<s>
The	O
Professional	O
325	O
(	O
PRO-325	B-Device
)	O
,	O
Professional	B-Device
350	I-Device
(	O
PRO-350	B-Device
)	O
,	O
and	O
Professional	O
380	O
(	O
PRO-380	B-Device
)	O
are	O
PDP-11	B-Device
compatible	O
microcomputers	B-Architecture
introduced	O
in	O
1982	O
by	O
Digital	O
Equipment	O
Corporation	O
(	O
DEC	O
)	O
as	O
high-end	O
competitors	O
to	O
the	O
IBM	B-Device
PC	I-Device
.	O
</s>
<s>
Like	O
the	O
cosmetically	O
similar	O
Rainbow	B-Device
100	I-Device
and	O
DECmate	O
II	O
(	O
also	O
introduced	O
at	O
that	O
time	O
)	O
,	O
</s>
<s>
the	O
PRO	O
series	O
uses	O
the	O
LK201	B-Device
keyboard	O
and	O
400KB	O
single-sided	O
quad-density	O
floppy	B-Device
disk	I-Device
drives	I-Device
(	O
known	O
as	O
RX50	O
)	O
,	O
and	O
offers	O
a	O
choice	O
of	O
color	O
or	O
monochrome	O
monitors	O
.	O
</s>
<s>
For	O
DEC	O
,	O
none	O
of	O
the	O
three	O
would	O
be	O
favorably	O
received	O
,	O
and	O
the	O
industry	O
instead	O
standardized	O
on	O
Intel	O
8088-based	O
IBM	B-Device
PC	I-Device
compatibles	O
which	O
are	O
all	O
binary	O
program	O
compatible	O
with	O
each	O
other	O
.	O
</s>
<s>
In	O
some	O
ways	O
,	O
the	O
PDP-11	B-Device
microprocessors	O
are	O
technically	O
superior	O
to	O
the	O
Intel-based	O
chips	O
.	O
</s>
<s>
While	O
the	O
8088	B-Device
is	O
restricted	O
to	O
1MB	O
of	O
memory	O
because	O
of	O
its	O
20-bit	O
address	O
bus	O
,	O
DEC	O
microprocessors	O
are	O
capable	O
of	O
accessing	O
4MB	O
with	O
their	O
22-bit	O
addressing	O
(	O
although	O
direct	O
addressing	O
of	O
memory	O
is	O
limited	O
in	O
both	O
approaches	O
to	O
64KB	O
segments	O
,	O
limiting	O
the	O
size	O
of	O
individual	O
code	O
and	O
data	O
objects	O
)	O
.	O
</s>
<s>
BYTE	O
in	O
1984	O
reported	O
that	O
Venix	B-Operating_System
on	O
the	O
PC	O
outperformed	O
the	O
same	O
operating	B-General_Concept
system	I-General_Concept
on	O
the	O
DEC	B-Device
Professional	I-Device
and	O
PDP-11/23	O
.	O
</s>
<s>
Further	O
,	O
although	O
the	O
PDP-11	B-Device
was	O
a	O
very	O
successful	O
minicomputer	B-Architecture
,	O
it	O
lacked	O
a	O
wide	O
base	O
of	O
affordable	O
small	O
business	O
software	O
.	O
</s>
<s>
By	O
comparison	O
,	O
many	O
existing	O
CP/M	B-Application
applications	O
(	O
see	O
the	O
Rainbow	B-Device
100	I-Device
)	O
were	O
easily	O
ported	O
to	O
the	O
similar	O
8086/8088	O
chips	O
and	O
MS-DOS	B-Application
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
Porting	O
existing	O
PDP-11	B-Device
software	O
to	O
the	O
PRO	O
was	O
complicated	O
by	O
design	O
decisions	O
that	O
rendered	O
it	O
partially	O
incompatible	O
with	O
its	O
parent	O
product	O
