<s>
BASIC-PLUS	B-Language
is	O
an	O
extended	O
dialect	O
of	O
the	O
BASIC	O
programming	O
language	O
that	O
was	O
developed	O
by	O
Digital	O
Equipment	O
Corporation	O
(	O
DEC	O
)	O
for	O
use	O
on	O
its	O
RSTS/E	B-Operating_System
time-sharing	O
operating	O
system	O
for	O
the	O
PDP-11	B-Device
series	O
of	O
16-bit	O
minicomputers	B-Architecture
in	O
the	O
early	O
1970s	O
through	O
the	O
1980s	O
.	O
</s>
<s>
BASIC-PLUS	B-Language
was	O
based	O
on	O
BASIC-8	O
for	O
the	O
TSS/8	B-Operating_System
,	O
itself	O
based	O
very	O
closely	O
on	O
the	O
original	O
Dartmouth	B-Language
BASIC	I-Language
.	O
</s>
<s>
BASIC-PLUS	B-Language
added	O
a	O
number	O
of	O
new	O
structures	O
,	O
as	O
well	O
as	O
features	O
from	O
JOSS	B-Language
concerning	O
conditional	O
statements	O
and	O
formatting	O
.	O
</s>
<s>
In	O
turn	O
,	O
BASIC-PLUS	B-Language
was	O
the	O
version	O
on	O
which	O
the	O
original	O
Microsoft	B-Language
BASIC	I-Language
was	O
patterned	O
.	O
</s>
<s>
Notable	O
among	O
the	O
additions	O
made	O
to	O
BASIC-PLUS	B-Language
was	O
the	O
introduction	O
of	O
string	O
functions	O
like	O
and	O
,	O
in	O
addition	O
to	O
Dartmouth	O
's	O
original	O
all-purpose	O
command	O
.	O
</s>
<s>
In	O
future	O
versions	O
of	O
the	O
language	O
,	O
notably	O
Microsoft	O
's	O
,	O
was	O
removed	O
and	O
BASIC-PLUS	B-Language
'	O
s	O
string	O
functions	O
became	O
the	O
only	O
ways	O
to	O
perform	O
these	O
sorts	O
of	O
operations	O
.	O
</s>
<s>
The	O
language	O
was	O
later	O
rewritten	O
as	O
a	O
true	O
compiler	B-Language
as	O
BASIC-Plus-2	O
,	O
and	O
was	O
ported	O
to	O
the	O
VAX-11	O
platform	O
as	O
that	O
machine	O
's	O
native	O
BASIC	O
implementation	O
.	O
</s>
<s>
This	O
version	O
survived	O
several	O
platform	O
changes	O
,	O
and	O
is	O
today	O
known	O
as	O
VSI	B-Language
BASIC	I-Language
for	I-Language
OpenVMS	I-Language
.	O
</s>
<s>
The	O
statements	O
could	O
either	O
be	O
entered	O
into	O
the	O
system	O
's	O
command	O
interpreter	O
directly	O
,	O
or	O
entered	O
into	O
a	O
text	B-Application
editor	I-Application
,	O
saved	O
to	O
a	O
file	O
,	O
and	O
loaded	O
into	O
the	O
command	O
interpreter	O
from	O
the	O
file	O
.	O
</s>
<s>
As	O
a	O
smart	O
terminal	O
with	O
cursor	O
control	O
could	O
not	O
be	O
guaranteed	O
,	O
BASIC-PLUS	B-Language
used	O
the	O
common	O
system	O
of	O
prefixing	O
all	O
source	O
code	O
with	O
a	O
line	O
number	O
.	O
</s>
<s>
The	O
virtual	O
address	O
space	O
of	O
an	O
RSTS/E	B-Operating_System
user	O
was	O
limited	O
to	O
a	O
little	O
less	O
than	O
64KB	O
of	O
space	O
.	O
</s>
<s>
Using	O
BASIC-PLUS	B-Language
,	O
about	O
half	O
of	O
this	O
virtual	O
address	O
space	O
was	O
used	O
by	O
the	O
combined	O
command	O
interpreter	O
and	O
run-time	O
library	O
(	O
named	O
the	O
Run	B-Device
Time	I-Device
System	I-Device
on	O
RSTS/E	B-Operating_System
)	O
.	O
</s>
<s>
Large	O
programs	O
were	O
