<s>
The	O
HP-20S	O
(	O
F1890A	O
)	O
is	O
an	O
algebraic	O
programmable	B-Application
scientific	O
calculator	O
produced	O
by	O
Hewlett	O
Packard	O
from	O
1989	O
to	O
2000	O
.	O
</s>
<s>
A	O
member	O
of	O
HP	O
's	O
Pioneer	O
series	O
,	O
the	O
20S	O
was	O
a	O
low	O
cost	O
model	O
targeted	O
at	O
students	O
,	O
using	O
the	O
same	O
hardware	O
as	O
the	O
HP-10B	B-Device
business	I-Device
calculator	O
.	O
</s>
<s>
Compared	O
with	O
the	O
higher-end	O
32S	B-Device
and	O
42S	B-Device
scientific	O
calculators	O
,	O
the	O
20S	O
includes	O
much	O
more	O
basic	O
functionality	O
.	O
</s>
<s>
As	O
a	O
student	O
calculator	O
,	O
it	O
also	O
uses	O
infix	O
notation	O
rather	O
than	O
the	O
Reverse	O
Polish	O
notation	O
found	O
in	O
higher-end	O
HP	B-Device
calculators	I-Device
.	O
</s>
<s>
Despite	O
these	O
limitations	O
,	O
the	O
20S	O
is	O
keystroke	B-Device
programmable	I-Device
,	O
supporting	O
up	O
to	O
99	O
program	O
lines	O
of	O
fully	O
merged	O
instructions	O
and	O
ten	O
memory	O
registers	O
.	O
</s>
<s>
Introduced	O
simultaneously	O
was	O
the	O
HP-10B	B-Device
,	O
based	O
on	O
the	O
same	O
hardware	O
but	O
targeting	O
the	O
business	O
calculator	O
market	O
.	O
</s>
<s>
The	O
CPU	O
is	O
an	O
HP	B-Application
Saturn	I-Application
(	O
Bert	O
)	O
chip	O
clocked	O
at	O
640kHz	O
.	O
</s>
<s>
While	O
higher	O
end	O
scientific	O
models	O
in	O
the	O
Pioneer	O
series	O
were	O
fitted	O
with	O
dot-matrix	B-General_Concept
displays	I-General_Concept
that	O
allowed	O
their	O
functionality	O
to	O
be	O
organized	O
into	O
menus	O
(	O
the	O
22S	B-Device
,	O
32S	B-Device
and	O
42S	B-Device
being	O
examples	O
)	O
,	O
the	O
20S	O
has	O
only	O
a	O
more	O
primitive	O
12-digit	O
seven-segment	B-General_Concept
display	I-General_Concept
.	O
</s>
<s>
The	O
20S	O
contained	O
six	O
preloaded	O
programs	O
in	O
ROM	B-Device
for	O
common	O
mathematical	O
operations	O
.	O
</s>
<s>
HP	O
's	O
stated	O
goal	O
in	O
releasing	O
the	O
21S	O
was	O
to	O
eliminate	O
the	O
need	O
for	O
statistics	O
tables	O
,	O
just	O
as	O
the	O
HP-35	B-Device
had	O
previously	O
eliminated	O
for	O
trigonometric	O
and	O
log	O
tables	O
.	O
</s>
<s>
The	O
majority	O
of	O
the	O
features	O
of	O
the	O
20S	O
are	O
still	O
present	O
,	O
including	O
keystroke	B-Device
programming	I-Device
support	O
and	O
the	O
typical	O
trigonometric	O
,	O
logarithmic	O
and	O
exponential	O
functions	O
found	O
on	O
most	O
scientific	O
calculators	O
.	O
</s>
<s>
Probability	O
and	O
distribution	O
:	O
factorial	O
,	O
permutation	B-Algorithm
and	O
combination	O
functions	O
.	O
</s>
