Dectape Transport Design

This document describes the design philosophy and technical specifications of the DECtape transport system developed by Digital Equipment Corporation. Moving away from conventional "start-stop" tape mechanisms, the designers focused on simplicity and reliability by creating a system that utilizes continuous motion.

Key technical highlights include:

• Tape Handling: The system uses reels rather than bins to achieve compact storage. To manage the tape, engineers utilized ac induction motors that provide constant torque, eliminating the need for complex torque reversals and reducing electrical sparking.
• Tape Guiding: To minimize wear and avoid the use of dirt-collecting pressure pads, the design employs hydrodynamic lubrication—using the air's viscosity—to create a cushion that floats the tape over the head and guide track.
• Recording Technique: Instead of amplitude-sensing, which is sensitive to speed fluctuations, the system uses a polarity-sensing technique. This allows the system to read data reliably across a wide range of tape speeds.
• Addressing: The system features a prerecorded timing track, which allows users to address and rewrite specific characters or even individual bits without affecting surrounding data.

The document concludes with a summary of specifications for the 555 transport model, noting its capacity, transfer rates, and mechanical requirements.