11/3/71 /DEV/PPT (IV)
NAME ppt -- punched paper tape
SYNOPSIS --
DESCRIPTION ppt refers to the paper tape reader or punch, de-
pending on whether it is read or written.
When ppt is opened for writing, a 100-character
leader is punched. Thereafter each byte written
is punched on the tape. No editing of the char-
acters is performed. When the file is closed, a
100-character trailer is punched.
When ppt is opened for reading, the process waits
until tape is placed in the reader and the reader
is on-line. Then requests to read cause the
characters read to be passed back to the program,
again without any editing. This means that sev-
eral null characters will usually appear at the
beginning of the file. Likewise several nulls
are likely to appear at the end. End-of-file is
generated when the tape runs out.
Seek calls for this file are meaningless and are
effectively ignored (however, the read/write
pointers are maintained and an arbitrary sequence
of reads or writes intermixed with seeks will
give apparently correct results when checked with
tell).
FILES --
SEE ALSO lbppt, dbppt, bppt format
DIAGNOSTICS --
BUGS Previously, there were separate special files for
ASCII tape (which caused null characters to be
suppressed) and binary tape (which used a blocked
format with checksums). These notions were con-
ceptually quite attractive, but they were dis-
carded to save space in the system.
OWNER ken, dmr