<s>
The	O
HP-41C	B-Device
series	O
are	O
programmable	B-Application
,	O
expandable	O
,	O
continuous	B-Device
memory	I-Device
handheld	O
RPN	O
calculators	B-Application
made	O
by	O
Hewlett-Packard	O
from	O
1979	O
to	O
1990	O
.	O
</s>
<s>
The	O
original	O
model	O
,	O
HP-41C	B-Device
,	O
was	O
the	O
first	O
of	O
its	O
kind	O
to	O
offer	O
alphanumeric	B-General_Concept
display	I-General_Concept
capabilities	O
.	O
</s>
<s>
Later	O
came	O
the	O
HP-41CV	O
and	O
HP-41CX	B-Device
,	O
offering	O
more	O
memory	O
and	O
functionality	O
.	O
</s>
<s>
The	O
alphanumeric	O
LCD	B-Device
screen	I-Device
of	O
the	O
HP-41C	B-Device
revolutionized	O
the	O
way	O
a	O
pocket	O
calculator	B-Application
could	O
be	O
used	O
,	O
providing	O
user	O
friendliness	O
(	O
for	O
its	O
time	O
)	O
and	O
expandability	O
(	O
keyboard-unassigned	O
functions	O
could	O
be	O
spelled	O
out	O
alphabetically	O
)	O
.	O
</s>
<s>
By	O
using	O
an	O
alphanumeric	B-General_Concept
display	I-General_Concept
,	O
the	O
calculator	B-Application
could	O
tell	O
the	O
user	O
what	O
was	O
going	O
on	O
:	O
it	O
could	O
display	O
error	O
messages	O
,	O
such	O
as	O
showing	O
(	O
"	O
DATA	O
ERROR	O
"	O
)	O
upon	O
attempting	O
to	O
divide	O
by	O
zero	O
instead	O
of	O
simply	O
displaying	O
a	O
blinking	O
zero	O
;	O
it	O
could	O
also	O
specifically	O
prompt	O
the	O
user	O
for	O
arguments	O
(	O
"	O
ENTER	O
RADIUS	O
"	O
)	O
instead	O
of	O
just	O
displaying	O
a	O
question	O
mark	O
.	O
</s>
<s>
Earlier	O
calculators	B-Application
needed	O
a	O
key	O
,	O
or	O
key	O
combination	O
,	O
for	O
every	O
available	O
function	O
.	O
</s>
<s>
The	O
HP-67	B-Device
had	O
three	O
shift	O
keys	O
(	O
gold	O
"	O
f	O
"	O
,	O
blue	O
"	O
g	O
"	O
and	O
black	O
"	O
h	O
"	O
prefix	O
keys	O
)	O
;	O
the	O
competing	O
Texas	O
Instruments	O
calculators	B-Application
had	O
two	O
(	O
2nd	O
and	O
INV	O
)	O
and	O
close	O
to	O
50	O
keys	O
(	O
the	O
TI-59	B-Device
had	O
45	O
)	O
.	O
</s>
<s>
Hewlett-Packard	O
were	O
constrained	O
by	O
their	O
one	O
byte	B-Application
only	O
instruction	O
format	O
.	O
</s>
<s>
The	O
more	O
flexible	O
storage	O
format	O
for	O
programs	O
in	O
the	O
TI-59	B-Device
allowed	O
combining	O
more	O
keys	O
into	O
one	O
instruction	O
.	O
</s>
<s>
The	O
TI-59	B-Device
also	O
made	O
use	O
of	O
the	O
Op	O
key	O
followed	O
by	O
two	O
digits	O
to	O
access	O
another	O
40	O
different	O
functions	O
,	O
but	O
the	O
user	O
had	O
to	O
remember	O
the	O
codes	O
for	O
them	O
.	O
</s>
<s>
Clearly	O
,	O
a	O
more	O
convenient	O
and	O
flexible	O
method	O
of	O
executing	O
the	O
calculator	B-Application
's	O
instructions	O
was	O
needed	O
.	O
</s>
<s>
The	O
HP-41C	B-Device
had	O
a	O
relatively	O
small	O
keyboard	O
,	O
and	O
only	O
one	O
shift	O
key	O
,	O
but	O
provided	O
hundreds	O
of	O
functions	O
.	O
</s>
<s>
The	O
calculator	B-Application
had	O
a	O
special	O
user	O
mode	O
where	O
the	O
user	O
could	O
assign	O
any	O
function	O
to	O
any	O
key	O
if	O
the	O
default	O
assignments	O
provided	O
by	O
HP	O
were	O
not	O
suited	O
to	O
a	O
specific	O
