<s>
The	O
Rainbow	B-Device
100	I-Device
is	O
a	O
microcomputer	B-Architecture
introduced	O
by	O
Digital	O
Equipment	O
Corporation	O
(	O
DEC	O
)	O
in	O
1982	O
.	O
</s>
<s>
This	O
desktop	O
unit	O
had	O
a	O
monitor	O
similar	O
to	O
the	O
VT220	B-Device
and	O
a	O
dual-CPU	B-Operating_System
box	O
with	O
both	O
Zilog	B-General_Concept
Z80	I-General_Concept
and	O
Intel	B-Device
8088	I-Device
CPUs	O
.	O
</s>
<s>
The	O
Rainbow	B-Device
100	I-Device
was	O
a	O
triple-use	O
machine	O
:	O
VT100	B-Device
mode	O
(	O
industry	O
standard	O
terminal	O
for	O
interacting	O
with	O
DEC	O
's	O
own	O
VAX	B-Device
)	O
,	O
8-bit	O
CP/M	B-Application
mode	O
(	O
using	O
the	O
Z80	B-General_Concept
)	O
,	O
and	O
CP/M	B-Operating_System
-86	I-Operating_System
or	O
MS-DOS	B-Application
mode	O
using	O
the	O
8088	B-Device
.	O
</s>
<s>
It	O
ultimately	O
failed	O
to	O
in	O
the	O
marketplace	O
which	O
became	O
dominated	O
by	O
the	O
simpler	O
IBM	O
PC	O
and	O
its	O
clones	O
which	O
established	O
the	O
industry	O
standard	O
as	O
compatibility	O
with	O
CP/M	B-Application
became	O
less	O
important	O
than	O
IBM	O
PC	O
compatibility	O
.	O
</s>
<s>
Writer	O
David	O
Ahl	O
called	O
it	O
a	O
disastrous	O
foray	O
into	O
the	O
personal	B-Device
computer	I-Device
market	O
.	O
</s>
<s>
The	O
Rainbow	O
was	O
launched	O
along	O
with	O
the	O
similarly	O
packaged	O
DEC	B-Device
Professional	I-Device
and	O
DECmate	O
II	O
which	O
were	O
also	O
not	O
successful	O
.	O
</s>
<s>
The	O
failure	O
of	O
DEC	O
to	O
gain	O
a	O
significant	O
foothold	O
in	O
the	O
high-volume	O
PC	O
market	O
would	O
be	O
the	O
beginning	O
of	O
the	O
end	O
of	O
the	O
computer	O
hardware	O
industry	O
in	O
New	O
England	O
,	O
as	O
nearly	O
all	O
computer	O
companies	O
located	O
there	O
were	O
focused	O
on	O
minicomputers	B-Architecture
for	O
large	O
organizations	O
,	O
from	O
DEC	O
to	O
Data	O
General	O
,	O
Wang	O
,	O
Prime	O
,	O
Computervision	O
,	O
Honeywell	O
,	O
and	O
Symbolics	O
Inc	O
.	O
</s>
<s>
In	O
addition	O
,	O
the	O
100A	O
was	O
unable	O
to	O
move	O
its	O
hardware	O
interrupt	O
vectors	O
to	O
avoid	O
the	O
conflict	O
with	O
MS-DOS	B-Application
soft	O
INT	O
21	O
,	O
etc	O
.	O
</s>
<s>
The	O
"	O
B	O
"	O
model	O
also	O
allowed	O
remapping	O
of	O
hardware	O
interrupts	O
to	O
be	O
more	O
compatible	O
with	O
MS-DOS	B-Application
.	O
</s>
<s>
The	O
Rainbow	O
contained	O
two	O
separate	O
data	O
buses	O
controlled	O
by	O
the	O
Zilog	B-General_Concept
Z80	I-General_Concept
and	O
the	O
Intel	B-Device
8088	I-Device
respectively	O
.	O
</s>
<s>
The	O
8088	B-Device
bus	O
was	O
used	O
for	O
control	O
of	O
all	O
other	O
subsystems	O
,	O
including	O
graphics	O
,	O
hard	O
disk	O
access	O
,	O
and	O
communications	O
.	O
</s>
<s>
While	O
it	O
may	O
have	O
been	O
theoretically	O
possible	O
to	O
load	O
