<s>
DNIX	B-Operating_System
(	O
original	O
spelling	O
:	O
D-Nix	O
)	O
is	O
a	O
discontinued	O
Unix-like	B-Operating_System
real-time	B-Operating_System
operating	I-Operating_System
system	I-Operating_System
from	O
the	O
Swedish	O
company	O
Dataindustrier	O
AB	O
(	O
DIAB	O
)	O
.	O
</s>
<s>
A	O
version	O
named	O
ABCenix	O
was	O
developed	O
for	O
the	O
ABC	B-Operating_System
1600	I-Operating_System
computer	O
from	O
Luxor	O
.	O
</s>
<s>
Daisy	O
Systems	O
also	O
had	O
a	O
system	O
named	O
Daisy	O
DNIX	B-Operating_System
on	O
some	O
of	O
their	O
computer-aided	B-Application
design	I-Application
(	O
CAD	B-Application
)	O
workstations	B-Device
.	O
</s>
<s>
Dataindustrier	O
AB	O
(	O
literal	O
translation	O
:	O
computer	O
industries	O
shareholding	O
company	O
)	O
was	O
started	O
in	O
1970	O
by	O
Lars	O
Karlsson	O
as	O
a	O
single-board	B-Device
computer	I-Device
manufacture	O
in	O
Sundsvall	O
,	O
Sweden	O
,	O
producing	O
a	O
Zilog	O
Z80-based	O
computer	O
named	O
Data	O
Board	O
4680	O
.	O
</s>
<s>
In	O
1978	O
,	O
DIAB	O
started	O
to	O
work	O
with	O
the	O
Swedish	O
television	O
company	O
Luxor	O
AB	O
to	O
produce	O
the	O
home	O
and	O
office	O
computer	O
series	O
ABC	B-Device
80	I-Device
and	O
ABC	B-Device
800	I-Device
.	O
</s>
<s>
In	O
1983	O
DIAB	O
independently	O
developed	O
the	O
first	O
Unix-compatible	O
machine	O
,	O
DIAB	O
DS90	O
based	O
on	O
the	O
Motorola	B-Device
68000	I-Device
CPU	O
.	O
</s>
<s>
D-NIX	O
here	O
made	O
its	O
appearance	O
,	O
based	O
on	O
a	O
UNIX	B-Operating_System
System	I-Operating_System
V	I-Operating_System
license	O
from	O
AT&T	O
Corporation	O
.	O
</s>
<s>
DIAB	O
was	O
however	O
an	O
industrial	O
control	O
system	O
(	O
automation	O
)	O
company	O
,	O
and	O
needed	O
a	O
real-time	B-Operating_System
operating	I-Operating_System
system	I-Operating_System
,	O
so	O
the	O
company	O
replaced	O
the	O
AT&	O
T-supplied	O
UNIX	B-Application
kernel	B-Operating_System
with	O
their	O
own	O
in-house	O
developed	O
,	O
yet	O
compatible	O
real-time	B-Operating_System
variant	O
.	O
</s>
<s>
This	O
kernel	B-Operating_System
was	O
inspired	O
by	O
a	O
Z80	B-General_Concept
kernel	B-Operating_System
named	O
OS.8	O
created	O
for	O
Monroe	O
Systems	O
division	O
of	O
Litton	O
Industries	O
.	O
</s>
<s>
Over	O
time	O
,	O
the	O
company	O
also	O
replaced	O
several	O
of	O
the	O
UNIX	B-Application
standard	O
userspace	O
tools	O
with	O
their	O
own	O
implementations	O
,	O
to	O
the	O
point	O
where	O
no	O
code	O
was	O
derived	O
from	O
UNIX	B-Application
,	O
and	O
their	O
machines	O
could	O
be	O
deployed	O
independently	O
of	O
any	O
AT&T	B-Operating_System
UNIX	I-Operating_System
license	O
.	O
</s>
<s>
Two	O
years	O
later	O
and	O
in	O
cooperation	O
with	O
Luxor	O
,	O
a	O
computer	O
called	O
ABC	B-Operating_System
1600	I-Operating_System
was	O
developed	O
for	O
the	O
office	O
market	O
,	O
while	O
in	O
parallel	O
,	O
DIAB	O
continue	O
to	O
produce	O
enhanced	O
versions	O
of	O
the	O
DS90	O
computer	O
using	O
newer	O
versions	O
of	O
the	O
Motorola	O
CPUs	O
such	O
as	O
Motorola	B-Device
68010	I-Device
,	O
68020	B-Device
,	O
68030	B-Device
and	O
eventually	O
68040	B-Device
.	O
</s>
<s>
In	O
1990	O
DIAB	O
was	O
acquired	O
by	O
Groupe	O
Bull	O
who	O
continued	O
to	O
produce	O
and	O
support	O
the	O
DS	O
machines	O
under	O
the	O
brand	O
name	O
DIAB	O
,	O
with	O
names	O
such	O
as	O
DIAB	O
2320	O
,	O
DIAB	O
2340	O
etc.	O
,	O
still	O
running	O
DIABs	O
version	O
of	O
DNIX	B-Operating_System
.	O
</s>
<s>
ISC	O
Systems	O
Corporation	O
(	O
ISC	O
)	O
purchased	O
the	O
right	O
to	O
use	O
DNIX	B-Operating_System
in	O
the	O
late	O
1980s	O
for	O
use	O
in	O
its	O
line	O
of	O
Motorola	O
68k-based	O
banking	O
computers	O
.	O