application	O
.	O
</s>
<s>
For	O
this	O
mode	O
,	O
the	O
HP-41C	B-Device
came	O
with	O
blank	O
keyboard	O
templates	O
;	O
i.e.	O
</s>
<s>
Hewlett-Packard	O
even	O
sold	O
a	O
version	O
of	O
the	O
calculator	B-Application
where	O
hardly	O
any	O
keys	O
had	O
function	O
names	O
printed	O
on	O
them	O
,	O
meant	O
for	O
users	O
who	O
would	O
be	O
using	O
the	O
HP-41C	B-Device
for	O
custom	O
calculations	O
only	O
(	O
thus	O
not	O
needing	O
the	O
standard	O
key	O
layout	O
at	O
all	O
)	O
;	O
this	O
version	O
of	O
the	O
calculator	B-Application
was	O
colloquially	O
known	O
,	O
within	O
HP	O
's	O
Corvallis	O
calculator	B-Application
team	O
,	O
as	O
a	O
"	O
Blanknut	O
"	O
(	O
because	O
the	O
development	O
code	O
name	O
for	O
the	O
HP-41C	B-Device
'	O
s	O
processor	O
was	O
known	O
as	O
the	O
"	O
coconut	O
"	O
)	O
.	O
</s>
<s>
Alphanumeric	B-General_Concept
display	I-General_Concept
also	O
greatly	O
eased	O
editing	O
programs	O
,	O
as	O
functions	O
were	O
spelled	O
out	O
in	O
full	O
.	O
</s>
<s>
Numeric-only	O
calculators	B-Application
displayed	O
programming	O
steps	O
as	O
a	O
list	O
of	O
numbers	O
,	O
each	O
number	O
generally	O
mapped	O
to	O
a	O
key	O
on	O
the	O
keyboard	O
,	O
often	O
via	O
row	O
and	O
column	O
coordinates	O
.	O
</s>
<s>
The	O
HP-41C	B-Device
displayed	O
each	O
character	O
in	O
a	O
block	O
consisting	O
of	O
14	O
segments	O
that	O
could	O
be	O
turned	O
on	O
or	O
off	O
;	O
a	O
so-called	O
fourteen	B-General_Concept
segment	I-General_Concept
display	I-General_Concept
(	O
similar	O
to	O
the	O
much	O
more	O
common	O
seven	B-General_Concept
segment	I-General_Concept
displays	I-General_Concept
,	O
which	O
can	O
be	O
used	O
to	O
display	O
digits	O
only	O
)	O
.	O
</s>
<s>
The	O
HP-41C	B-Device
used	O
a	O
liquid-crystal	B-Device
display	I-Device
instead	O
of	O
the	O
ubiquitous	O
LED	O
displays	O
of	O
the	O
era	O
,	O
to	O
reduce	O
power	O
consumption	O
.	O
</s>
<s>
While	O
this	O
allowed	O
the	O
display	O
of	O
uppercase	O
letters	O
,	O
digits	O
,	O
and	O
a	O
few	O
punctuation	O
characters	O
(	O
the	O
FOCAL	B-Language
character	O
set	O
)	O
,	O
some	O
designs	O
needed	O
to	O
be	O
twisted	O
arbitrarily	O
(	O
e.g.	O
</s>
<s>
HP	O
's	O
competitor	O
Sharp	O
,	O
when	O
introducing	O
the	O
PC-1211	B-Device
,	O
used	O
a	O
dot	B-General_Concept
matrix	I-General_Concept
of	O
5×7	O
dots	O
and	O
displayed	O
the	O
characters	O
in	O
principle	O
as	O
we	O
see	O
them	O
today	O
on	O
computer	O
screens	O
(	O
and	O
,	O
in	O
fact	O
,	O
many	O
LCD	B-Device
screens	I-Device
on	O
various	O
embedded	B-Architecture
systems	I-Architecture
)	O
;	O
this	O
was	O
later	O
used	O
by	O
HP	O
with	O
the	O
HP-71B	B-Device
handheld	O
computer	O
.	O
</s>
<s>
The	O
HP-41CV	O
(	O
V	O
being	O
the	O
Roman	O
numeral	O
for	O
5	O
)	O
included	O
this	O
memory	O
module	O
on	O
the	O
main	O
board	O
,	O
thus	O
providing	O
five	O
times	O
the	O
memory	O
of	O
the	O
HP-41C	B-Device
,	O
and	O
four	O
available	O
slots	O
.	O
</s>
<s>
To	O
the	O
calculator	B-Application
(	O
and	O
the	O
user	O
)	O