Z80	B-General_Concept
binary	O
code	O
into	O
the	O
Rainbow	O
to	O
execute	O
alongside	O
8088	B-Device
code	O
,	O
this	O
procedure	O
has	O
never	O
been	O
demonstrated	O
.	O
</s>
<s>
The	O
8088	B-Device
could	O
be	O
upgraded	O
to	O
the	O
faster	O
NEC	B-Device
V20	I-Device
chip	O
.	O
</s>
<s>
However	O
,	O
later	O
versions	O
of	O
MS-DOS	B-Application
and	O
CP/M	B-Application
allowed	O
formatting	O
of	O
diskettes	O
.	O
</s>
<s>
Digital	O
Equipment	O
Corporation	O
produced	O
a	O
Winchester	O
disk	O
controller	O
capable	O
of	O
controlling	O
hard	O
disks	O
compatible	O
with	O
the	O
ST-506	B-Device
interface	O
.	O
</s>
<s>
The	O
Graphic	O
module	O
was	O
based	O
on	O
a	O
NEC	B-Device
7220	I-Device
graphic	O
display	O
controller	O
(	O
GDC	O
)	O
and	O
an	O
8×64KB	O
DRAM	O
video	O
memory	O
.	O
</s>
<s>
The	O
base	O
Rainbow	O
system	O
generates	O
a	O
TTL	B-General_Concept
15kHz	O
composite-video	O
signal	O
compatible	O
with	O
RS-170	O
(	O
NTSC	O
)	O
in	O
monochrome	O
mode	O
.	O
</s>
<s>
With	O
the	O
inclusion	O
of	O
the	O
graphics	O
option	O
,	O
the	O
Rainbow	O
could	O
also	O
output	O
sync-on-green	O
RGB	O
video	O
signals	O
at	O
TTL	B-General_Concept
levels	O
.	O
</s>
<s>
The	O
Rainbow	B-Device
100	I-Device
and	O
the	O
other	O
two	O
microcomputers	B-Architecture
which	O
DEC	O
announced	O
at	O
the	O
same	O
time	O
(	O
DECmate	O
II	O
and	O
Pro-350	B-Device
)	O
had	O
two	O
quirks	O
that	O
annoyed	O
conservative	O
users	O
.	O
</s>
<s>
The	O
LK201	B-Device
keyboard	O
used	O
a	O
new	O
layout	O
that	O
made	O
some	O
Teletype	B-Application
Model	I-Application
33	I-Application
and	O
VT100	B-Device
users	O
unhappy	O
.	O
</s>
<s>
However	O
,	O
the	O
VT220	B-Device
style	O
of	O
this	O
keyboard	O
can	O
clearly	O
be	O
seen	O
in	O
the	O
layout	O
of	O
the	O
enhanced	B-Device
101-key	I-Device
keyboard	I-Device
adopted	O
by	O
IBM	O
in	O
1985	O
.	O
</s>
<s>
Third-party	O
upgrades	O
were	O
also	O
available	O
,	O
including	O
an	O
80286	B-General_Concept
(	O
286	B-General_Concept
)	O
processor	O
upgrade	O
(	O
Turbow-286	O
)	O
,	O
a	O
3.5-inch	O
disk	O
adapter	O
kit	O
(	O
IDrive	O
)	O
,	O
and	O
a	O
battery-backed	O
clock	O
chip	O
(	O
ClikClok	O
)	O
,	O
all	O
from	O
Suitable	O
Solutions	O
.	O
</s>
<s>
In	O
1984	O
,	O
the	O
first	O
computer	O
support	O
for	O
Native	O
American	O
languages	O
began	O
with	O
the	O
Rainbow	B-Device
100	I-Device
.	O
</s>
<s>
Created	O
a	O
dual-Winchester	O
controller	O
for	O
the	O
DEC	B-Device
Rainbow	I-Device
as	O
well	O
.	O
</s>
<s>
It	O
included	O
software	O
to	O
backup	O
MS-DOS	B-Application
,	O
CP/M	B-Application
and	O
CCP/M	O
partitions	O
.	O
</s>
<s>
The	O
Rainbow	O
runs	O
the	O
CP/M	B-Application
operating	I-Application
system	I-Application
,	O
which	O
detects	O
whether	O
software	O
is	O
written	O
for	O
8-bit	O
CP/M	B-Application
