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The 3270's block-oriented approach was more consistent with IBM's batch-and punched card-oriented view of computing, and was particularly important for IBM mainframes of the day.

Unlike contemporary minicomputers, most IBM mainframes were not equipped for character-at-a-time interrupts.

Dumb terminal support relied on terminal control units such as the IBM 270x ( see IBM 3705 ) or Memorex 1270.

These asynchronous terminal controllers assembled a line of characters, up to a fixed maximum length, until the RETURN key was pressed.

Typing too many characters would result in an error, a familiar situation to users of the day.

( Most data centers did not include this equipment, except as needed for dial-up access.

The 3270 approach was preferred.