<s>
The	O
PDP-4	B-Device
was	O
the	O
successor	O
to	O
the	O
Digital	O
Equipment	O
Corporation	O
's	O
PDP-1	B-Device
.	O
</s>
<s>
This	O
18-bit	O
machine	O
,	O
first	O
shipped	O
in	O
1962	O
,	O
was	O
a	O
compromise	O
:	O
"	O
with	O
slower	O
memory	O
and	O
different	O
packaging	O
"	O
than	O
the	O
PDP-1	B-Device
,	O
but	O
priced	O
at	O
$	O
65,000	O
-	O
less	O
than	O
half	O
the	O
price	O
of	O
its	O
predecessor	O
.	O
</s>
<s>
All	O
later	O
18-bit	O
PDP	O
machines	O
(	O
7	B-Device
,	O
9	B-Device
and	O
15	B-Device
)	O
are	O
based	O
on	O
a	O
similar	O
,	O
but	O
enlarged	O
instruction	B-General_Concept
set	I-General_Concept
,	O
more	O
powerful	O
than	O
,	O
but	O
based	O
on	O
the	O
same	O
concepts	O
as	O
,	O
the	O
12-bit	O
PDP-5/PDP	O
-8	O
series	O
.	O
</s>
<s>
The	O
system	O
's	O
memory	O
cycle	O
was	O
8	O
microseconds	O
,	O
compared	O
to	O
5	O
microseconds	O
for	O
the	O
PDP-1	B-Device
.	O
</s>
<s>
The	O
PDP-4	B-Device
weighed	O
about	O
.	O
</s>
<s>
Both	O
the	O
PDP-1	B-Device
and	O
the	O
PDP-4	B-Device
were	O
introduced	O
as	O
paper	O
tape-based	O
systems	O
.	O
</s>
<s>
It	O
was	O
in	O
this	O
setting	O
that	O
DEC	O
introduced	O
DECtape	O
,	O
initially	O
called	O
"	O
MicroTape	O
"	O
,	O
for	O
both	O
the	O
PDP-1	B-Device
and	O
PDP-4	B-Device
.	O
</s>
<s>
DEC	O
provided	O
an	O
editor	O
,	O
an	O
assembler	B-Application
,	O
and	O
a	O
FORTRAN	O
II	O
compiler	O
.	O
</s>
<s>
The	O
assembler	B-Application
was	O
different	O
from	O
that	O
of	O
the	O
PDP-1	B-Device
in	O
two	O
ways	O
:	O
</s>
<s>
Unlike	O
the	O
PDP-1	B-Device
,	O
macros	O
were	O
not	O
supported	O
.	O
</s>
<s>
It	O
was	O
a	O
one-pass	O
assembler	B-Application
;	O
paper-tape	O
input	O
did	O
not	O
have	O
to	O
be	O
read	O
twice	O
.	O
</s>
