<s>
The	O
HP	O
48	O
is	O
a	O
series	O
of	O
graphing	B-Application
calculators	I-Application
designed	O
and	O
produced	O
by	O
Hewlett-Packard	O
from	O
1990	O
until	O
2003	O
.	O
</s>
<s>
The	O
models	O
with	O
an	O
X	O
suffix	O
are	O
expandable	O
via	O
special	O
RAM	B-Architecture
(	O
memory	O
expansion	O
)	O
and	O
ROM	B-Device
(	O
software	O
application	O
)	O
cards	O
.	O
</s>
<s>
Note	O
that	O
the	O
similarly	O
named	O
hp	B-Device
48gII	I-Device
(	O
2004	O
)	O
is	O
not	O
a	O
member	O
of	O
the	O
series	O
but	O
closely	O
related	O
to	O
the	O
HP	B-Device
49G+	I-Device
.	O
</s>
<s>
The	O
calculators	O
use	O
Reverse	O
Polish	O
Notation	O
(	O
RPN	O
)	O
and	O
the	O
RPL	B-Device
programming	I-Device
language	I-Device
.	O
</s>
<s>
The	O
hardware	B-General_Concept
architecture	I-General_Concept
developed	O
for	O
the	O
HP48	O
series	O
became	O
the	O
basis	O
for	O
the	O
HP	O
38G	O
,	O
with	O
a	O
simplified	O
user	O
interface	O
and	O
an	O
infix	O
input	O
method	O
,	O
and	O
the	O
HP	O
49G	O
with	O
various	O
software	O
enhancements	O
.	O
</s>
<s>
Likewise	O
,	O
the	O
hardware	O
and	O
software	O
design	O
of	O
the	O
HP48	O
calculators	O
are	O
themselves	O
strongly	O
influenced	O
by	O
other	O
calculators	O
in	O
the	O
HP	O
line	O
,	O
most	O
of	O
all	O
by	O
the	O
HP-18C	B-Device
and	O
the	O
HP-28	B-Device
series	I-Device
.	O
</s>
<s>
The	O
HP	B-Device
48SX	I-Device
was	O
introduced	O
on	O
1990-03-06	O
.	O
</s>
<s>
The	O
HP48	O
series	O
 '	O
Saturn	B-Application
microprocessor	B-Architecture
is	O
a	O
hybrid	O
64-bit	B-Device
/	O
20-bit	O
CPU	B-General_Concept
hardware-wise	O
but	O
acts	O
like	O
a	O
4-bit	O
processor	O
in	O
that	O
it	O
presents	O
nibble-based	O
data	O
to	O
programs	O
and	O
uses	O
a	O
nibble-based	O
addressing	O
system	O
.	O
</s>
<s>
The	O
main	O
registers	O
A	O
,	O
B	O
,	O
C	O
,	O
D	O
,	O
along	O
with	O
temp	O
registers	O
R0	O
,	O
R1	O
,	O
R2	O
,	O
R3	O
,	O
and	O
R4	O
are	O
a	O
full	O
64-bits	B-Device
wide	O
,	O
but	O
the	O
data	O
registers	O
D0	O
&	O
D1	O
are	O
only	O
20-bit	O
.	O
</s>
<s>
The	O
processor	O
has	O
a	O
20-bit	O
address	B-Architecture
bus	I-Architecture
available	O
to	O
code	O
but	O
due	O
to	O
the	O
presence	O
of	O
the	O
high/low	O
nibble	O
selection	O
bit	O
,	O
only	O
19	O
bits	O
are	O
available	O
externally	O
.	O
</s>
<s>
In	O
both	O
the	O
HP48S/SX	O
and	O
G/GX	O
series	O
,	O
the	O
Saturn	B-Application
CPU	B-General_Concept
core	O
is	O
integrated	O
as	O
part	O
of	O
a	O
more	O
complex	O
integrated	O
circuit	O
(	O
IC	O
)	O
package	O
.	O
</s>
<s>
The	O
previous	O
series	O
of	O
Saturn-based	O
ICs	O
were	O
codenamed	O
Lewis	O
,	O
after	O
Meriwether	O
Lewis	O
.	O
</s>
<s>
Screen	O
resolution	O
:	O
131×64	O
pixels	B-Algorithm
.	O
</s>
<s>
The	O
HP48	O
series	O
of	O
calculators	O
support	O
a	O
stack-based	O
programming	O
language	O
named	O
RPL	B-Device
,	O
a	O
supposed	O
combination	O
of	O
Reverse	O
Polish	O
notation	O
(	O
RPN	O
)	O
and	O
Lisp	B-Language
.	O
</s>
<s>
RPL	B-Device
adds	O
the	O
concepts	O
of	O
lists	O
and	O
functions	O
to	O
stack-based	O
programming	O
,	O
allowing	O
the	O
programmer	O
to	O
pass	O
unevaluated	O
code	O
as	O
arguments	O
to	O
functions	O
,	O
or	O
return	O
unevaluated	O
code	O
from	O
a	O
function	O
by	O
leaving	O
it	O
on	O
the	O
stack	B-Application
.	O
</s>
<s>
RPL	B-Device
comes	O
in	O
two	O
flavors	O
:	O
User	O
RPL	B-Device
and	O
System	O
RPL	B-Device
.	O
</s>
<s>
User	O
RPL	B-Device
is	O
the	O
language	O
that	O
a	O
user	O
can	O
program	O
directly	O
on	O
the	O
calculator	O
.	O
</s>
<s>
System	O
RPL	B-Device
requires	O
an	O
external	O
compiler	O
;	O
this	O
may	O
be	O
done	O
on	O
the	O
calculator	O
with	O
a	O
third-party	O
utility	O
,	O
or	O
on	O
another	O
machine	O
.	O
</s>
<s>
User	O
RPL	B-Device
does	O
not	O
expose	O
any	O
commands	O
that	O
do	O
not	O
check	O
their	O
arguments	O
.	O
</s>
<s>
Consequently	O
,	O
User	O
RPL	B-Device
programs	O
cannot	O
normally	O
crash	O
the	O
calculator	O
(	O
and	O
are	O
therefore	O
slower	O
than	O
System	O
RPL	B-Device
programs	O
)	O
,	O
whereas	O
a	O
System	O
RPL	B-Device
program	O
that	O
invokes	O
a	O
command	O
with	O
incorrect	O
arguments	O
will	O
almost	O
certainly	O
leave	O
the	O
calculator	O
in	O
a	O
state	O
which	O
requires	O
a	O
full	O
memory	O
reset	O
.	O
</s>
<s>
It	O
is	O
also	O
possible	O
to	O
program	O
the	O
HP48	O
directly	O
in	O
machine	B-Language
language	I-Language
.	O
</s>
