<s>
A	O
machine	B-General_Concept
code	I-General_Concept
monitor	I-General_Concept
(	O
machine	B-General_Concept
language	I-General_Concept
monitor	I-General_Concept
)	O
is	O
software	B-Application
that	O
allows	O
a	O
user	O
to	O
enter	O
commands	O
to	O
view	O
and	O
change	O
memory	B-General_Concept
locations	I-General_Concept
on	O
a	O
computer	O
,	O
with	O
options	O
to	O
load	O
and	O
save	O
memory	O
contents	O
from/to	O
secondary	O
storage	O
.	O
</s>
<s>
Some	O
full-featured	O
machine	B-General_Concept
code	I-General_Concept
monitors	I-General_Concept
provide	O
detailed	O
control	O
(	O
"	O
single-stepping	O
"	O
)	O
of	O
the	O
execution	O
of	O
machine	B-Language
language	I-Language
programs	O
(	O
much	O
like	O
a	O
debugger	B-Application
)	O
,	O
and	O
include	O
absolute-address	O
code	O
assembly	O
and	O
disassembly	O
capabilities	O
.	O
</s>
<s>
Motorola	O
published	O
the	O
MIKBUG	B-Device
ROM	O
monitor	O
for	O
the	O
6800	O
in	O
1973	O
and	O
the	O
BUFFALO	O
ROM	O
monitor	O
for	O
the	O
68HC11	B-Device
.	O
</s>
<s>
Machine	B-General_Concept
code	I-General_Concept
monitors	I-General_Concept
became	O
popular	O
during	O
the	O
home	O
computer	O
era	O
of	O
the	O
1970s	O
and	O
1980s	O
and	O
were	O
sometimes	O
available	O
as	O
resident	O
firmware	B-Application
in	O
some	O
computers	O
(	O
e.g.	O
,	O
the	O
built-in	O
monitors	O
in	O
the	O
Commodore	B-Device
128	I-Device
,	O
Heathkit	B-Device
H89	I-Device
and	O
Zenith	O
laptops	O
)	O
.	O
</s>
<s>
It	O
was	O
not	O
unheard	O
of	O
to	O
perform	O
all	O
of	O
one	O
's	O
programming	O
in	O
a	O
monitor	O
in	O
lieu	O
of	O
a	O
full-fledged	O
symbolic	O
assembler	B-Language
.	O
</s>
<s>
Even	O
after	O
full-featured	O
assemblers	B-Language
became	O
readily	O
available	O
,	O
a	O
machine	B-General_Concept
code	I-General_Concept
monitor	I-General_Concept
was	O
indispensable	O
for	O
debugging	O
programs	O
.	O
</s>
<s>
The	O
usual	O
technique	O
was	O
to	O
set	O
break	O
points	O
in	O
the	O
code	O
undergoing	O
testing	O
(	O
e.g.	O
,	O
with	O
a	O
BRK	B-General_Concept
instruction	O
in	O
6502	B-General_Concept
assembly	B-Language
language	I-Language
)	O
and	O
start	O
the	O
program	O
.	O
</s>
<s>
When	O
the	O
microprocessor	B-Architecture
encountered	O
a	O
break	O
point	O
,	O
the	O
test	O
program	O
would	O
be	O
interrupted	B-Application
and	O
control	O
would	O
be	O
transferred	O
to	O
the	O
machine	B-General_Concept
code	I-General_Concept
monitor	I-General_Concept
.	O
</s>
<s>
Typically	O
,	O
this	O
would	O
trigger	O
a	O
register	B-General_Concept
dump	I-General_Concept
and	O
then	O
the	O
monitor	O
would	O
await	O
programmer	O
input	O
.	O
</s>
<s>
Activities	O
at	O
this	O
point	O
might	O
include	O
examining	O
memory	O
contents	O
,	O
patching	O
code	O
and/or	O
perhaps	O
altering	O
the	O
processor	B-General_Concept
registers	I-General_Concept
prior	O
to	O
restarting	O
the	O
test	O
program	O
.	O
</s>
<s>
The	O
general	O
decline	O
of	O
scratch-written	O
assembly	B-Language
language	I-Language
software	B-Application
has	O
made	O
the	O
use	O
of	O
a	O
machine	B-General_Concept
code	I-General_Concept
monitor	I-General_Concept
somewhat	O
of	O
a	O
lost	O
art	O
.	O
</s>
<s>
In	O
most	O
systems	O
where	O
higher-level	O
languages	O
are	O
employed	O
,	O
debuggers	B-Application
are	O
used	O
to	O
present	O
a	O
more	O
abstract	O
and	O
friendly	O
view	O
of	O
what	O
is	O
happening	O
within	O
a	O
program	O
.	O
</s>
<s>
However	O
,	O
the	O
use	O
of	O
machine	B-General_Concept
code	I-General_Concept
monitors	I-General_Concept
persists	O
,	O
especially	O
in	O
the	O
area	O
of	O
hobby-built	O
computers	O
.	O
</s>
