IBM System/370 145 Manual page 187

40:15 OS DOS EMULATOR PROGRAM
The availability of the OS DOS emulator offers DOS Version 3 and 4
(Releases 25, 26, and 21) users ",rho upgrade to a Model 145 the
opportunity to convert to an OS operating environment more easily than
is possible without the use of enmlation. In addition, the OS DOS
emulator user can benefit from the use of integrated emulation, since
the OS DOS emulator can execute c:oncurrently with other OS jobs.
The OS DOS emulator for the Medel 145, which is the same DOS emulator
provided for System/310Models 13~5 and 155, is a combination of the OS
DOS emulator processing program alnd the standard OS/DOS Compatibility
feature. This feature provides t~he relocation necessary for execution
of a DOS supervisor and DOS progz'ams under
as
control in any processing
program storage location.
An
OS MFT, MVT, VS1, or VS2 control program
generated for a Model 145 is required also.
The OS OOS emulator program and the DOS system being emulated (DOS
supervisor and up to three proces.sing program partitions) execute
together in an
MFT
minimum partit.ion size of 39K (40K if storage
protection is included in the
MF'I'
control program) or a minimum MVT
region size of 46K. The OS DOS e~mulator program and tables require a
minimum of 23K plus another 4K if I/O staging is used. Additional OS
DOS emulator program storage may
be
required depending on the I/O
devices used. Up to ten I/O devi.ces are supported in 23K, and 250 bytes
are required for each additional device. The I/O staging requirement of
4K supports unblocked reader, pri.nter, and punch records and residence
of the required QSAM routines in the OS DOS emulator partition or
region. The use of certain other' emulator options will also require an
increase in the size o,f the- OS DOS emulator program.
The DOS system being emulated can be 16K. 24K, or 32K and up, in 4K
increments. The
as
DOS emulator is scheduled to operate in the same
manner as any other OS job, and one or more
as
DOS emulator jobs can
execute concurrently with
as
jobs if enough I/O devices and processor
storage are available. In addition, the Model 145
as
1401/1440/1460 and
1410/1010 Emulator programs can execute concurrently with the
as
DOS
emulator if enough resources are present.
The user need not make any changes to the existing DOS supervisor,
job control statements, tape files, or disk files in order to use the OS
DOS emulator. Modification of, existing DOS programs is required only
for programs that contain features unsupported by the OS DOS emulator.
The major advantages of the OS DOS emulator are:
• Transition from a DOS to an
as
operating environment is smoother,.
The conversion of DOS source programs, job control, and data files
to
as
formats can be done gradually for emulated DOS jobs.
• Dedicated emulation is not required, thus allowing the user to take
advantage of OS facilities.
• OS data sets and OS-compatible DOS files can
be
accessed by emulated
DOS programs (without modification of the DOS programs) and by DOS
programs that have been converted to OS format.
• Direct access volumes can contain both DOS files and OS data sets so
that direct access devices can be accessed by concurrently executing
OS jobs and DOS emulator jobs.
• Model 145 OS DOS emulator use:rs can continue to use most IBM-
supplied application programs (Type II and' program products) that
operate under DOS but not und,er OS and do not use QTAM, by emulating
them under
as.
A Guide to the IBM System/310 Modlel 145 111