IBM System/370 145 Manual page 123

is loaded in the columns and positioned at load point within ten seconds·
after the bu·tton is depressed fo:[' Models 3 and 5. On the Model 1, only
seven seconds are required. In iaddi tion, unload and rewind/unload
operations cause the tape to be Icompletely rewound on the tape reel and
the power window to be lowered so that the reel is ready for immediate
demounting.
If the tape is enclosed in a llII1raparound cartridge (10. 5-inch reels
only), an operator need only mow~t the cartridge and does not have to
place the tape end on the threadIer 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 1the tape ·and retries threading. Unload
operations rewind and close the 4~artridge automatically. In addition to
fast tape reel mounting, the use of a wraparound cartridge offers other
advantages. Handling of the
tap4~
reel itself is not required when the
tape is used, because the wraparound cartridge is also the shelf storage
container. The only time the calt:'tridge need be opened is when it is
opened by the 3420 during use. ~rhis enhances the reliability of the
tape media.
The 3420 tape unit also has a new automatic reel latch instead
snap-type hub latch implemented on newer 2400-series tape units.
operator places ·the tape reel on the hub and the automatic latch
mechanically aligns the reel and then pneumatically locks it in
position.
of the
The
The advantage of these featurE~s can be shown by comparing setup times
for tape units with and without t:he autothread feature.
A
tape study
using experienced operators indi(:ated the total time required to remove
a tape reel, mount a new reel, tlrread the tape, and come to ready status
was the following:
2401 tape unit - 40 seconds
Autothread tape unit withc:)ut 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 3B03 control units and 3420 tape units.
They are mutally excl usi ve featw::es. The Dual Densi ty 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 SE!Ven 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 556/S00-BPI or nine-track 800-BPI tape. (See
section 60 for a discussion of conversion to 3420 tape units.)
A
3803 control unit with the Single Density feature (without a
switching feature) can handle up to eight 3420 tape units (Models 3. 5,
and
1)
with the companion Sing1e Density feature installed. Only 1600-
BPI PE tape can be read and writt.en. When the Dual Density feature is
present on the 3803 control unit, hoth nine-track 1600-BPI PE and nine-
track 800-BPI NRZI tape operations can be performed on 3420 units
(~lodels
3, 5, and
1)
with the companion Dual Density feature installed.
('Iape units with the Single Density feature still handle only nine-track
1600-BPI PE tape.) When the Seve~n Track feature is present on the 3803
control unit, seven-track 556/800-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
fe~ature
installed. The data convert and
translate facilities are a standard part of the Seven Track feature.
Table 20.25.1 summarizes 3803 control unit capabilities without and with
these features.
A
Guide to the IBM System/370 Model 145 113