<s>
TR-DOS	B-Operating_System
is	O
a	O
disk	B-Operating_System
operating	I-Operating_System
system	I-Operating_System
for	O
the	O
ZX	B-Operating_System
Spectrum	I-Operating_System
with	O
Beta	B-Device
Disc	I-Device
and	O
Beta	B-Device
128	I-Device
disc	O
interfaces	O
.	O
</s>
<s>
TR-DOS	B-Operating_System
and	O
Beta	B-Device
disc	I-Device
were	O
developed	O
by	O
Technology	B-Device
Research	I-Device
Ltd	I-Device
(	O
UK	O
)	O
,	O
in	O
1984	O
.	O
</s>
<s>
A	O
clone	O
of	O
this	O
interface	O
is	O
also	O
used	O
in	O
the	O
Russian	O
Pentagon	B-Device
and	O
Scorpion	B-Operating_System
machines	O
.	O
</s>
<s>
It	O
became	O
a	O
standard	O
and	O
most	O
disk	O
releases	O
for	O
the	O
ZX	B-Operating_System
Spectrum	I-Operating_System
,	O
especially	O
of	O
modern	O
programs	O
,	O
are	O
made	O
for	O
TR-DOS	B-Operating_System
as	O
opposed	O
to	O
other	O
disk	O
systems	O
.	O
</s>
<s>
TR-DOS	B-Operating_System
handles	O
SS/DS	O
,	O
SD/DD	O
floppy	B-Device
disks	I-Device
.	O
</s>
<s>
All	O
modern	O
versions	O
support	O
RAM	B-Application
Disk	I-Application
and	O
some	O
versions	O
support	O
hard	B-Device
disks	I-Device
.	O
</s>
<s>
Current	O
emulators	O
support	O
TR-DOS	B-Operating_System
disk	B-Application
images	I-Application
in	O
the	O
formats	O
.TRD	O
or	O
.SCL	O
.	O
</s>
<s>
The	O
following	O
list	O
of	O
commands	B-Application
is	O
supported	O
by	O
TR-DOS	B-Operating_System
V4	O
.	O
</s>
