<s>
Pasquale	O
"	O
Pat	O
"	O
J	O
.	O
Villani	O
(	O
18	O
April	O
1954	O
–	O
27	O
August	O
2011	O
)	O
was	O
an	O
American	O
computer	B-Application
programmer	I-Application
,	O
author	O
,	O
and	O
advocate	O
of	O
free	B-Application
software	I-Application
,	O
best	O
known	O
for	O
his	O
creation	O
of	O
DOS-C	O
,	O
a	O
DOS	B-Device
emulator	B-Application
written	O
in	O
the	O
C	B-Language
language	I-Language
and	O
subsequently	O
adapted	O
as	O
the	O
kernel	B-Operating_System
of	O
the	O
FreeDOS	B-Application
operating	B-General_Concept
system	I-General_Concept
and	O
a	O
number	O
of	O
other	O
projects	O
including	O
DOSEMU	B-Application
for	O
Linux	B-Application
.	O
</s>
<s>
Villani	O
had	O
already	O
been	O
working	O
on	O
a	O
DOS-like	O
operating	B-General_Concept
system	I-General_Concept
for	O
use	O
in	O
embedded	O
systems	O
for	O
some	O
while	O
before	O
the	O
advent	O
of	O
FreeDOS	B-Application
.	O
</s>
<s>
His	O
efforts	O
started	O
when	O
he	O
developed	O
an	O
MS-DOS	B-Application
3.1-compatible	O
interface	O
emulator	B-Application
to	O
write	O
device	O
drivers	O
in	O
the	O
C	B-Language
high-level	O
language	O
instead	O
of	O
in	O
assembly	B-Language
language	I-Language
,	O
as	O
was	O
the	O
usual	O
approach	O
at	O
that	O
time	O
.	O
</s>
<s>
This	O
interface	O
emulator	B-Application
grew	O
into	O
a	O
minimal	O
operating	B-General_Concept
system	I-General_Concept
named	O
XDOS	O
around	O
1988	O
.	O
</s>
<s>
He	O
added	O
an	O
IPL	O
to	O
set	O
up	O
a	O
boot	O
environment	O
before	O
loading	O
the	O
actual	O
operating	B-General_Concept
system	I-General_Concept
and	O
developed	O
an	O
MS-DOS-compatible	O
frontend	O
API	O
to	O
applications	O
.	O
</s>
<s>
In	O
contrast	O
to	O
MS-DOS	B-Application
,	O
which	O
is	O
not	O
designed	O
to	O
be	O
reentrant	B-Operating_System
,	O
the	O
system	O
calls	O
of	O
his	O
operating	B-General_Concept
system	I-General_Concept
were	O
,	O
which	O
is	O
often	O
a	O
requirement	O
for	O
multitasking	B-Operating_System
and	O
real-time	B-General_Concept
applications	I-General_Concept
in	O
embedded	O
systems	O
.	O
</s>
<s>
This	O
system	O
was	O
named	O
NSS-DOS	O
and	O
also	O
offered	O
commercially	O
.	O
</s>
<s>
When	O
one	O
potential	O
contractor	O
sought	O
to	O
use	O
the	O
OS	O
in	O
a	O
system	O
equipped	O
with	O
Motorola	O
680x0	B-Device
processors	O
instead	O
of	O
Intel	O
x86	B-General_Concept
processors	O
,	O
for	O
which	O
the	O
system	O
was	O
designed	O
originally	O
and	O
which	O
utilize	O
different	O
instruction	B-General_Concept
sets	I-General_Concept
and	O
memory	B-General_Concept
models	O
,	O
Villani	O
was	O
able	O
to	O
redesign	O
his	O
system	O
to	O
become	O
portable	O
across	O
a	O
range	O
of	O
different	O
compilers	O
and	O
target	O
environments	O
.	O
</s>
<s>
This	O
move	O
to	O
a	O
completely	O
different	O
target	O
platform	O
,	O
while	O
losing	O
binary	O
compatibility	O
with	O
existing	O
applications	O
,	O
would	O
have	O
required	O
a	O
complete	O
rewrite	O
from	O
scratch	O
had	O
his	O
system	O
not	O
been	O
written	O
in	O
a	O
high-level	O
language	O
such	O
as	O
C	B-Language
,	O
which	O
allowed	O
him	O
to	O
reuse	O
large	O
parts	O
.	O
</s>
<s>
His	O
new	O
DOS/NT	B-Operating_System
used	O
a	O
microkernel	B-Operating_System
architecture	O
with	O
logical	O
separation	O