and	O
CP/M	B-Operating_System
-86	I-Operating_System
and	O
runs	O
it	O
on	O
the	O
appropriate	O
processor	O
.	O
</s>
<s>
DEC	O
later	O
released	O
MS-DOS	B-Application
,	O
but	O
little	O
DOS	O
software	O
was	O
released	O
on	O
Rainbow	O
media	O
.	O
</s>
<s>
While	O
it	O
provided	O
the	O
same	O
MS-DOS	B-Application
functions	O
that	O
IBM	O
's	O
PC	B-Operating_System
DOS	I-Operating_System
did	O
,	O
it	O
lacked	O
the	O
IBM	O
PC	O
's	O
video	O
and	O
keyboard	O
ROM	O
BIOS	O
interface	O
which	O
most	O
MS-DOS	B-Application
software	O
relied	O
upon	O
,	O
limiting	O
the	O
commercial	O
software	O
that	O
would	O
run	O
.	O
</s>
<s>
Towards	O
the	O
end	O
of	O
its	O
life	O
,	O
Rainbow	O
users	O
were	O
able	O
to	O
run	O
some	O
IBM	O
PC-compatible	O
MS-DOS	B-Application
software	O
using	O
an	O
emulation	O
application	O
called	O
Code	O
Blue	O
,	O
though	O
it	O
emulated	O
only	O
the	O
IBM	O
PC	O
's	O
BIOS	O
and	O
some	O
of	O
the	O
hardware	O
,	O
so	O
programs	O
that	O
accessed	O
the	O
video	O
cards	O
directly	O
would	O
not	O
work	O
very	O
well	O
.	O
</s>
<s>
MS-DOS	B-Application
compatibility	O
was	O
added	O
late	O
in	O
the	O
design	O
,	O
so	O
hardware	O
interrupts	O
and	O
MS-DOS	B-Application
software	O
interrupts	O
overlapped	O
.	O
</s>
<s>
This	O
means	O
that	O
the	O
MS-DOS	B-Application
3.10b	O
version	O
for	O
the	O
Rainbow	O
can	O
only	O
run	O
on	O
the	O
Rainbow	O
100B	O
.	O
</s>
<s>
DEC	O
itself	O
ported	O
Microsoft	B-Application
Windows	I-Application
1.0	I-Application
to	O
the	O
Rainbow	O
.	O
</s>
<s>
The	O
Suitable	O
Solutions	O
Turbow-286	O
board	O
could	O
run	O
a	O
modified	O
version	O
of	O
Windows	B-Application
3.0	I-Application
.	O
</s>
<s>
Software	O
bundled	O
with	O
DEC	B-Device
Rainbow	I-Device
floor	O
model	O
included	O
:	O
</s>
<s>
The	O
Rainbow	O
used	O
a	O
distinct	O
version	O
of	O
MS-DOS	B-Application
,	O
so	O
it	O
was	O
not	O
completely	O
software	O
-	O
or	O
hardware-compatible	O
with	O
the	O
IBM	O
PC	O
or	O
PC	B-Operating_System
DOS	I-Operating_System
.	O
</s>
<s>
The	O
expectation	O
was	O
for	O
programs	O
to	O
target	O
the	O
MS-DOS	B-Application
interface	O
and	O
not	O
the	O
underlying	O
hardware	O
.	O
</s>
<s>
After	O
the	O
Compaq	B-Device
Portable	I-Device
and	O
other	O
clones	O
,	O
the	O
market	O
expectation	O
was	O
that	O
all	O
MS-DOS	B-Application
versions	O
would	O
be	O
fully	O
IBM	O
PC	O
compatible	O
.	O
</s>
<s>
Later	O
,	O
Microsoft	O
would	O
stop	O
licensing	O
distinctive	O
OEM	O
versions	O
and	O
sell	O
standardized	O
MS-DOS	B-Application
5.0	O
at	O
retail	O
.	O
</s>
<s>
The	O
FOSSIL	O
TSR	O
allowed	O
several	O
terminal	O
programs	O
and	O
editors	O
to	O
run	O
on	O
the	O
IBM-PC	O
,	O
Rainbow	O
,	O
and	O
other	O
early	O
8088/8086	O
computers	O
,	O
but	O
its	O
limited	O
adoption	O
hampered	O
its	O
usefulness	O