,	O
data	O
located	O
in	O
the	O
extended	O
memory	O
looked	O
like	O
files	O
on	O
a	O
modern	O
hard	O
disk	O
do	O
for	O
a	O
PC	O
(	O
user	O
)	O
.	O
</s>
<s>
The	O
final	O
HP-41	B-Device
model	O
,	O
the	O
HP-41CX	B-Device
,	O
included	O
extended	O
memory	O
,	O
a	O
built-in	O
time	O
module	O
,	O
and	O
extended	O
functions	O
.	O
</s>
<s>
The	O
HP-41C	B-Device
is	O
keystroke	B-Device
programmable	I-Device
meaning	O
that	O
it	O
can	O
remember	O
and	O
later	O
execute	O
sequences	O
of	O
keystrokes	O
to	O
solve	O
particular	O
problems	O
of	O
interest	O
to	O
the	O
user	O
.	O
</s>
<s>
The	O
HP-41C	B-Device
also	O
supports	O
indirect	O
addressing	O
(	O
computed	O
goto	O
)	O
with	O
which	O
it	O
is	O
possible	O
to	O
implement	O
a	O
Universal	O
Turing	O
machine	O
and	O
therefore	O
the	O
programming	O
model	O
of	O
the	O
HP-41C	B-Device
can	O
be	O
considered	O
Turing	B-Algorithm
complete	I-Algorithm
.	O
</s>
<s>
needing	O
an	O
exponent	O
greater	O
than	O
99	O
,	O
the	O
calculator	B-Application
's	O
maximum	O
)	O
.	O
</s>
<s>
The	O
program	O
takes	O
up	O
2	O
registers	O
,	O
which	O
is	O
≈14	O
bytes	B-Application
.	O
</s>
<s>
Though	O
the	O
programming	O
language	O
used	O
on	O
the	O
41	B-Device
series	O
is	O
a	O
version	O
of	O
the	O
keystroke	B-Device
programming	I-Device
languages	O
used	O
all	O
preceding	O
programmable	B-Application
HP	B-Device
calculators	I-Device
,	O
the	O
range	O
of	O
technologies	O
,	O
and	O
programming-related	O
usability	O
and	O
extensibility	O
features	O
available	O
in	O
41	B-Device
series	O
models	O
(	O
notably	O
keyboard	O
overlays	O
,	O
a	O
fully	O
remappable	O
keyboard	O
,	O
I/O	O
capabilities	O
for	O
storing	O
and	O
sharing	O
programs	O
,	O
and	O
alphanumeric	O
support	O
)	O
,	O
led	O
some	O
users	O
to	O
propose	O
a	O
new	O
name	O
for	O
the	O
language	O
,	O
resulting	O
in	O
a	O
competition	O
that	O
was	O
won	O
by	O
"	O
FOCAL	B-Language
"	O
for	O
"	O
Forty	O
One	O
Calculator	B-Application
Language	O
"	O
.	O
</s>
<s>
As	O
the	O
name	O
FOCAL	B-Language
was	O
already	B-Language
in	I-Language
use	I-Language
by	O
the	O
Digital	O
Equipment	O
Corporation	O
,	O
the	O
name	O
was	O
never	O
formally	O
adopted	O
by	O
HP	O
.	O
</s>
<s>
A	O
large	O
users	O
 '	O
community	O
was	O
built	O
around	O
the	O
HP-41C	B-Device
.	O
</s>
<s>
Enthusiasts	O
around	O
the	O
world	O
found	O
new	O
ways	O
of	O
programming	O
,	O
created	O
their	O
own	O
software	O
(	O
such	O
as	O
a	O
codebreaking	O
game	O
,	O
and	O
a	O
version	O
of	O
Hunt	B-Application
the	I-Application
Wumpus	I-Application
)	O
and	O
expansion	O
modules	O
,	O
and	O
sped	O
up	O
the	O
clock	O
(	O
see	O
overclocking	B-Application
)	O
.	O
</s>
<s>
Most	O
of	O
these	O
activities	O
were	O
coordinated	O
by	O
the	O
PPC	B-Application
club	O
and	O
its	O
president	O
,	O
Richard	O
J	O
.	O
Nelson	O
.	O
</s>
<s>
The	O
PPC	B-Application
club	O
published	O
the	O
PPC	B-Application
Journal	O
and	O
produced	O
the	O
PPC	B-Application
ROM	B-Device
,	O
a	O
collection	O
of	O
highly	O
optimized	O
low-level	O
programs	O
