<s>
UCSD	B-Language
Pascal	I-Language
is	O
a	O
Pascal	B-Application
programming	I-Application
language	I-Application
system	O
that	O
runs	O
on	O
the	O
UCSD	B-Language
p-System	I-Language
,	O
a	O
portable	O
,	O
highly	O
machine-independent	B-Operating_System
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
UCSD	B-Language
Pascal	I-Language
was	O
first	O
released	O
in	O
1977	O
.	O
</s>
<s>
In	O
1977	O
,	O
the	O
University	O
of	O
California	O
,	O
San	O
Diego	O
(	O
UCSD	O
)	O
Institute	O
for	O
Information	O
Systems	O
developed	O
UCSD	B-Language
Pascal	I-Language
to	O
provide	O
students	O
with	O
a	O
common	O
environment	O
that	O
could	O
run	O
on	O
any	O
of	O
the	O
then	O
available	O
microcomputers	B-Architecture
as	O
well	O
as	O
campus	O
DEC	B-Device
PDP-11	I-Device
minicomputers	B-Architecture
.	O
</s>
<s>
The	O
operating	B-General_Concept
system	I-General_Concept
became	O
known	O
as	O
UCSD	B-Language
p-System	I-Language
.	O
</s>
<s>
There	O
were	O
three	O
operating	B-General_Concept
systems	I-General_Concept
that	O
IBM	O
offered	O
for	O
its	O
original	O
IBM	B-Device
PC	I-Device
.	O
</s>
<s>
The	O
first	O
was	O
UCSD	B-Language
p-System	I-Language
,	O
with	O
IBM	B-Operating_System
PC	I-Operating_System
DOS	I-Operating_System
and	O
CP/M	B-Operating_System
-86	I-Operating_System
as	O
the	O
other	O
two	O
.	O
</s>
<s>
Vendor	O
SofTech	O
Microsystems	O
emphasized	O
p-System	B-Language
'	O
s	O
application	O
portability	O
,	O
with	O
virtual	B-Architecture
machines	I-Architecture
for	O
20	O
CPUs	O
as	O
of	O
the	O
IBM	B-Device
PC	I-Device
's	O
release	O
.	O
</s>
<s>
It	O
predicted	O
that	O
users	O
would	O
be	O
able	O
to	O
use	O
applications	O
they	O
purchased	O
on	O
future	O
computers	O
running	O
p-System	B-Language
;	O
advertisements	O
called	O
it	O
"	O
the	O
Universal	O
Operating	B-General_Concept
System	I-General_Concept
"	O
.	O
</s>
<s>
PC	O
Magazine	O
denounced	O
UCSD	B-Language
p-System	I-Language
on	O
the	O
IBM	B-Device
PC	I-Device
,	O
stating	O
in	O
a	O
review	O
of	O
Context	B-Language
MBA	I-Language
,	O
written	O
in	O
the	O
language	O
,	O
that	O
it	O
"	O
simply	O
does	O
not	O
produce	O
good	O
code	O
"	O
.	O
</s>
<s>
The	O
p-System	B-Language
did	O
not	O
sell	O
very	O
well	O
for	O
the	O
IBM	B-Device
PC	I-Device
,	O
because	O
of	O
a	O
lack	O
of	O
applications	O
and	O
because	O
it	O
was	O
more	O
expensive	O
than	O
the	O
other	O
choices	O
.	O
</s>
<s>
Previously	O
,	O
IBM	O
had	O
offered	O
the	O
UCSD	B-Language
p-System	I-Language
as	O
an	O
option	O
for	O
Displaywriter	B-Protocol
,	O
an	O
8086-based	O
dedicated	O
word	O
processing	O
machine	O
.	O
</s>
<s>
(	O
The	O
Displaywriter	B-Protocol
's	O
native	O
operating	B-General_Concept
system	I-General_Concept
had	O
been	O
developed	O
completely	O
internally	O
and	O
was	O
not	O
opened	O
for	O
end-user	O
programming	O
.	O
)	O
</s>
<s>
Notable	O
extensions	O
to	O
standard	O
Pascal	B-Application
include	O
separately	O
compilable	O
Units	B-Architecture
and	O
a	O
String	O
type	O
.	O
</s>
<s>
scanning	O
in	O
an	O
array	O
for	O
a	O
particular	O
search	O
pattern	O
)	O
;	O
other	O
language	O
extensions	O
were	O
provided	O
to	O
allow	O
the	O
UCSD	B-Language
p-System	I-Language
to	O
be	O
self-compiling	O
and	O
self-hosted	O
.	O
