Directory Program
DED cuu rdev volser 3330V This format is the same as the preceding, except that the virtual
device becomes a 3330V, such that VM/370 does not intercept any
cylinder fault interrupts or the associated attention interrupts.
4. There are considerations that must be made when dedicating real 3330Vs to a virtual machine that also has a dedicated MSC port and
is running an OS/VS operating system with support. (See
"Appendix F: VM/370 Restrictions.")
5. When dedicating a real CTCA, the CTCA should be on a separate real
channel from all other virtual devices because of a possible lOCK-out problem.
The LINK control statement makes a device that belongs to another user
(userid) available to this virtual machine at logon time. If you want
to make one volume available to several virtual machines: • Define the volume for one of the virtual machines with an statement. • Define a link to that volume, with the LINK statement for all other
virtual machines that use the volume.
Then, if you later must move or change that volume, you need only update
the one statement, the LINK statements need not be updated. The
format of the LINK control statement is: r I Link userid ldev [cuu (mode]]
L
userid
ldev
cuu
mode
is the 1-to 8-character user identification of the user to be
linked tOe is the virtual device address of the device owned by userid to
be linked to (3 hexadecimal This is the virtual
device address, assigned by userid, of the disk you wish to
link to.
is the virtual device address for the virtual machine being
defined. "cuu" defaults to the same address as the linked-to
device (3-hexadecimal digits). If your virtual machine has
the option, any address up to X'FFF' is valid;
otherwise, any address up to X'SFF' is valid.
is the primary access mode requested for the device
(read-only, write, or multiple-write), and the alternate
access (read-only or write) desired, if any, as follows:
R specifies that read-only (R/O) access is requested. The
link is not given if any other user has the disk in
write status.
RR specifies that read-only access is requested, even if
another user has the disk in write status.
Part 2r Defining Your VM/370 System 213

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