for	O
the	O
HP-41C	B-Device
.	O
</s>
<s>
One	O
of	O
the	O
discoveries	O
of	O
the	O
community	O
was	O
that	O
,	O
because	O
some	O
FOCAL	B-Language
instructions	O
were	O
stored	O
in	O
memory	O
as	O
more	O
than	O
one	O
byte	B-Application
,	O
it	O
is	O
possible	O
to	O
exploit	O
a	O
bug	O
in	O
the	O
program	O
editor	O
to	O
assign	O
strange	O
functions	O
to	O
keys	O
.	O
</s>
<s>
The	O
most	O
important	O
function	O
was	O
known	O
as	O
the	O
byte	B-Application
jumper	O
,	O
a	O
way	O
to	O
step	O
partially	O
through	O
programming	O
instructions	O
and	O
edit	O
them	O
in	O
ways	O
that	O
were	O
not	O
otherwise	O
allowed	O
.	O
</s>
<s>
The	O
use	O
of	O
the	O
resulting	O
instructions	O
was	O
called	O
synthetic	B-Device
programming	I-Device
.	O
</s>
<s>
Through	O
synthetic	B-Device
instructions	I-Device
,	O
a	O
user	O
could	O
access	O
memory	O
and	O
special	O
status	O
flags	O
reserved	O
for	O
the	O
operating	O
system	O
,	O
and	O
do	O
very	O
strange	O
things	O
,	O
including	O
completely	O
locking	O
the	O
machine	O
.	O
</s>
<s>
Hewlett-Packard	O
did	O
not	O
officially	O
support	O
synthetic	B-Device
programming	I-Device
,	O
but	O
neither	O
did	O
it	O
do	O
anything	O
to	O
prevent	O
it	O
,	O
and	O
eventually	O
even	O
provided	O
internal	O
documentation	O
to	O
the	O
user	O
groups	O
.	O
</s>
<s>
In	O
its	O
December	O
1980	O
issue	O
,	O
BYTE	B-Application
magazine	O
described	O
the	O
HP-41C	B-Device
as	O
"	O
the	O
most	O
versatile	O
machine	O
ever	O
"	O
.	O
</s>
<s>
The	O
author	O
praised	O
HP	O
's	O
documentation	O
as	O
"	O
among	O
the	O
best	O
in	O
the	O
industry	O
"	O
,	O
and	O
reported	O
that	O
the	O
calculator	B-Application
was	O
"	O
much	O
easier	O
to	O
program	O
and	O
debug	O
"	O
than	O
the	O
TI-59	B-Device
.	O
</s>
<s>
Stating	O
"	O
I	O
found	O
the	O
HP-41C	B-Device
far	O
more	O
pleasurable	O
to	O
program	O
and	O
use	O
than	O
its	O
predecessors	O
"	O
because	O
of	O
its	O
alphanumeric	B-General_Concept
display	I-General_Concept
,	O
the	O
author	O
concluded	O
that	O
it	O
was	O
"	O
maybe	O
not	O
quite	O
"	O
a	O
pocket	O
computer	O
.	O
</s>
<s>
In	O
the	O
next	O
issue	O
,	O
another	O
author	O
wrote	O
that	O
"	O
The	O
41C	O
...	O
is	O
among	O
the	O
programmable	B-Application
calculators	I-Application
that	O
lie	O
closest	O
to	O
the	O
computer	O
borderline	O
.	O
</s>
<s>
It	O
comes	O
close	O
enough	O
for	O
the	O
jargon	O
of	O
computers	O
to	O
be	O
useful	O
in	O
describing	O
it	O
"	O
,	O
and	O
praised	O
the	O
simplicity	O
and	O
reliability	O
of	O
the	O
card	O
reader	O
and	O
compatibility	O
with	O
HP-67	B-Device
and	O
HP-97	O
software	O
.	O
</s>
<s>
The	O
review	O
criticized	O
the	O
inaccuracies	O
in	O
calculations	O
from	O
the	O
lack	O
of	O
guard	B-Algorithm
digits	I-Algorithm
;	O
"	O
There	O
is	O
something	O
absurd	O
about	O
the	O
world	O
's	O
fanciest	O
calculator	B-Application
not	O
being	O
able	O
to	O
give	O
results	O
accurate	O
to	O
more	O
than	O
seven	O
or	O
eight	O
decimal	O
places	O
"	O
.	O
</s>
<s>
An	O
HP-41C	B-Device
that	O
flew	O
on	O
nine	O