</s>
<s>
UCSD	B-Language
Pascal	I-Language
was	O
based	O
on	O
a	O
p-code	B-Language
machine	I-Language
architecture	O
.	O
</s>
<s>
Its	O
contribution	O
to	O
these	O
early	O
virtual	B-Architecture
machines	I-Architecture
was	O
to	O
extend	O
p-code	B-Language
away	O
from	O
its	O
roots	O
as	O
a	O
compiler	B-Language
intermediate	O
language	O
into	O
a	O
full	O
execution	O
environment	O
.	O
</s>
<s>
The	O
UCSD	B-Language
Pascal	I-Language
p-Machine	O
was	O
optimized	O
for	O
the	O
new	O
small	O
microcomputers	B-Architecture
with	O
addressing	O
restricted	O
to	O
16-bit	O
(	O
only	O
64	O
KB	O
of	O
memory	O
)	O
.	O
</s>
<s>
James	O
Gosling	O
cites	O
UCSD	B-Language
Pascal	I-Language
as	O
a	O
key	O
influence	O
(	O
along	O
with	O
the	O
Smalltalk	B-Application
virtual	B-Architecture
machine	I-Architecture
)	O
on	O
the	O
design	O
of	O
the	O
Java	B-Device
virtual	B-Architecture
machine	I-Architecture
.	O
</s>
<s>
UCSD	B-Language
p-System	I-Language
achieved	O
machine	B-Operating_System
independence	I-Operating_System
by	O
defining	O
a	O
virtual	B-Architecture
machine	I-Architecture
,	O
called	O
the	O
p-Machine	O
(	O
or	O
pseudo-machine	O
,	O
which	O
many	O
users	O
began	O
to	O
call	O
the	O
"	O
Pascal-machine	O
"	O
like	O
the	O
OSalthough	O
UCSD	O
documentation	O
always	O
used	O
"	O
pseudo-machine	O
"	O
)	O
with	O
its	O
own	O
instruction	B-General_Concept
set	I-General_Concept
called	O
p-code	B-Language
(	O
or	O
pseudo-code	O
)	O
.	O
</s>
<s>
Urs	O
Ammann	O
,	O
a	O
student	O
of	O
Niklaus	O
Wirth	O
,	O
originally	O
presented	O
a	O
p-code	B-Language
in	O
his	O
PhD	O
thesis	O
,	O
from	O
which	O
the	O
UCSD	O
implementation	O
was	O
derived	O
,	O
the	O
Zurich	O
Pascal-P	O
implementation	O
.	O
</s>
<s>
The	O
UCSD	O
p-code	B-Language
was	O
optimized	O
for	O
execution	O
of	O
the	O
Pascal	B-Application
programming	I-Application
language	I-Application
.	O
</s>
<s>
Each	O
hardware	O
platform	O
then	O
only	O
needed	O
a	O
p-code	B-Language
interpreter	O
program	O
written	O
for	O
it	O
to	O
port	O
the	O
entire	O
p-System	B-Language
and	O
all	O
the	O
tools	O
to	O
run	O
on	O
it	O
.	O
</s>
<s>
Later	O
versions	O
also	O
included	O
additional	O
languages	O
that	O
compiled	B-Language
to	O
the	O
p-code	B-Language
base	O
.	O
</s>
<s>
For	O
example	O
,	O
Apple	O
Computer	O
offered	O
a	O
Fortran	O
Compiler	B-Language
(	O
written	O
by	O
Silicon	O
Valley	O
Software	O
,	O
Sunnyvale	O
California	O
)	O
producing	O
p-code	B-Language
that	O
ran	O
on	O
the	O
Apple	O
version	O
of	O
the	O
p-system	B-Language
.	O
</s>
<s>
Later	O
,	O
TeleSoft	O
(	O
also	O
located	O
in	O
San	O
Diego	O
)	O
offered	O
an	O
early	O
Ada	B-Language
development	O
environment	O
that	O
used	O
p-code	B-Language
and	O
was	O
therefore	O
able	O
to	O
run	O
on	O
a	O
number	O
of	O
hardware	O
platforms	O
including	O
the	O
Motorola	B-Device
68000	I-Device
,	O
the	O
System/370	B-Device
,	O
and	O
the	O
Pascal	B-Device
MicroEngine	I-Device
.	O
</s>
<s>
UCSD	B-Language
p-System	I-Language
shares	O
some	O
concepts	O
with	O
the	O
later	O
Java	B-Device
platform	I-Device
.	O
</s>
<s>
Both	O
use	O
a	O
virtual	B-Architecture
machine	I-Architecture
to	O
hide	O
operating	B-General_Concept
system	I-General_Concept
and	O
hardware	O
differences	O
,	O
and	O
both	O