</s>
<s>
Notable	O
features	O
of	O
this	O
operating	B-General_Concept
system	I-General_Concept
were	O
its	O
support	O
of	O
demand	B-General_Concept
paging	I-General_Concept
,	O
diskless	B-Device
workstations	I-Device
,	O
multiprocessing	B-Operating_System
,	O
asynchronous	B-Architecture
input/output	I-Architecture
(	O
I/O	B-General_Concept
)	O
,	O
the	O
ability	O
to	O
mount	O
processes	O
(	O
handlers	O
)	O
on	O
directories	O
in	O
the	O
file	B-Application
system	I-Application
,	O
and	O
message	B-Architecture
passing	I-Architecture
.	O
</s>
<s>
Its	O
real-time	B-Operating_System
support	O
consisted	O
largely	O
of	O
internal	O
event-driven	B-Application
queues	O
rather	O
than	O
list	O
search	O
mechanisms	O
(	O
no	O
'	O
thundering	O
herd	O
 '	O
)	O
,	O
static	O
process	O
priorities	O
in	O
two	O
classes	O
(	O
run	O
to	O
completion	O
and	O
timesliced	O
)	O
,	O
support	O
for	O
contiguous	O
files	O
(	O
to	O
avoid	O
fragmentation	B-Architecture
of	O
critical	O
resources	O
)	O
,	O
and	O
memory	O
locking	O
.	O
</s>
<s>
The	O
quality	O
of	O
the	O
orthogonal	O
asynchronous	B-Operating_System
event	O
implementation	O
has	O
yet	O
to	O
be	O
equalled	O
in	O
current	O
commercial	O
operating	B-General_Concept
systems	I-General_Concept
,	O
though	O
some	O
approach	O
it	O
.	O
</s>
<s>
(	O
The	O
concept	O
that	O
has	O
yet	O
to	O
be	O
adopted	O
is	O
that	O
the	O
synchronous	O
marshalling	O
point	O
of	O
all	O
the	O
asynchronous	B-Operating_System
activity	O
could	O
also	O
be	O
asynchronous	B-Operating_System
,	O
ad	O
infinitum	O
.	O
</s>
<s>
DNIX	B-Operating_System
handled	O
this	O
with	O
aplomb	O
.	O
)	O
</s>
<s>
The	O
asynchronous	B-Architecture
I/O	I-Architecture
facility	O
obviated	O
the	O
need	O
for	O
Berkeley	B-Protocol
sockets	I-Protocol
select	O
or	O
SVR4	O
's	O
STREAMS	B-Operating_System
poll	O
mechanism	O
,	O
though	O
there	O
was	O
a	O
socket	B-Protocol
emulation	O
library	O
that	O
preserved	O
the	O
socket	B-Protocol
semantics	O
for	O
backward	O
compatibility	O
.	O
</s>
<s>
Another	O
feature	O
of	O
DNIX	B-Operating_System
was	O
that	O
none	O
of	O
the	O
standard	O
utilities	O
(	O
such	O
as	O
ps	O
,	O
a	O
frequent	O
offender	O
)	O
rummaged	O
around	O
in	O
the	O
kernel	B-Operating_System
's	O
memory	O
to	O
do	O
their	O
job	O
.	O
</s>
<s>
System	O
calls	O
were	O
used	O
instead	O
,	O
and	O
this	O
meant	O
the	O
kernel	B-Operating_System
's	O
internal	O
architecture	O
was	O
free	O
to	O
change	O
as	O
required	O
.	O
</s>
<s>
The	O
handler	O
concept	O
allowed	O
network	B-Protocol
protocol	I-Protocol
stacks	I-Protocol
to	O
be	O
outside	O
the	O
kernel	B-Operating_System
,	O
which	O
greatly	O
eased	O
development	O
and	O
improved	O
overall	O
reliability	O
,	O
though	O
at	O
a	O
performance	O
cost	O
.	O
</s>
<s>
It	O
also	O
allowed	O
for	O
foreign	O
file	B-Application
systems	I-Application
to	O
be	O
user-level	O
processes	O
,	O
again	O
for	O
improved	O
reliability	O
.	O
</s>
<s>
The	O
main	O
file	B-Application
system	I-Application
,	O
though	O
it	O
could	O
have	O
been	O
(	O
and	O
once	O
was	O
)	O
an	O
external	O
process	O
,	O
was	O
pulled	O
into	O
the	O
kernel	B-Operating_System
for	O
performance	O
reasons	O
.	O
</s>
<s>
Were	O
it	O
not	O
for	O
this	O
DNIX	B-Operating_System
could	O
well	O
have	O
been	O
considered	O
a	O
microkernel	B-Operating_System
,	O
though	O
it	O
was	O
not	O
formally	O
developed	O
as	O
such	O
.	O
</s>
<s>
Handlers	O
could	O
appear	O
as	O
any	O
type	O
of	O
'	O
native	O
 '	O
Unix	B-Application
file	O
,	O
directory	O
structure	O
,	O
or	O
device	O
,	O
and	O
file	O
I/O	B-General_Concept
requests	O
that	O
the	O
handler	O
could	O
not	O
process	O
could	O
be	O
passed	O
off	O
to	O
other	O
handlers	O
,	O