early	O
Space	O
Shuttle	O
missions	O
is	O
on	O
display	O
in	O
the	O
National	O
Air	O
and	O
Space	O
Museum	O
in	O
Washington	O
,	O
D.C.	O
HP-41Cs	B-Device
with	O
some	O
special	O
hardware	O
configurations	O
(	O
the	O
addition	O
of	O
Velcro	O
strips	O
,	O
pre-production	O
time	O
module	O
,	O
and	O
louder	O
beeper	O
,	O
as	O
well	O
as	O
the	O
removal	O
of	O
parts	O
whose	O
outgassing	O
could	O
cause	O
contamination	O
)	O
were	O
carried	O
on	O
early	O
Shuttle	O
missions	O
for	O
the	O
purpose	O
of	O
performing	O
mundane	O
but	O
necessary	O
calculations	O
,	O
such	O
as	O
calculating	O
the	O
change	O
to	O
the	O
center	O
of	O
gravity	O
due	O
to	O
fuel	O
consumption	O
.	O
</s>
<s>
The	O
HP-41C	B-Device
was	O
also	O
programmed	O
to	O
handle	O
calculations	O
usually	O
performed	O
by	O
the	O
main	O
on-board	O
computer	O
,	O
such	O
as	O
determining	O
ignition	O
times	O
for	O
re-entry	O
,	O
in	O
the	O
case	O
of	O
a	O
main	O
computer	O
failure	O
.	O
</s>
<s>
The	O
functions	O
of	O
the	O
calculator	B-Application
could	O
be	O
expanded	O
by	O
adding	O
modules	O
at	O
the	O
top	O
of	O
the	O
machine	O
.	O
</s>
<s>
As	O
such	O
,	O
an	O
HP-41	B-Device
could	O
in	O
fact	O
be	O
tailored	O
to	O
the	O
personal	O
needs	O
of	O
the	O
user	O
.	O
</s>
<s>
Hardware	O
extensions	O
included	O
a	O
thermal	O
printer	O
,	O
a	O
magnetic	O
card	O
reader	O
(	O
HP-67	B-Device
compatible	O
via	O
converter	O
software	O
)	O
,	O
and	O
a	O
barcode	O
"	O
wand	O
"	O
(	O
reader	O
)	O
.	O
</s>
<s>
The	O
standard	O
set	O
of	O
mathematical	O
functions	O
of	O
the	O
41-series	O
was	O
somewhat	O
limited	O
when	O
compared	O
to	O
the	O
functionality	O
of	O
some	O
contemporary	O
HP	B-Device
calculators	I-Device
(	O
notably	O
the	O
HP-34C	B-Device
and	O
the	O
HP-15C	B-Device
)	O
.	O
</s>
<s>
Another	O
module	O
,	O
known	O
as	O
the	O
Interface	B-Architecture
Loop	I-Architecture
allowed	O
for	O
connection	O
of	O
more	O
peripherals	O
:	O
larger	O
printers	O
,	O
microcassette	O
tape	O
recorders	O
,	O
3-inch	O
floppy	B-Device
disk	I-Device
drives	I-Device
,	O
RS-232	O
communication	O
interfaces	O
,	O
video	O
display	O
interfaces	O
,	O
etc	O
.	O
</s>
<s>
The	O
Interface	B-Architecture
Loop	I-Architecture
could	O
also	O
be	O
used	O
with	O
the	O
HP-71B	B-Device
,	O
HP-75	B-Device
and	O
HP-110	B-Device
computers	O
.	O
</s>
<s>
HP-41	B-Device
extension	O
(	O
or	O
expansion	O
)	O
modules	O
allowed	O
the	O
user	O
of	O
an	O
HP-41	B-Device
programmable	B-Application
calculator	I-Application
to	O
extend	O
the	O
functionality	O
of	O
the	O
machine	O
.	O
</s>
<s>
The	O
HP-41	B-Device
had	O
room	O
for	O
up	O
to	O
four	O
expansion	O
modules	O
at	O
the	O
back	O
of	O
calculator	B-Application
.	O
</s>
<s>
The	O
HP-41	B-Device
was	O
not	O
the	O
only	O
calculator	B-Application
of	O
its	O
generation	O
that	O
allowed	O
expansion	O
modules	O
.	O
</s>
<s>
The	O
TI-58	B-Device
and	O
TI-59	B-Device
also	O
had	O
pluggable	O
ROM	B-Device
modules	O
.	O
</s>
<s>
The	O
HP-41	B-Device
modules	O
were	O
however	O
much	O
more	O
versatile	O
