<s>
Apple	B-Device
II	I-Device
graphics	I-Device
debuted	O
on	O
the	O
1977	O
Apple	B-Device
II	I-Device
and	O
was	O
used	O
throughout	O
the	O
Apple	B-Device
II	I-Device
line	O
.	O
</s>
<s>
The	O
Apple	B-Device
IIe	I-Device
added	O
"	O
double	O
"	O
versions	O
of	O
each	O
of	O
these	O
,	O
most	O
prominently	O
"	O
double	O
high	O
resolution	O
"	O
with	O
twice	O
the	O
horizontal	O
resolution	O
in	O
16	O
colors	O
.	O
</s>
<s>
Internally	O
,	O
Apple	B-Device
II	I-Device
graphics	I-Device
modes	O
are	O
idiosyncratic	O
and	O
do	O
not	O
simply	O
use	O
a	O
linear	O
frame	B-Algorithm
buffer	I-Algorithm
.	O
</s>
<s>
The	O
1986	O
Apple	B-Device
IIgs	I-Device
split	O
from	O
previous	O
Apple	B-Device
II	I-Device
architecture	B-General_Concept
and	O
the	O
graphics	O
have	O
more	O
in	O
common	O
with	O
the	O
Atari	B-Device
ST	I-Device
and	O
Amiga	B-Device
.	O
</s>
<s>
The	O
graphic	O
modes	O
of	O
the	O
Apple	B-Device
II	I-Device
series	O
were	O
peculiar	O
even	O
by	O
the	O
standards	O
of	O
the	O
late	O
1970s	O
and	O
early	O
1980s	O
.	O
</s>
<s>
Many	O
home	O
computer	O
systems	O
of	O
the	O
time	O
(	O
as	O
well	O
as	O
today	O
's	O
IBM	B-Device
PC	I-Device
compatibles	O
)	O
had	O
an	O
architecture	B-General_Concept
which	O
assigned	O
consecutive	O
blocks	O
of	O
memory	B-Architecture
to	O
non-consecutive	O
rows	O
on	O
the	O
screen	O
in	O
graphic	O
modes	O
,	O
i.e.	O
,	O
interleaving	B-Application
.	O
</s>
<s>
Apple	O
's	O
text	O
and	O
graphics	O
modes	O
are	O
based	O
on	O
two	O
different	O
interleave	B-Application
factors	O
of	O
8:1	O
and	O
64:1	O
.	O
</s>
<s>
A	O
second	O
peculiarity	O
of	O
Apple	B-Device
II	I-Device
graphics	I-Device
—	O
the	O
so-called	O
"	O
color	O
fringes	O
"	O
—	O
is	O
yet	O
another	O
by-product	O
of	O
Wozniak	O
's	O
design	O
.	O
</s>
<s>
While	O
these	O
occur	O
in	O
all	O
graphics	O
modes	O
,	O
they	O
play	O
a	O
crucial	O
role	O
in	O
Hi-Resolution	B-General_Concept
or	O
Hi-Res	O
mode	O
(	O
see	O
below	O
)	O
.	O
</s>
<s>
Reading	O
a	O
value	O
from	O
,	O
or	O
writing	O
any	O
value	O
to	O
,	O
certain	O
memory	B-Architecture
addresses	O
controlled	O
so	O
called	O
"	O
soft	B-Device
switches	I-Device
"	O
.	O
</s>
<s>
This	O
allowed	O
the	O
user	O
to	O
do	O
many	O
different	O
things	O
including	O
displaying	O
the	O
graphics	O
screen	O
(	O
any	O
type	O
)	O
without	O
erasing	O
it	O
,	O
displaying	O
the	O
text	O
screen	O
,	O
clearing	O
the	O
last	O
key	O
pressed	O
,	O
or	O
accessing	O
different	O
memory	B-Architecture
banks	O
.	O
</s>
<s>
All	O
Apple	B-Device
II	I-Device
machines	O
featured	O
an	O
RCA	B-Protocol
jack	I-Protocol
providing	O
a	O
rough	O
NTSC	O
,	O
PAL	B-Language
,	O
or	O
SECAM	O
composite	O
video	O
output	O
(	O
on	O
non-NTSC	O
machines	O
