Xerox 900 series User Manual

METHOD:
(cont .)
60
RDISC/WDISC has the capability to read or write a specified number of disc
sectors. It contains the only coding that actually addresses the disc. RDISC/
WDISC is random access in operation, and assumes that the 9367 is connected
to a chpnnel having interlace.
The system processors, on the other hand, deal with sequential fi I es, and
never write 64-word records. In essence, QFMR is an interface between the
system processors and RDISC/WDISC. It has the following responsibilities:
Position retention
Repositi on
Buffer
I/O
it must keep track of the origin and current position
for each fi I e.
it must be able to find elements within the S file
and to rewind all files.
it must buffer I/O between the record-oriented
processors and sector-oriented hand I er.
The fi Ie management package behaves as though the RAD were word address-
able. For each active file, it maintains the "current sector II in core until it
has been fully utilized, at which time the buffer is emptied/refilled in prep-
aration for the next sector. Since the sectors are in numerical sequence, the
p-th word is located at word r in sector q, where
p = q * 64 + r, 0 ~ q ~ 2047, 0 ~ r ~ 63.
X2 and BO are actually the same file, but are distinguishable from the stand-
poi nt of rewi nd. RAD fi I es are si mi lar to tape fi I es, and are destructibl e
when rewound. Therefore, the same control cards can be used for ei ther
Tape or RAD MO NARCH. However, SKIPFILE, SKIPREC, BACKFILE and
BACKREC are not provided for RAD files.
Each write on Xl and X2 is checked for infringement upon the other file
(overflow of storage space). Both files are rewound between JOBs.
Since RAD logical files only rarely would be expected to begin at a sector
boundary, it is necessary to open the file prior to recording or writing. For
example, if the Xl file begins with the fourth word in sector 04053
8
,
the file
management routine must first transfer sector 04053
8
to the core buffer before
reading or writing can commence.
Similarly, all output files should be closed after the last write operation.
The file management package automatically opens a file after a rewind op-
eration.
Organizati on of RAD Storage
RAD:
5 J BO X2

Xerox 900 series Specifications

General

Brand	Xerox
Model	900 series
Category	Copier
Language	English