IBM System/370 145 Manual page 191

programs are not modified to use a new device and then reassembled).
First, I/O staging can be used for unit record devices. Second, certain
I/O devices can be emulated on an I/O device of the same type with a
different device number, without modification of existing DOS programs,
if the old and the new I/O
devicE~
are command code compatible as
follows:
Current Device
2540 reader punch (read. operat:.ions)
2540 reader punch (punch operations)
1403 printer
2400-series tape units
Emulation Device
3505 reader
3525 punch
3211 printer
3420 tape units
I/O operations and I/O error l:-ecovery procedures for emulated OOS
programs are handled by the OS control program, with one exception. DOS
ERP's are used to handle I/O errors for terminals supported by BTAM.
All I/O devices to be used by .em\uated DOS programs must be allocated to
the DOS emulation partition or rE!gion when the OS DOS emulator job is
begun. All non-direct access de,,'ices allocated to a OOS emulator
partition are dedicated to DOS enlulation and cannot
be
allocated to any
other executing OS jobs whil.e DOS emulation is in operation in the
partition. Direct access device!:; allocated to a DOS emulator partition
do not have to be dedicated to DOS emulation. Therefore, optionally, a
direct access volume that contains both OOS files and OS data sets can
be accessed concurrently by OS jobs and a DOS emulation job.
The appropriate DD job control. statements must be included for each
DOS emulation job step for which direct access device sharing is to be
supported. When direct access dEwices are shared, space allocation on
direct access volumes and VTOC updating are performed by OS, and DOS
equivalent functions are bypassed. Thus, OS password protection is
active and DOS files with securit~y protection indicated in their labels
will be password-protected.
Restrictions on the use of dil::ect access device sharing are the
following:
• OOS files must be opened (to cause the execution of OS space
allocation routines>.
• Only single volume DOS files with up to 16 extents are supported on
shared direct access devices.
• OOS job steps that specify ac:tual direct access extents for new
files are not supported SinCE! space will be allocated according to
OS rules and the DOS specific:ation is effectively overriden.
• The first extent of a DOS file with split cylinders must be the
spli t cylinder extent and all. data sets sharing a split cylinder
must be processed by the samE~ job step.
• Programs that access a file on a shared volume must not use embedded
seek commands within channel programs.
When direct access device sha:r:'ing is used, emulator size is
increased. Direct access devices: can be accessed by concurrently
executing DOS emulator jobs and aLIso
by
DOS partitions being emulated in
the same OS DOS emulator partition.
It is the user's
responsibilit~y
to ensure that all online OS DOS
emulator direct access volumes haLve unique volume serial numbers wi.th
respect to other DOS and OS direct access volumes online at the same
time.
A Guide to the IBM System/370 Modlel 145