<s>
The	O
+D	B-Device
(	O
or	O
Plus	O
D	O
)	O
was	O
a	O
floppy	B-Device
disk	I-Device
and	O
printer	O
interface	B-Protocol
for	O
the	O
ZX	B-Operating_System
Spectrum	I-Operating_System
home	O
computer	O
,	O
developed	O
as	O
a	O
successor	O
to	O
Miles	O
Gordon	O
Technology	O
's	O
earlier	O
product	O
,	O
the	O
DISCiPLE	B-Device
.	O
</s>
<s>
It	O
discarded	O
a	O
number	O
of	O
the	O
less	O
important	O
features	O
of	O
the	O
earlier	O
product	O
—	O
the	O
network	B-Architecture
and	O
joystick	B-Device
ports	O
,	O
the	O
inhibit	O
button	O
and	O
the	O
pass-through	O
connector	O
—	O
and	O
replaced	O
its	O
ancestor	O
's	O
plastic	O
wedge-shaped	O
design	O
which	O
fit	O
under	O
the	O
Spectrum	O
with	O
a	O
simple	O
flat	O
metal	O
slab	O
which	O
protruded	O
from	O
the	O
rear	O
of	O
the	O
computer	O
.	O
</s>
<s>
It	O
provided	O
only	O
floppy	B-Device
disk	I-Device
and	O
Centronics	O
parallel	O
interfaces	O
,	O
plus	O
a	O
non-maskable	B-General_Concept
interrupt	I-General_Concept
button	O
.	O
</s>
<s>
The	O
D	O
's	O
casing	O
was	O
simple	O
folded	O
steel	O
,	O
which	O
was	O
not	O
only	O
stronger	O
than	O
before	O
but	O
acted	O
as	O
a	O
heatsink	O
,	O
improving	O
reliability	O
.	O
</s>
<s>
The	O
D	O
's	O
DOS	B-Operating_System
was	O
named	O
G+DOS	O
,	O
and	O
was	O
compatible	O
with	O
the	O
DISCiPLE	B-Device
's	O
DOS	B-Operating_System
,	O
GDOS	O
.	O
</s>
<s>
SAM	O
DOS	B-Operating_System
for	O
MGT	O
's	O
SAM	B-Device
Coupé	I-Device
was	O
backwards-compatible	O
with	O
GDOS	O
and	O
G+DOS	O
.	O
</s>
<s>
"	O
The	O
Complete	O
+D	B-Device
Disassembly	O
"	O
by	O
Rudy	O
Biesma	O
documents	O
the	O
"	O
G+DOS	O
system	O
2a	O
"	O
version	O
.	O
</s>
<s>
An	O
enhanced	O
version	O
called	O
Beta	O
DOS	B-Operating_System
fixed	O
bugs	O
and	O
added	O
features	O
.	O
</s>
<s>
In	O
later	O
years	O
a	O
complete	O
new	O
system	O
called	O
UNI-DOS	O
was	O
developed	O
by	O
SD	O
Software	O
for	O
the	O
DISCiPLE	B-Device
and	O
+D	B-Device
interfaces	O
.	O
</s>
<s>
The	O
popularity	O
of	O
the	O
DISCiPLE	B-Device
led	O
to	O
the	O
formation	O
of	O
a	O
user	O
group	O
and	O
magazine	O
,	O
INDUG	O
,	O
which	O
later	O
became	O
Format	B-Device
Publications	I-Device
.	O
</s>
<s>
Usergroups	O
like	O
INDUG/Format	O
in	O
the	O
UK	O
or	O
DISCiPLE-Nieuwsbrief	O
in	O
the	O
Netherlands	O
produced	O
enhancements	O
such	O
as	O
extended	O
printer	O
support	O
.	O
</s>
<s>
The	O
+D	B-Device
design	O
was	O
later	O
licensed	O
by	O
Datel	O
and	O
it	O
continued	O
on	O
sale	O
for	O
some	O
years	O
after	O
MGT	O
's	O
demise	O
.	O
</s>
