Directory Program W specifies that write access is requested. The
not defined if any other user has the disk in
write status.
disk is
read or WR specifies that write access is requested if no other
user has the disk in read or write status, but that an
alternate access of read-only is acceptable if others do
have a link to the disk. M specifies that multiple access is requested. This means
that a write link is to be given to the disk unless
another user already has write access to it, in which
case no link is to be given. MR specifies that a write link is to be given to the disk
unless another user already has write access to it. In
this case, a read link is to be given to the user, and
the "DEV xxxx FORCED R/O" message is issued. that a Yrite link is to be given to disk in any case. !Qie: If the mode is not specified, the default is R.
It is the responsibility of the operating system executing in each
virtual machine to keep data from being destroyed or altered on shared
disks. CMS supports multiply-accessed read-only disks in full. eMS does not
support write access to disks by multiple users. A disk accessed in
write mode by one CMS user is available to other CMS users in read-only
mode, but those files altered by the write-mode user cannot be read by the other users. CMS disks should never be linked in write mode to more than one user.
If two or more CMS users have write access to the same disk, all data on
the disk may be dedtroyed. Statement
The SPECIAL control statement specifies the I/O units available to the
user that need not have a real I/O unit available. Special devices are
program simulated devices that mayor may not be connected to real or
virtual devices after the user has logged off. The format of the SPECIAL control statement is:
r I SPEcial cuu devtype [IBMITele] L
cuu is a 1-to 3-character virtual device address.
214 IBM VM/370 Planning and System Generation Guide

Directory Program
devtype is the device type: IBM TELE 2701 2702 2703 3138 (virtual 3138 console)
3148 (virtual 3148 console)
3158 (virtu al 3158 console) 3270 (virtual 3270 only)
CTCA (channel-to-channel adapter) TIl!ER (pseudo-timer device)
valid only if devtype is 2701, 2702, or 2703 For example, a virtual machine executing a multiple-access
system that supports four IBM Type 1 adapter lines, would have
four SPECIAL entries, one for each of those addresses. This
provides a virtual 270x line to allow a user to dial to this
multiple-access system rather than logging on as a separate
virtual machine. No!e: The Integrated Communications Attachment (rCA) on the System/370 Models 135, 135-3, or 138 should be specified as a 2701. DIRECTORY ENTRIES FOR Cl!S/DOS The DOS/VS system and private libraries are accessed in mode
under Cl!S/DOS. If more than one CMS virtual machine 1S uS1ng the Cl!S/DOS environment, you should update the V8/370 directory entries so
that the DOS/VS system residence volume and the DOS/VS private libraries
are shared by all the CMS/DOS users.
The VM/370 directory entry for one of the Cl!S virtual machines should
contain the MDISK statements defining the DOS/VS volumes. The VM/370 directory entries for the other Cl!S/DOS users should contain LINK statements. For example, assume the DOS/VS system libraries are on cylinders 0-14Q of a 3330 volume labeled DOSRES. Also, assume the DOS/VS private
libraries are on cylinders 0-99 of a 2314 volume labeled DOSPRI. Then
one CMS machine (for example, DOSUSER1) would have the MDISK statements
in its directory entry. USER DOSUSER1 password 320K 2M G MDISK 331 3330 0 150 DOSRES R rpass MDISK 231 2314 0 100 DOSPRI R rpass All the other CMS/DOS users would have links to these disks. For
example
LINK DOSUSER1 331 331 R rpass LINK DOSUSER1 231 231 R rpass
For more information about directory entries for CMS/DOS virtual
machines, see the Ope£ating in Part 2. Defining Your VM/370 System 215