<s>
The	O
Altair	B-Architecture
8800	I-Architecture
is	O
a	O
microcomputer	B-Architecture
designed	O
in	O
1974	O
by	O
MITS	O
and	O
based	O
on	O
the	O
Intel	B-General_Concept
8080	I-General_Concept
CPU	I-General_Concept
.	O
</s>
<s>
The	O
Altair	O
is	O
widely	O
recognized	O
as	O
the	O
spark	O
that	O
ignited	O
the	O
microcomputer	B-Architecture
revolution	O
as	O
the	O
first	O
commercially	O
successful	O
personal	O
computer	O
.	O
</s>
<s>
The	O
computer	B-General_Concept
bus	I-General_Concept
designed	O
for	O
the	O
Altair	O
was	O
to	O
become	O
a	O
de	O
facto	O
standard	O
in	O
the	O
form	O
of	O
the	O
S-100	B-Architecture
bus	I-Architecture
,	O
and	O
the	O
first	O
programming	O
language	O
for	O
the	O
machine	O
was	O
Microsoft	O
's	O
founding	O
product	O
,	O
Altair	B-Language
BASIC	I-Language
.	O
</s>
<s>
He	O
was	O
impressed	O
with	O
Don	O
Lancaster	O
's	O
TV	B-Device
Typewriter	I-Device
(	O
Radio	O
Electronics	O
,	O
September	O
1973	O
)	O
article	O
and	O
wanted	O
computer	O
projects	O
for	O
Popular	O
Electronics	O
.	O
</s>
<s>
They	O
were	O
evaluating	O
a	O
computer	O
trainer	O
project	O
by	O
Jerry	O
Ogden	O
when	O
the	O
Mark-8	B-Device
8008-based	O
computer	O
by	O
Jonathan	O
Titus	O
appeared	O
on	O
the	O
July	O
1974	O
cover	O
of	O
Radio-Electronics	O
.	O
</s>
<s>
One	O
of	O
the	O
editors	O
,	O
Les	O
Solomon	O
,	O
knew	O
MITS	O
was	O
working	O
on	O
an	O
Intel	B-General_Concept
8080	I-General_Concept
based	O
computer	O
project	O
and	O
thought	O
Roberts	O
could	O
provide	O
the	O
project	O
for	O
the	O
always	O
popular	O
January	O
issue	O
.	O
</s>
<s>
The	O
TV	B-Device
Typewriter	I-Device
and	O
the	O
Mark-8	B-Device
computer	O
projects	O
were	O
just	O
a	O
detailed	O
set	O
of	O
plans	O
and	O
a	O
set	O
of	O
bare	O
printed	O
circuit	O
boards	O
.	O
</s>
<s>
The	O
computer	O
on	O
the	O
magazine	O
cover	O
is	O
an	O
empty	O
box	O
with	O
just	O
switches	O
and	O
LEDs	O
on	O
the	O
front	B-Device
panel	I-Device
.	O
</s>
<s>
He	O
thought	O
the	O
Intel	B-General_Concept
4004	I-General_Concept
and	O
Intel	B-General_Concept
8008	I-General_Concept
were	O
not	O
powerful	O
enough	O
(	O
in	O
fact	O
several	O
microcomputers	B-Architecture
based	O
on	O
Intel	O
chips	O
were	O
already	O
on	O
the	O
market	O
:	O
the	O
Canadian	O
company	O
Microsystems	O
International	O
's	O
CPS-1	O
built-in	O
1972	O
used	O
a	O
MIL	O
MF7114	O
chip	O
modeled	O
on	O
the	O
4004	B-General_Concept
,	O
the	O
Micral	B-Device
marketed	O
in	O
January	O
1973	O
by	O
the	O
French	O
company	O
R2E	O
and	O
the	O
MCM/70	B-Device
marketed	O
in	O
1974	O
by	O
the	O
Canadian	O
company	O
Micro	B-Device