before	O
the	O
Apple	B-Device
IIe	I-Device
this	O
output	O
is	O
black-and-white	O
only	O
)	O
.	O
</s>
<s>
In	O
addition	O
to	O
the	O
composite	O
video	O
output	O
jack	O
,	O
the	O
IIc	O
,	O
IIc	O
Plus	O
,	O
and	O
the	O
IIGS	B-Device
featured	O
a	O
two-row	B-Protocol
,	I-Protocol
15-pin	I-Protocol
output	I-Protocol
.	O
</s>
<s>
In	O
the	O
IIc	O
and	O
IIc	O
Plus	O
,	O
this	O
connector	O
was	O
a	O
special-purpose	O
video	O
connector	O
for	O
adapters	O
to	O
digital	O
RGB	B-Device
monitors	I-Device
and	O
RF	O
modulators	O
.	O
</s>
<s>
In	O
the	O
IIGS	B-Device
it	O
was	O
an	O
output	O
for	O
an	O
analog	O
RGB	O
monitor	O
specially	O
designed	O
for	O
the	O
IIGS	B-Device
.	O
</s>
<s>
Numerous	O
add-on	O
video	O
display	O
cards	O
were	O
available	O
for	O
the	O
Apple	B-Device
II	I-Device
series	O
,	O
such	O
as	O
the	O
Apple	B-Device
80-Column	I-Device
Text	I-Device
Card	I-Device
.	O
</s>
<s>
There	O
were	O
PAL	B-Language
color	O
cards	O
which	O
enabled	O
color	O
output	O
on	O
early	O
PAL	B-Language
machines	O
.	O
</s>
<s>
Some	O
other	O
cards	O
simply	O
added	O
80-column	O
and	O
lowercase	O
display	O
capabilities	O
,	O
while	O
others	O
allowed	O
output	O
to	O
an	O
IBM	B-Device
CGA	I-Device
monitor	O
through	O
a	O
DE9	B-Protocol
output	O
jack	O
.	O
</s>
<s>
The	O
Apple	B-Device
II	I-Device
video	O
output	O
is	O
really	O
a	O
monochrome	O
display	O
based	O
upon	O
the	O
bit	O
patterns	O
in	O
the	O
video	O
memory	B-Architecture
(	O
or	O
pixels	B-Algorithm
)	O
.	O
</s>
<s>
These	O
pixels	B-Algorithm
are	O
combined	O
in	O
quadrature	B-Device
with	O
the	O
colorburst	O
signal	O
to	O
be	O
interpreted	O
as	O
color	O
by	O
a	O
composite	O
video	O
display	O
.	O
</s>
<s>
High	O
resolution	O
provides	O
two	O
pixels	B-Algorithm
per	O
Colorburst	O
cycle	O
,	O
allowing	O
for	O
two	O
possible	O
colors	O
if	O
one	O
pixel	B-Algorithm
is	O
on	O
,	O
black	O
if	O
no	O
pixels	B-Algorithm
are	O
on	O
,	O
or	O
white	O
if	O
both	O
pixels	B-Algorithm
are	O
on	O
.	O
</s>
<s>
By	O
shifting	O
the	O
alignment	O
of	O
the	O
pixels	B-Algorithm
to	O
the	O
colorburst	O
signal	O
by	O
90°	O
,	O
two	O
more	O
colors	O
can	O
be	O
displayed	O
for	O
a	O
total	O
of	O
four	O
possible	O
colors	O
.	O
</s>
<s>
Low	O
resolution	O
allows	O
for	O
four	O
bits	O
per	O
cycle	O
,	O
but	O
repeats	O
the	O
bit	O
pattern	O
several	O
times	O
per	O
low	O
resolution	O
pixel	B-Algorithm
.	O
</s>
<s>
Double	O
high	O
resolution	O
also	O
displays	O
four	O
pixels	B-Algorithm
per	O
cycle	O
.	O
</s>
<s>
The	O
blocky	O
,	O
but	O
fast	O
and	O
colorful	O
Lo-Res	O
graphics	O
mode	O
(	O
often	O
known	O
as	O
GR	O
after	O
the	O
BASIC	O
command	O
)	O
was	O
40	O
pixels	B-Algorithm
wide	O
,	O
corresponding	O
to	O
the	O
40	O
columns	O
