IBM System/370 Guide

Page of GC20-1730-0
Added 11/20/70
By TNL GN20-2277
If the tape is enclosed in a wraparound cartridge (10.S-inch reels
only), an operator need only mount the cartridge and does not have
to place tt tape end on the threader chute. Once the load-rewind
button is depressed, ten seconds are required to open the cartridge
and perform automatic threading. If automatic threading fails on the
first try, the 3420 unit automatically rewinds the tape and retries
threading. Unload operations rewind and close the cartridge
automatically. In addition to fast tape reel mounting, the use of
a wraparound cartridge offers other advantages. Handling of the tape
reel itself is not required when the tape is used, because the
wraparound cartridge is also the shelf storage container. The only
time the cartridge need be opened is when it is opened by the 3420
during use. This enhances the reliability of the tape media.
The 3420 tape unit also has a new automatic reel latch instead of
the snap type hub latch implemented on newer 2400-series tape units.
The operator places the tape reel on the hub and the automatic latch
mechanically aligns the reel and then pneumatically locks it in
position.
The advantage of these features can be shown by comparing setup
times for tape units with and without the autothread feature. A tape
study using experienced operators indicated the total time required
to remove a tape reel, mount a new reel, thread the tape, and come
to ready status was the following:
2401 tape unit - 40 seconds
Autothread tape unit without cartridge - 29 seconds
Autothread tape unit with cartridge - 13 seconds
Single Density, Dual Density, and Seven-Track features. These three
features are provided for both 3S03 control units and 3420 tape units.
Dual Density can be field-installed on a 3S03; however, the Seven-Track
feature is not recommended for field installation. They are mutally
exclusive features. The Dual Density or the Seven-Track NRZI feature
can be field installed on a 3420 tape unit only if it is replacing
another NRZI feature. (For example, Dual Density can be field installed
to replace the Seven-Track but not the Single Density feature.) The
Dual Density and Seven-Track features facilitate efficient conversion
of existing NRZI-recorded tapes to 1600-BPI phase-encoded format and
permit tape volume interchange with other systems that use seven-track
SS6/S00-BPI or nine-track SOO-BPI tape. (See Section 60 for a
discussion of conversion to 3420 tape units.)
A 3S03 control unit with the Single Density feature (without a
switching feature) can handle up to eight 3420 tape units (Models 3,
5, and 7) with the companion single Density feature installed. Only
1600-BPI PE tape can be read and written. When the Dual Density feature
is present on the 3S03 control unit, both nine-track 1600-BPI PE and
nine-track SOO-BPI NRZI tape operations can be performed on 3420 units
(Models 3, 5, and 7) with the companion Dual Density feature installed.
(Tape units with the Single Density feature still handle only nine-
track 1600-BPI PE tape.) When the Seven-Track feature is present on
the 3S03 control unit, seven-track 5S6/S00-BPI NRZI operations (both
BCD and binary format) can be performed on 3420 tape units (Models
3, 5, and 7) with the companion Seven-Track feature installed. The
data convert and translate facilities are a standard part of the Seven-
Track feature. Table 20.25.1 summarizes 3S03 control unit capabilities
without and with these features.
51.4

IBM System/370 Specifications

General

Brand	IBM
Model	System/370
Category	Server
Language	English