including	O
the	O
underlying	O
one	O
on	O
which	O
the	O
handler	O
was	O
mounted	O
.	O
</s>
<s>
Handler	O
connections	O
could	O
also	O
exist	O
and	O
be	O
passed	O
around	O
independent	O
of	O
the	O
file	B-Application
system	I-Application
,	O
much	O
like	O
a	O
pipe	B-Operating_System
.	O
</s>
<s>
One	O
effect	O
of	O
this	O
is	O
that	O
text	O
terminal	O
(	O
TTY	O
)	O
like	O
devices	O
could	O
be	O
emulated	O
without	O
needing	O
a	O
kernel-based	O
pseudo	B-Protocol
terminal	I-Protocol
facility	O
.	O
</s>
<s>
An	O
example	O
of	O
where	O
a	O
handler	O
saved	O
the	O
day	O
was	O
in	O
ISC	O
's	O
diskless	B-Device
workstation	I-Device
support	O
,	O
where	O
a	O
bug	O
in	O
the	O
implementation	O
meant	O
that	O
using	O
named	B-Operating_System
pipes	I-Operating_System
on	O
the	O
workstation	B-Device
could	O
induce	O
undesirable	O
resource	O
locking	O
on	O
the	O
fileserver	O
.	O
</s>
<s>
A	O
handler	O
was	O
created	O
on	O
the	O
workstation	B-Device
to	O
field	O
accesses	O
to	O
the	O
afflicted	O
named	B-Operating_System
pipes	I-Operating_System
until	O
the	O
appropriate	O
kernel	B-Operating_System
fixes	O
could	O
be	O
developed	O
.	O
</s>
<s>
The	O
multiprocessor	B-Operating_System
DS90-20	O
'	O
s	O
,	O
however	O
,	O
were	O
too	O
expensive	O
for	O
the	O
target	O
market	O
and	O
ISC	O
designed	O
its	O
own	O
servers	O
and	O
ported	O
DNIX	B-Operating_System
to	O
them	O
.	O
</s>
<s>
ISC	O
designed	O
its	O
own	O
GUI-based	O
diskless	B-Device
workstations	I-Device
for	O
use	O
with	O
these	O
file	O
servers	O
,	O
and	O
ported	O
DNIX	B-Operating_System
again	O
.	O
</s>
<s>
(	O
Though	O
ISC	O
used	O
Daisy	O
workstations	B-Device
running	O
Daisy	O
DNIX	B-Operating_System
to	O
design	O
the	O
machines	O
that	O
would	O
run	O
DIAB	O
's	O
DNIX	B-Operating_System
,	O
there	O
was	O
negligible	O
confusion	O
internally	O
as	O
the	O
drafting	O
and	O
layout	O
staff	O
rarely	O
talked	O
to	O
the	O
software	O
staff	O
.	O
</s>
<s>
The	O
asynchronous	B-Architecture
I/O	I-Architecture
support	O
of	O
DNIX	B-Operating_System
allowed	O
for	O
easy	O
event-driven	B-Application
programming	I-Application
in	O
the	O
workstations	B-Device
,	O
which	O
performed	O
well	O
even	O
though	O
they	O
had	O
relatively	O
limited	O
resources	O
.	O
</s>
<s>
(	O
The	O
GUI	B-Application
diskless	B-Device
workstation	I-Device
had	O
a	O
7MHz	O
68010	B-Device
processor	O
and	O
was	O
usable	O
with	O
only	O
512K	O
of	O
memory	O
,	O
of	O
which	O
the	O
kernel	B-Operating_System
consumed	O
approximately	O
half	O
.	O
</s>
<s>
Most	O
workstations	B-Device
had	O
1	O
MB	O
of	O
memory	O
,	O
though	O
there	O
were	O
later	O
2	O
MB	O
and	O
4	O
MB	O
versions	O
,	O
along	O
with	O
10MHz	O
processors	O
.	O
)	O
</s>
<s>
A	O
full-blown	O
installation	O
could	O
consist	O
of	O
one	O
server	O
(	O
16MHz	O
68020	B-Device
,	O
8	O
MB	O
of	O
RAM	O
,	O
and	O
a	O
200	O
MB	O
hard	O
disk	O
)	O
and	O
up	O
to	O
64	O
workstations	B-Device
.	O
</s>
<s>
Besides	O
the	O
innate	O
efficiency	O
of	O
DNIX	B-Operating_System
,	O
the	O
associated	O
DIAB	O
C	O
compiler	O
was	O
key	O
to	O
high	O
performance	O
.	O
</s>
<s>
It	O
generated	O
particularly	O
good	O
code	O
for	O
the	O
68010	B-Device
,	O
especially	O
after	O
ISC	O
got	O
done	O
with	O
it	O
.	O
</s>
<s>
(	O
ISC	O
also	O
retargeted	O
it	O
to	O
the	O
Texas	O
Instruments	O
TMS34010	B-General_Concept
graphics	O
coprocessor	O
used	O
in	O
its	O
last	O
workstation	B-Device
.	O
)	O
</s>
<s>
The	O
DIAB	O
C	O
compiler	O
was	O
,	O
of	O
course	O
,	O
used	O
to	O
build	O
DNIX	B-Operating_System
,	O
which	O
was	O
one	O
of	O
the	O
factors	O
contributing	O
to	O
its	O
efficiency	O
,	O
and	O
is	O
still	O
available	O
,	O
in	O
some	O
form	O
,	O
through	O
Wind	O
