IBM 1301 disk storage unit

IBM 1301 Disk Storage Unit

• Models 1 & 2 announced June 2, 1961
  
  
• Models 11, 12, 21 & 22 announced October 8, 1963
  
  
• All models withdrawn October 1, 1970

The IBM 1301 Disk Storage Unit, with its larger capacity, flexibility and speed, greatly expanded the operational capability of the IBM 7000 series of computers (7070, 7094, 7080 and 7090). The 1301 increased the throughput of those large systems for many types of jobs, and with its unique organization of data, the 1301 added significantly to the time the 7000 mainframes could actually compute.

Used in combination with the 7000 series, the 1301 had many of the same general physical and operating characteristics as when used with the IBM 1410 Data Processing System. Those characteristics included: the cylinder concept (vertically-aligned read/write heads, one to a disk surface, to provide reading and writing of related information in corresponding disk tracks and to eliminate the need for vertical access motion); flexible record length (different length records could be stored within the file, greatly increasing actual storage capacity); and selective addressing (record numbers were assigned by the user for greater efficiency in many jobs; addresses did not have to be consecutive, sequential or even numeric).

The 1301's disks rotated at 1,800 rpm. The 1301 provided for 50 tracks per inch and recording of up to 520 bits per inch of track (thanks to a reduction in the average head-to-surface distance of from 800 to 250 microinches). As a result, storage capacity per square inch of surface was increased 13 times over what it had been with IBM's RAMAC technology of 1956.

The Model 1 of the 1301 had one module; the Model 2 had two modules. Module capacity of the 1301 used with 7000 series computers was 28 million characters; used with the 1410 computer, the module capacity was 25 million characters. As many as 10 modules (five 1301 units) could be attached -- using the IBM 7631 file control unit, and in some cases, adapters and data channels -- to a computer system, providing maximum capacity of 280 million characters for the 7000 series machine and 250 million for the 1410.

Manufactured at IBM's plant in San Jose, California, the 1301s were first delivered to customers in the third quarter of 1962. (A few days before the 1301 was officially announced in June 1961, an engineering model of the 1301 was shipped to IBM's Poughkeepsie, N.Y., facility for use in tests of the celebrated SABRE reservation system. Later, in full operation, the SABRE system attached six magnetic storage drums and 16 IBM 1301s.)

The Model 1 with one module cost $2,100 a month to lease or could be purchased for $115,500. The Model 2 with two modules cost $3,500 a month to lease or $185,500 to purchase.

According to IBM computer historian Dr. Emerson Pugh and his co-authors, "The 1301 pioneered in two major areas: self-acting, air-bearing slider technology and a separate read-write head for each disk surface with a comblike structure to hold the heads and move them in concert from one cylinder of data to the next. These innovations were the bases for decades of improvements in storage density and access times."*