.	O
</s>
<s>
The	O
DEC	B-Device
Rainbow	I-Device
100	O
MS-DOS	B-Application
did	O
support	O
FAT	B-Application
formatted	O
floppies	O
.	O
</s>
<s>
The	O
first	O
two	O
tracks	O
were	O
reserved	O
for	O
the	O
boot	O
loader	O
,	O
but	O
did	O
n't	O
contain	O
an	O
MBR	B-Device
nor	O
a	O
BPB	B-Device
(	O
MS-DOS	B-Application
2.x	O
and	O
3.10	O
on	O
the	O
Rainbow	O
used	O
a	O
static	O
in-memory	O
BPB	B-Device
instead	O
)	O
.	O
</s>
<s>
The	O
boot	O
sector	O
(	O
track	O
0	O
,	O
side	O
0	O
,	O
sector	O
1	O
)	O
was	O
Z80	B-General_Concept
code	O
beginning	O
with	O
DI	O
0xF3	O
.	O
</s>
<s>
The	O
8088	B-Device
bootstrap	O
was	O
loaded	O
by	O
the	O
Z80	B-General_Concept
.	O
</s>
<s>
Track	O
1	O
,	O
side	O
0	O
,	O
sector	O
2	O
starts	O
with	O
the	O
Media/FAT	O
ID	O
byte	O
0xFA	O
.	O
</s>
<s>
There	O
are	O
2	O
copies	O
of	O
the	O
FAT	B-Application
and	O
96	O
entries	O
in	O
the	O
root	O
directory	O
.	O
</s>
<s>
This	O
makes	O
it	O
hard	O
to	O
create	O
Rainbow	O
disk	O
images	O
since	O
all	O
existing	O
tools	O
assume	O
there	O
will	O
be	O
an	O
MBR	B-Device
with	O
a	O
BPB	B-Device
,	O
and	O
required	O
various	O
hacks	O
to	O
make	O
up	O
for	O
the	O
lack	O
of	O
on-disk	O
BPB	B-Device
.	O
</s>
<s>
The	O
DEC	B-Device
Rainbow	I-Device
100	O
had	O
no	O
general	O
expansion	O
bus	O
.	O
</s>
<s>
The	O
Multi	B-Application
Emulator	I-Application
Super	I-Application
System	I-Application
can	O
run	O
the	O
Rainbow-specific	O
Windows	B-Application
1.0	I-Application
.	O
</s>
<s>
The	O
Rainbow	B-Device
100	I-Device
plays	O
a	O
small	O
but	O
important	O
role	O
in	O
the	O
creation	O
of	O
the	O
FidoNet	O
system	O
.	O
</s>
<s>
A	O
computer	O
club	O
in	O
St.	O
Louis	O
was	O
in	O
the	O
process	O
of	O
setting	O
up	O
a	O
BBS	B-Application
system	O
using	O
CBBS	B-Protocol
on	O
CP/M	B-Application
when	O
they	O
learned	O
that	O
DEC	O
would	O
be	O
giving	O
the	O
club	O
a	O
Rainbow	B-Device
100	I-Device
for	O
free	O
.	O
</s>
<s>
The	O
group	O
planned	O
on	O
starting	O
the	O
BBS	B-Application
on	O
this	O
machine	O
as	O
soon	O
as	O
it	O
arrived	O
;	O
but	O
,	O
when	O
it	O
did	O
,	O
they	O
found	O
that	O
the	O
Z80	B-General_Concept
did	O
not	O
have	O
access	O
to	O
the	O
serial	O
ports	O
.	O
</s>
<s>
Casting	O
about	O
for	O
a	O
new	O
BBS	B-Application
platform	O
that	O
ran	O
on	O
DOS	O
,	O
they	O
learned	O
of	O
FidoBBS	O
and	O
arranged	O
to	O
have	O
its	O
developer	O
port	O
the	O
serial	O
drivers	O
to	O
the	O
Rainbow	O
platform	O
.	O
</s>
<s>
Piers	O
Anthony	O
wrote	O
many	O
of	O
his	O
books	O
from	O
the	O
'	O
80s	O
on	O
his	O
DEC	B-Device
Rainbow	I-Device
.	O
</s>
<s>
The	O
DEC	B-Device
Rainbow	I-Device
can	O
be	O
seen	O
in	O
the	O
films	O
Ghostbusters	B-Operating_System
,	O
Beverly	B-Application
Hills	I-Application
Cop	I-Application
,	O
and	O
Firestarter	O
.	O
</s>
