IBM 5110 User Manual page 118

Mixed Format
The mixed format, like the APL internal format, allows data to be
written to the data file in the same format as the data is stored in the
active workspace. However, the mixed format also allows you to
write records that have different internal representations on the same
data file. For example, you can write character data, logical data,
numeric fixed-point data; and numeric floating-point data on the same
data file. With the mixed format, the first record written to the data
file determines how much file storage is allocated for each additional
record to be written to the data file. For example:
1 st Record
100 Bytes
If the first record requires 100 bytes of file storage, 100 bytes of
storage are allocated for each additional record. See Storage
Requirements in the 5110 APL Reference Manual for information on
how many bytes of storage are required for each data type.
As variolls size records are written to a mixed format data file, any
unused diskette storage allocated for each record is unavailable for
storing data (see Type M Data File in Chapter 8, Diskette Concepts).
Because the records in a mixed format data file do not have to be the
same shape or internal representation, only one record at a time can
be directly accessed from the data file. That is, multiple records
cannot be laminated together.
Input/Output Control
113