on	O
the	O
normal	O
Apple	B-Device
II	I-Device
text	O
screen	O
.	O
</s>
<s>
This	O
mode	O
could	O
display	O
either	O
40	O
rows	O
of	O
pixels	B-Algorithm
with	O
four	O
lines	O
of	O
text	O
at	O
the	O
bottom	O
of	O
the	O
screen	O
,	O
or	O
48	O
rows	O
of	O
pixels	B-Algorithm
with	O
no	O
text	O
.	O
</s>
<s>
Thus	O
two	O
pixels	B-Algorithm
,	O
vertically	O
stacked	O
,	O
would	O
fill	O
the	O
screen	O
real	O
estate	O
corresponding	O
to	O
one	O
character	O
in	O
text	O
mode	O
.	O
</s>
<s>
There	O
are	O
16	O
colors	O
available	O
for	O
use	O
in	O
this	O
mode	O
(	O
actually	O
15	O
in	O
most	O
cases	O
,	O
since	O
the	O
two	O
shades	O
of	O
gray	O
are	O
identical	O
in	O
brightness	O
on	O
original	O
Apple	O
hardware	O
,	O
except	O
on	O
the	O
Apple	B-Device
IIGS	I-Device
)	O
.	O
</s>
<s>
The	O
colors	O
were	O
created	O
by	O
filling	O
the	O
pixel	B-Algorithm
with	O
a	O
repeating	O
4-bit	O
binary	O
pattern	O
in	O
such	O
a	O
manner	O
that	O
each	O
bit	O
group	O
fit	O
within	O
one	O
cycle	O
of	O
the	O
Colorburst	O
reference	O
signal	O
.	O
</s>
<s>
There	O
are	O
two	O
equivalent	O
grey	O
shades	O
as	O
5	O
(	O
0101	O
)	O
is	O
equivalent	O
to	O
10	O
(	O
1010	O
)	O
based	O
on	O
how	O
the	O
colors	O
mix	O
together	O
;	O
the	O
"	O
on	O
"	O
bits	O
are	O
polar	O
opposites	O
of	O
each	O
other	O
on	O
the	O
quadrature	B-Device
color	O
signal	O
,	O
so	O
they	O
cancel	O
each	O
other	O
and	O
display	O
as	O
grey	O
.	O
</s>
<s>
This	O
mode	O
is	O
mapped	O
to	O
the	O
same	O
area	O
of	O
memory	B-Architecture
as	O
the	O
main	O
40-column	O
text	O
screen	O
(	O
0x400	O
through	O
0x7FF	O
)	O
,	O
with	O
each	O
byte	B-Application
storing	O
two	O
pixels	B-Algorithm
one	O
on	O
top	O
of	O
the	O
other	O
.	O
</s>
<s>
The	O
Lo-Res	O
graphics	O
mode	O
offered	O
built-in	O
commands	O
to	O
clear	O
the	O
screen	O
,	O
change	O
the	O
drawing	O
color	O
,	O
plot	O
individual	O
pixels	B-Algorithm
,	O
plot	O
horizontal	O
lines	O
,	O
and	O
plot	O
vertical	O
lines	O
.	O
</s>
<s>
There	O
was	O
also	O
a	O
"	O
SCRN	O
"	O
function	O
to	O
extract	O
the	O
color	O
stored	O
in	O
any	O
pixel	B-Algorithm
,	O
one	O
lacking	O
in	O
the	O
other	O
modes	O
.	O
</s>
<s>
A	O
block	O
of	O
128	O
bytes	B-Application
stores	O
three	O
rows	O
of	O
40	O
characters	O
each	O
,	O
with	O
a	O
remainder	O
of	O
eight	O
bytes	B-Application
left	O
after	O
the	O
third	O
row	O
is	O
stored	O
.	O
</s>
<s>
But	O
these	O
bytes	B-Application
are	O
not	O
left	O
empty	O
.	O
</s>
<s>
This	O
created	O
problems	O
when	O
the	O
user	O
loaded	O
a	O
text	O
or	O
a	O
lo-res	O
graphics	O
screen	O
directly	O
into	O
video	O
memory	B-Architecture
—	O
replacing	O
the	O
current	O
information	O
in	O
the	O
holes	O
with	O
what	O
was	O
there	O
at	O
save-time	O
.	O
