<s>
Sierra	B-Device
was	O
the	O
code	O
name	O
for	O
a	O
16-bit/32	O
-bit	O
personal	B-Device
computer	I-Device
designed	O
by	O
the	O
Sunnyvale	O
Research	O
Lab	O
(	O
SRL	O
)	O
of	O
Atari	O
,	O
Inc	O
.	O
starting	O
around	O
1983	O
.	O
</s>
<s>
The	O
design	O
was	O
one	O
of	O
several	O
new	O
16-bit	B-Device
computer	I-Device
systems	O
proposing	O
to	O
use	O
a	O
new	O
chipset	O
from	O
Atari	O
Corporate	O
Research	O
.	O
</s>
<s>
The	O
CPU	B-General_Concept
had	O
not	O
been	O
chosen	O
,	O
but	O
the	O
Motorola	B-Device
68000	I-Device
,	O
National	B-Device
Semiconductor	I-Device
32016	I-Device
and	O
Intel	B-General_Concept
286	I-General_Concept
were	O
being	O
considered	O
.	O
</s>
<s>
Several	O
proposed	O
operating	O
systems	O
were	O
considered	O
including	O
VisiCorps	O
Visi	B-Application
On	I-Application
and	O
Atari	O
's	O
own	O
internal	O
OS	O
code-named	O
"	O
Snowcap	O
"	O
.	O
</s>
<s>
Sierra	B-Device
was	O
bogged	O
down	O
since	O
its	O
inception	O
through	O
a	O
committee	O
process	O
that	O
never	O
could	O
come	O
to	O
a	O
consensus	O
on	O
the	O
design	O
specifications	O
.	O
</s>
<s>
A	O
second	O
project	O
,	O
Atari	O
Gaza	O
,	O
ran	O
in	O
parallel	O
,	O
designing	O
an	O
upscale	O
workstation	B-Device
machine	O
running	O
either	O
BSD	B-Operating_System
Unix	I-Operating_System
or	O
CP/M	B-Application
-68k	I-Application
.	O
</s>
<s>
Atari	O
management	O
concluded	O
they	O
had	O
no	O
way	O
to	O
sell	O
into	O
the	O
business	O
market	O
,	O
redirecting	O
Gaza	O
engineers	O
to	O
a	O
new	O
low-cost	O
machine	O
based	O
on	O
the	O
Amiga	B-Device
chipset	O
,	O
"	O
Mickey	O
"	O
.	O
</s>
<s>
With	O
most	O
designs	O
of	O
the	O
era	O
,	O
graphics	O
,	O
sound	O
and	O
similar	O
tasks	O
would	O
normally	O
be	O
handled	O
by	O
the	O
main	O
CPU	B-General_Concept
,	O
and	O
converted	O
to	O
output	O
using	O
relatively	O
simple	O
analog-to-digital	O
converters	O
.	O
</s>
<s>
Offloading	O
these	O
duties	O
to	O
the	O
custom	O
chips	O
allowed	O
the	O
CPU	B-General_Concept
in	O
Atari	O
's	O
design	O
to	O
spend	O
less	O
time	O
on	O
housekeeping	O
chores	O
.	O
</s>
<s>
In	O
the	O
Atari	B-General_Concept
2600	I-General_Concept
,	O
a	O
single	O
all-in-one	O
support	O
chip	O
known	O
as	O
the	O
TIA	B-General_Concept
provided	O
graphics	O
and	O
sound	O
support	O
to	O
its	O
stripped-down	O
MOS	O
Technology	O
6502-derivative	O
,	O
the	O
6507	B-General_Concept
.	O
</s>
<s>
Due	O
to	O
the	O
high	O
price	O
of	O
computer	B-General_Concept
memory	I-General_Concept
,	O
the	O
TIA	B-General_Concept
was	O
designed	O
to	O
use	O
almost	O
no	O
traditional	O
RAM	B-Architecture
.	O
</s>
<s>
The	O
much	O
more	O
powerful	O
Atari	B-Device
8-bit	I-Device
family	I-Device
used	O
the	O
same	O
