F-13 555brochure May63

This document describes the Digital Equipment Corporation (DEC) 555/550 Micro-Tape system, a data storage and transfer solution primarily for PDP-1 and PDP-4 computers.

The system consists of two main components:

1. Micro-Tape Type 555 Dual Transport:

   • Features two logically independent tape drives.
   • Uses 250-foot reels of 3/4-inch Mylar tape, operating at 80 inches per second.
   • Records data on 10 tracks (five duplexed channels) using a Phase Recording System with non-adjacent redundant tracks for reliability.
   • Achieves data densities of 350 three-bit characters per inch and a transfer rate of 180,000 bits per second.
   • Allows a standard block of 256 18-bit words to be transferred in 53 milliseconds.
   • A full reel can be read or written in 42 seconds.
   • A key feature is its "drum-like" exact tape addressing, facilitated by a serially coded Mark Track, enabling the replacement of single words or blocks without disturbing surrounding data.
   • Supports bi-directional reading and writing.

2. Micro-Magnetic Tape Control 550:

   • Houses the system's electronics and connects the transports to the host computer (PDP-1 or PDP-4).
   • Can manage up to four Type 555 Dual Tape Transports (eight individual drives).
   • Performs the assembly and disassembly of 3-bit tape data into 18-bit computer words.
   • Manages data transfer (word-by-word or in blocks), search operations (reading only block numbers), and provides timing and motion control.
   • Utilizes various flags (Data, Block End, Error) and programmed check sums for status monitoring and error detection.
   • The standard block length is 256 18-bit words (plus two check sum words).