.	O
</s>
<s>
Memory	O
modules	O
added	O
RAM	B-Architecture
main	O
memory	O
to	O
the	O
calculator	B-Application
,	O
allowing	O
more	O
programming	O
steps	O
and/or	O
more	O
data	O
registers	O
.	O
</s>
<s>
The	O
original	O
HP-41C	B-Device
had	O
a	O
main	O
memory	O
of	O
63	O
registers	O
of	O
7	O
bytes	B-Application
each	O
.	O
</s>
<s>
Each	O
register	O
could	O
hold	O
either	O
a	O
number	O
,	O
a	O
6-character	O
string	O
,	O
or	O
up	O
to	O
seven	O
program	O
steps	O
in	O
the	O
FOCAL	B-Language
language	O
(	O
program	O
steps	O
used	O
a	O
variable	O
number	O
of	O
bytes	B-Application
)	O
.	O
</s>
<s>
Each	O
memory	O
module	O
added	O
64	O
registers	O
,	O
and	O
the	O
calculator	B-Application
could	O
hold	O
up	O
to	O
four	O
of	O
them	O
,	O
for	O
a	O
grand	O
total	O
of	O
319	O
registers	O
.	O
</s>
<s>
The	O
ROM-based	O
application	O
'	O
pac	O
 '	O
modules	O
added	O
up	O
to	O
4	O
kilobytes	O
of	O
read-only	B-Device
memory	I-Device
(	O
some	O
up	O
to	O
8	O
kilobytes	O
,	O
but	O
these	O
were	O
simply	O
two	O
independent	O
4K	O
modules	O
in	O
the	O
same	O
box	O
)	O
.	O
</s>
<s>
Most	O
modules	O
held	O
dozens	O
of	O
programs	O
written	O
in	O
the	O
HP-41C	B-Device
programming	O
language	O
,	O
FOCAL	B-Language
.	O
</s>
<s>
Programs	O
in	O
the	O
ROM	B-Device
modules	O
could	O
be	O
called	O
from	O
a	O
user	O
program	O
,	O
using	O
the	O
ubiquitous	O
XEQ	O
function	O
.	O
</s>
<s>
In	O
the	O
program	O
code	O
,	O
XEQ	O
appeared	O
as	O
"	O
XROM	O
"	O
when	O
it	O
was	O
used	O
to	O
call	O
a	O
ROM	B-Device
program	O
.	O
</s>
<s>
As	O
the	O
HP-41C	B-Device
had	O
non-volatile	B-General_Concept
memory	I-General_Concept
(	O
user	O
programs	O
and	O
data	O
were	O
not	O
wiped	O
out	O
when	O
power	O
was	O
off	O
)	O
there	O
was	O
no	O
absolute	O
need	O
for	O
a	O
permanent	O
storage	O
device	O
,	O
so	O
the	O
card	O
reader	O
was	O
optional	O
.	O
</s>
<s>
Each	O
card	O
held	O
two	O
strips	O
of	O
112	O
bytes	B-Application
each	O
,	O
that	O
could	O
hold	O
16	O
data	O
registers	O
or	O
up	O
to	O
112	O
program	O
steps	O
.	O
</s>
<s>
The	O
card	O
reader	O
could	O
read	O
magnetic	O
cards	O
from	O
the	O
earlier	O
model	O
HP-67	B-Device
.	O
</s>
<s>
HP-67	B-Device
programs	O
were	O
translated	O
into	O
HP-41C	B-Device
instructions	O
,	O
as	O
the	O
HP-67	B-Device
and	O
HP-41	B-Device
share	O
the	O
same	O
programming	O
model	O
and	O
operation	O
stack	B-Application
.	O
</s>
<s>
Some	O
instructions	O
however	O
were	O
specific	O
to	O
the	O
HP-67	B-Device
,	O
and	O
the	O
card	O
reader	O
provided	O
additional	O
instructions	O
to	O
emulate	O
the	O
67	O
.	O
</s>
<s>
However	O
,	O
the	O
electric	O
motor	O
put	O
a	O
heavy	O
strain	O
on	O
the	O
calculator	B-Application
batteries	O
,	O
and	O
the	O
price	O
tag	O
for	O
blank	O
cards	O
put	O
an	O
even	O
heavier	O
strain	O
on	O
the	O
user	O
's	O
wallet	O
.	O
</s>
<s>
The	O
alarms	O
were	O
able	O
to	O
switch	O
the	O
calculator	B-Application
on	O
,	O
so	O
it	O
was	O
possible	O
to	O
create	O
programs	O
that	O
executed	O
at	O
some	O
point	O
during	O
the	O
