IBM 1311 disk storage drive

IBM 1311 Disk Storage Drive (center)

• Models 1 through 4 announced October 11, 1962
  
  
• Model 5 announced January 7, 1963
  
  
• Models 6 and 7 announced March 5, 1968
  
  
• Models 6 & 7 withdrawn February 2, 1971
  
  
• Models 1 & 4 withdrawn February 8, 1971
  
  
• Models 3 & 5 withdrawn May 12, 1971
  
  
• Model 2 withdrawn January 6, 1975

The IBM 1311 Disk Storage Drive provided storage for 2 million characters. Developers of the 1311 engineered twice the recording density of the IBM 1301 Disk Storage Unit by reducing the space between the head and the disk by about a factor of two.

The 1311 used the IBM Disk Pack (later designated the IBM 1316 ), an interchangeable package containing six 14-inch-diameter disks in a four-inch stack, weighing 10 pounds (seen above in the man's left hand). Each disk surface contained 20 pie-shaped regions. Sectors were segments of track lying within a region, and were the smallest addressable unit, with a capacity of 100 characters. Average access time to any sector was 250 milliseconds, which could be reduced to 150 milliseconds with an optional direct-seek feature. The disks were rotated at 1500 rpm, tracks (50 to the inch) were recorded at up to 1025 bits per inch, and the usual head-to-surface spacing was 125 microinches. The ten recording surfaces provided in normal usage a storage capacity of 2 million characters, the equivalent of approximately 25,000 punched cards or a fifth of a reel of magnetic tape.

The first host mainframes for the 1311 were the IBM 1401 Data Processing System , 1440 Data Processing System , 1620 Data Processing System and 1710 Control System.