basic	O
design	O
concept	O
,	O
but	O
this	O
time	O
supported	O
by	O
three	O
chips	O
.	O
</s>
<s>
The	O
C/GTIA	B-General_Concept
was	O
a	O
graphics	O
chip	O
,	O
greatly	O
updated	O
compared	O
to	O
the	O
TIA	B-General_Concept
,	O
sound	O
was	O
moved	O
to	O
the	O
new	O
POKEY	B-Device
which	O
provided	O
four-channel	O
sound	O
as	O
well	O
as	O
handing	O
some	O
basic	O
input/output	B-General_Concept
tasks	O
like	O
keyboard	O
handling	O
,	O
and	O
finally	O
,	O
the	O
software-based	O
display	O
system	O
used	O
in	O
the	O
2600	O
was	O
implemented	O
in	O
hardware	O
in	O
the	O
ANTIC	B-General_Concept
,	O
which	O
was	O
responsible	O
for	O
handling	O
background	O
graphics	O
(	O
bitmaps	O
)	O
and	O
character-based	O
output	O
.	O
</s>
<s>
ANTIC	B-General_Concept
allowed	O
the	O
programmer	O
to	O
provide	O
a	O
simple	O
list	O
of	O
instructions	O
which	O
it	O
would	O
then	O
convert	O
into	O
data	O
to	O
be	O
fed	O
to	O
the	O
C/GTIA	B-General_Concept
,	O
freeing	O
the	O
programmer	O
of	O
this	O
task	O
.	O
</s>
<s>
This	O
separation	O
of	O
duties	O
allowed	O
each	O
sub-system	O
to	O
be	O
more	O
powerful	O
than	O
the	O
all-in-one	O
TIA	B-General_Concept
,	O
while	O
their	O
updated	O
design	O
also	O
greatly	O
reducing	O
programming	O
complexity	O
compared	O
to	O
the	O
2600	O
.	O
</s>
<s>
By	O
the	O
early	O
1980s	O
,	O
a	O
new	O
generation	O
of	O
CPU	B-General_Concept
designs	O
was	O
coming	O
to	O
market	O
with	O
much	O
greater	O
capability	O
than	O
the	O
earlier	O
8-bit	O
designs	O
.	O
</s>
<s>
Notable	O
among	O
these	O
were	O
the	O
Intel	B-Device
8088	I-Device
and	O
similar	O
designs	O
using	O
16-bit	B-Device
internals	O
,	O
which	O
initially	O
became	O
available	O
as	O
daughtercards	O
on	O
S-100	B-Architecture
bus	I-Architecture
machines	O
and	O
other	O
platforms	O
as	O
early	O
as	O
the	O
late	O
1970s	O
.	O
</s>
<s>
A	O
variety	O
of	O
even	O
more	O
powerful	O
32-bit	O
designs	O
were	O
also	O
in	O
the	O
pipeline	O
,	O
notably	O
the	O
Motorola	B-Device
68000	I-Device
(	O
m68k	O
)	O
of	O
1979	O
.	O
</s>
<s>
One	O
color	O
from	O
each	O
rectangle	O
's	O
color	B-Data_Structure
lookup	I-Data_Structure
table	I-Data_Structure
could	O
be	O
defined	O
as	O
transparent	O
,	O
allowing	O
objects	O
below	O
it	O
to	O
be	O
visible	O
even	O
at	O
a	O
lower	O
priority	O
.	O
</s>
<s>
Each	O
of	O
the	O
rectangles	O
had	O
its	O
own	O
bit	O
depth	O
,	O
1	O
,	O
2	O
,	O
4	O
or	O
8-bit	O
,	O
and	O
each	O
one	O
had	O
its	O
own	O
color	B-Data_Structure
lookup	I-Data_Structure
table	I-Data_Structure
that	O
mapped	O
the	O
1	O
,	O
4	O
,	O
16	O
or	O
256	O
color	B-Data_Structure
registers	I-Data_Structure
of	O
the	O
selected	O
bit	O
depth	O
onto	O
an	O
underlying	O
hardware	O
pallet	O