Computer	I-Device
Machines	I-Device
)	O
;	O
the	O
National	O
Semiconductor	O
IMP-8	O
and	O
IMP-16	B-Device
required	O
external	O
hardware	O
;	O
the	O
Motorola	B-Device
6800	I-Device
was	O
still	O
in	O
development	O
.	O
</s>
<s>
So	O
he	O
chose	O
the	O
8-bit	O
Intel	B-General_Concept
8080	I-General_Concept
.	O
</s>
<s>
When	O
the	O
8080	B-General_Concept
was	O
introduced	O
in	O
April	O
1974	O
,	O
Intel	O
set	O
the	O
single	O
unit	O
price	O
at	O
( $	O
in	O
)	O
.	O
</s>
<s>
Ed	O
Roberts	O
had	O
experience	O
in	O
buying	O
OEM	O
quantities	O
of	O
calculator	O
chips	O
and	O
he	O
was	O
able	O
to	O
negotiate	O
a	O
price	O
( $	O
in	O
)	O
for	O
the	O
8080	B-General_Concept
microprocessor	I-General_Concept
chips	O
.	O
</s>
<s>
It	O
was	O
functionally	O
similar	O
to	O
the	O
Altair	B-Architecture
8800	I-Architecture
but	O
it	O
was	O
a	O
commercial	O
grade	O
system	O
with	O
a	O
wide	O
selection	O
of	O
peripherals	O
and	O
development	O
software	O
.	O
</s>
<s>
In	O
July	O
1975	O
,	O
Intel	O
sent	O
a	O
letter	O
to	O
its	O
sales	O
force	O
stating	O
that	O
the	O
MITS	B-Architecture
Altair	I-Architecture
8800	I-Architecture
computer	O
used	O
standard	O
Intel	B-General_Concept
8080	I-General_Concept
parts	O
.	O
</s>
<s>
For	O
a	O
decade	O
,	O
colleges	O
had	O
required	O
science	O
and	O
engineering	O
majors	O
to	O
take	O
a	O
course	O
in	O
computer	O
programming	O
,	O
typically	O
using	O
the	O
FORTRAN	B-Application
or	O
BASIC	O
languages	O
.	O
</s>
<s>
Calculators	O
and	O
video	O
games	O
like	O
Pong	B-Application
introduced	O
computer	O
power	O
to	O
the	O
general	O
public	O
.	O
</s>
<s>
In	O
February	O
MITS	O
received	O
1,000	O
orders	O
for	O
the	O
Altair	B-Architecture
8800	I-Architecture
.	O
</s>
<s>
MITS	O
claimed	O
to	O
have	O
delivered	O
2,500	O
Altair	B-Architecture
8800s	I-Architecture
by	O
the	O
end	O
of	O
May	O
.	O
</s>
<s>
The	O
Altair	B-Architecture
8800	I-Architecture
computer	O
was	O
a	O
break-even	O
sale	O
for	O
MITS	O
.	O
</s>
<s>
Their	O
4K	O
memory	O
board	O
used	O
dynamic	O
RAM	B-Architecture
and	O
it	O
had	O
several	O
design	O
problems	O
.	O
</s>
<s>
An	O
enterprising	O
Altair	O
owner	O
,	O
Robert	O
Marsh	O
,	O
designed	O
a	O
4K	O
static	O
memory	O
that	O
was	O
plug-in	O
compatible	O
with	O
the	O
Altair	B-Architecture
8800	I-Architecture
and	O
sold	O
for	O
$255	O
.	O
</s>
<s>
In	O
the	O
October	O
1975	O
issue	O
of	O
Popular	O
Electronics	O
,	O
a	O
small	O
advertisement	O
announced	O
the	O
IMSAI	B-Device
8080	I-Device
computer	O
.	O
</s>
<s>
The	O
ad	O
noted	O
that	O
all	O
boards	O
were	O
"	O
plug	B-Device
compatible	I-Device
"	O
with	O
the	O