River	O
Systems	O
.	O
</s>
<s>
There	O
may	O
be	O
,	O
and	O
probably	O
are	O
,	O
other	O
ISC	O
customers	O
still	O
using	O
DNIX	B-Operating_System
in	O
some	O
capacity	O
.	O
</s>
<s>
Through	O
ISC	O
there	O
was	O
a	O
considerable	O
DNIX	B-Operating_System
presence	O
in	O
Central	O
and	O
South	O
America	O
.	O
</s>
<s>
DNIX	B-Operating_System
's	O
native	O
system	O
call	O
was	O
the	O
dnix(2 )	O
library	O
function	O
,	O
analogous	O
to	O
the	O
standard	O
Unix	B-Application
unix(2 )	O
or	O
syscall(2 )	O
function	O
.	O
</s>
<s>
Semantically	O
this	O
single	O
call	O
provided	O
all	O
appropriate	O
Unix	B-Application
functionality	O
,	O
though	O
it	O
was	O
syntactically	O
different	O
from	O
Unix	B-Application
and	O
had	O
,	O
of	O
course	O
,	O
numerous	O
DNIX-only	O
extensions	O
.	O
</s>
<s>
DNIX	B-Operating_System
function	O
codes	O
were	O
organized	O
into	O
two	O
classes	O
:	O
Type	O
1	O
and	O
Type	O
2	O
.	O
</s>
<s>
Type	O
1	O
commands	O
were	O
those	O
that	O
were	O
associated	O
with	O
I/O	B-General_Concept
activity	O
,	O
or	O
anything	O
that	O
could	O
potentially	O
cause	O
the	O
issuing	O
process	O
to	O
block	O
.	O
</s>
<s>
They	O
could	O
be	O
satisfied	O
by	O
the	O
kernel	B-Operating_System
immediately	O
.	O
</s>
<s>
To	O
invoke	O
asynchronicity	O
,	O
a	O
special	O
file	B-Application
descriptor	I-Application
called	O
a	O
trap	O
queue	O
had	O
to	O
have	O
been	O
created	O
via	O
the	O
Type	O
2	O
opcode	O
,	O
F_OTQ	O
.	O
</s>
<s>
A	O
Type	O
1	O
call	O
would	O
have	O
the	O
,	O
F_NOWAIT	O
bit	O
OR-ed	O
with	O
its	O
function	O
value	O
,	O
and	O
one	O
of	O
the	O
additional	O
parameters	O
to	O
,	O
dnix(2 )	O
was	O
the	O
trap	O
queue	O
file	B-Application
descriptor	I-Application
.	O
</s>
<s>
The	O
return	O
value	O
from	O
an	O
asynchronous	B-Operating_System
call	O
was	O
not	O
the	O
normal	O
value	O
but	O
a	O
kernel-assigned	O
identifier	O
.	O
</s>
<s>
At	O
such	O
time	O
as	O
the	O
asynchronous	B-Operating_System
request	O
completed	O
,	O
a	O
,	O
read(2 )	O
(	O
or	O
,	O
F_READ	O
)	O
of	O
the	O
trap	O
queue	O
file	B-Application
descriptor	I-Application
would	O
return	O
a	O
small	O
kernel-defined	O
structure	O
containing	O
the	O
identifier	O
and	O
result	O
status	O
.	O
</s>
<s>
The	O
,	O
F_CANCEL	O
operation	O
was	O
available	O
to	O
cancel	O
any	O
asynchronous	B-Operating_System
operation	O
that	O
had	O
n't	O
yet	O
been	O
completed	O
,	O
one	O
of	O
its	O
arguments	O
was	O
the	O
kernel-assigned	O
identifier	O
.	O
</s>
<s>
In	O
addition	O
to	O
the	O
kernel-assigned	O
identifier	O
,	O
one	O
of	O
the	O
arguments	O
given	O
to	O
any	O
asynchronous	B-Operating_System
operation	O
was	O
a	O
32-bit	O
user-assigned	O
identifier	O
.	O
</s>
<s>
This	O
most	O
often	O
referenced	O
a	O
function	O
pointer	O
to	O
the	O
appropriate	O
subroutine	O
that	O
would	O
handle	O
the	O
I/O	B-General_Concept
completion	O
method	O
,	O
but	O
this	O
was	O
merely	O
convention	O
.	O
</s>
<s>
Of	O
note	O
is	O
that	O
the	O
asynchronous	B-Operating_System
events	O
were	O
gathered	O
via	O
normal	O
file	B-Application
descriptor	I-Application
read	O
operations	O
,	O
and	O
that	O
such	O
reading	O
was	O
also	O
able	O
to	O
be	O
asynchronous	B-Operating_System
.	O
</s>
<s>
This	O
had	O
implications	O
for	O
semi-autonomous	O
asynchronous	B-Operating_System
event	O
handling	O
packages	O
that	O
could	O
exist	O
within	O
one	O
process	O
.	O
</s>
<s>
(	O
DNIX	B-Operating_System
5.2	O
did	O
not	O
have	O
lightweight	B-Operating_System
processes	I-Operating_System
or	O
threads	O
.	O
)	O
</s>
<s>
Also	O
of	O
note	O
is	O
that	O
any	O
potentially	O
blocking	O
operation	O
could	O
be	O
issued	O
asynchronously	O
,	O
so	O
DNIX	B-Operating_System
was	O
well	O
