<s>
The	O
ZEBRA	B-Device
(	O
Zeer	O
Eenvoudige	O
Binaire	O
Reken	O
Automaat	O
translated	O
Very	O
Simple	O
Binary	O
Automatic	O
Calculator	O
)	O
was	O
one	O
of	O
the	O
first	O
computers	O
to	O
be	O
designed	O
in	O
the	O
Netherlands	O
,	O
(	O
the	O
first	O
one	O
was	O
the	O
"	O
ARRA	B-Device
"	O
)	O
and	O
one	O
of	O
the	O
first	O
Dutch	O
computers	O
to	O
be	O
commercially	O
available	O
.	O
</s>
<s>
The	O
ZEBRA	B-Device
was	O
a	O
binary	O
,	O
two-address	O
machine	O
with	O
a	O
33-bit	O
word	O
length	O
.	O
</s>
<s>
Storage	O
was	O
provided	O
by	O
a	O
magnetic	B-General_Concept
drum	I-General_Concept
memory	I-General_Concept
holding	O
8K	O
words	O
organised	O
as	O
256	O
tracks	O
of	O
32	O
instructions	O
;	O
accumulators	O
were	O
also	O
implemented	O
as	O
recirculating	O
drum	O
tracks	O
in	O
a	O
manner	O
similar	O
to	O
that	O
used	O
in	O
the	O
Bendix	B-Device
G-15	I-Device
.	O
</s>
<s>
In	O
1967	O
,	O
six	O
Zebra	B-Device
computers	O
were	O
in	O
use	O
in	O
UK	O
universities	O
and	O
technical	O
colleges	O
.	O
</s>
<s>
Large	O
parts	O
of	O
the	O
code	O
and	O
operating	O
systems	O
for	O
ZEBRA	B-Device
were	O
written	O
by	O
deafblind	O
mathematician	O
Gerrit	O
van	O
der	O
Mey	O
.	O
</s>
<s>
In	O
contrast	O
to	O
most	O
processors	O
,	O
the	O
ZEBRA	B-Device
did	O
n't	O
have	O
different	O
types	O
of	O
instructions	O
.	O
</s>
<s>
Instead	O
,	O
the	O
operation	O
of	O
an	O
instruction	O
was	O
controlled	O
by	O
fifteen	O
bits	O
in	O
the	O
operation	B-Language
field	I-Language
.	O
</s>
<s>
The	O
ZEBRA	B-Device
instruction	B-Language
word	I-Language
is	O
33	O
bits	O
,	O
consisting	O
of	O
a	O
13-bit	O
drum	O
address	O
,	O
referencing	O
one	O
of	O
the	O
256	O
tracks	O
of	O
32	O
entries	O
on	O
the	O
memory	B-General_Concept
drum	I-General_Concept
,	O
a	O
five-bit	O
register	B-General_Concept
(	O
or	O
I/O	O
)	O
address	O
,	O
and	O
the	O
15-bit	O
operation	B-Language
field	I-Language
.	O
</s>
<s>
Each	O
bit	O
of	O
the	O
operation	B-Language
field	I-Language
had	O
a	O
distinct	O
meaning	O
and	O
could	O
be	O
used	O
in	O
nearly	O
any	O
combination	O
,	O
leading	O
to	O
many	O
elegant	O
tricks	O
that	O
today	O
might	O
be	O
considered	O
the	O
domain	O
of	O
microprogramming	B-Device
.	O
</s>
<s>
Also	O
,	O
there	O
was	O
an	O
operation	O
bits	O
that	O
determined	O
if	O
the	O
next	O
instruction	O
would	O
come	O
from	O
register	B-General_Concept
or	O
memory	O
,	O
or	O
the	O
sum	O
of	O
both	O
.	O
</s>
<s>
Some	O
bits	O
made	O
an	O
instruction	O
conditional	O
on	O
the	O
accumulator	O
state	O
,	O
as	O
with	O
the	O
Zuse	B-Device
Z22	I-Device
or	O
Electrologica	B-Device
X1	I-Device
.	O
</s>
<s>
Multiplication	O
,	O
division	O
,	O
square	O
root	O
,	O
as	O
well	O
as	O
all	O
floating-point	O
operations	O
,	O
were	O
performed	O
by	O
subroutines	O
,	O
using	O
the	O
underlying	O
serial	B-Device
computer	I-Device
ALU	O
primitives	O
add	O
,	O
subtract	O
,	O
shift	O
right	O
,	O
shift	O
left	O
,	O
and	O
increment	O
.	O
</s>
<s>
Since	O
a	O
magnetic	B-General_Concept
drum	I-General_Concept
does	O
not	O
support	O
random	O
access	O
,	O
some	O
time	O
is	O
lost	O
waiting	O
for	O
an	O
instruction	O
or	O
piece	O
of	O
data	O
become	O
available	O
.	O
</s>
<s>
A	O
notable	O
feature	O
of	O
the	O
ZEBRA	B-Device
was	O
a	O
meter	O
that	O
measured	O
how	O
much	O
of	O
the	O
machine	O
's	O
time	O
was	O
spent	O
in	O
non-wait	O
states	O
;	O
this	O
was	O
called	O
the	O
"	O
efficiency	O
meter.	O
"	O
</s>
