IBM System/370 145 Manual page 181

The emulators accept as input and produce as output two tape file
formats:
1. 1400 format, which is produced by a 1400/1010 system, a stand-
alone emulator, CS/30. CS/IIIO, the Tape Postprocessor formatting
program, or the System/370 1400 emulators
2. Spanned variable-length relC;ord format, which is produced by the
Tape Preprocessor formatting program or a System/310 1400
emulator
Processing tape files in spann4ed variable-length record format
provides several advantages:
•
Bloc~ing
short records reduces the time for emulating, I/O operations.
• The Tape Preprocessor or the
~rape
Postprocessor program can be run
concurrently with the emulatol[,S in a multiprogramming system.
• Files in spanned variable-lenq-th record format can be used by other
System/310 programs if the programs provide for handling the
1400/7010 label records and 1JtJOO/7010 tapemark records.
• The Tape Postprocessor pro graIn ~an be used to convert a file in
spanned variable-length record format back to 1400 format for use on
a 1400/7010 system.
Tape files in spanned record f9rmat have standard DOS labels;
1400/1010 labels are treated as data records, since they are processed
by the 1400/7010 program. The 1400/1010 tapemarks appear as special
data records and are recognized b)( the emulators.
The character codes supported by the emulators for magnetic tape data
are:
• BCD representation in even and odd parity for seven-track tape (data
translator on) in 1400 format
• BCDIC-8 representation for nine-:-track tapes in either 1400 or
spanned record format, and
£0]:-
seven-track tapes (data converter on)
in spanned record format. This character code, which is the eight-
bit representation of BCD, is used to simulate parity. In normal
mode, bit 1 is set to one for even parity, to zero for odd parity.
In alternate mode, bit 1 is a]Lways set to one and no distinction is
made between even and odd parity_
Two tape formatting programs,
Cl
preprocessor and a postprocessor, are
available for converting tape fiIE~s. They are distributed to run as
problem programs under DOS contro].. They can be executed only in the
background partition. The Tape ~~eprocessor program converts seven-
track or nine-track tapes in 1400 format to seven-track (data converter
on) or nine-track tapes in spanned variable-length record format with
standard OOS labels. The Tape Postprocessor converts seven-track or
nine-track tapes in spanned recorCll format to seven-track or nine-track
tapes in 1400 format.
The DOS Clear Disk utility pro~~am is required to preformat Model 145
disk packs that are used for emulation of 1400 disk files. Each Model
145 disk record represents one 1400 disk track. Each Model 145 disk
record is a
fixed~length
record, its 1ength being a function of the
emulated 1400/7010 device and modE~ rather than the amount of 1400/7010
data on each track. A 1400/7010 disk file can occupy one or more
extents on Model 145 disk packs but only one extent per pack. Extents
must be allocated complete cylinders. When a file requires more than
one Model 145 disk pack, the packs must be the same type. Two different
A Guide to the IBM System/370 ModE!l 145 171