<s>
The	O
original	B-Device
Macintosh	I-Device
was	O
a	O
relatively	O
simple	O
machine	O
,	O
now	O
of	O
interest	O
for	O
its	O
simplicity	O
and	O
for	O
the	O
fact	O
that	O
it	O
was	O
the	O
first	O
computer	O
produced	O
by	O
Apple	O
under	O
the	O
name	O
Macintosh	B-Device
.	O
</s>
<s>
The	O
Macintosh	B-Device
used	O
standard	O
off-the-shelf	O
components	O
to	O
the	O
greatest	O
extent	O
possible	O
,	O
achieving	O
a	O
moderate	O
price	O
point	O
by	O
mixing	O
complex	O
LSI	O
chips	O
,	O
readily	O
customizable	O
programmable	O
array	O
logic	O
,	O
and	O
off-the-shelf	O
components	O
.	O
</s>
<s>
The	O
Macintosh	B-Device
used	O
the	O
Motorola	B-Device
68000	I-Device
.	O
</s>
<s>
The	O
68000	B-Device
's	O
bus	B-General_Concept
was	O
wired	O
directly	O
to	O
the	O
other	O
programmable	O
components	O
of	O
the	O
computer	O
:	O
the	O
IWM	B-Device
floppy	B-Device
controller	I-Device
,	O
the	O
Zilog	O
8530	O
SCC	O
,	O
and	O
the	O
MOS	B-Device
Technology	I-Device
6522	I-Device
.	O
</s>
<s>
The	O
bus	B-General_Concept
also	O
connected	O
the	O
68000	B-Device
to	O
the	O
128	O
or	O
512	O
KiB	O
of	O
main	O
memory	O
(	O
DRAM	O
)	O
,	O
which	O
was	O
shared	O
between	O
the	O
processor	O
and	O
the	O
multimedia	O
circuits	O
in	O
a	O
direct	B-General_Concept
memory	I-General_Concept
access	I-General_Concept
(	O
DMA	O
)	O
arrangement	O
.	O
</s>
<s>
Either	O
the	O
processor	O
or	O
the	O
video/sound	O
engine	O
could	O
access	O
the	O
memory	O
,	O
but	O
not	O
both	O
,	O
resulting	O
in	O
up	O
to	O
a	O
10%	O
loss	O
in	O
performance	O
;	O
the	O
DMA	O
circuit	O
also	O
performed	O
necessary	O
maintenance	O
on	O
the	O
RAM	B-Architecture
which	O
would	O
otherwise	O
add	O
overhead	O
,	O
a	O
trick	O
previously	O
used	O
in	O
the	O
Apple	B-Device
II	I-Device
.	O
</s>
<s>
Precise	O
timing	O
information	O
was	O
relayed	O
to	O
the	O
68000	B-Device
by	O
interrupts	B-Application
.	O
</s>
<s>
The	O
68000	B-Device
provides	O
three	O
interrupt	B-Application
inputs	O
,	O
which	O
in	O
the	O
Macintosh	O
128K/512K	O
were	O
connected	O
to	O
the	O
6522	B-Device
,	O
the	O
8530	O
,	O
and	O
a	O
human	O
input	O
designed	O
for	O
programmers	O
,	O
in	O
order	O
of	O
increasing	O
priority	O
.	O
</s>
<s>
Thus	O
typing	O
on	O
the	O
keyboard	O
(	O
attached	O
to	O
the	O
6522	B-Device
)	O
did	O
not	O
reduce	O
serial	O
data	O
(	O
8530	O
)	O
performance	O
,	O
yet	O
the	O
program	O
controlling	O
the	O
serial	O
bus	B-General_Concept
could	O
be	O
debugged	O
by	O
the	O
programmer	O
.	O
</s>
<s>
To	O
further	O
reduce	O
the	O
cost	O
of	O
manufacture	O
,	O
as	O
compared	O
with	O
its	O
predecessor	O
the	O
Lisa	B-Device
,	O
Apple	O
did	O
not	O
