<s>
The	O
HEC	O
(	O
Hollerith	B-Device
Electronic	I-Device
Computer	I-Device
)	O
,	O
built	O
by	O
the	O
British	O
Tabulating	O
Machine	O
Company	O
(	O
later	O
to	O
become	O
International	O
Computers	O
and	O
Tabulators	O
(	O
ICT	O
)	O
,	O
then	O
International	O
Computers	O
Limited	O
(	O
ICL	O
)	O
)	O
,	O
a	O
commercial	O
machine	O
sold	O
in	O
several	O
models	O
and	O
later	O
known	O
as	O
the	O
ICT200	O
series	O
.	O
</s>
<s>
The	O
APEHC	O
was	O
a	O
punched	B-Architecture
card	I-Architecture
machine	O
while	O
the	O
APEXC	B-Device
,	O
APERC	O
and	O
APENC	O
were	O
teletypers	O
(	O
keyboard	B-Device
and	O
printer	O
,	O
plus	O
paper	O
tape	O
reader	O
and	O
puncher	O
)	O
.	O
</s>
<s>
They	O
then	O
used	O
his	O
design	O
to	O
create	O
the	O
Hollerith	B-Device
Electronic	I-Device
Computer	I-Device
1	O
(	O
HEC	O
1	O
)	O
before	O
the	O
end	O
of	O
1951	O
.	O
</s>
<s>
The	O
HEC	O
used	O
standard	O
punched	B-Architecture
cards	I-Architecture
;	O
the	O
HEC	O
4	O
had	O
a	O
printer	O
,	O
too	O
,	O
and	O
it	O
featured	O
several	O
instructions	O
(	O
such	O
as	O
divide	O
)	O
and	O
registers	O
not	O
found	O
on	O
the	O
APEXC	B-Device
.	O
</s>
<s>
An	O
emulator	O
for	O
the	O
APEXC	B-Device
series	O
has	O
been	O
developed	O
by	O
MESS	O
.	O
</s>
<s>
The	O
APEXC	B-Device
is	O
an	O
incredibly	O
simple	O
machine	O
.	O
</s>
<s>
The	O
APEXC	B-Device
has	O
no	O
RAM	B-Architecture
,	O
except	O
for	O
a	O
32-bit	O
accumulator	O
and	O
a	O
32-bit	O
data	O
register	O
(	O
used	O
along	O
with	O
the	O
32-bit	O
accumulator	O
to	O
implement	O
64-bit	O
shift	O
instructions	O
and	O
hold	O
the	O
64-bit	O
result	O
of	O
a	O
multiplication	O
)	O
.	O
</s>
<s>
Instructions	O
and	O
data	O
are	O
stored	O
in	O
two	O
magnetic	B-General_Concept
drums	I-General_Concept
,	O
for	O
a	O
total	O
of	O
32	O
circular	O
magnetic	O
tracks	O
of	O
32	O
words	O
.	O
</s>
<s>
Nowadays	O
,	O
many	O
say	O
a	O
pocket	O
calculator	B-Application
is	O
faster	O
.	O
</s>
<s>
One	O
oddity	O
is	O
that	O
there	O
is	O
no	O
program	B-General_Concept
counter	I-General_Concept
:	O
each	O
machine	O
instruction	O
includes	O
the	O
address	B-General_Concept
of	O
the	O
next	B-General_Concept
instruction	I-General_Concept
.	O
</s>
<s>
The	O
machine	O
code	O
is	O
made	O
of	O
15	O
instructions	O
only	O
,	O
namely	O
addition	O
,	O
subtraction	O
,	O
multiplication	O
,	O
load	O
(	O
3	O
variants	O
)	O
,	O
store	O
(	O
2	O
variants	O
)	O
,	O
conditional	B-General_Concept
branch	I-General_Concept
,	O
right	O
arithmetic	O
bit	O
shift	O
,	O
right	O
bit	O
rotation	O
,	O
punched-card	B-Architecture
input	O
,	O
punched-card	B-Architecture
output	O
,	O
machine	O
stop	O
,	O
and	O
bank-switching	O
(	O
which	O
is	O
never	O
used	O
on	O
the	O
APEXC	B-Device
,	O
since	O
it	O
only	O
has	O
1024	O
words	O
of	O
storage	O
,	O
and	O
addresses	O
are	O
10-bit-long	O
)	O
.	O
</s>
<s>
A	O
so-called	O
vector	O
mode	O
enables	O
to	O
repeat	O
the	O
same	O
operation	O
32	O
times	O
with	O
32	O
successive	O
memory	B-General_Concept
locations	I-General_Concept
.	O
</s>
<s>
Another	O
oddity	O
is	O
that	O
the	O
memory	O
bus	O
and	O
the	O
ALU	B-General_Concept
are	O
1-bit-wide	O
.	O
</s>
<s>
The	O
APEXC	B-Device
CPU	O
qualifies	O
as	O
RISC	B-Architecture
;	O
there	O
is	O
no	O
other	O
adequate	O
word	O
.	O
</s>
<s>
Note	O
there	O
is	O
no	O
read-only	B-Device
memory	I-Device
(	O
ROM	B-Device
)	O
,	O
and	O
therefore	O
no	O
bootstrap	B-Operating_System
loader	I-Operating_System
or	O
default	O
start-up	O
program	O
whatsoever	O
.	O
</s>
<s>
It	O
is	O
believed	O
that	O
no	O
executive	O
or	O
operating	B-General_Concept
system	I-General_Concept
was	O
ever	O
written	O
for	O
the	O
APEXC	B-Device
,	O
although	O
there	O
were	O
subroutine	B-Library
libraries	I-Library
of	O
sorts	O
for	O
common	O
arithmetic	O
,	O
I/O	O
and	O
debug	O
tasks	O
.	O
</s>
<s>
Operation	O
of	O
the	O
machine	O
is	O
normally	O
done	O
through	O
a	O
control	O
panel	O
which	O
allows	O
the	O
user	O
to	O
start	O
,	O
stop	O
and	O
resume	O
the	O
central	B-General_Concept
processing	I-General_Concept
unit	I-General_Concept
,	O
and	O
to	O
alter	O
registers	O
and	O
memory	O
when	O
the	O
CPU	O
is	O
stopped	O
.	O
</s>
<s>
When	O
starting	O
the	O
machine	O
,	O
the	O
address	B-General_Concept
of	O
the	O
first	O
instruction	O
of	O
the	O
program	O
to	O
be	O
executed	O
must	O
be	O
entered	O
in	O
the	O
control	O
panel	O
,	O
then	O
the	O
run	O
switch	O
must	O
be	O
pressed	O
.	O
</s>
<s>
Most	O
programs	O
end	O
with	O
a	O
stop	O
instruction	O
,	O
which	O
enables	O
the	O
operator	O
to	O
check	O
the	O
state	O
of	O
the	O
machine	O
,	O
possibly	O
run	O
some	O
post-mortem	O
debugging	O
procedures	O
(	O
a	O
core	B-Error_Name
dump	I-Error_Name
routine	O
is	O
described	O
in	O
an	O
APEXC	B-Device
programming	O
book	O
)	O
,	O
then	O
enter	O
the	O
address	B-General_Concept
of	O
another	O
program	O
and	O
run	O
it	O
.	O
</s>