day	O
,	O
then	O
switch	O
the	O
calculator	B-Application
off	O
until	O
the	O
next	O
alarm	O
.	O
</s>
<s>
As	O
the	O
HP-41	B-Device
was	O
often	O
used	O
as	O
a	O
data-gathering	O
device	O
in	O
labs	O
,	O
this	O
allowed	O
the	O
calculator	B-Application
to	O
read	O
data	O
from	O
monitored	O
devices	O
at	O
specific	O
times	O
every	O
day	O
,	O
without	O
having	O
to	O
remain	O
fully	O
powered	O
up	O
in	O
between	O
readings	O
(	O
thus	O
saving	O
battery	O
capacity	O
)	O
.	O
</s>
<s>
The	O
HP-41CX	B-Device
had	O
the	O
time	O
module	O
built	O
in	O
.	O
</s>
<s>
The	O
optical	O
wand	O
was	O
a	O
barcode	O
reader	O
shaped	O
like	O
a	O
thick	O
pen	O
,	O
and	O
was	O
designed	O
to	O
read	O
lines	O
of	O
HP-proprietary	O
standard	O
barcodes	O
into	O
the	O
calculator	B-Application
memory	O
.	O
</s>
<s>
HP	O
solutions	O
books	O
,	O
could	O
consist	O
of	O
programs	O
,	O
numeric	O
or	O
alphabetical	O
constants	O
,	O
and	O
even	O
keypresses	O
(	O
letting	O
the	O
calculator	B-Application
be	O
operated	O
without	O
using	O
the	O
keyboard	O
)	O
useful	O
for	O
diagnosing	O
calculators	B-Application
where	O
the	O
keyboard	O
was	O
suspected	O
to	O
be	O
faulty	O
.	O
</s>
<s>
Extended	O
memory	O
could	O
also	O
hold	O
ASCII	B-Protocol
files	I-Protocol
,	O
and	O
a	O
rudimentary	O
text	B-Application
editor	I-Application
was	O
added	O
also	O
.	O
</s>
<s>
The	O
HP-41CX	B-Device
contained	O
the	O
Extended	O
Functions	O
module	O
as	O
standard	O
.	O
</s>
<s>
Extended	O
memory	O
modules	O
added	O
more	O
extended	O
memory	O
to	O
the	O
HP-41C	B-Device
.	O
</s>
<s>
HP-41CX	B-Device
version	O
of	O
the	O
calculator	B-Application
.	O
</s>
<s>
addressable	O
registers	O
,	O
for	O
a	O
total	O
of	O
919	O
registers	O
,	O
or	O
6433	O
bytes	B-Application
.	O
</s>
<s>
See	O
the	O
main	O
article	O
on	O
HP-IL	B-Architecture
.	O
</s>
<s>
The	O
continued	O
popularity	O
of	O
the	O
HP-41CX	B-Device
among	O
users	O
prompted	O
SwissMicros	O
to	O
produce	O
a	O
miniature	O
calculator	B-Application
approximating	O
the	O
size	O
of	O
an	O
ID-1	O
credit	O
card	O
(	O
88mm×	O
59mm×	O
7mm	O
)	O
in	O
2015	O
.	O
</s>
<s>
Named	O
DM41	O
,	O
it	O
runs	O
the	O
original	O
HP-41CX	B-Device
firmware	O
with	O
extended	O
memory	O
and	O
realtime	O
clock	O
in	O
an	O
emulator	B-Application
on	O
an	O
ARM	O
Cortex-M0-based	O
NXP	O
LPC1115	O
processor	O
.	O
</s>
<s>
Deviating	O
from	O
the	O
original	O
,	O
it	O
comes	O
in	O
a	O
landscape	O
form	O
factor	O
(	O
as	O
known	O
from	O
Hewlett-Packard	O
'	O
s	O
Voyager	B-Device
series	I-Device
)	O
with	O
rearranged	O
keys	O
,	O
it	O
features	O
a	O
dot-matrix	B-General_Concept
display	O
,	O
switchable	O
clock	O
speeds	O
,	O
and	O
,	O
based	O
on	O
a	O
Silicon	O
Labs	O
CP2102	O
converter	O
chip	O
,	O
it	O
comes	O
with	O
a	O
USB	B-Protocol
(	O
Mini-B	O
)	O
serial	O
interface	O
to	O
exchange	O
data	O
with	O
a	O
PC	O
etc	O
.	O
</s>
<s>
for	O
backup	O
purposes	O
,	O
to	O
possibly	O
communicate	O
with	O
applications	O
(	O
like	O
PC-based	O
emulators	B-Application
)	O
,	O
or	O
to	O
update	O
