<s>
The	O
modular	B-Application
debugger	I-Application
(	O
mdb	O
)	O
is	O
an	O
extensible	O
,	O
low-level	O
debugger	O
developed	O
by	O
Sun	O
Microsystems	O
for	O
the	O
Solaris	B-Application
7	I-Application
operating	O
system	O
.	O
</s>
<s>
It	O
is	O
now	O
open	O
sourced	O
,	O
under	O
the	O
Common	B-Application
Development	I-Application
and	I-Application
Distribution	I-Application
License	I-Application
(	O
CDDL	B-Application
)	O
.	O
</s>
<s>
Its	O
source	O
code	O
is	O
now	O
available	O
in	O
all	O
open	O
source	O
derivatives	O
of	O
Solaris	B-Application
,	O
such	O
as	O
Illumos	B-Application
.	O
</s>
<s>
The	O
mdb	O
project	O
was	O
started	O
in	O
1997	O
by	O
Mike	O
Shapiro	O
and	O
others	O
when	O
the	O
Solaris	B-Application
operating	I-Application
system	I-Application
was	O
adding	O
support	O
for	O
64-bit	O
architectures	O
.	O
</s>
<s>
Up	O
until	O
that	O
point	O
,	O
Solaris	B-Application
was	O
using	O
the	O
aging	O
adb	B-Application
debugger	O
developed	O
by	O
Steve	O
Bourne	O
(	O
initially	O
for	O
the	O
AT&T	O
SVR4	O
Unix	O
distribution	O
)	O
.	O
</s>
<s>
It	O
was	O
very	O
difficult	O
to	O
simply	O
port	O
adb	B-Application
from	O
a	O
32-bit	O
architecture	O
to	O
a	O
64-bit	O
architecture	O
,	O
so	O
Sun	O
engineers	O
decided	O
to	O
make	O
a	O
new	O
debugger	O
that	O
would	O
feature	O
enhanced	O
debugging	O
capabilities	O
,	O
while	O
being	O
backward	O
compatible	O
with	O
adb	B-Application
.	O
</s>
