MPE/iX 5.5 Operating System Limits

For applications which do not use timed reads and writes, the number of FSIPC
ENTRIES PER FILE will be (N+2)+(N-1) or 2N+1. For applications which do use timed
reads and writes, the number of FSIPC ENTRIES PER FILE will be (N+2)+(N-1)+N or
3N+1.
Let's assume that ALL the applications are simple applications with two processes
accessing each message file, (N = 2), and that the applications are not using timed reads
and writes. Then, the maximum number of OPEN MESSAGE FILES would be
40,000,000 / 5 = 8,000,000.
If the applications are using timed reads, (and N = 2), then the maximum number of
OPEN MESSAGE FILES would be 40,000,000 / 7 = 5,714,285.
(5) Fmavt DST - DST044
One FMAVT entry is allocated for each unique Compatibility Mode (CM) file that is
opened for Multi Access. Currently, this means the following file types: Message files,
Circular files, RIO files, and Device files.
Note that $STDIN and $STDLIST are opened for Multi Access. Since terminals are still
considered to be CM Device files, each session will require one entry in the FMAVT,
assuming that $STDIN and $STDLIST are the same terminal. (The FMAVT entry is
shared between them in this case).
This table limits the number of unique CM files that can be opened simultaneously for
Multi Access to 5460. Files that are opened more than once will share an FMAVT entry.
(6) Input/output device directory
The Input Device Directory (IDD) and Output Device Directory (ODD) data structures
are kept in CM DSTs. The IDD is DST 45, and the ODD is DST 46. The format/layout of
the IDD and the ODD are identical. For this reason they are often referred to using the
generic acronym XDD.
The maximum number of entries in the XDD is limited by the maximum size to which
the table can grow. Since the XDD is a CM table, this section will use CM words (16-
bits) for all size calculations. The table is managed in "sectors" (128 CM word chunks).
The maximum size of the table is 255 "sectors" times 128 CM words per "sector", or
32640 CM words. This is only slightly less than the maximum size of a CM DST (32764
CM words) so it does not significantly reduce the maximum number of entries. The XDD