sys-read(2) - Unix First Edition Manual Page
11/3/71SYS_READ (II)

NAME read -- read from file
SYNOPSIS (file descriptor in r0)sys read; buffer; nchars / read = 3.

(nread in r0)
DESCRIPTION A file descriptor is a word returned from a successful open call.

Buffer is the location of nchars contiguous bytes into which theinput will be placed. It is not guaranteed that all nchars bytes will be read, however; for example if the file refers to atypewriter at most one line will be returned. In any event the number of characters read is returned in r0. If r0 returns with value 0, then end--of--file has been reached.
DIAGNOSTICS As , r0 is 0 on return when the end of the file has been reached. If theread was otherwise unsuccessful the error bit (c--bit) is set. Many

conditions, all rare, can generate an error: physical I/O errors, badbuffer address, preposterous nchars, file descriptor not that of an input file.
OWNER ken, dmr