</s>
<s>
(	O
Disk	O
head	O
recalibration	O
was	O
a	O
common	O
side-effect	O
,	O
when	O
the	O
disk	O
controller	O
found	O
its	O
memory	B-Architecture
—	O
in	O
a	O
screen	O
hole	O
—	O
of	O
where	O
the	O
head	O
was	O
,	O
suddenly	O
not	O
to	O
match	O
the	O
header	O
data	O
of	O
the	O
track	O
that	O
it	O
was	O
reading	O
)	O
.	O
</s>
<s>
The	O
programmers	O
at	O
Apple	O
responded	O
by	O
programming	B-General_Concept
ProDOS	B-Operating_System
so	O
the	O
user	O
could	O
not	O
directly	O
load	O
a	O
file	O
(	O
screen	O
data	O
,	O
or	O
otherwise	O
)	O
into	O
0x400-0x7FF	O
.	O
</s>
<s>
ProDOS	B-Operating_System
programs	O
to	O
properly	O
load	O
data	O
to	O
this	O
portion	O
of	O
memory	B-Architecture
soon	O
arose	O
;	O
several	O
appeared	O
in	O
Nibble	O
magazine	O
.	O
</s>
<s>
Having	O
two	O
screens	O
for	O
displaying	O
video	O
images	O
was	O
an	O
integral	O
part	O
of	O
the	O
Apple	B-Device
II	I-Device
family	O
design	O
.	O
</s>
<s>
Accessing	O
memory	B-Architecture
location	O
0xC055	O
(	O
49237	O
)	O
displayed	O
"	O
Screen	O
2	O
"	O
regardless	O
of	O
how	O
the	O
other	O
"	O
soft	B-Device
switches	I-Device
"	O
were	O
set	O
.	O
</s>
<s>
The	O
interleaving	B-Application
is	O
exactly	O
the	O
same	O
as	O
for	O
the	O
main	O
screen	O
(	O
"	O
Screen	O
1	O
"	O
)	O
.	O
</s>
<s>
Applesoft	B-Language
BASIC	I-Language
programs	O
are	O
loaded	O
at	O
801h	O
(	O
2049	O
)	O
by	O
default	O
;	O
therefore	O
,	O
they	O
will	O
occupy	O
the	O
Text	O
Screen	O
2	O
space	O
unless	O
the	O
computer	O
is	O
instructed	O
to	O
load	O
a	O
program	O
elsewhere	O
in	O
memory	B-Architecture
.	O
</s>
<s>
By	O
contrast	O
,	O
some	O
commercial	O
software	O
programs	O
for	O
the	O
Apple	B-Device
II	I-Device
used	O
this	O
memory	B-Architecture
space	O
for	O
various	O
purposes	O
usually	O
to	O
display	O
a	O
help	O
screen	O
.	O
</s>
<s>
Unlike	O
the	O
other	O
Apple	B-Device
II	I-Device
machine	O
types	O
,	O
the	O
Apple	B-Device
IIGS	I-Device
featured	O
a	O
processor	O
(	O
the	O
65816	B-General_Concept
)	O
which	O
could	O
address	O
more	O
than	O
64K	O
of	O
RAM	B-Architecture
without	O
special	O
tricks	O
.	O
</s>
<s>
In	O
the	O
IIgs	B-Device
,	O
RAM	B-Architecture
was	O
demarcated	O
into	O
banks	O
of	O
64K	O
.	O
</s>
<s>
The	O
Apple	B-Device
IIgs	I-Device
had	O
a	O
chip	O
called	O
the	O
"	O
Mega	O
II	O
"	O
which	O
allowed	O
it	O
to	O
run	O
most	O
programs	O
written	O
for	O
other	O
Apple	B-Device
II	I-Device
computers	O
.	O
</s>
<s>
The	O
IIgs	B-Device
architecture	B-General_Concept
mapped	O
the	O
screen	O
data	O
to	O
memory	B-Architecture
bank	O
0xE0	O
.	O
</s>
<s>
However	O
,	O
in	O
IIe	B-Device
emulation	B-Application
mode	O
,	O
screen	O
data	O
was	O
stored	O
in	O
bank	O
0x00	O
.	O
</s>
<s>
This	O
was	O