the	O
firmware	O
.	O
</s>
<s>
In	O
December	O
2015	O
,	O
SwissMicros	O
introduced	O
the	O
DM41L	O
,	O
a	O
version	O
of	O
the	O
calculator	B-Application
about	O
the	O
same	O
size	O
as	O
the	O
calculators	B-Application
of	O
the	O
HP	B-Device
Voyager	I-Device
series	I-Device
.	O
</s>
<s>
It	O
still	O
comes	O
with	O
a	O
USB	B-Protocol
Mini-B	O
connector	O
.	O
</s>
<s>
In	O
addition	O
to	O
clones	O
based	O
on	O
emulated	B-Application
HP-41	B-Device
hardware	O
,	O
there	O
exists	O
at	O
least	O
one	O
actual	O
hardware	O
clone	O
of	O
the	O
HP-41	B-Device
series	O
.	O
</s>
<s>
This	O
is	O
the	O
HP41CL	O
HP-41-series	O
CPU	O
board	O
upgrade	O
created	O
by	O
Monte	O
Dalrymple	O
at	O
Systemyde	O
.	O
</s>
<s>
The	O
HP41CL	O
is	O
a	O
ground	O
up	O
redesign	O
of	O
the	O
components	O
found	O
on	O
the	O
HP-41	B-Device
CPU	O
board	O
,	O
including	O
the	O
CPU	O
,	O
which	O
is	O
implemented	O
on	O
an	O
FPGA	B-Architecture
and	O
coded	O
in	O
Verilog	B-Language
RTL	O
.	O
</s>
<s>
The	O
HP41CL	O
upgrade	O
board	O
is	O
made	O
as	O
a	O
drop-in	O
replacement	O
for	O
the	O
HP-41	B-Device
series	O
CPU	O
board	O
,	O
assuming	O
that	O
one	O
has	O
an	O
HP-41	B-Device
that	O
has	O
a	O
compatible	O
CPU	O
board	O
connector	O
and	O
a	O
separate	O
CPU	O
board	O
as	O
well	O
.	O
</s>
<s>
This	O
is	O
possible	O
due	O
to	O
the	O
fact	O
that	O
the	O
HP41CL	O
has	O
over	O
1024	O
pages	O
of	O
4K-word	O
flash	O
memory	O
built	O
in	O
,	O
of	O
which	O
over	O
500	O
pages	O
are	O
pre-loaded	O
with	O
HP-41	B-Device
software	O
,	O
as	O
well	O
as	O
the	O
upgrade	O
board	O
providing	O
128	O
RAM	B-Architecture
pages	O
,	O
which	O
are	O
made	O
available	O
to	O
the	O
user	O
via	O
a	O
custom	O
MMU	B-General_Concept
.	O
</s>
<s>
In	O
addition	O
,	O
a	O
"	O
turbo	O
"	O
mode	O
is	O
provided	O
by	O
the	O
HP41CL	O
upgrade	O
board	O
's	O
"	O
NEWT	O
"	O
CPU	O
design	O
,	O
which	O
allows	O
the	O
user	O
to	O
speed	O
up	O
their	O
calculator	B-Application
by	O
a	O
factor	O
of	O
around	O
50	O
times	O
.	O
</s>
<s>
Also	O
,	O
the	O
HP41CL	O
maintains	O
full	O
compatibility	O
with	O
the	O
HP-41	B-Device
series	O
bus	O
,	O
so	O
that	O
most	O
plug-in	O
modules	O
can	O
still	O
be	O
used	O
in	O
a	O
fully	O
backward	O
compatible	O
fashion	O
.	O
</s>
<s>
Additionally	O
,	O
Systemyde	O
makes	O
an	O
HP-41	B-Device
compatible	O
timer	O
module	O
clone	O
as	O
well	O
as	O
a	O
GPS	O
receiver	O
interface	O
module	O
.	O
</s>
<s>
Unusually	O
for	O
pocket	O
calculators	B-Application
,	O
the	O
devices	O
still	O
have	O
a	O
fan	O
base	O
more	O
than	O
30	O
years	O
after	O
their	O
production	O
was	O
discontinued	O
in	O
1989	O
.	O
</s>
<s>
As	O
a	O
result	O
,	O
emulator	B-Application
programs	O
are	O
available	O
for	O
a	O
variety	O
of	O
operating	O
systems	O
,	O
including	O
Windows	B-Application
,	O
Mac	B-Application
OS	I-Application
,	O
Unix	B-Application
variants	O
,	O
Pocket	B-Device
PC	I-Device
,	O
Palm	B-Operating_System
OS	I-Operating_System
,	O
Apple	B-Application
iOS	I-Application
and	O
Android	B-Application
.	O
</s>