of	O
4,096	O
colors	O
.	O
</s>
<s>
The	O
data	O
could	O
be	O
encoded	O
using	O
run	B-Algorithm
length	I-Algorithm
encoding	I-Algorithm
(	O
RLE	O
)	O
to	O
reduce	O
memory	O
needs	O
.	O
</s>
<s>
The	O
logic	O
was	O
initially	O
implemented	O
as	O
a	O
single-chip	O
design	O
,	O
but	O
the	O
only	O
cost-effective	O
chip	O
packaging	O
at	O
the	O
time	O
was	O
the	O
40-pin	O
DIP	B-Algorithm
,	O
which	O
required	O
the	O
system	O
to	O
be	O
reimplemented	O
as	O
two	O
separate	O
VLSI	O
chips	O
.	O
</s>
<s>
Silver	O
was	O
responsible	O
for	O
handling	O
memory	O
fetching	O
and	O
implementing	O
the	O
priority	O
system	O
,	O
while	O
Gold	O
took	O
the	O
resulting	O
data	O
from	O
Silver	O
,	O
performing	O
the	O
color	O
lookup	O
,	O
and	O
produced	O
the	O
video	O
output	O
using	O
a	O
bank	O
of	O
timers	O
that	O
implemented	O
the	O
NTSC	O
or	O
PAL	B-Language
signal	O
output	O
.	O
</s>
<s>
Sierra	B-Device
came	O
about	O
through	O
a	O
conversation	O
between	O
Alkire	O
and	O
Doug	O
Crockford	O
.	O
</s>
<s>
Alkire	O
borrowed	O
Palevich	O
's	O
new	O
Mac	O
computer	O
,	O
using	O
it	O
to	O
make	O
block	O
diagrams	O
of	O
a	O
machine	O
that	O
slowly	O
emerged	O
as	O
the	O
Sierra	B-Device
effort	O
.	O
</s>
<s>
Each	O
engineer	O
in	O
SRL	O
had	O
their	O
own	O
favorite	O
new	O
CPU	B-General_Concept
design	O
,	O
and	O
the	O
preferred	O
selection	O
changed	O
constantly	O
as	O
work	O
on	O
Rainbow	O
continued	O
.	O
</s>
<s>
Numerous	O
options	O
were	O
explored	O
,	O
including	O
the	O
Intel	B-Device
80186	I-Device
and	O
286	B-General_Concept
,	O
National	B-Device
Semiconductor	I-Device
NS16032	I-Device
,	O
Motorola	B-Device
68000	I-Device
and	O
Zilog	B-Device
Z8000	I-Device
.	O
</s>
<s>
The	O
original	O
design	O
documents	O
suggest	O
different	O
Sierra	B-Device
concepts	O
aimed	O
at	O
the	O
home	O
computer	O
market	O
with	O
a	O
price	O
point	O
as	O
low	O
as	O
$300	O
using	O
a	O
low	O
power	O
CPU	B-General_Concept
,	O
all	O
the	O
way	O
through	O
business	O
machines	O
,	O
student	O
computers	O
and	O
low-end	O
workstations	B-Device
.	O
</s>
<s>
Sierra	B-Device
proceeded	O
alongside	O
similar	O
projects	O
within	O
Atari	O
being	O
run	O
by	O
other	O
divisions	O
,	O
including	O
an	O
upscale	O
m68k	O
machine	O
known	O
as	O
Gaza	O
.	O
</s>
<s>
The	O
business	O
computing	O
market	O
appeared	O
to	O
be	O
weathering	O
the	O
storm	O
,	O
and	O
the	O
new	O
IBM	B-Device
PC	I-Device
was	O
starting	O
off	O
well	O
in	O
spite	O
of	O
being	O
much	O
less	O
sophisticated	O
than	O
Sierra	B-Device
or	O
Gaza	O
,	O
but	O
Atari	O
had	O
no	O
presence	O
in	O
the	O
business	O
world	O
.	O
</s>
<s>
Workstations	B-Device
were	O
an	O
emerging	O
niche	O
that	O
the	O
company	O
might	O
be	O
able	O
to	O
