HP 82479A Owner's Manual page 216

HPAF File Standard
H.1 Header Information
The header must contain the following items:
1) Record zero contains a type string. The type string serves two purposes. The first four characters
indicate the file is an HPAF file. The remaining characters describe the number of data items in
each record, and their type. For example, HF HFtMH=: the characters MMS indicate that there are
three items in each record: the first two are numbers, and the third is a string.
2) Record 1 contains the number of data records that contain information. This number may be
less than the total number of available records, allowing room for additional records to be added
later, or for the optional descriptor block.
3) Record 2 contains the address of the optional descriptor block. If no descriptor block is present,
this number should be zero.
H.2 Data Records
The data records begin in record 3, and must end before the descriptor block. Note that all data items for
each record must fit within each logical record, so that any record may be accessed randomly. To
compute the optimal logical record length for the file, remember that each number written in the record
occupies eight bytes, and each string occupies three bytes plus the number of bytes in the string. In
addition, there must be one byte for the end of record mark. For example, if each record is going to hold
two numbers and a ten character string, the record length must be at least 2*8+3+10+1, or 30 bytes. For
more information about creating DATA files, refer to the HP-71 Owner's Manual, section 14.
H.3 Descriptor Block
The descriptor block is optional in the HPAF definition. Record 2 of the file contains the starting address
of the descriptor block. An address of zero indicates that no descriptor block is present.
Information in the descriptor block consists of tags which identify the type of information that follows,
followed by the number of items associated with the tag, followed by the items themselves. The fag must
be a string, the number of items must be a number, and the items must be strings. If numeric values are
to be in the items, they should be string representations (= TF).
The information in the descriptor block may be written serially, or, if the logical record size is sufficiently
large, written one tag to a record. In either case, the descriptor block must be able to be read serially.