include	O
an	O
MMU	B-General_Concept
.	O
</s>
<s>
As	O
a	O
result	O
,	O
the	O
Macintosh	B-Device
did	O
not	O
support	O
protected	O
memory	O
,	O
and	O
this	O
feature	O
remained	O
absent	O
from	O
the	O
OS	O
until	O
2001	O
with	O
the	O
Mac	B-Operating_System
OS	I-Operating_System
X	I-Operating_System
operating	O
system	O
.	O
</s>
<s>
According	O
to	O
Andy	O
Hertzfeld	O
the	O
Macintosh	B-Device
used	O
for	O
the	O
introduction	O
demo	O
on	O
January	O
24	O
,	O
1984	O
,	O
was	O
a	O
prototype	O
with	O
512k	O
RAM	B-Architecture
,	O
even	O
though	O
the	O
first	O
model	O
offered	O
for	O
sale	O
implemented	O
just	O
128k	O
of	O
non-expandable	O
memory	O
.	O
</s>
<s>
This	O
prototype	O
was	O
used	O
to	O
provide	O
adequate	O
RAM	B-Architecture
to	O
run	O
the	O
memory-intensive	O
demo	O
,	O
which	O
showcased	O
speech	O
synthesis	O
software	O
intended	O
to	O
impress	O
the	O
crowd	O
.	O
</s>
<s>
This	O
is	O
a	O
comprehensive	O
list	O
of	O
the	O
integrated	O
circuits	O
in	O
the	O
original	B-Device
Macintosh	I-Device
:	O
</s>
<s>
Most	O
of	O
the	O
simpler	O
chips	O
would	O
be	O
consolidated	O
into	O
a	O
few	O
custom	O
chips	O
in	O
the	O
next	B-Device
generation	I-Device
,	O
much	O
reducing	O
cost	O
.	O
</s>
<s>
The	O
above	O
components	O
implemented	O
the	O
Macintosh	B-Device
GUI	B-Application
and	O
networking	B-Architecture
as	O
described	O
below	O
.	O
</s>
<s>
The	O
centerpiece	O
of	O
the	O
new	O
interface	O
was	O
mouse-driven	O
control	O
.	O
</s>
<s>
The	O
mouse	B-Device
contained	O
only	O
electromechanical	O
components	O
:	O
a	O
button	O
,	O
and	O
two	O
optical	B-Algorithm
encoders	I-Algorithm
.	O
</s>
<s>
The	O
button	O
was	O
connected	O
to	O
the	O
6522	B-Device
.	O
</s>
<s>
The	O
encoders	O
 '	O
four	O
outputs	O
were	O
connected	O
two	O
to	O
the	O
8530	O
and	O
two	O
to	O
the	O
6522	B-Device
.	O
</s>
<s>
The	O
optical	B-Algorithm
encoders	I-Algorithm
detected	O
movement	O
by	O
quadrature	B-Algorithm
.	O
</s>
<s>
Each	O
encoder	O
had	O
a	O
wheel	O
with	O
radial	O
stripes	O
which	O
would	O
interrupt	B-Application
the	O
light	O
passing	O
between	O
an	O
LED	O
and	O
a	O
light-detecting	O
photodiode	O
,	O
producing	O
electrical	O
pulses	O
with	O
mouse	B-Device
movement	O
.	O
</s>
<s>
Both	O
the	O
X	O
and	O
the	O
Y	O
encoders	O
were	O
turned	O
by	O
frictional	O
contact	O
with	O
the	O
mouse	B-Device
ball	O
.	O
</s>
<s>
When	O
the	O
mouse	B-Device
moved	O
by	O
a	O
certain	O
amount	O
,	O
the	O
model	O
connect/disconnect	O
signal	O
would	O
change	O
state	O
and	O
the	O
8530	O
would	O
interrupt	B-Application
the	O
processor	O
.	O
</s>
<s>
The	O
operating	O
system	O
would	O
then	O
read	O