sell	O
into	O
,	O
but	O
the	O
market	O
was	O
very	O
new	O
.	O
</s>
<s>
Work	O
on	O
the	O
various	O
Sierra	B-Device
concepts	O
continued	O
through	O
1983	O
and	O
into	O
1984	O
,	O
by	O
which	O
point	O
little	O
progress	O
had	O
been	O
made	O
on	O
the	O
complete	O
design	O
.	O
</s>
<s>
Likewise	O
,	O
little	O
concrete	O
work	O
on	O
the	O
operating	O
system	O
had	O
taken	O
place	O
,	O
and	O
the	O
idea	O
of	O
using	O
a	O
Unix	B-Operating_System
System	I-Operating_System
V	I-Operating_System
port	O
was	O
being	O
considered	O
.	O
</s>
<s>
Lorraine	O
was	O
also	O
based	O
on	O
the	O
68000	B-Device
and	O
generally	O
similar	O
to	O
Sierra	B-Device
and	O
Gaza	O
in	O
almost	O
every	O
design	O
note	O
,	O
which	O
is	O
not	O
surprising	O
given	O
that	O
the	O
teams	O
originally	O
came	O
from	O
the	O
same	O
company	O
.	O
</s>
<s>
The	O
rest	O
of	O
the	O
Sierra	B-Device
team	O
were	O
scattered	O
.	O
</s>
<s>
As	O
a	O
result	O
,	O
any	O
progress	O
on	O
the	O
Sierra	B-Device
platform	O
ended	O
,	O
Gaza	O
was	O
completed	O
and	O
demonstrated	O
and	O
Mickey	O
was	O
completed	O
,	O
awaiting	O
the	O
Chipset	O
from	O
Amiga	B-Device
that	O
would	O
never	O
arrive	O
.	O
</s>
<s>
The	O
"	O
Cray	O
"	O
development	O
frame	O
for	O
Gaza	O
and	O
reused	O
for	O
Mickey	O
was	O
used	O
by	O
the	O
Tramiel	O
engineers	O
to	O
develop	O
the	O
Atari	B-Device
ST	I-Device
prototype	O
.	O
</s>
<s>
The	O
company	O
's	O
option	O
to	O
use	O
Lorraine	O
for	O
a	O
games	O
console	O
also	O
ended	O
,	O
and	O
Amiga	B-Device
would	O
later	O
sign	O
a	O
deal	O
with	O
Commodore	O
International	O
to	O
produce	O
a	O
machine	O
very	O
similar	O
to	O
Mickey	O
,	O
the	O
Amiga	B-Device
1000	I-Device
.	O
</s>
<s>
The	O
Atari	B-Device
ST	I-Device
,	O
Atari	O
Corp	O
's	O
68k-based	O
machine	O
,	O
would	O
be	O
built	O
with	O
custom	O
chips	O
and	O
off-the-shelf	O
hardware	O
,	O
and	O
was	O
significantly	O
less	O
advanced	O
than	O
Sierra	B-Device
,	O
GAZA	O
or	O
Mickey	O
.	O
</s>
<s>
Previous	O
designs	O
had	O
generally	O
used	O
one	O
of	O
two	O
solutions	O
;	O
one	O
was	O
to	O
carefully	O
time	O
the	O
CPU	B-General_Concept
and	O
GPU	O
so	O
they	O
could	O
access	O
memory	O
within	O
the	O
timing	O
constraints	O
of	O
the	O
video	O
system	O
,	O
while	O
other	O
platforms	O
used	O
some	O
sort	O
of	O
system	O
to	O
pause	O
the	O
CPU	B-General_Concept
during	O
the	O
times	O
the	O
GPU	O
needed	O
memory	O
.	O
</s>
<s>
The	O
colors	O
were	O
selected	O
from	O
a	O
color	B-Data_Structure
lookup	I-Data_Structure
table	I-Data_Structure
of	O
4,096	O
colors	O
.	O
</s>
<s>
The	O
system	O
naturally	O
output	O
RGB	O
and	O
could	O
be	O
converted	O
to	O
NTSC	O
or	O
PAL	B-Language
using	O
commonly	O
available	O
chips	O
.	O
</s>