not	O
discovered	O
until	O
the	O
Mega	O
II	O
chips	O
had	O
made	O
it	O
into	O
the	O
IIgs	B-Device
machines	O
.	O
</s>
<s>
So	O
the	O
firmware	O
designers	O
added	O
a	O
CDA	O
(	O
classic	O
desk	O
accessory	O
—	O
accessible	O
from	O
the	O
IIgs	B-Device
Desk	O
Accessories	O
menu	O
,	O
invoked	O
with	O
)	O
called	O
"	O
Alternate	O
Display	O
Mode	O
"	O
,	O
which	O
,	O
at	O
the	O
expense	O
of	O
a	O
little	O
bit	O
of	O
CPU	O
time	O
,	O
performed	O
the	O
task	O
for	O
the	O
few	O
programs	O
that	O
needed	O
it	O
.	O
</s>
<s>
Improved	O
compatibility	O
with	O
Text	O
Screen	O
2	O
was	O
addressed	O
with	O
the	O
introduction	O
of	O
the	O
Apple	B-Device
IIGS	I-Device
with	O
1	O
megabyte	O
of	O
RAM	B-Architecture
(	O
better	O
known	O
as	O
the	O
ROM	O
3	O
)	O
in	O
1989	O
.	O
</s>
<s>
When	O
the	O
Apple	B-Device
II	I-Device
came	O
out	O
,	O
a	O
new	O
mode	O
had	O
been	O
added	O
for	O
280×192	O
high-resolution	O
graphics	O
.	O
</s>
<s>
Like	O
Lo-Res	O
mode	O
,	O
hi-res	O
mode	O
had	O
two	O
screens	O
;	O
in	O
Applesoft	B-Language
BASIC	I-Language
,	O
either	O
one	O
could	O
be	O
initialized	O
,	O
using	O
the	O
commands	O
HGR	O
for	O
the	O
first	O
screen	O
or	O
HGR2	O
for	O
the	O
second	O
.	O
</s>
<s>
The	O
Applesoft	B-Language
BASIC	I-Language
ROM	O
contained	O
routines	O
to	O
clear	O
either	O
of	O
two	O
Hi-Res	O
screens	O
,	O
draw	O
lines	O
and	O
points	O
,	O
and	O
set	O
the	O
drawing	O
color	O
.	O
</s>
<s>
There	O
were	O
no	O
routines	O
to	O
plot	O
bitmapped	B-Algorithm
shapes	I-Algorithm
,	O
draw	O
circles	O
and	O
arcs	O
,	O
or	O
fill	O
a	O
drawn	O
area	O
,	O
but	O
many	O
programs	O
were	O
written	O
;	O
many	O
appeared	O
in	O
Nibble	O
and	O
other	O
Apple	B-Device
II	I-Device
magazines	O
.	O
</s>
<s>
The	O
Apple	B-Device
II	I-Device
's	O
Hi-Res	O
mode	O
was	O
peculiar	O
even	O
by	O
the	O
standards	O
of	O
the	O
day	O
.	O
</s>
<s>
While	O
the	O
CGA	B-Device
card	O
released	O
four	O
years	O
after	O
the	O
Apple	B-Device
II	I-Device
on	O
the	O
IBM	B-Device
PC	I-Device
allowed	O
the	O
user	O
to	O
select	O
one	O
of	O
two	O
color	O
sets	O
for	O
creating	O
320×200	O
graphics	O
,	O
only	O
four	O
colors	O
(	O
the	O
background	O
color	O
and	O
three	O
drawing	O
colors	O
)	O
were	O
available	O
at	O
a	O
time	O
.	O
</s>
<s>
Each	O
row	O
of	O
280	O
pixels	B-Algorithm
was	O
broken	O
up	O
into	O
40	O
blocks	O
of	O
seven	O
pixels	B-Algorithm
each	O
,	O
represented	O
in	O
a	O
single	O
byte	B-Application
.	O
</s>
<s>
Each	O
pair	O
of	O
adjacent	O
pixels	B-Algorithm
generated	O
a	O
single	O
color	O
pixel	B-Algorithm
via	O
artifact	O
color	O
,	O
resulting	O
in	O
an	O
effective	O
resolution	O
of	O
140×192	O
.	O
</s>
<s>
The	O
lower	O
seven	O
bits	O
of	O
each	O
byte	B-Application
