IBM 350 Disk Storage (RAMAC disk drive)

1957 IBM 350 Disk Storage (RAMAC disk drive)
First production disk drive

Why It's Important

The 350 disk storage also known as the RAMAC disk (RAMAC stands for Random Access Method of Accounting and Control) was the first device able to provide direct access of less than a second for reading and writing or updating individually a very large number of records. The IBM 350 disk drive marked the beginning of a revolution in computing by introducing transaction processing, replacing sequential processing, until then required with the storage of databases on inherently serial access media like paper or magnetic tape and punched cards


The IBM 350 disk drive stored 5 million characters (using a 6 bit character code plus a parity and space bit per character) in the formof 50,000 100 character sectors. The disks were 2 feet in diameter and the disk stack consisted of 50 magnetic disks for data storage in a stack 20 inches high. The maximum access time was 0.8 seconds to any record in the stack.
Among the radical innovations made to realize the IBM 350 disk storage included:

  • using a rotating stack of closely spaced magnetic disks
  • positioning of two read/write heads to serve many tracks
  • like magnetic drums, the read/write head spacing had to be close but always out of contact with the storage media. The RAMAC used a pressurized air or floating head for this purpose
  • self-clocking for the reading of data.
  • wide erase narrow read/write magnetic heads
  • small read/write transducer to fit between closely spaced disks
  • spin coated iron oxide paint on aluminum disks
IBM 350 disk storage (courtesy IBM Corp.)
Brief History

IBM established a small "advanced technology" laboratory, the first on the West Coast, in San Jose in 1952. the size was limited to 50 people and the main purpose was to acquire engineering talent on the West Coast given the reluctance on so many there to move to the IBM Labs back East. Rey Johnson, an inventive genius, was put in charge and given free rein to focus on projects that sometime in the future may benefit IBM. This freedom and exploratory environment led to the concept of a mass storage device as a part of a transaction processing system. Rey Johnson is universally recognized as the creator, inventor or father of disk drives and received the National Medal of Technology for his contributions to data storage in 1986.

Earlier punch card accounting relied on pre-punched cards in a tub file to store frequently used data. These would be manually selected to merge with newly keypunched data for batch processing of business data. .Johnson eventually recognized that by mechanizing the role of a tub file for many applications transactions could be processed directly. From this concept to a transaction processing system with its enabling magnetic disk file was a journey requiring innovation and dedication.
The two individual most responsible for the implemetation of these concepts were John Haanstra for both the system and the intital drive design and Lou Stevens who led the drive design after November 1953.

Given the size of today's disk drive development groups, it is surprising how few people worked on developing the RAMAC. When the first successful transfer of information to and from a model I RAMAC occured in February 1954 [Note 1] the San Jose Laboratory staff was about seventy persons [Note 2] of which perhaps twenty had spend significant time on the model I RAMAC [Note 3].

The RAMAC program led to a number of pioneering patents including amongst others, the fundamental disk drive patent, US 3,503,060 issued March 24, 1970 and US 3,058,844 the basic disk magnetic coating patent used on all disk drives into the 1990s. There is an urban legend, now know to be false, that disk coating used on production RAMAC disks was somehow equivalent to the paint used on the Golden Gate Bridge - neither the pigment nor the binder of either paint was similar.

During development, the RAMAC 350 disk file was not particularly popular, being known as the "baloney slicer" within the San Jose Laboratory and cancelled, possibly twice by IBM's headquarters. Disk drives went on to become at times the most profitable IBM product line and in this century a worldwide industry with revenues in the tens of billions of dollars

Public disclosure dates:

May 1955IBM press conference describes new method for data storage being pursued, “that takes information from a stored program using a multi-million character random access memory.

July 1955
"This Exciting Device Stores 5 Million Thoughts," PG&E Progress, Pacific Gas & Electric Company, San Francisco CA

April 1956Details of RAMAC disk drive designpresented in a paper "Engineering design of a magnetic-disk random-access memory" at the Western Joint Computer Conference

Jun 1956Shipment to Zellerbach Paper Company, SF CA, of one of 14 IBM 305 system prototypes including one 350 disk storage per system

Sep 4, 1956IBM internal announcement of both the IBM RAM 650 and IBM 305 RAMAC systems, both of which included a RAMAC disk drive, the Model 355 and Model 350 respectively.

Sep 13, 1956One day prior to a public announcement, the press witnessed a demonstration of a 305 RAMAC data processing machine including a RAMAC 350 disk file. [NY Times, Sept 14, 1956]

Sep 14,1956At a press conference chaired by IBM’s President T.J. Watson, Jr., the RAMAC disk storage was announced as a component of the 305 RAMAC and 650 RAMAC data processing machines. It was described as “IBM's random access memory, a stack of disks that stores millions of facts and figures less than a second from management's reach.”
See: 650 RAMAC announcement - Press release

Prototype units built with engineering assistance first shipped in June 1956 to Zellerbach Paper, SF, CA. All prototype models, designated 350A units were recalled and replaced with production units that began shipping about November 1957.[Note 5] A second drive, the 350 Model 2, for the 305 system was announced in May 1958 for delivery scheduled for September 1958. Dual actuator versions, Models 3 and 4 were announced on September 15, 1958.Double capacity versions, Models 11, 12, 13 and 14 were announced January 12, 1959, and shipped later that year. The Model 11 thru 14 were double capacity versions of the Models 1 thru 4 respectively.

The 350 disk storage as the key component of the IBM 305 RAMAC System demonstrated the value of magnetic disk storage for accounting and control applications.Today magnetic disk storage is pervasive in all computing applications and has become the way essentially all on-line information is stored, and shared world-wide

  1. [Kean1977], pg 32. Model I, "First operable on February 10, 1954"
  2. [Kean1977], Appendix A lists 71 persons employed by year end 1953
  3. [Kean1977] and [Bashe1986] explicitly name about 18 persons with specific involvement on the 350 disc storage Model 1.
  4. Between the internal announcement on September 4 and the press conference on September 14 the name was changed from RAM 650 to 650 RAMAC
  5. Correspondence with Bruce Allal, IBM SJ production technician, as confirmed inThe Indiana Gazette (Indiana, Pennsylvania), 4 Nov 1957,Page 22

Additional Information

[Kean1977]Kean, David W., "IBM San Jose, A Quarter Century Of Innovation”, 1977, CHM accession number: 102687875
[Bashe1986] Bashe et al., "IBM'S Early Computers", MIT Press,1986, especially Chapter 8, "Disk Storage."
RAMAC oral history project: Five oral histories conducted by Jim Porter at IBM Almaden Research Labs
  • November 20, 2001 - Lou Stevens, Jack Harker and Tom Leary
  • December 3, 2001 - Lou Stevens, Jack Harker and Al Shugart
  • January 11, 2002 - Lou Stevens, Jack Harker and Al Shugart
  • January 21, 2002 - Lou Stevens, Bill Crooks and Norm Vogel
  • March 22, 2002 - Lou Stevens and Wes Dickenson
Collection Of Rey Johnson Papers at Computer History Museum
IBM Archives 350 Site
IBM Celebrates 50 Years Of Storage a video press release by IBM circa Sept 6, 2006, featuring the RAMAC 350
IBM 350 RAMAC Disk File Brochure, for designation as historical landmark by ASME, Feb 24, 1984
RAMAC 350 Restoration Web Site

Provenance note: This page was originally authored by Al Hoagland; his last approved revision was version 80. It has been substantially modified since T. Gardner. Hogaland does not agree with the changes made