Spectravideo MKI, Service – Technical Manual

Page: 121 / 134

Dat a on t h e D i sc Me dia
The d i s c ca r t r i dge con t a i n s a magne t i c ox ide-co a t e d d i s c , wh ich i s
v
i s i b l e
thr ough acce s s ho l e s i n t h e p l a s t i c j acket . The ho s t s y s t e m , through the D i sc
D r i ve , r e c o r d s data on the d i s c at addre s s e d locat i on s . G iven the addr e s s o f
dat a o n the d i s c , the read /wr i t e he a d qu i c k l y loca t e s a n d re t r ieve s the de s i re d
da t a . A s t he di sc s p i ns , s e r i a l b i na ry d a t a is recorded ( or rea d ) on
co nc e n t r i c c i rc l e s ca l l e d t r ack s .
Be low p i c t u re shows t rack 00 on the ou ter
e dg e o f the di sc ; the i n ne rmos t t rack i s t rack
40.
Each of the tracks is
d i v i d e d i n t o se c t o r s , wh i c h are ma rke d by one ho l e punche d in the d i s c . An
a dd i t i ona l ho l e , INDE X , oc c u rs app ro x ima t e ly 1 8 0 degre e s be fore sec t o r 0
( se c t or locat ion depen d s up on the re l a t ive po s i t ion of the rea d /wri t e hea d and
t he index sensor ) . E ac h t r ack s ta r t s w i th a p u l se i n i t i a ted by the Index
h
o l e
wh i l e e a ch sector s t a r t s by a pu l s e in i t ia t e d by a sec to r h o l e . N o t i c e tha t
t he phy s i c a l l ength o f s e c t o rs va r i es d i rec t ly in p rop o r t i on to the d i s t ance o f
th e t r ack f rom t h e ce n t e r o f t h e d i s c , d a t a b i t s a r e c l o s e r together o n
the
h i gh e r numbe re d t r acks .
Doub l e
Dou b l e capac i t y can be ob t a i ne d by use o f MFM ( modi f ie d f re quency modu l a t ion )
me thod o f �ncod ing d a t a on t he d i sc .
HFM
1
B I T
C
ELL
2
S EC
CELL ENCODING
8 0
I I
I I
:...n.. n...:
NO PULSE NEEDED FOR ZERO
I F PRECEDED BY
A
ONE .
MFM d i sc encoding forma t .
4 . 88
SERIAL BIT STREAM
I
o
o o
1
I I
I t
1 I I
I f