use	O
programs	O
written	O
to	O
that	O
virtual	B-Architecture
machine	I-Architecture
to	O
provide	O
cross-platform	B-Operating_System
support	O
.	O
</s>
<s>
Likewise	O
both	O
systems	O
allow	O
the	O
virtual	B-Architecture
machine	I-Architecture
to	O
be	O
used	O
either	O
as	O
the	O
complete	O
operating	B-General_Concept
system	I-General_Concept
of	O
the	O
target	O
computer	O
or	O
to	O
run	O
in	O
a	O
"	O
box	O
"	O
under	O
another	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
The	O
UCSD	B-Language
Pascal	I-Language
compiler	B-Language
was	O
distributed	O
as	O
part	O
of	O
a	O
portable	O
operating	B-General_Concept
system	I-General_Concept
,	O
the	O
p-System	B-Language
.	O
</s>
<s>
UCSD	B-Language
p-System	I-Language
began	O
around	O
1974	O
as	O
the	O
idea	O
of	O
UCSD	O
's	O
Kenneth	O
Bowles	O
,	O
who	O
believed	O
that	O
the	O
number	O
of	O
new	O
computing	O
platforms	O
coming	O
out	O
at	O
the	O
time	O
would	O
make	O
it	O
difficult	O
for	O
new	O
programming	O
languages	O
to	O
gain	O
acceptance	O
.	O
</s>
<s>
He	O
based	O
UCSD	B-Language
Pascal	I-Language
on	O
the	O
Pascal-P2	B-Application
release	O
of	O
the	O
portable	O
compiler	B-Language
from	O
Zurich	O
.	O
</s>
<s>
He	O
was	O
particularly	O
interested	O
in	O
Pascal	B-Application
as	O
a	O
language	O
to	O
teach	O
programming	O
.	O
</s>
<s>
UCSD	O
introduced	O
two	O
features	O
that	O
were	O
important	O
improvements	O
on	O
the	O
original	O
Pascal	B-Application
:	O
variable	O
length	O
strings	O
,	O
and	O
"	O
units	B-Architecture
"	O
of	O
independently	O
compiled	B-Language
code	O
(	O
an	O
idea	O
included	O
into	O
the	O
then-evolving	O
Ada	B-Language
programming	I-Language
language	I-Language
)	O
.	O
</s>
<s>
Niklaus	O
Wirth	O
credits	O
the	O
p-System	B-Language
,	O
and	O
UCSD	B-Language
Pascal	I-Language
in	O
particular	O
,	O
with	O
popularizing	O
Pascal	B-Application
.	O
</s>
<s>
It	O
was	O
not	O
until	O
the	O
release	O
of	O
Turbo	B-Application
Pascal	I-Application
that	O
UCSD	O
's	O
version	O
started	O
to	O
slip	O
from	O
first	O
place	O
among	O
Pascal	B-Application
users	O
.	O
</s>
<s>
The	O
Pascal	B-Application
dialect	O
of	O
UCSD	B-Language
Pascal	I-Language
came	O
from	O
the	O
subset	O
of	O
Pascal	B-Application
implemented	O
in	O
Pascal-P2	B-Application
,	O
which	O
was	O
not	O
designed	O
to	O
be	O
a	O
full	O
implementation	O
of	O
the	O
language	O
,	O
but	O
rather	O
"	O
the	O
minimum	O
subset	O
that	O
would	O
self-compile	O
"	O
,	O
to	O
fit	O
its	O
function	O
as	O
a	O
bootstrap	O
kit	O
for	O
Pascal	B-Application
compilers	B-Language
.	O
</s>
<s>
Although	O
UCSD	B-Language
Pascal	I-Language
later	O
obtained	O
many	O
of	O
the	O
other	O
features	O
of	O
the	O
full	O
Pascal	B-Application
language	I-Application
,	O
the	O
Pascal-P2	B-Application
subset	O
persisted	O
in	O
other	O
dialects	O
,	O
notably	O
Borland	B-Application
Pascal	I-Application
,	O
which	O
copied	O
much	O
of	O
the	O
UCSD	O
dialect	O
.	O
</s>
<s>
There	O
were	O
four	O
versions	O
of	O
UCSD	O
p-code	B-Language
engine	O
,	O
each	O
with	O
several	O
revisions	O
of	O
the	O
p-System	B-Language
and	O
UCSD	B-Language
Pascal	I-Language
.	O
</s>
<s>
A	O
revision	O
of	O
the	O
p-code	B-Language
engine	O
(	O
i.e.	O
,	O
the	O
p-Machine	O
)	O
meant	O
a	O
