IBM System/370 145 Manual page 190

included in the OS control program, all DOS emulation messages can be
routed to a specific console, and thus isolated.
The entire
os
DOS emulator partition/region operates with a nonzero
storage protect key to prevent it from interfering with the
os
control
program and other executing OS jobs. Therefore, the DOS emulator
program, the DOS supervisor, and other DOS jobs in the OS DOS emulator
partition/region are not protected from inadvertent modification by an
executing DOS program.
I/O DEVICE STAGING AND SHARING
If enough Model 145 processor storage is available, I/O staging can
be used to increase OS DOS emulator job throughput and reduce the number
of devices that have to be dedicated to the DOS emulation partition or
region. It allows DOS unit record files SYSRDR, SYSPCH, and SYSLST to
be emulated on direct access devices, using the OS reader interpreter
and output writer. DOS job control statements and/or card input to DOS
programs to be emulated can be placed in the OS input stream and will
be
transcribed by the reader interpreter to SYSIN data sets on direct
access devices. Thus, emulated DOS job steps will obtain their card
input from
as
SYSIN disk data sets. Output from emulated. DOS programs
can be placed in OS SYSOUT data sets on disk to be transcribed to the
printer or punch by an output writer.
The following should
be
noted about the use of I/O staging. In OS, a
job is not placed in the input queue, from which all jobs are scheduled,
until the entire job (job control and input stream data for the job) has
been read by the reader interpreter. Similarly, SYSOUT data sets
produced during job step execution are not placed in the output queue
for transcription by an output writer until job termination.
Thus, if all DOS jobs t.o be emulated are grouped together as a single
OS DOS emulator job, DOS emulation cannot begin until all DOS jobs (and
-their input stream data) have been read by the reader interpreter, and
none of the SYSOUT data sets from completed emulated DOS jobs can be
transcribed until the OS DOS emulator job itself terminates (all DOS
jobs processed). This negates one advantage of I/O staging, which is
the overlapping of unit record input and output data transcription with
processing.
Therefore, consideration should be given to grouping DOS jobs into
two or more
as
DOS emulator jobs that execute one after the other in the
OS DOS emulator partition/region. In addition, if the output from a
particular DOS job is desired immediately, i t should not be staged
(written to a SYSOUT data set). The use of multiple OS DOS emulator
jobs, ins·tead of one, in an OS DOS emulator partition/region offers an
additiona1 advantage in optimizing device usage, as discussed below.
When the OS input stream contains multiple OS DOS emulator jobs, the
automatic DOS IPL facility can be used to eliminate the need for the
operator to enter DOS IPL commands each time a DOS emulator job is
initiated (which causes an IPL of the DOS system). Another emulator
option provides the capability of requesting abbreviated initial prompt
messages. Normally, as an operational aid, four prompt messages are
given to the operator at the time emulation begins. When abbreviated
initial prompt is requested, a single prompt message is given, instead
of four. This facility can be used once the operator has become familar
with the emulator initialization procedure.
The I/O devices used in emulation need not have the same address on
the Model 145 as on the current system. However, in all but two
situations, the same device types currently being used by DOS p~ograms
must be used when these DOS programs are emulated (assuming the DOS
180
A Guide to the IBM System/310 Model 145