the	O
direction	O
signals	O
from	O
the	O
6522	B-Device
to	O
differentiate	O
left	O
from	O
right	O
,	O
and	O
up	O
from	O
down	O
,	O
and	O
move	O
the	O
mouse	B-Device
cursor	O
.	O
</s>
<s>
The	O
mouse	B-Device
cursor	O
was	O
drawn	O
on	O
the	O
screen	O
by	O
software	O
,	O
as	O
were	O
all	O
other	O
on-screen	O
objects	O
.	O
</s>
<s>
To	O
support	O
real-time	O
animation	O
the	O
screen	O
timing	O
PAL	O
circuit	O
would	O
send	O
a	O
pulse	O
to	O
the	O
6522	B-Device
once	O
per	O
vertical	O
retrace	O
.	O
</s>
<s>
It	O
could	O
sometimes	O
be	O
difficult	O
to	O
avoid	O
a	O
race	B-Operating_System
condition	I-Operating_System
between	O
a	O
game	O
and	O
the	O
raster	O
display	O
.	O
</s>
<s>
Flicker	O
could	O
result	O
from	O
the	O
processor	O
writing	O
to	O
the	O
image	O
while	O
it	O
was	O
being	O
sent	O
to	O
the	O
CRT	B-Device
.	O
</s>
<s>
Therefore	O
,	O
the	O
Macintosh	B-Device
provided	O
a	O
choice	O
of	O
two	O
images	O
in	O
memory	O
,	O
so	O
one	O
could	O
be	O
read	O
while	O
the	O
other	O
was	O
written	O
.	O
</s>
<s>
The	O
"	O
page	O
"	O
was	O
selected	O
by	O
a	O
general-purpose	O
I/O	O
output	O
connected	O
from	O
the	O
6522	B-Device
to	O
the	O
video	O
DMA	O
.	O
</s>
<s>
As	O
two	O
images	O
added	O
up	O
to	O
42.75	O
KiB	O
of	O
precious	O
RAM	B-Architecture
,	O
however	O
,	O
this	O
feature	O
was	O
unpopular	O
.	O
</s>
<s>
One-bit	O
pixels	O
were	O
fetched	O
sixteen	O
at	O
a	O
time	O
over	O
a	O
16-bit	O
data	B-General_Concept
bus	I-General_Concept
and	O
output	O
at	O
just	O
less	O
16MHz	O
,	O
necessitating	O
almost	O
one	O
million	O
fetches	O
per	O
second	O
.	O
</s>
<s>
The	O
6522	B-Device
provided	O
a	O
general-purpose	O
serial	O
bus	B-General_Concept
.	O
</s>
<s>
The	O
keyboard	O
contained	O
an	O
Intel	B-Device
8021	I-Device
microprocessor	B-Architecture
which	O
transmitted	O
user	O
input	O
to	O
the	O
6522	B-Device
over	O
standard	O
phone	O
patch	O
cable	O
.	O
</s>
<s>
A	O
new	O
keystroke	O
resulted	O
in	O
a	O
processor	O
interrupt	B-Application
.	O
</s>
<s>
As	O
the	O
raster	O
scan	O
returned	O
from	O
the	O
right	O
side	O
of	O
the	O
screen	O
to	O
the	O
left	O
,	O
one	O
byte	O
of	O
data	O
was	O
placed	O
into	O
a	O
PWM	B-Algorithm
generator	O
instead	O
of	O
the	O
screen	O
.	O
</s>
<s>
General	O
purpose	O
6522	B-Device
outputs	O
could	O
mute	O
the	O
sampled	O
sound	O
,	O
or	O
set	O
its	O
volume	O
to	O
one	O
of	O
8	O
levels	O
of	O
attenuation	O
.	O
</s>
<s>
A	O
square	O
wave	O
generator	O
was	O
included	O
on	O
the	O
6522	B-Device
.	O
</s>
<s>
This	O
system	O
was	O
not	O
compatible	O
with	O
the	O
Lisa	B-Device
/	O
Mac	O
XL	O
hardware	O
,	O
which	O
in	O
other	O
respects	O