equipped	O
to	O
handle	O
many	O
clients	O
with	O
a	O
single	O
server	O
process	O
.	O
</s>
<s>
A	O
process	O
was	O
not	O
restricted	O
to	O
having	O
only	O
one	O
trap	O
queue	O
,	O
so	O
I/O	B-General_Concept
requests	O
could	O
be	O
grossly	O
prioritized	O
in	O
this	O
way	O
.	O
</s>
<s>
In	O
addition	O
to	O
the	O
native	O
dnix(2 )	O
call	O
,	O
a	O
complete	O
set	O
of	O
'	O
standard	O
 '	O
libc	B-Language
interface	O
calls	O
was	O
available	O
.	O
</s>
<s>
Besides	O
being	O
useful	O
for	O
backwards	O
compatibility	O
,	O
these	O
were	O
implemented	O
in	O
a	O
binary-compatible	O
manner	O
with	O
the	O
NCR	O
Tower	O
computer	O
,	O
so	O
that	O
binaries	O
compiled	O
for	O
it	O
would	O
run	O
unchanged	O
under	O
DNIX	B-Operating_System
.	O
</s>
<s>
The	O
DNIX	B-Operating_System
kernel	B-Operating_System
had	O
two	O
trap	O
dispatchers	O
internally	O
,	O
one	O
for	O
the	O
DNIX	B-Operating_System
method	O
and	O
one	O
for	O
the	O
Unix	B-Application
method	O
.	O
</s>
<s>
(	O
In	O
these	O
machines	O
the	O
68000	B-Device
trap	O
#0	O
instruction	O
was	O
used	O
for	O
the	O
unix(2 )	O
calls	O
,	O
and	O
the	O
trap	O
#4	O
instruction	O
for	O
dnix(2 )	O
.	O
</s>
<s>
The	O
two	O
trap	O
handlers	O
were	O
very	O
similar	O
,	O
though	O
the	O
[	O
usually	O
hidden ]	O
unix(2 )	O
call	O
held	O
the	O
function	O
code	O
in	O
the	O
processor	O
's	O
D0	O
register	O
,	O
whereas	O
dnix(2 )	O
held	O
it	O
on	O
the	O
stack	O
with	O
the	O
rest	O
of	O
the	O
parameters	O
.	O
)	O
</s>
<s>
DNIX	B-Operating_System
5.2	O
had	O
no	O
networking	O
protocol	B-Protocol
stacks	I-Protocol
internally	O
(	O
except	O
for	O
the	O
thin	O
X.25-based	O
Ethernet	O
protocol	B-Protocol
stack	I-Protocol
added	O
by	O
ISC	O
for	O
use	O
by	O
its	O
diskless	B-Device
workstation	I-Device
support	O
package	O
)	O
,	O
all	O
networking	O
was	O
conducted	O
by	O
reading	O
and	O
writing	O
to	O
Handlers	O
.	O
</s>
<s>
Thus	O
,	O
there	O
was	O
no	O
socket	B-Protocol
mechanism	O
,	O
but	O
a	O
libsocket(3 )	O
existed	O
that	O
used	O
asynchronous	B-Architecture
I/O	I-Architecture
to	O
talk	O
to	O
the	O
TCP/IP	B-Protocol
handler	O
.	O
</s>
<s>
The	O
typical	O
Berkeley-derived	O
networking	O
program	O
could	O
be	O
compiled	O
and	O
run	O
unchanged	O
(	O
modulo	O
the	O
usual	O
Unix	B-Application
porting	O
problems	O
)	O
,	O
though	O
it	O
might	O
not	O
be	O
as	O
efficient	O
as	O
an	O
equivalent	O
program	O
that	O
used	O
native	O
asynchronous	B-Architecture
I/O	I-Architecture
.	O
</s>
<s>
Under	O
DNIX	B-Operating_System
,	O
a	O
process	O
could	O
be	O
used	O
to	O
handle	O
I/O	B-General_Concept
requests	O
and	O
to	O
extend	O
the	O
file	B-Application
system	I-Application
.	O
</s>
<s>
Such	O
a	O
process	O
was	O
called	O
a	O
Handler	O
,	O
and	O
was	O
a	O
major	O
feature	O
of	O
the	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
A	O
handler	O
was	O
defined	O
as	O
a	O
process	O
that	O
owned	O
at	O
least	O
one	O
request	O
queue	O
,	O
a	O
special	O
file	B-Application
descriptor	I-Application
that	O
was	O
procured	O
in	O
one	O
of	O
two	O
ways	O
:	O
with	O
a	O
F_ORQ	O
or	O
a	O
F_MOUNT	O
call	O
.	O
</s>
<s>
(	O
The	O
network	O
remote	O
execution	O
programs	O
,	O
of	O
which	O
there	O
were	O
many	O
,	O
used	O
this	O
method	O
to	O
provide	O
standard	O
I/O	B-General_Concept
paths	O
to	O
their	O
children	O
.	O
)	O
</s>
<s>
The	O
latter	O
hooked	O
into	O
the	O
file	B-Application
system	I-Application
so	O
that	O
file	O
I/O	B-General_Concept
requests	O
could	O
be	O
adopted	O
by	O
handlers	O
.	O
</s>
<s>
(	O
The	O
network	O
login	O
programs	O
,	O
of	O
which	O
there	O
were	O
even	O
more	O
,	O
used	O
this	O
method	O
to	O
provide	O
standard	O
I/O	B-General_Concept
paths	O
to	O
their	O
children	O
