Each instruction is m a d e up of a short c o m m a n d word (which tells the
c o m p u t e r which D O S p r o g r a m to select) followed by some qualifying
data which the p r o g r a m must have before it can run. For example, one
instruction enables the contents of a disc in one disc drive unit to be
copied to a disc in a n o t h e r drive. The c o m m a n d word is C O P Y , which is
followed by some qualifying data to tell the c o m p u t e r exactly which
drive unit is to be read from and which drive unit data is to be sent to.
Finally, to put the instruction into the c o m p u t e r having checked that it is
correct on the screen, you simply press the R E T U R N key.
T h e addition of a disc system to your m i c r o c o m p u t e r does not reduce
the a m o u n t of free R A M available to you for storing programs or data,
the A T M O S (48K) and O R I C - 1 (48K) microcomputers still give you a
m i n i m u m of 37K bytes free.
THE DISC DRIVE
It is important to appreciate from the beginning that there are two types
of microdisc drive unit called
m a s t e r
and
slave.
The
m a s t e r
contains
electronic interface circuitry which enables it to be connected directly to
and controlled directly from, the microcomputer. It also has a red 'reset'
button on the rear, the p u r p o s e of which is explained in C h a p t e r 4.
The
slave
contains no interface circuitry and no 'reset' button, in other
words it cannot be connected directly to the c o m p u t e r and it is
controlled by the c o m p u t e r via the
master
drive interface. This is why,
when you have m o r e than one disc drive, the drive units are all
connected together in 'chain' fashion with only the
m a s t e r
(at the end of
the chain) being connected to the computer. The O R I C system can be
fitted with up to four disc drives (one
master
and three
slaves)
as shown
by Figure 3.
Each disc drive unit has internal switching which allows it to be
n u m b e r e d 0, 1, 2 or 3, this is how the c o m p u t e r recognises a disc drive.
The microdisc drive which you purchase as part of the microdisc system
will always be a
m a s t e r
and its internal switching will always be set up for
n u m b e r 0. If you purchase an additional drive, this must be a
slave
and
will always be n u m b e r e d 1. Y o u may also wish to purchase up to two
additional drives which must also be
slaves
and will also be n u m b e r e d 1.
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