Control Data Corporation 3300 Reference Manual page 30

60229400
A
{RANDOM }'
__ CCESS MODE IS SEQUENTIAL
The ACCESS MODE clause must be included for mass storage files. When
ACCESS MODE IS SEQUENTIAL, the mass storage records are obtained or
placed sequentially. That is, the next logical record is made available from
the file on execution of a READ statement, or a specific logical record is
placed into the file on execution of a WRITE statement. No ACTUAL KEY
entries are necessary for the SEQUENTIAL mode.
When ACCESS MODE IS RANDOM, mass storage records are organized
randomly and records are retrieved according to the contents of the ACTUAL
KEY data name.
PROCESSING MODE IS SEQUENTIAL
This clause specifies that mass storage records are processed in the order
in which they are accessed; it is documentary only.
ACTUAL KEY IS data-name-l
The ACTUAL KEY clause must be specified for random access files. The
mass storage control system obtains or writes each record randomly. The
specific logical record is located through data-name-l of the ACTUAL KEY
clause and is made available on execution of a READ statement. When a
WRITE statement is executed for a random access file, effectively, the
record is placed at the location in the file specified by data-name-l of the
ACTUAL KEY clause. Mass storage records in a random file are processed
in the order in which they are accessed.
If a SEEK statement is executed prior to a READ or WRITE, the location of
the record as specified by the value of data-name-l is made available to the
next
READ
or WRITE executed.
If no SEEK is issued, the record is automatically located from the value of
data-name-l upon execution of a READ or WRITE. The user is responsible
for setting the value of data-name-l prior to execution of each SEEK or
READ or WRITE statement associated with a random access file.
Data-name-l is a 12-character numeric group item, subdivided into two
fields. The first is a seven-character block number indicating the relative
position of this block from the beginning of the file (1
=
the first block, etc.).
The second field is a five-character position number giving the first character
position of the record relative to the beginning of a block (0
=
the first char-
acter, etc.).
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