RANA Systems Elite Controller, User Manual

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ELITE SERIES USER MANUAL APPEN. A - DISK I/O
A . 3 . T r a c k F o r m a t t i n g
Data is recorded on the diskette uses a “group
coded recording” technique (GCR) which requires
that a bit with a value of 1 he recorded onto
the diskette within a given maximum period of
time. This method has some very significant
differences from other possible recording tech-
niques, but all of these differences only occur
at the hardware level of the computer. Once the
data is presented to the software (by the hard-
ware), no real difference can he detected.
This appendix will not attempt to explain the
OCR recording technique in the brief explanation
of data recording which preceeds the software
discussion. Instead, the “frequency modulated”
recording technique (FM) will he substituted.
This is due to a rather extensive difference in
the complexity of explaining the two techniques.
This will not hinder the remainder of the ex-
planation since, as was already mentioned, dif-
ferences from the software standpoint are com-
pletely hidden by certain rules which must be
obeyed when accessing Apple-type disk drives.
In the frequency modulated recording technique,
data written on and read back from the diskette
takes the form shown in the figure to follow,
which represents the binary data pattern 101.
The clock bits and data bits are interleaved, as
shown in the next figure. A data bit between
two clock bits represents a binary 1. An ab-
sence of that bit represents a binary 0. The
period between the edge of one clock bit and the
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