broken	O
up	O
into	O
various	O
pieces	O
by	O
use	O
of	O
the	O
statement	O
,	O
and	O
programs	O
could	O
chain	B-Operating_System
to	O
specific	O
line	O
numbers	O
in	O
a	O
secondary	O
program	O
to	O
indicate	O
that	O
a	O
program	O
should	O
begin	O
execution	O
at	O
a	O
different	O
point	O
from	O
its	O
first	O
line	O
.	O
</s>
<s>
The	O
use	O
of	O
a	O
shared	O
memory	O
section	O
called	O
core	B-Operating_System
common	I-Operating_System
also	O
allowed	O
programs	O
to	O
pass	O
data	O
to	O
each	O
other	O
as	O
needed	O
.	O
</s>
<s>
Disk	B-Device
files	O
could	O
also	O
be	O
used	O
but	O
were	O
slower	O
.	O
</s>
<s>
BASIC-PLUS	B-Language
is	O
patterned	O
closely	O
on	O
later	O
versions	O
of	O
Dartmouth	B-Language
BASIC	I-Language
,	O
including	O
its	O
powerful	O
MAT	O
commands	O
.	O
</s>
<s>
For	O
ease	O
of	O
external	O
editing	O
of	O
the	O
source	O
file	O
,	O
later	O
versions	O
of	O
BASIC-PLUS	B-Language
also	O
allowed	O
the	O
character	O
as	O
a	O
line	O
continuation	O
character	O
.	O
</s>
<s>
Comments	O
used	O
either	O
the	O
keyword	O
or	O
the	O
character	O
,	O
as	O
opposed	O
to	O
MS	B-Language
BASICs	I-Language
,	O
which	O
used	O
and	O
.	O
</s>
<s>
In	O
addition	O
to	O
the	O
and	O
functions	O
that	O
converted	O
single	O
characters	O
to	O
and	O
from	O
string	O
format	O
,	O
BASIC-PLUS	B-Language
also	O
supported	O
Dartmouth	O
's	O
command	O
.	O
</s>
<s>
BASIC-PLUS	B-Language
added	O
the	O
concept	O
of	O
"	O
statement	O
modifiers	O
"	O
,	O
JOSS-like	O
conditions	O
that	O
could	O
be	O
applied	O
to	O
any	O
statement	O
.	O
</s>
<s>
Variable	O
names	O
in	O
the	O
early	O
versions	O
of	O
BASIC-PLUS	B-Language
could	O
be	O
a	O
single	O
letter	O
or	O
a	O
single	O
letter	O
followed	O
by	O
a	O
single	O
digit	O
.	O
</s>
<s>
For	O
math	O
,	O
,	O
,	O
,	O
and	O
were	O
supported	O
,	O
along	O
with	O
as	O
an	O
alternate	O
form	O
of	O
for	O
computer	B-General_Concept
terminals	I-General_Concept
that	O
might	O
not	O
have	O
that	O
character	O
.	O
</s>
<s>
The	O
"	O
virtual	O
DIM	O
"	O
statement	O
could	O
map	O
"	O
virtual	O
data	O
array(s )	O
"	O
or	O
"	O
virtual	O
array(s )	O
"	O
to	O
a	O
disk	B-Device
file	O
,	O
which	O
allowed	O
arrays	O
larger	O
than	O
the	O
computer	O
's	O
available	O
memory	O
(	O
or	O
even	O
its	O
address	O
space	O
)	O
,	O
and	O
allowed	O
use	O
of	O
array	O
elements	O
to	O
read	O
,	O
write	O
,	O
and	O
extend	O
disk	B-Device
files	O
(	O
persistent	O
storage	O
)	O
.	O
</s>
<s>
They	O
called	O
this	O
arrangement	O
"	O
virtual	O
data	O
storage	O
"	O
and	O
"	O
virtual	O
core	O
"	O
,	O
but	O
it	O
did	O
not	O
use	O
the	O
modern	O
approach	O
of	O
allocating	O
the	O
arrays	O
and	O
a	O
memory-mapped	B-General_Concept
file	I-General_Concept
.	O
</s>
<s>
Because	O
no	O
additional	O
sectors	O
were	O
cached	O
,	O
accessing	O
data	O
in	O
the	O
"	O
wrong	O
"	O
order	O
could	O
multiply	O
the	O
number	O