of	O
file	B-Application
system	I-Application
,	O
memory	B-General_Concept
and	O
task	B-General_Concept
manager	I-General_Concept
.	O
</s>
<s>
Villani	O
joined	O
the	O
FreeDOS	B-Application
project	O
in	O
1994	O
after	O
reading	O
Jim	O
Hall	O
's	O
announcement	O
of	O
a	O
"	O
PD-DOS	B-Application
"	O
on	O
.	O
</s>
<s>
In	O
response	O
to	O
Hall	O
's	O
announcement	O
,	O
Villani	O
devised	O
a	O
derivative	O
of	O
DOS/NT	B-Operating_System
named	O
DOS-C	O
with	O
a	O
monolithic	B-Operating_System
kernel	I-Operating_System
and	O
an	O
architecture	O
more	O
similar	O
to	O
the	O
non-multitasking	O
MS-DOS	B-Application
,	O
and	O
in	O
1995	O
he	O
made	O
it	O
available	O
for	O
dual-use	O
under	O
a	O
GPL	B-License
open-source	O
license	O
to	O
become	O
the	O
kernel	B-Operating_System
component	O
of	O
the	O
new	O
"	O
Free-DOS	B-Application
"	O
operating	B-General_Concept
system	I-General_Concept
,	O
as	O
"	O
PD-DOS	B-Application
"	O
was	O
called	O
at	O
this	O
time	O
.	O
</s>
<s>
In	O
1996	O
,	O
Villani	O
wrote	O
the	O
book	O
FreeDOS	B-Application
Kernel	B-Operating_System
,	O
which	O
describes	O
the	O
design	O
of	O
the	O
DOS-C	O
/	O
FreeDOS	B-Application
kernel	B-Operating_System
and	O
the	O
original	O
FreeDOS	B-Application
COMMAND.COM	B-Operating_System
command	O
line	O
interpreter	O
.	O
</s>
<s>
The	O
name	O
of	O
the	O
operating	B-General_Concept
system	I-General_Concept
was	O
subsequently	O
officially	O
changed	O
to	O
FreeDOS	B-Application
to	O
reflect	O
the	O
spelling	O
used	O
in	O
the	O
book	O
.	O
</s>
<s>
Internally	O
,	O
the	O
FreeDOS	B-Application
kernel	B-Operating_System
was	O
still	O
significantly	O
different	O
from	O
MS-DOS	B-Application
,	O
which	O
,	O
while	O
no	O
problem	O
for	O
embedded	O
applications	O
specifically	O
written	O
for	O
FreeDOS	B-Application
,	O
caused	O
various	O
compatibility	O
issues	O
in	O
conjunction	O
with	O
misbehaving	O
DOS	B-Device
applications	O
.	O
</s>
<s>
Villani	O
and	O
other	O
contributors	O
analyzed	O
and	O
addressed	O
many	O
of	O
these	O
issues	O
over	O
the	O
years	O
for	O
FreeDOS	B-Application
to	O
become	O
much	O
more	O
MS-DOS	B-Application
compatible	O
.	O
</s>
<s>
With	O
some	O
breaks	O
Villani	O
remained	O
active	O
with	O
the	O
FreeDOS	B-Application
project	O
,	O
including	O
preparations	O
for	O
the	O
release	O
of	O
FreeDOS	B-Application
1.1	O
.	O
</s>
<s>
The	O
FreeDOS	B-Application
1.1	O
release	O
,	O
published	O
on	O
2	O
January	O
2012	O
,	O
is	O
dedicated	O
to	O
him	O
.	O
</s>
<s>
He	O
previously	O
worked	O
for	O
Stratus	B-General_Concept
Computers	I-General_Concept
,	I-General_Concept
Inc	I-General_Concept
.	I-General_Concept
on	O
their	O
Continuum	O
fault-tolerant	O
product	O
line	O
and	O
also	O
as	O
a	O
consultant	O
for	O
AT&T	O
Bell	O
Laboratories	O
.	O
</s>
<s>
At	O
Digital	O
Equipment	O
Corporation	O
/	O
Compaq	O
he	O
worked	O
as	O
a	O
principal	O
software	O
engineer	O
on	O
the	O
OSF/1	B-Operating_System
/	O
Digital	B-Operating_System
UNIX	I-Operating_System
/	O
Tru64	B-Operating_System
UNIX	I-Operating_System
operating	B-General_Concept
system	I-General_Concept
beginning	O
in	O
1995	O
,	O
and	O
since	O
2006	O
had	O
been	O
Acting	O
Director	O
of	O
Communications	O
Infrastructure	O
and	O
Software	O
Architect	O
for	O
Vonage	O
.	O
</s>
