The IBM 650 was IBM's first commercial business computer, a 2-address, bi-quinary coded decimal computer, with memory on a rotating drum, introduced in 1954. It was specifically designed for users of existing IBM unit record equipment upgrading from Calculating Punches (e.g., IBM 604) to computers.

The basic 650 system consisted of three equipment cabinets:

  • Console Unit (Type 650)
  • Power Unit (Type 655)
  • Card Reader/Punch Unit (Type 533 or Type 537)
Optional equipment cabinets:
  • Disk Unit (Type 355)
  • Card Reader Unit (Type 543)
  • Card Punch Unit (Type 544)
  • Control Unit (Type 652)
  • Auxiliary Unit (Type 653)
  • Auxiliary Alphabetic Unit (Type 654)
  • Magnetic Tape Unit (Type 727)
  • Inquiry Station (Type 838)

The rotating drum memory provided 2000 10-digit words of memory, but was slow as a word could not be accessed until it passed under the read/write heads (avg. access time 2.5mS). The optional Auxiliary Unit (Type 653), providing 60 10-digit words of Magnetic Core, was introduced on May 3, 1955 to provide a little fast memory (access time 96uS).

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