line	O
.	O
</s>
<s>
Industry	O
critics	O
observed	O
that	O
this	O
incompatibility	O
appeared	O
at	O
least	O
in	O
part	O
deliberate	O
,	O
as	O
DEC	O
belatedly	O
sought	O
to	O
"	O
protect	O
"	O
its	O
more-profitable	O
mainstream	O
PDP-11s	B-Device
from	O
price	O
competition	O
with	O
lower-priced	O
PCs	O
.	O
</s>
<s>
The	O
PRO	O
was	O
never	O
widely	O
accepted	O
as	O
an	O
office	O
personal	O
computer	O
,	O
nor	O
as	O
a	O
scientific	O
workstation	O
,	O
where	O
the	O
market	O
was	O
also	O
headed	O
to	O
Intel	B-General_Concept
8086	I-General_Concept
,	O
or	O
alternately	O
to	O
Motorola	O
68000-based	O
computers	O
.	O
</s>
<s>
The	O
failure	O
of	O
DEC	O
to	O
gain	O
a	O
significant	O
foothold	O
in	O
the	O
high-volume	O
PC	O
market	O
would	O
be	O
the	O
beginning	O
of	O
the	O
end	O
of	O
the	O
computer	O
hardware	O
industry	O
in	O
New	O
England	O
,	O
as	O
nearly	O
all	O
computer	O
companies	O
located	O
there	O
were	O
focused	O
on	O
minicomputers	B-Architecture
for	O
large	O
organizations	O
,	O
from	O
DEC	O
to	O
Data	O
General	O
,	O
Wang	O
,	O
Prime	O
,	O
Computervision	O
,	O
Honeywell	O
,	O
and	O
Symbolics	O
Inc	O
.	O
</s>
<s>
The	O
PRO-325	B-Device
and	O
-350	O
use	O
the	O
F-11	O
chipset	B-Device
(	O
as	O
used	O
in	O
LSI-11/23	O
systems	O
)	O
to	O
create	O
a	O
single-board	O
PDP-11	B-Device
with	O
up	O
to	O
six	O
expansion	O
slots	O
of	O
a	O
proprietary	O
CTI	O
(	O
Computing	O
Terminal	O
Interconnect	O
)	O
bus	O
using	O
90-pin	O
ZIF	B-General_Concept
connectors	O
.	O
</s>
<s>
The	O
PRO	O
family	O
uses	O
dual	O
RX50	O
floppy	B-Device
drives	I-Device
for	O
storage	O
;	O
the	O
PRO-325	B-Device
has	O
only	O
floppies	B-Device
,	O
and	O
the	O
350	O
and	O
380	O
also	O
include	O
an	O
internal	O
hard	O
drive	O
.	O
</s>
<s>
Mainline	O
PDP-11s	B-Device
generally	O
use	O
separate	O
serial	O
terminals	O
as	O
console	B-Device
and	O
display	O
devices	O
;	O
the	O
PRO	O
family	O
uses	O
built-in	O
bit-mapped	B-Algorithm
graphics	I-Algorithm
to	O
drive	O
a	O
combined	O
console	B-Device
and	O
display	O
.	O
</s>
<s>
All	O
other	O
I/O	O
devices	O
in	O
the	O
PRO	O
family	O
are	O
also	O
different	O
(	O
in	O
most	O
cases	O
,	O
radically	O
different	O
)	O
from	O
their	O
counterparts	O
on	O
other	O
PDP-11	B-Device
models	O
.	O
</s>
<s>
For	O
example	O
,	O
while	O
the	O
internal	O
bus	O
supports	O
direct	B-General_Concept
memory	I-General_Concept
access	I-General_Concept
(	O
DMA	O
)	O
,	O
none	O
of	O
the	O
available	O
I/O	O
devices	O
actually	O
use	O
this	O
feature	O
.	O
</s>
<s>
The	O
interrupt	B-Application
system	O
is	O
implemented	O
using	O
Intel	O
