IBM System/370 Guide

Page of GC20-1730-0
Added 11/20/70
By TNL GN20-2277
20:25 THE 3803/3420 MAGNETIC TAPE SUBSYSTEM
The new 3803/3420 Magnetic Tape Subsystem consists of 3803 Tape
Control and a family of three 3420 Magnetic Tape Units which read and
write nine-track, 1600-BPI, phase-encoded, half-inch magnetic tape.
The three tape units, Models 3, 5, and 1, have a data rate of 120 RB,
200 RB, and 320 RB, respectively, and up to eight tape units, in any
mixture of models, can be attached to a 3803 control unit. This tape
subsystem, which embodies a completely new control unit technology,
offers price performance improvements, compatibility with existing
seven- and nine-track tape volumes and programs, enhanced reliability,
availability, and serviceability features, lower cost tape switching
capabilities, and standard automated tape-handling features presently
available only on 2420 Magnetic Tape Unitsa (Table 20.25.2 at the
end of this sUbsection compares 3420, 2420, and 2401 tape unit
characteristics.)
The 3803/3420 subsystem can be attached to all System/310 models
and to System/360 Models 30 to 195 (Model 61 in 65 mode only) except
Model 44 for which there is no program support. The tape commands,
status responses, and basic sense data of this tape sUbsystem are
compatible with those of 2400-series tape units. Thus, any correctly
written, non-time-dependent System/360 program for 2400-series tape
units will operate without change on the Model 165 (subject to
restrictions stated in section 10:05) to handle operations on 3803/3420
subsystems with equivalent features installed. That is, existing nine-
track 1600-BPI phase-encoded (PE), nine-track 800-BPI non-return-to-
zero (NRZI), and seven-track 556/800-BPI NRZI-encoded tapes can be
processed on 3420 tape units using existing programs without change
to the tape volumes or programs.
The 3803/3420 tape subsystem offers 2400-series tape users the
advantages of the latest significant advances in tape speed and design
while maintaining media compatibility with existing tape volumes and
providing enhanced RAS features. Specifically, the following are
provided:
• Data rates of 120 KB, 200 KB, and 320 RB at 1600-BPI density
• Phase-encoded data recording that automatically detects and corrects
single-bit read errors in-flight
• A tape transport design that minimizes tape wear and increases
reliability, a single-drive capstan to control tape movement that
provides faster data access times and rewinds, and more precise
control of motor speed to help minimize damage to tape media
• Cartridge loading of tape, automatic tape threading, and a new
automatic tape reel hub latch, all to reduce tape setup time
• Dual Density and Seve.Tl-Track (mutll;:~ lly excll1~i Vp.) features to
enable a 3420 tape unit to handle either nine~track SOO-BPI ~mZI
and 1600 BPI PE tape or seven-track 556/800-BPI NRZI (BCD or binary)
tape
• Flexible, lower cost tape switching implemented in a new compact
physical design - a two-channel switch is available also
• Features such as new technology to improve subsystem reliability
and new diagnostic facilities to aid serviceability and thereby
increase subsystem availability
51.1
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IBM System/370 Specifications

General

Brand	IBM
Model	System/370
Category	Server
Language	English