ensured uniform magnetic properties.
- A “landing zone” on the disk prevented head crashes on power down.
- Precise spindle servo control maintained proper disk speeds.
- Heads automatically unloaded if rotational speed dropped.
- Dual read/write heads provided redundancy.
- Elaborate air filtration system protected disk surfaces.
This robust engineering contributed to the 350’s industry leading performance and reliability. The disk error rate was an impressively low 1 in 100,000,000 bits read.
How was data organized on the IBM 350 disk packs?
The IBM 350 used open loop servo positioning. This meant data tracks were referenced to an internal offset rather than actual physical tracks on the disks. To help controllers maintain proper positioning, data was organized into distinct bands:
- 100 tracks per disk surface were divided into 4 bands of 25 tracks each.
- Bands were separated by guard spaces where no data was written.
- This prevented tracks in adjacent bands from interfering.
- If heads drifted, the guard band ensured it would still read the correct band.
Within each track, data was stored in 25 sectors of equal size. Fixed length records allowed simpler data processing. Later closed loop servo designs referenced physical tracks for more precise positioning.
How was data read and written on the IBM 350?
Data was read and written magnetically using heads positioned over the spinning disks. Here is a brief overview of the process:
- Two read/write heads per disk surface were mounted on a common arm.
- The heads flew just above the disk surface on an air bearing.
- Electric currents passing through the heads magnetized spots on the disk to write data.
- As magnetized spots passed under the heads, they induced currents to read the data.
- The heads were positioned by a linear servo motor using coarse hydraulics and fine leadscrew.
Signals picked up by the heads were amplified by vacuum tube circuits. The control unit coordinated timing and data transfer between the compute system and disks.
How was the IBM 350 disk file used by computers?
The IBM 350 Disk File served as an external storage unit that could be shared by multiple computer systems. Here are some of its typical usages:
- Secondary storage – Used for storing programs and data, backing up primary system memory.
- Data processing – Stored large volumes of business data for processing.
- Timesharing – Allowed multiple users to access the same data and programs.
- Offline storage – Disk packs could be removed and stored offline for security, archival.
- Programming – Provided rapid access to compilers, libraries and other tools.
The IBM 350 was connected to computers using specific data synchronizer units. Custom hardware and software interfaces were engineered for each computer system.
What impact did the IBM 350 have on computer history?
The IBM 350 had an immense impact shaping the future of data storage technology. Some of its major historical contributions include:
- Introduced concept of removable and interchangeable disk storage.
- Proved viability of disks for commercial data storage needs.
- Demonstrated advantages of random access storage over tape systems.
- Pioneered servo control mechanisms for precise disk head positioning.
- Established engineering approaches for future disk drive designs.
- Enabled new applications in business data processing and timesharing.
- Inspired decades of advancement in magnetic disk data storage.
IBM continued to rapidly advance disk storage capacity over the 1960s, with the IBM 1301 prvoding up to 2 million characters of storage. However the fundamental architecture pioneered by the IBM 350 remained hugely influential for years.
What were the limitations of the IBM 350 disk storage system?
Despite being a remarkable breakthrough, the IBM 350 had some inherent limitations that were improved in later disk drive designs:
- Limited storage capacity by modern standards (5MB).
- Large physical size and heavy weight.
- Used vacuum tube circuits instead of transistors.
- Heads could crash onto disk surfaces.
- Open loop servo positioning was less accurate.
- No built-in error detection codes.
- No caching mechanisms to optimize data access.
- Fixed record lengths wasteful of disk space.
As technology advanced, storage capacity, performance and reliability saw massive improvements. Capacities grew from megabytes to gigabytes to terabytes. The basic architecture of removable disk packs pioneered by the IBM 350 was eventually superseded as well.
Conclusion
The introduction of the IBM 350 Disk File marked a major milestone in the evolution of computer data storage. It pioneered the concept of a removable random-access magnetic disk memory that could serve as an external storage system. The innovations of the IBM 350 paved the path for all subsequent advances in magnetic disk storage technology.
Its 5 million character capacity, while minuscule today, was a game changer in 1956. By enabling computers to store and rapidly access large databases for business applications, the IBM 350 helped fuel increasing adoption of computer technology.
The roots of modern disk drives that underpin mass data storage can be traced back directly to the pioneering engineering of the IBM 350. It was an enormously influential product in computer history and a testament to the vision of IBM’s technical team in recognizing the future possibilities of disk storage.