could	O
run	O
Mac	O
software	O
with	O
commonly	O
available	O
software/firmware	O
modifications	O
.	O
</s>
<s>
Running	O
programs	O
on	O
Lisas	B-Device
which	O
made	O
use	O
of	O
the	O
Mac	O
sound	O
features	O
would	O
cause	O
severe	O
video	O
problems	O
and	O
system	O
crashes	O
.	O
</s>
<s>
The	O
RS-422	O
protocol	O
was	O
implemented	O
except	O
for	O
the	O
connection-established	O
line	O
,	O
which	O
was	O
used	O
to	O
support	O
the	O
mouse	B-Device
.	O
</s>
<s>
Apple	O
later	O
changed	O
to	O
an	O
8-pin	B-Protocol
connector	O
which	O
dropped	O
it	O
entirely	O
.	O
</s>
<s>
The	O
Macintosh	B-Device
's	O
persistent	O
storage	O
medium	O
was	O
Sony	O
's	O
floppy	O
diskette	O
drive	O
.	O
</s>
<s>
</s>
<s>
The	O
single-sided	O
3.5	O
inch	O
floppy	O
stored	O
400	O
KB	O
by	O
spinning	O
the	O
disk	O
slower	B-Device
when	O
the	O
outer	O
edge	O
was	O
used	O
.	O
</s>
<s>
A	O
separate	O
microcontroller	O
,	O
the	O
IWM	B-Device
(	O
Integrated	B-Device
Woz	I-Device
Machine	I-Device
)	O
,	O
was	O
dedicated	O
to	O
disk	O
control	O
.	O
</s>
<s>
The	O
Macintosh	B-Device
featured	O
a	O
real-time	O
clock	O
counting	O
seconds	O
,	O
and	O
a	O
countdown	O
timer	O
with	O
near-microsecond	O
resolution	O
.	O
</s>
<s>
The	O
former	O
was	O
connected	O
to	O
the	O
6522	B-Device
by	O
a	O
serial	O
bus	B-General_Concept
on	O
three	O
general-purpose	O
I/O	O
lines	O
.	O
</s>
<s>
The	O
latter	O
was	O
built	O
into	O
the	O
6522	B-Device
itself	O
.	O
</s>
<s>
Either	O
could	O
generate	O
interrupts	B-Application
.	O
</s>
<s>
RAM	B-Architecture
begins	O
at	O
and	O
ends	O
at	O
(	O
128K	O
)	O
/	O
(	O
512K	O
)	O
and	O
is	O
divided	O
up	O
into	O
a	O
series	O
of	O
different	O
functional	O
areas	O
:	O
</s>
<s>
System	O
heap	B-General_Concept
(	O
)	O
.	O
</s>
<s>
Application	O
heap	B-General_Concept
(	O
ApplZone	O
;	O
grows	O
upwards	O
.	O
</s>
<s>
Stack	B-General_Concept
.	O
</s>
<s>
Grows	O
downwards	O
from	O
CurStackBase	O
;	O
SP	O
=	O
A7	O
points	O
to	O
top	O
of	O
stack	B-General_Concept
.	O
</s>
<s>
QuickDraw	B-Operating_System
globals	O
.	O
</s>
<s>
The	O
RAM	B-Architecture
map	O
is	O
organised	O
so	O
that	O
the	O
system	O
globals	O
,	O
system	O
and	O
application	O
heaps	O
grow	O
upwards	O
from	O
low	O
memory	O
,	O
everything	O
else	O
grows	O
downwards	O
from	O
MemTop	O
,	O
from	O
high	O
memory	O
towards	O
low	O
memory	O
.	O
</s>
<s>
On	O
the	O
512K	O
Macintosh	B-Device
,	O
the	O
"	O
extra	O
"	O
RAM	B-Architecture
thus	O
appears	O
as	O
a	O
wider	O
gap	O
between	O
the	O
application	O
heap	B-General_Concept
and	O
the	O
stack	B-General_Concept
,	O
where	O
it	O
is	O
available	O
for	O
application	O
use	O
.	O
</s>