represented	O
the	O
pixels	B-Algorithm
,	O
while	O
the	O
most	O
significant	O
bit	O
controlled	O
the	O
phase	O
offset	O
for	O
that	O
block	O
of	O
pixels	B-Algorithm
,	O
altering	O
the	O
color	O
that	O
was	O
displayed	O
.	O
</s>
<s>
This	O
is	O
because	O
drawing	O
the	O
blue	O
line	O
sets	O
the	O
MSB	O
for	O
each	O
block	O
of	O
seven	O
pixels	B-Algorithm
in	O
this	O
case	O
.	O
</s>
<s>
"	O
Green	O
"	O
and	O
"	O
orange	O
"	O
pixels	B-Algorithm
are	O
represented	O
the	O
same	O
way	O
in	O
memory	B-Architecture
;	O
the	O
difference	O
is	O
in	O
the	O
setting	O
(	O
or	O
clearing	O
)	O
of	O
the	O
MSB	O
.	O
</s>
<s>
Another	O
side	O
effect	O
is	O
that	O
drawing	O
a	O
pixel	B-Algorithm
required	O
dividing	O
by	O
seven	O
.	O
</s>
<s>
If	O
drawing	O
a	O
pixel	B-Algorithm
had	O
only	O
required	O
dividing	O
by	O
a	O
simple	O
power	O
of	O
two	O
,	O
such	O
as	O
eight	O
,	O
this	O
would	O
have	O
only	O
needed	O
a	O
sequence	O
of	O
bit	O
shifts	O
,	O
which	O
would	O
have	O
been	O
much	O
faster	O
.	O
)	O
</s>
<s>
The	O
Hi-Res	O
mode	O
on	O
the	O
Apple	B-Device
II	I-Device
was	O
also	O
peculiar	O
for	O
its	O
64:1	O
interleave	B-Application
factor	O
.	O
</s>
<s>
The	O
64:1	O
factor	O
resulted	O
in	O
a	O
"	O
Venetian	O
blind	O
"	O
effect	O
when	O
loading	O
a	O
Hi-Res	O
screen	O
into	O
memory	B-Architecture
from	O
floppy	B-Device
disk	I-Device
(	O
or	O
sometimes	O
RAM	B-Application
disk	I-Application
)	O
with	O
the	O
soft	B-Device
switches	I-Device
already	O
set	O
.	O
</s>
<s>
Another	O
notable	O
exception	O
is	O
the	O
Fotofile	O
(	O
FOT	O
)	O
format	O
inherited	O
by	O
ProDOS	B-Operating_System
from	O
Apple	B-Operating_System
SOS	I-Operating_System
,	O
which	O
included	O
metadata	O
in	O
the	O
121st	O
byte	B-Application
(	O
the	O
first	O
byte	B-Application
of	O
the	O
first	O
hole	O
)	O
indicating	O
how	O
it	O
should	O
be	O
displayed	O
(	O
color	O
mode	O
,	O
resolution	O
)	O
,	O
or	O
converted	O
to	O
other	O
graphics	O
formats	O
.	O
</s>
<s>
Finally	O
,	O
another	O
quirk	O
of	O
Wozniak	O
's	O
design	O
is	O
that	O
while	O
any	O
pixel	B-Algorithm
could	O
be	O
black	O
or	O
white	O
,	O
only	O
pixels	B-Algorithm
with	O
odd	O
X-coordinates	O
could	O
be	O
green	O
or	O
orange	O
.	O
</s>
<s>
Likewise	O
,	O
only	O
even-numbered	O
pixels	B-Algorithm
could	O
be	O
purple	O
or	O
blue	O
.	O
</s>
<s>
The	O
Apple	O
video	O
hardware	O
interprets	O
a	O
sequence	O
of	O
two	O
or	O
more	O
turned-on	O
horizontal	O
pixels	B-Algorithm
as	O
solid	O
white	O
,	O
while	O
a	O
sequence	O
of	O
alternating	O
pixels	B-Algorithm
would	O
display	O
as	O
color	O
.	O
</s>
<s>
Similarly	O
,	O
a	O
sequence	O
of	O
two	O
or	O
more	O
turned-off	O
horizontal	O
pixels	B-Algorithm
would	O
display	O
as	O
black	O
.	O