,	O
as	O
the	O
semantics	O
of	O
logging	O
in	O
under	O
Unix	B-Application
requires	O
a	O
way	O
for	O
multiple	O
perhaps-unrelated	O
processes	O
to	O
horn	O
in	O
on	O
the	O
standard	O
I/O	B-General_Concept
path	O
to	O
the	O
operator	O
.	O
)	O
</s>
<s>
Once	O
mounted	O
on	O
a	O
directory	O
in	O
the	O
file	B-Application
system	I-Application
,	O
the	O
handler	O
then	O
received	O
all	O
I/O	B-General_Concept
calls	O
to	O
that	O
point	O
.	O
</s>
<s>
A	O
handler	O
would	O
then	O
read	O
small	O
kernel-assigned	O
request	O
data	O
structures	O
from	O
the	O
request	O
queue	O
.	O
</s>
<s>
The	O
handler	O
would	O
then	O
do	O
whatever	O
each	O
request	O
required	O
to	O
be	O
satisfied	O
,	O
often	O
using	O
the	O
DNIX	B-Operating_System
F_UREAD	O
and	O
F_UWRITE	O
calls	O
to	O
read	O
and	O
write	O
into	O
the	O
request	O
's	O
data	O
space	O
,	O
and	O
then	O
would	O
terminate	O
the	O
request	O
appropriately	O
using	O
F_TERMIN	O
.	O
</s>
<s>
A	O
privileged	O
handler	O
could	O
adopt	O
the	O
permissions	O
of	O
its	O
client	O
for	O
individual	O
requests	O
to	O
subordinate	O
handlers	O
(	O
such	O
as	O
the	O
file	B-Application
system	I-Application
)	O
via	O
the	O
F_T1REQ	O
call	O
,	O
so	O
it	O
did	O
n't	O
need	O
to	O
reproduce	O
the	O
subordinate	O
's	O
permission	O
scheme	O
.	O
</s>
<s>
If	O
a	O
handler	O
was	O
unable	O
to	O
complete	O
a	O
request	O
alone	O
,	O
the	O
F_PASSRQ	O
function	O
could	O
be	O
used	O
to	O
pass	O
I/O	B-General_Concept
requests	O
from	O
one	O
handler	O
to	O
another	O
.	O
</s>
<s>
This	O
was	O
used	O
to	O
provide	O
networking	O
facilities	O
to	O
chroot	B-Application
jails	I-Application
,	O
for	O
example	O
.	O
</s>
<s>
ISC	O
purchased	O
both	O
5.2	O
(	O
SVR2	O
compatible	O
)	O
and	O
5.3	O
(	O
SVR3	B-Operating_System
compatible	O
)	O
versions	O
of	O
DNIX	B-Operating_System
.	O
</s>
<s>
At	O
the	O
time	O
of	O
purchase	O
,	O
DNIX	B-Operating_System
5.3	O
was	O
still	O
undergoing	O
development	O
at	O
DIAB	O
so	O
DNIX	B-Operating_System
5.2	O
was	O
what	O
was	O
deployed	O
.	O
</s>
<s>
Over	O
time	O
,	O
ISC	O
's	O
engineers	O
incorporated	O
most	O
of	O
their	O
5.3	O
kernel	B-Operating_System
's	O
features	O
into	O
5.2	O
,	O
primarily	O
shared	B-Operating_System
memory	I-Operating_System
and	O
IPC	B-Operating_System
,	O
so	O
there	O
was	O
some	O
divergence	O
of	O
features	O
between	O
DIAB	O
and	O
ISC	O
's	O
versions	O
of	O
DNIX	B-Operating_System
.	O
</s>
<s>
DIAB	O
's	O
5.3	O
likely	O
went	O
on	O
to	O
contain	O
more	O
SVR3	B-Operating_System
features	O
than	O
ISC	O
's	O
5.2	O
ended	O
up	O
with	O
.	O
</s>
<s>
Also	O
,	O
DIAB	O
went	O
on	O
to	O
DNIX	B-Operating_System
5.4	O
,	O
a	O
SVR4	O
compatible	O
OS	O
.	O
</s>
<s>
At	O
ISC	O
,	O
developers	O
considerably	O
extended	O
their	O
version	O
of	O
DNIX	B-Operating_System
5.2	O
(	O
only	O
listed	O
are	O
features	O
involving	O
the	O
kernel	B-Operating_System
)	O
based	O
upon	O
both	O
their	O
needs	O
and	O
the	O
general	O
trends	O
of	O
the	O
Unix	B-Application
industry	O
:	O
</s>
<s>
Diskless	B-Device
workstation	I-Device
support	O
.	O
</s>
<s>
The	O
workstation	B-Device
's	O
kernel	B-Operating_System
file	B-Application
system	I-Application
was	O
removed	O
,	O
and	O
replaced	O
with	O
an	O
X.25-based	O
Ethernet	O
communications	O
stub	O
.	O
</s>
<s>
The	O
file	O
server	O
's	O
kernel	B-Operating_System
was	O
also	O
extended	O
with	O
a	O
mating	O
component	O
that	O
received	O
the	O
remote	O
requests	O
and	O
handed	O
them	O
to	O
a	O
pool	O
of	O
kernel	B-Operating_System
processes	O
for	O
service	O
,	O
though	O
a	O
standard	O
handler	O
could	O
have	O
been	O
written	O
to	O
do	O
this	O
.	O
</s>
<s>
(	O
Later	O
in	O
its	O
product	O
lifecycle	O
,	O
ISC	O