Altair	B-Architecture
8800	I-Architecture
.	O
</s>
<s>
The	O
IMSAI	B-Device
8080	I-Device
computer	O
improved	O
on	O
the	O
original	O
Altair	O
design	O
in	O
several	O
areas	O
.	O
</s>
<s>
It	O
was	O
easier	O
to	O
assemble	O
:	O
The	O
Altair	O
required	O
60	O
wire	O
connections	O
between	O
the	O
front	B-Device
panel	I-Device
and	O
the	O
motherboard	B-Device
(	O
backplane	B-Architecture
.	O
)	O
</s>
<s>
The	O
IMSAI	O
motherboard	B-Device
had	O
18	O
slots	O
.	O
</s>
<s>
The	O
MITS	O
motherboard	B-Device
consisted	O
of	O
4	O
slots	O
segments	O
that	O
had	O
to	O
be	O
connected	O
together	O
with	O
100	O
wires	O
.	O
</s>
<s>
In	O
the	O
first	O
design	O
of	O
the	O
Altair	O
,	O
the	O
parts	O
needed	O
to	O
make	O
a	O
complete	O
machine	O
would	O
not	O
fit	O
on	O
a	O
single	O
motherboard	B-Device
,	O
and	O
the	O
machine	O
consisted	O
of	O
four	O
boards	O
stacked	O
on	O
top	O
of	O
each	O
other	O
with	O
stand-offs	O
.	O
</s>
<s>
So	O
during	O
the	O
construction	O
of	O
the	O
second	O
model	O
,	O
he	O
decided	O
to	O
build	O
most	O
of	O
the	O
machine	O
on	O
removable	O
cards	O
,	O
reducing	O
the	O
motherboard	B-Device
to	O
nothing	O
more	O
than	O
an	O
interconnect	B-General_Concept
between	O
the	O
cards	O
,	O
a	O
backplane	B-Architecture
.	O
</s>
<s>
The	O
basic	O
machine	O
consisted	O
of	O
five	O
cards	O
,	O
including	O
the	O
CPU	B-General_Concept
on	O
one	O
and	O
memory	O
on	O
another	O
.	O
</s>
<s>
The	O
S-100	B-Architecture
bus	I-Architecture
was	O
eventually	O
acknowledged	O
by	O
the	O
professional	O
computer	O
community	O
and	O
adopted	O
as	O
the	O
IEEE-696	B-Architecture
computer	B-General_Concept
bus	I-General_Concept
standard	O
.	O
</s>
<s>
The	O
Altair	B-Architecture
bus	I-Architecture
consists	O
of	O
the	O
pins	O
of	O
the	O
Intel	B-General_Concept
8080	I-General_Concept
run	O
out	O
onto	O
the	O
backplane	B-Architecture
.	O
</s>
<s>
No	O
particular	O
level	O
of	O
thought	O
went	O
into	O
the	O
design	O
,	O
which	O
led	O
to	O
disasters	O
such	O
as	O
shorting	B-Application
from	O
various	O
power	O
lines	O
of	O
differing	O
voltages	O
being	O
located	O
next	O
to	O
each	O
other	O
.	O
</s>
<s>
Another	O
oddity	O
was	O
that	O
the	O
system	O
included	O
two	O
unidirectional	O
8-bit	O
data	B-General_Concept
buses	I-General_Concept
,	O
when	O
the	O
normal	O
practice	O
was	O
for	O
a	O
single	O
bidirectional	O
bus	O
(	O
this	O
oddity	O
did	O
,	O
however	O
,	O
allow	O
a	O
later	O
expansion	O
of	O
the	O
S-100	O
standard	O
to	O
16	O
bits	O
bidirectional	O
by	O
using	O
both	O
8-bit	O
buses	O
in	O
parallel	O
)	O
.	O
</s>
<s>
A	O
deal	O
on	O
power	O
supplies	O
led	O
to	O
the	O
