You can specify the size of the records in your file by using the
BUILD (for disk files) or FILE commands, or the
HPFOPEN/FOPEN intrinsic; however, the interpretation of the
requested record size can be affected by the record structure and
data format chosen as well as the device for the file.
NOTE: Within MPE/iX and in various subsystems, the record
size for an ASCII file is usually identified in terms of bytes (8
bits) and the record size for a binary file is identified in terms
of half-words (16 bits). This convention is a matter of convenience
only, since most users think of ASCII files as being character oriented.
When you specify the record size for a fixed-length ASCII
file, the record size determined for the file is the same as that
which you specified for it. The maximum record size allowed for
fixed-length ASCII files is 32767 bytes.
To maintain compatibility with pre-900 Series HP 3000 computer
systems, the following file types always begin records on half-word
boundaries:
ASCII files with variable-length or undefined-length record
format
binary files with fixed-length, variable-length, or
undefined-length record format
For these file types, when you specify an odd-byte record
size, the file system rounds up the value to an even number to reflect
the fact that these records always begin on half-word boundaries.
The maximum record size you can specify for these file types is
32766 bytes.
When the file is a binary file or a variable-length ASCII file, the extra byte
is available to be used for data. Figure 2-5
"Record Placement for ASCII Files" illustrates the placement of odd-bytes
records and the disposition of the added byte.
Figure 2-5 Record Placement for ASCII Files
Rather than specify your own record size, you can accept the
default record size for the device that you are using. Default record
sizes are listed in Table 2-5 "Standard Default
Record Sizes" Note that subsystem
defaults may be different from MPE defaults; for example, the Editor
default may be 72 or 80 bytes (depending on text format) while the
MPE standard default is the record size configured for the device.
Table 2-5 Standard Default Record Sizes