deployed	O
standard	O
SVR4-based	O
Unix	B-Application
servers	O
in	O
place	O
of	O
the	O
DNIX	B-Operating_System
servers	O
.	O
</s>
<s>
These	O
used	O
X.25	B-Protocol
STREAMS	B-Operating_System
and	O
a	O
custom-written	O
file	O
server	O
program	O
.	O
</s>
<s>
It	O
is	O
unfortunate	O
that	O
this	O
file	O
server	O
program	O
did	O
not	O
support	O
all	O
of	O
the	O
functionality	O
of	O
the	O
native	O
DNIX	B-Operating_System
server	O
.	O
</s>
<s>
Tricky	O
things	O
,	O
like	O
named	B-Operating_System
pipes	I-Operating_System
,	O
never	O
worked	O
at	O
all	O
.	O
</s>
<s>
This	O
was	O
another	O
justification	O
for	O
the	O
named	B-Operating_System
pipe	I-Operating_System
handler	O
process	O
.	O
)	O
</s>
<s>
gdb	B-Language
watchpoint	O
support	O
using	O
the	O
features	O
of	O
ISC	O
's	O
MMU	B-General_Concept
.	O
</s>
<s>
Asynchronous	B-Architecture
I/O	I-Architecture
to	O
the	O
file	B-Application
system	I-Application
was	O
made	O
real	O
.	O
</s>
<s>
Kernel	B-Operating_System
processes	O
(	O
kprocs	O
,	O
or	O
threads	O
)	O
were	O
used	O
to	O
do	O
this	O
.	O
</s>
<s>
Support	O
for	O
a	O
truss	O
-	O
or	O
strace-like	O
program	O
.	O
</s>
<s>
In	O
addition	O
to	O
some	O
repairs	O
to	O
bugs	O
in	O
the	O
standard	O
Unix	B-Application
ptrace	O
single-stepping	O
mechanism	O
,	O
this	O
required	O
adding	O
a	O
temporary	O
process	O
adoption	O
facility	O
so	O
that	O
the	O
tracer	O
could	O
use	O
the	O
standard	O
single-stepping	O
mechanism	O
on	O
existing	O
processes	O
.	O
</s>
<s>
SVR4	O
signal	B-Operating_System
mechanism	O
extensions	O
.	O
</s>
<s>
Primarily	O
for	O
the	O
new	O
STOP	O
and	O
CONT	O
signals	O
,	O
but	O
encompassing	O
the	O
new	O
signal	B-Operating_System
control	O
calls	O
as	O
well	O
.	O
</s>
<s>
Due	O
to	O
ISC	O
's	O
lack	O
of	O
source	O
code	O
for	O
the	O
adb	B-Application
and	O
sdb	O
debuggers	O
the	O
u-page	O
could	O
not	O
be	O
modified	O
,	O
so	O
the	O
new	O
signals	O
could	O
only	O
be	O
blocked	O
or	O
receive	O
default	O
handling	O
,	O
they	O
could	O
not	O
be	O
caught	O
.	O
</s>
<s>
Support	O
for	O
network	O
sniffing	B-Protocol
.	O
</s>
<s>
This	O
required	O
extending	O
the	O
Ethernet	O
driver	O
so	O
that	O
a	O
single	O
event	O
could	O
satisfy	O
more	O
than	O
one	O
I/O	B-General_Concept
request	O
,	O
and	O
conditionally	O
implementing	O
the	O
hardware	O
filtering	O
in	O
software	O
to	O
support	O
promiscuous	B-Protocol
mode	I-Protocol
.	O
</s>
<s>
Disk	B-General_Concept
mirroring	I-General_Concept
.	O
</s>
<s>
This	O
was	O
done	O
in	O
the	O
file	B-Application
system	I-Application
and	O
not	O
the	O
device	O
driver	O
,	O
so	O
that	O
slightly	O
(	O
or	O
even	O
completely	O
)	O
different	O
devices	O
could	O
still	O
be	O
mirrored	O
together	O
.	O
</s>
<s>
32-bit	O
inode	B-Application
,	O
30-character	O
filename	O
,	O
symbolic	B-Application
link	I-Application
,	O
and	O
sticky	B-Application
directory	O
extensions	O
to	O
the	O
file	B-Application
system	I-Application
.	O
</s>
<s>
Serial	O
port	O
multiplication	O
using	O
ISC	O
's	O
Z-80	B-General_Concept
based	O
VMEbus	B-Architecture
communications	O
boards	O
.	O
</s>
<s>
Support	O
for	O
fuser	B-Device
command	O
.	O
</s>
<s>
Very	O
useful	O
for	O
determining	O
what	O
the	O
current	O
working	B-General_Concept
set	I-General_Concept
is	O
,	O
as	O
opposed	O
to	O
what	O
is	O
still	O
available	O
to	O
it	O
but	O
not	O
necessarily	O
being	O
used	O
.	O
</s>
<s>
This	O
was	O
associated	O
with	O
a	O
GUI	B-Application
utility	O
showing	O
the	O
status	O
of	O
all	O
1024	O
pages	O
of	O
a	O
process	O
's	O
memory	O
map	O
.	O
</s>
<s>
(	O
This	O
being	O
the	O
number	O
of	O
memory	O
pages	O
supported	O
by	O
ISC	O
's	O
MMU	B-General_Concept
.	O
)	O
</s>
<s>
When	O