PC	O
chips	O
of	O
the	O
time	O
,	O
which	O
again	O
makes	O
it	O
very	O
different	O
from	O
the	O
PDP-11	B-Device
standard	O
interrupt	B-Application
architecture	O
.	O
</s>
<s>
For	O
all	O
these	O
reasons	O
,	O
support	O
of	O
the	O
PRO	O
family	O
requires	O
extensive	O
modifications	O
to	O
the	O
previously-existing	O
operating	B-General_Concept
system	I-General_Concept
software	O
,	O
and	O
the	O
PRO	O
cannot	O
run	O
standard	O
PDP-11	B-Device
software	O
without	O
modification	O
.	O
</s>
<s>
The	O
default	O
PRO-3xx	O
operating	B-General_Concept
system	I-General_Concept
is	O
DEC	O
's	O
Professional	O
Operating	B-General_Concept
System	I-General_Concept
(	O
P/OS	B-Application
)	O
,	O
a	O
modified	O
version	O
of	O
RSX-11M	B-Application
with	O
a	O
menu-driven	O
core	O
user	O
interface	O
.	O
</s>
<s>
Industry	O
critics	O
complained	O
that	O
this	O
user	O
interface	O
was	O
awkward	O
,	O
slow	O
,	O
and	O
inflexible	O
,	O
offering	O
few	O
advantages	O
over	O
the	O
command-line	O
based	O
MS-DOS	B-Application
user	O
interface	O
that	O
was	O
coming	O
into	O
widespread	O
use	O
.	O
</s>
<s>
Other	O
available	O
operating	B-General_Concept
systems	I-General_Concept
include	O
DEC	O
RT-11	B-Operating_System
,	O
VenturCom	O
Venix	B-Operating_System
,	O
and	O
2.9BSD	B-Operating_System
Unix	I-Operating_System
.	O
</s>
<s>
Later	O
,	O
the	O
Professional	O
380	O
(	O
PRO-380	B-Device
)	O
was	O
introduced	O
using	O
the	O
much	O
faster	O
J-11	B-Device
chip	B-Device
set	I-Device
(	O
as	O
used	O
in	O
11/73	B-Device
systems	O
)	O
.	O
</s>
<s>
However	O
,	O
due	O
to	O
clocking	O
issues	O
on	O
the	O
motherboard	O
,	O
the	O
J-11	B-Device
chip	O
runs	O
at	O
10MHz	O
instead	O
of	O
16-18MHz	O
,	O
thus	O
making	O
the	O
PRO-380	B-Device
slower	O
than	O
a	O
stock	O
11/73	B-Device
system	O
.	O
</s>
<s>
The	O
DEC	B-Device
Professional	I-Device
Series	O
PC-38N	O
is	O
a	O
PRO-380	B-Device
with	O
a	O
real-time	O
interface	O
(	O
RTI	O
)	O
that	O
is	O
used	O
as	O
the	O
console	B-Device
for	O
the	O
VAX	B-Device
8500	I-Device
and	I-Device
8550	I-Device
.	O
</s>
<s>
The	O
RTI	O
also	O
has	O
a	O
programmable	O
peripheral	O
interface	O
(	O
PPI	O
)	O
consisting	O
of	O
three	O
8-bit	O
ports	O
for	O
transferring	O
data	O
,	O
address	O
,	O
and	O
control	O
signals	O
between	O
the	O
console	B-Device
and	O
the	O
VAX	O
console	B-Device
interface	O
.	O
</s>
<s>
Like	O
the	O
PDP-8	O
and	O
PDP-11	B-Device
before	O
it	O
,	O
the	O
Professional	B-Device
350	I-Device
was	O
cloned	O
by	O
Elektronika	O
in	O
the	O
Soviet	O
Union	O
.	O
</s>
<s>
Other	O
PDP-11	B-Device
clones	O
:	O
</s>
