<s>
HDOS	B-Application
is	O
an	O
early	O
microcomputer	B-Architecture
operating	B-General_Concept
system	I-General_Concept
,	O
originally	O
written	O
for	O
the	O
Heathkit	B-Device
H8	I-Device
computer	O
system	O
and	O
later	O
also	O
available	O
for	O
the	O
Heathkit	B-Device
H89	I-Device
and	O
Zenith	B-Device
Z-89	I-Device
computers	O
.	O
</s>
<s>
The	O
author	O
was	O
Heath	O
Company	O
employee	O
Gordon	O
Letwin	O
,	O
who	O
later	O
was	O
an	O
early	O
employee	O
of	O
Microsoft	O
and	O
lead	O
architect	O
of	O
OS/2	B-Application
.	O
</s>
<s>
HDOS	B-Application
originally	O
came	O
with	O
a	O
limited	O
set	O
of	O
system	O
software	O
tools	O
,	O
including	O
an	O
assembler	B-Language
,	O
but	O
many	O
commercial	O
and	O
large	O
set	O
of	O
freeware	O
programs	O
from	O
HUG	O
(	O
Heath	O
User	O
Group	O
)	O
became	O
available	O
for	O
it	O
eventually	O
.	O
</s>
<s>
HDOS	B-Application
2.0	O
is	O
notable	O
because	O
it	O
was	O
one	O
of	O
the	O
first	O
microcomputer	B-Architecture
operating	B-General_Concept
systems	I-General_Concept
to	O
use	O
loadable	O
device	B-Application
drivers	I-Application
to	O
achieve	O
a	O
degree	O
of	O
device	O
independence	O
and	O
extensibility	O
.	O
</s>
<s>
Device	O
names	O
followed	O
the	O
RSX-11-style	O
convention	O
of	O
DKn	O
:	O
where	O
the	O
first	O
two	O
letters	O
were	O
the	O
device	B-Application
driver	I-Application
file	O
name	O
and	O
n	O
was	O
a	O
number	O
(	O
DK0	O
:	O
,	O
DK1	O
:	O
,	O
and	O
so	O
on	O
would	O
all	O
be	O
handled	O
by	O
DK.SYS	O
)	O
.	O
</s>
<s>
Other	O
similarities	O
to	O
RSX	O
included	O
the	O
use	O
of	O
PIP	B-Application
for	O
file	O
transfer	O
,	O
and	O
the	O
use	O
of	O
EOT	O
for	O
file	O
termination	O
.	O
</s>
<s>
Similar	O
to	O
how	O
Heath/Zenith	O
published	O
complete	O
schematics	O
and	O
part	O
lists	O
for	O
its	O
computers	O
,	O
the	O
company	O
sold	O
to	O
users	O
the	O
source	O
code	O
for	O
HDOS	B-Application
.	O
</s>
<s>
The	O
following	O
list	O
of	O
commands	O
are	O
supported	O
by	O
HDOS	B-Application
.	O
</s>
