<s>
The	O
TI-81	B-Device
was	O
the	O
first	O
graphing	B-Application
calculator	I-Application
made	O
by	O
Texas	O
Instruments	O
.	O
</s>
<s>
Since	O
its	O
release	O
,	O
it	O
has	O
been	O
superseded	O
by	O
a	O
series	O
of	O
newer	O
calculators	O
:	O
the	O
TI-85	B-Device
,	O
TI-82	B-Device
,	O
TI-83	B-Device
,	O
TI-86	B-Device
,	O
TI-83	B-Device
Plus	I-Device
,	O
TI-83	B-Device
Plus	I-Device
Silver	I-Device
Edition	I-Device
,	O
TI-84	B-Device
Plus	I-Device
,	O
TI-84	B-Device
Plus	I-Device
Silver	I-Device
Edition	I-Device
,	O
TI-84	B-Device
Plus	I-Device
C	O
Silver	O
Editon	O
TI-Nspire	B-Device
,	O
TI-Nspire	B-Device
CAS	I-Device
,	O
TI-84	B-Device
Plus	I-Device
CE	O
,	O
and	O
most	O
recently	O
,	O
the	O
TI-84	B-Device
Plus	I-Device
CE	O
Python	O
.	O
</s>
<s>
Most	O
of	O
them	O
share	O
the	O
original	O
feature	O
set	O
and	O
96×	O
64-pixel	O
display	O
that	O
began	O
with	O
this	O
calculator	O
,	O
with	O
the	O
exceptions	O
of	O
the	O
TI-84	B-Device
Plus	I-Device
C	O
Silver	O
Edition	O
and	O
the	O
TI-84	B-Device
Plus	I-Device
CE	O
family	O
.	O
</s>
<s>
The	O
TI-81	B-Device
is	O
powered	O
by	O
a	O
Zilog	B-General_Concept
Z80	I-General_Concept
microprocessor	B-Architecture
,	O
like	O
those	O
used	O
in	O
almost	O
every	O
other	O
Texas	O
Instruments	O
graphing	B-Application
calculator	I-Application
(	O
except	O
the	O
TI-80	B-Device
,	O
TI-89	B-Device
,	O
TI-89	B-Device
Titanium	I-Device
,	O
TI-92	B-Device
,	O
TI-92	B-Device
Plus	I-Device
,	O
Voyage	O
200	O
and	O
TI-Nspire	B-Device
series	I-Device
)	O
.	O
</s>
<s>
However	O
,	O
the	O
processor	O
is	O
clocked	O
at	O
2	O
MHz	O
whereas	O
the	O
other	O
Z80-powered	O
Texas	O
Instruments	O
calculators	O
run	O
at	O
speeds	O
of	O
at	O
least	O
6	O
MHz	O
(	O
the	O
TI-83	B-Device
Plus	I-Device
Silver	I-Device
Edition	I-Device
,	O
TI-84	B-Device
Plus	I-Device
,	O
and	O
TI-84	B-Device
Plus	I-Device
Silver	I-Device
Edition	I-Device
can	O
run	O
at	O
15	O
MHz	O
)	O
.	O
</s>
<s>
It	O
contains	O
2400	O
bytes	B-Application
of	O
user	O
RAM	B-Architecture
,	O
with	O
additional	O
RAM	B-Architecture
used	O
internally	O
by	O
the	O
calculator	O
firmware	O
software	O
system	O
.	O
</s>
<s>
The	O
TI-81	B-Device
'	O
s	O
user	O
interactions	O
are	O
provided	O
by	O
its	O
so-called	O
Equation	O
Operation	O
System	O
.	O
</s>
<s>
This	O
is	O
comparable	O
to	O
the	O
interface	O
provided	O
by	O
the	O
more	O
recent	O
TI-82	B-Device
,	O
TI-83	B-Device
,	O
and	O
so	O
on	O
.	O
</s>
<s>
In	O
late	O
2009	O
an	O
exploit	O
was	O
found	O
that	O
can	O
be	O
used	O
to	O
execute	O
machine	O
code	O
on	O
the	O
TI-81	B-Device
,	O
using	O
manual	O
input	O
of	O
code	O
.	O
</s>
<s>
The	O
TI-81	B-Device
has	O
no	O
data	O
link	O
interface	O
;	O
its	O
only	O
means	O
of	O
input	O
and	O
output	O
are	O
the	O
keyboard	O
and	O
screen	O
.	O
</s>
<s>
As	O
with	O
its	O
successors	O
,	O
the	O
TI-81	B-Device
is	O
powered	O
by	O
four	O
AAA	B-Algorithm
batteries	I-Algorithm
and	O
one	O
CR1616	B-Algorithm
or	O
CR1620	B-Algorithm
lithium	O
backup	O
battery	O
(	O
to	O
ensure	O
programs	O
are	O
persistent	O
when	O
the	O
AAA	B-Algorithm
batteries	I-Algorithm
are	O
being	O
changed	O
)	O
.	O
</s>
<s>
Some	O
early	O
TI-81	B-Device
units	O
omit	O
the	O
backup	O
battery	O
;	O
if	O
the	O
AAA	B-Algorithm
batteries	I-Algorithm
of	O
one	O
of	O
these	O
units	O
are	O
changed	O
one	O
at	O
a	O
time	O
and	O
quickly	O
,	O
the	O
memory	O
contents	O
are	O
still	O
retained	O
.	O
</s>
<s>
Texas	O
Instruments	O
distributes	O
software	O
which	O
emulates	O
the	O
TI-81	B-Device
and	O
its	O
Equation	O
Operating	O
System	O
on	O
a	O
desktop	O
computer	O
using	O
MS-DOS	O
or	O
DOSBox	B-Application
.	O
</s>
