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• IBM 3310 Direct Access Storage
• Models A1, A2, B1 and B2 announced January 30, 1979 and withdrawn June 16, 1986

The IBM 3310 Direct Access Storage was a compact, economically priced, high-performance direct access storage device for use with the IBM 4331 Processor. The 3310 used a fixed media design. Heads, arms and the media were packaged in a fixed, sealed disk enclosure providing for increased data density. The sealed disk enclosure design assured a reduction in disk surface contamination and resulted in improved reliability. Operator involvement in auxiliary storage management was eliminated.

• Stored 64.5 million bytes of data in each of its drives, Up to four strings of four spindles each could be attached to a 4331 Processor for a maximum of 1.032 billion bytes of online data.
  
  
• Available in four models for configuration flexibility:
  • Models Al and A2 consisted of one and two drives with associated controls which attached to the 4331 via its DASD Adapter.
  • Models B1 and B2 were one- and two-drive units which attached through a Model A2.
    
    
• Low-priced single drive increments provided for granularity of capacity growth.
  
  
• Used fixed block architecture. Physically, data were stored on the disk in 512-byte blocks, providing logically continuous data. Software support mapped the data into the format required for user records.
  
  
• More data could potentially fit on a track due to the data structure used in fixed block architecture, providing increased capacity.
  
  
• DASD space was specified as a number of blocks on the device up to a maximum of 126,016 blocks, making space definition independent of tracks and cylinders.
  
  
• The device independence achieved provided for easy use and simplified later migration.
  
  
• Used a new, lightweight, low-inertia actuator driven by a voicecoil motor, providing a 27 millisecond average access time. This simple design required less power than previous actuators.
  
  
• The IBM 3310 contained rotation position sensing as a standard feature which could enhance subsystem performance.
  
  
• The DASD Adapter on the 4331 provided direct, low-cost attachment for the IBM 3310 without need for a control unit. Direct processor attachment of up to strings of eight 3340 actuators also was available as a special feature of the Adapter. A DASD Adapter with 3340 so attached operated in count-key-data emulation mode under DOS/VSE, VS1 or VM/370.
  
  
• An optional 2311 and 2314/19 compatibility feature allowed these devices to be emulated on the IBM 3310. Use of this feature allowed most DOS or DOS/VS programs written for the IBM 2311, 2314 or 2319 to be executed without modification.
  
  
• By installing a special feature, DASD Adapter could read data from an IBM 3348 Data Module which was recorded on an IBM System/3 Model 12 or 15, to aid in conversion from a System/3 to 4331 Processor.
  
  
• An optional Block Multiplexer Channel on the 4331 allowed direct attachment of 2311 and 2314/19 DASDs, when required.