of	O
disk	B-Device
accesses	O
.	O
</s>
<s>
BASIC-PLUS	B-Language
was	O
not	O
an	O
interpreter	O
but	O
a	O
compile	B-Language
and	O
go	O
system	O
:	O
each	O
line	O
of	O
BASIC	O
was	O
translated	O
into	O
"	O
PPCODE	O
"	O
(	O
Push-Pop	O
Code	O
)	O
as	O
it	O
was	O
entered	O
,	O
for	O
subsequent	O
fast	O
execution	O
on	O
its	O
virtual	O
machine	O
.	O
</s>
<s>
BASIC-PLUS	B-Language
included	O
a	O
command	O
,	O
but	O
this	O
was	O
not	O
a	O
true	O
compiler	B-Language
;	O
this	O
simply	O
saved	O
the	O
program	O
's	O
PPCODE	O
representation	O
so	O
that	O
it	O
did	O
not	O
have	O
to	O
be	O
recompiled	B-Language
when	O
the	O
BASIC	O
program	O
was	O
next	O
loaded	O
into	O
memory	O
.	O
</s>
<s>
A	O
related	O
product	O
called	O
Basic	B-Language
Plus	I-Language
2	O
(	O
"	O
BP2	O
"	O
or	O
BASIC-Plus-2	O
)	O
,	O
was	O
later	O
developed	O
by	O
DEC	O
to	O
add	O
additional	O
features	O
and	O
increased	O
performance	O
.	O
</s>
<s>
It	O
used	O
true	O
compilation	B-Language
into	O
threaded	B-Application
code	I-Application
and	O
wrote	O
its	O
output	O
to	O
object	O
files	O
compatible	O
with	O
the	O
machine	O
code	O
object	O
files	O
produced	O
by	O
the	O
assembler	O
and	O
other	O
language	O
systems	O
.	O
</s>
<s>
BP2	O
programs	O
ran	O
under	O
the	O
RSX	O
Run	B-Device
Time	I-Device
System	I-Device
;	O
this	O
RTS	O
only	O
occupied	O
8KB	O
of	O
the	O
user	O
's	O
virtual	O
address	O
space	O
,	O
leaving	O
56KB	O
for	O
the	O
user	O
's	O
program	O
.	O
</s>
<s>
(	O
RSTS/E	B-Operating_System
version	O
9	O
introduced	O
separate	O
Instruction	O
and	O
Data	O
space	O
,	O
and	O
the	O
"	O
disappearing	O
"	O
RSX	O
Run	B-Device
Time	I-Device
System	I-Device
,	O
permitting	O
up	O
to	O
64KB	O
of	O
each	O
of	O
instruction	O
code	O
and	O
data	O
.	O
)	O
</s>
<s>
These	O
two	O
factors	O
allowed	O
individual	O
BP2	O
programs	O
to	O
be	O
much	O
larger	O
than	O
BASIC-PLUS	B-Language
programs	O
,	O
often	O
reducing	O
the	O
need	O
for	O
CHAINing	O
among	O
multiple	O
programs	O
.	O
</s>
<s>
Unlike	O
BASIC-PLUS	B-Language
(	O
which	O
was	O
only	O
available	O
on	O
RSTS/E	B-Operating_System
)	O
,	O
BP2	O
was	O
also	O
available	O
for	O
the	O
RSX-11	B-Application
operating	O
system	O
.	O
</s>
<s>
BP2	O
programs	O
were	O
also	O
more	O
compatible	O
with	O
the	O
later	O
VAX	B-Language
BASIC	I-Language
.	O
</s>
<s>
Microsoft	B-Language
BASIC	I-Language
was	O
patterned	O
very	O
closely	O
on	O
BASIC-PLUS	B-Language
.	O
</s>
<s>
Earlier	O
versions	O
of	O
MS	B-Language
BASIC	I-Language
,	O
the	O
1.x	O
series	O
,	O
lacked	O
integer	O
variables	O
,	O
but	O
these	O
were	O
added	O
in	O
the	O
2.x	O
series	O
that	O
was	O
found	O
on	O
many	O
machines	O
,	O
including	O
the	O
later	O
models	O
of	O
the	O
Commodore	B-Device
PET	I-Device
and	O
Commodore	O
64	O
.	O
</s>
<s>
MS	B-Language
BASIC	I-Language
also	O
lacked	O
the	O
matrix	O
commands	O
.	O
</s>