change	O
to	O
the	O
p-code	B-Language
language	O
,	O
and	O
therefore	O
compiled	B-Language
code	O
is	O
not	O
portable	O
between	O
different	O
p-Machine	O
versions	O
.	O
</s>
<s>
Each	O
revision	O
was	O
represented	O
with	O
a	O
leading	O
Roman	O
Numeral	O
,	O
while	O
operating	B-General_Concept
system	I-General_Concept
revisions	O
were	O
enumerated	O
as	O
the	O
"	O
dot	O
"	O
number	O
following	O
the	O
p-code	B-Language
Roman	O
Numeral	O
.	O
</s>
<s>
For	O
example	O
,	O
II.3	O
represented	O
the	O
third	O
revision	O
of	O
the	O
p-System	B-Language
running	O
on	O
the	O
second	O
revision	O
of	O
the	O
p-Machine	O
.	O
</s>
<s>
However	O
,	O
the	O
Pascal	B-Application
sources	O
for	O
both	O
Versions	O
I.3	O
and	O
I.5	O
were	O
freely	O
exchanged	O
between	O
interested	O
users	O
.	O
</s>
<s>
Widely	O
distributed	O
,	O
available	O
on	O
many	O
early	O
microcomputers	B-Architecture
.	O
</s>
<s>
Numerous	O
versions	O
included	O
Apple	B-Device
II	I-Device
,	O
DEC	B-Device
PDP-11	I-Device
,	O
Intel	B-General_Concept
8080	I-General_Concept
,	O
Zilog	B-General_Concept
Z80	I-General_Concept
and	O
MOS	B-General_Concept
6502	I-General_Concept
based	O
machines	O
,	O
Motorola	B-Device
68000	I-Device
and	O
the	O
IBM	B-Device
PC	I-Device
(	O
Version	O
II	O
on	O
the	O
PC	O
was	O
restricted	O
to	O
one	O
64K	O
code	B-General_Concept
segment	I-General_Concept
and	O
one	O
64K	O
stack/heap	O
data	B-General_Concept
segment	I-General_Concept
;	O
Version	O
IV	O
removed	O
the	O
code	B-General_Concept
segment	I-General_Concept
limit	O
but	O
cost	O
a	O
lot	O
more	O
)	O
.	O
</s>
<s>
Custom	O
version	O
written	O
for	O
Western	O
Digital	O
to	O
run	O
on	O
their	O
Pascal	B-Device
MicroEngine	I-Device
microcomputer	B-Architecture
.	O
</s>
<s>
Did	O
not	O
sell	O
well	O
due	O
to	O
combination	O
of	O
their	O
pricing	O
structure	O
,	O
performance	O
problems	O
due	O
to	O
p-code	B-Language
interpreter	O
,	O
and	O
competition	O
with	O
native	O
operating	B-General_Concept
systems	I-General_Concept
(	O
on	O
top	O
of	O
which	O
it	O
often	O
ran	O
)	O
.	O
</s>
<s>
After	O
SofTech	O
dropped	O
the	O
product	O
,	O
it	O
was	O
picked	O
up	O
by	O
Pecan	O
Systems	O
,	O
a	O
relatively	O
small	O
company	O
formed	O
of	O
p-System	B-Language
users	O
and	O
fans	O
.	O
</s>
<s>
Sales	O
revived	O
somewhat	O
,	O
due	O
mostly	O
to	O
Pecan	O
's	O
reasonable	O
pricing	O
structure	O
,	O
but	O
the	O
p-System	B-Language
and	O
UCSD	B-Language
Pascal	I-Language
gradually	O
lost	O
the	O
market	O
to	O
native	O
operating	B-General_Concept
systems	I-General_Concept
and	O
compilers	B-Language
.	O
</s>
<s>
Available	O
for	O
the	O
TI-99/4A	B-Device
equipped	O
with	O
p-code	B-Language
card	O
,	O
Commodore	B-Device
CBM	I-Device
8096	I-Device
,	O
Sage	O
IV	O
,	O
and	O
BBC	B-Device
Micro	I-Device
with	O
6502	B-General_Concept
second	O
processor	O
.	O
</s>
<s>
The	O
Corvus	O
Systems	O
computer	O
used	O
UCSD	B-Language
Pascal	I-Language
for	O
all	O
its	O
user	O
software	O
.	O
</s>
<s>
The	O
"	O
innovative	O
concept	O
"	O
of	O
the	O
Constellation	O
OS	O
was	O
to	O
run	O
Pascal	B-Application
(	O
interpretively	O
or	O
compiled	B-Language
)	O
and	O
include	O
all	O
common	O
software	O
in	O
the	O
manual	O
,	O
so	O
users	O
could	O
modify	O
as	O
needed	O
.	O
</s>