DNIX	B-Operating_System
development	O
at	O
ISC	O
effectively	O
ceased	O
in	O
1997	O
,	O
a	O
number	O
of	O
planned	O
OS	O
features	O
were	O
left	O
on	O
the	O
table	O
:	O
</s>
<s>
Shared	O
objects	O
–	O
There	O
were	O
two	O
dynamically	O
loaded	O
libraries	O
in	O
existence	O
,	O
an	O
encryptor	O
for	O
DNET	O
and	O
the	O
GUI	B-Application
's	O
imaging	O
library	O
,	O
but	O
the	O
facility	O
was	O
never	O
generalized	O
.	O
</s>
<s>
ISC	O
's	O
machines	O
were	O
characterized	O
by	O
a	O
general	O
lack	O
of	O
virtual	B-General_Concept
address	I-General_Concept
space	I-General_Concept
,	O
so	O
extensive	O
use	O
of	O
memory-mapped	O
entities	O
would	O
not	O
have	O
been	O
possible	O
.	O
</s>
<s>
Lightweight	B-Operating_System
processes	I-Operating_System
–	O
The	O
kernel	B-Operating_System
already	O
had	O
multiple	O
threads	O
that	O
shared	O
a	O
single	O
MMU	B-General_Concept
context	O
,	O
extending	O
this	O
to	O
user	O
processes	O
should	O
have	O
been	O
straightforward	O
.	O
</s>
<s>
The	O
API	B-General_Concept
implications	O
would	O
have	O
been	O
the	O
most	O
difficult	O
part	O
of	O
this	O
.	O
</s>
<s>
Access-control	O
lists	O
(	O
ACL	O
)	O
–	O
Trivial	O
to	O
implement	O
using	O
an	O
ACL	O
handler	O
mounted	O
over	O
the	O
stock	O
file	B-Application
system	I-Application
.	O
</s>
<s>
Multiple	O
swap	O
partitions	O
–	O
DNIX	B-Operating_System
already	O
used	O
free	O
space	O
on	O
the	O
selected	O
volume	O
for	O
swapping	O
,	O
it	O
would	O
have	O
been	O
easy	O
to	O
give	O
it	O
a	O
list	O
of	O
volumes	O
to	O
try	O
in	O
turn	O
,	O
potentially	O
with	O
associated	O
space	O
limits	O
to	O
keep	O
it	O
from	O
consuming	O
all	O
free	O
space	O
on	O
a	O
volume	O
before	O
moving	O
on	O
to	O
the	O
next	O
one	O
.	O
</s>
<s>
Remote	O
kernel	B-Operating_System
debugging	O
via	O
gdb	B-Language
–	O
All	O
the	O
pieces	O
were	O
there	O
to	O
do	O
it	O
either	O
through	O
the	O
customary	O
serial	O
port	O
or	O
over	O
Ethernet	O
using	O
the	O
kernel	B-Operating_System
's	O
embedded	O
X.25	B-Protocol
link	O
software	O
,	O
but	O
they	O
were	O
never	O
assembled	O
.	O
</s>
<s>
68030	B-Device
support	O
–	O
ISC	O
's	O
prototypes	O
were	O
never	O
completed	O
.	O
</s>
<s>
Two	O
processor	O
piggyback	O
plug-in	O
cards	O
were	O
built	O
,	O
but	O
were	O
never	O
used	O
as	O
more	O
than	O
faster	O
68020	B-Device
's	O
.	O
</s>
<s>
They	O
were	O
not	O
reliable	O
,	O
nor	O
were	O
they	O
as	O
fast	O
as	O
they	O
could	O
have	O
been	O
due	O
to	O
having	O
to	O
fit	O
into	O
a	O
68020	B-Device
socket	B-Protocol
.	O
</s>
<s>
The	O
fast	O
context	O
switching	O
ISC	O
MMU	B-General_Concept
would	O
be	O
left	O
disabled	O
(	O
and	O
left	O
out	O
altogether	O
in	O
proposed	O
production	O
units	O
)	O
,	O
and	O
the	O
embedded	O
one	O
of	O
the	O
68030	B-Device
was	O
to	O
have	O
been	O
used	O
instead	O
,	O
using	O
a	O
derivative	O
of	O
the	O
DS90-20	O
'	O
s	O
MMU	B-General_Concept
code	O
.	O
</s>
<s>
While	O
the	O
ISC	O
MMU	B-General_Concept
was	O
very	O
efficient	O
and	O
supported	O
instant	O
switching	O
among	O
32	O
resident	O
processes	O
,	O
it	O
was	O
very	O
limited	O
in	O
addressability	O
.	O
</s>
<s>
The	O
68030	B-Device
MMU	B-General_Concept
would	O
have	O
allowed	O
for	O
much	O
more	O
than	O
8	O
MB	O
of	O
virtual	O
space	O
in	O
a	O
process	O
,	O
which	O
was	O
the	O
limit	O
of	O
the	O
ISC	O
MMU	B-General_Concept
.	O
</s>
<s>
Though	O
this	O
MMU	B-General_Concept
would	O
be	O
slower	O
,	O
the	O
overall	O
faster	O
speed	O
of	O
the	O
68030	B-Device
should	O
have	O
more	O
than	O
made	O
up	O
for	O
it	O
,	O
so	O
that	O
a	O
68030	B-Device
machine	O
was	O
expected	O
to	O
be	O
in	O
all	O
ways	O
faster	O
,	O
and	O
support	O
much	O
larger	O
processes	O
.	O
</s>