use	O
of	O
+8V	O
and	O
±18V	O
,	O
which	O
had	O
to	O
be	O
locally	O
regulated	O
on	O
the	O
cards	O
to	O
TTL	B-General_Concept
( +5V	O
)	O
or	O
RS-232	O
( ±12V	O
)	O
standard	O
voltage	O
levels	O
.	O
</s>
<s>
The	O
backplane	B-Architecture
and	O
power	O
supply	O
were	O
mounted	O
on	O
a	O
base	O
plate	O
,	O
along	O
with	O
the	O
front	O
and	O
rear	O
of	O
the	O
box	O
.	O
</s>
<s>
The	O
front	B-Device
panel	I-Device
,	O
which	O
was	O
inspired	O
by	O
the	O
Data	B-Device
General	I-Device
Nova	I-Device
minicomputer	O
,	O
included	O
a	O
large	O
number	O
of	O
toggle	O
switches	O
to	O
feed	O
binary	O
data	O
directly	O
into	O
the	O
memory	O
of	O
the	O
machine	O
,	O
and	O
a	O
number	O
of	O
red	O
LEDs	O
to	O
read	O
those	O
values	O
back	O
out	O
.	O
</s>
<s>
Programming	O
the	O
Altair	O
via	O
the	O
front	B-Device
panel	I-Device
could	O
be	O
a	O
tedious	O
and	O
time-consuming	O
process	O
.	O
</s>
<s>
Programming	O
required	O
the	O
toggling	O
of	O
the	O
switches	O
to	O
positions	O
corresponding	O
to	O
the	O
desired	O
8080	B-General_Concept
microprocessor	I-General_Concept
instruction	O
or	O
opcode	B-Language
in	O
binary	O
,	O
then	O
used	O
the	O
"	O
DEPOSIT	O
NEXT	O
"	O
switch	O
to	O
load	O
that	O
instruction	O
into	O
the	O
next	O
address	O
of	O
the	O
machine	O
's	O
memory	O
.	O
</s>
<s>
This	O
step	O
was	O
repeated	O
until	O
all	O
the	O
opcodes	B-Language
of	O
a	O
presumably	O
complete	O
and	O
correct	O
program	O
were	O
in	O
place	O
.	O
</s>
<s>
Development	O
was	O
already	O
underway	O
on	O
additional	O
cards	O
,	O
including	O
a	O
paper	O
tape	O
reader	O
for	O
storage	O
,	O
additional	O
RAM	B-Architecture
cards	O
,	O
and	O
an	O
RS-232	O
interface	O
to	O
connect	O
to	O
a	O
proper	O
teletype	O
terminal	B-General_Concept
.	O
</s>
<s>
When	O
they	O
called	O
Roberts	O
to	O
follow	O
up	O
on	O
the	O
letter	O
he	O
expressed	O
his	O
interest	O
,	O
and	O
the	O
two	O
started	O
work	O
on	O
their	O
BASIC	O
interpreter	B-Application
using	O
a	O
self-made	O
simulator	O
for	O
the	O
8080	B-General_Concept
on	O
a	O
PDP-10	B-Device
mainframe	B-Architecture
computer	I-Architecture
.	O
</s>
<s>
They	O
figured	O
that	O
they	O
had	O
30	O
days	O
before	O
someone	O
else	O
beat	O
them	O
to	O
the	O
punch	O
,	O
and	O
once	O
they	O
had	O
a	O
version	O
working	O
on	O
the	O
simulator	O
,	O
Allen	O
flew	O
to	O
Albuquerque	O
to	O
deliver	O
the	O
program	O
,	O
Altair	B-Language
BASIC	I-Language
(	O
aka	O
MITS	O
4K	O
BASIC	O
)	O
,	O
on	O
a	O
paper	O
tape	O
.	O
</s>
<s>
The	O
game	O
Lunar	B-Application
Lander	I-Application
was	O
entered	O
in	O
,	O
and	O
this	O
worked	O
as	O
well	O
.	O
</s>