</s>
<s>
There	O
was	O
no	O
built-in	O
command	O
to	O
extract	O
the	O
color	O
of	O
a	O
pixel	B-Algorithm
on	O
the	O
Hi-Res	O
screen	O
,	O
or	O
even	O
to	O
determine	O
whether	O
it	O
was	O
on	O
at	O
all	O
.	O
</s>
<s>
Several	O
programs	O
to	O
determine	O
if	O
a	O
pixel	B-Algorithm
was	O
lit	O
were	O
written	O
,	O
and	O
a	O
program	O
to	O
extract	O
the	O
pixel	B-Algorithm
's	O
true	O
color	O
was	O
published	O
in	O
the	O
April	O
1990	O
edition	O
of	O
Nibble	O
.	O
</s>
<s>
Just	O
as	O
there	O
are	O
two	O
text	O
screen	O
pages	O
(	O
and	O
two	O
Lo-Res	O
graphics	O
pages	O
)	O
,	O
so	O
there	O
are	O
also	O
two	O
Hi-Res	O
pages	O
,	O
mapped	O
one	O
right	O
after	O
the	O
other	O
in	O
memory	B-Architecture
.	O
</s>
<s>
IBM	O
's	O
CGA	B-Device
supported	O
only	O
one	O
graphics	O
page	O
at	O
a	O
time	O
.	O
</s>
<s>
This	O
simplified	O
animation	O
on	O
the	O
Apple	B-Device
II	I-Device
,	O
because	O
a	O
programmer	O
could	O
display	O
one	O
page	O
while	O
altering	O
the	O
other	O
(	O
hidden	O
)	O
page	O
.	O
</s>
<s>
The	O
use	O
of	O
would	O
force	O
a	O
reset	O
at	O
the	O
expense	O
of	O
a	O
small	O
amount	O
of	O
memory	B-Architecture
corruption	O
.	O
</s>
<s>
Creative	O
configuration	O
of	O
some	O
soft	B-Device
switches	I-Device
at	O
the	O
monitor	O
or	O
at	O
the	O
prompt	O
enabled	O
immediate	O
viewing	O
of	O
images	O
from	O
interrupted	O
programs	O
.	O
</s>
<s>
On	O
the	O
Apple	B-Device
//e	I-Device
and	O
//c	O
,	O
use	O
of	O
would	O
result	O
in	O
the	O
pattern	O
0xA0A0	O
being	O
written	O
sparsely	O
across	O
all	O
memory	B-Architecture
,	O
including	O
Hi-Res	O
pages	O
1	O
and	O
2	O
at	O
$2000	O
–	O
$5FFF	O
.	O
</s>
<s>
On	O
the	O
enhanced	O
Apple	B-Device
//e	I-Device
,	O
Hi-Res	O
video	O
memory	B-Architecture
could	O
be	O
preserved	O
without	O
artifact	O
by	O
the	O
following	O
sequence	O
:	O
pressing	O
,	O
and	O
feathering	O
the	O
key	O
up	O
then	O
down	O
for	O
a	O
fraction	O
of	O
a	O
second	O
,	O
repeating	O
until	O
the	O
self-diagnostic	O
color	O
pattern	O
began	O
to	O
fill	O
the	O
first	O
line	O
of	O
text	O
in	O
the	O
upper	O
left	O
corner	O
.	O
</s>
<s>
Since	O
the	O
self-diagnostic	O
progressed	O
from	O
$0000	O
upward	O
,	O
once	O
the	O
beginning	O
address	O
of	O
text	O
page	O
1	O
( $400	O
)	O
was	O
clobbered	O
,	O
so	O
then	O
was	O
the	O
checksum	O
of	O
the	O
reset	O
vector	O
( $3F4	O
)	O
,	O
which	O
meant	O
that	O
a	O
subsequent	O
rapid	O
press	O
of	O
would	O
force	O
the	O
firmware	O
to	O
reboot	O
without	O
clobbering	O
memory	B-Architecture
above	O
$0800	O
in	O
either	O
main	O
or	O
the	O
auxiliary	O
banks	O
.	O
</s>
<s>
It	O
was	O
possible	O
to	O
BSAVE	B-Protocol
these	O
images	O
to	O
a	O
floppy	B-Device
and	O
create	O
a	O
slide	O
show	O
or	O
a	O
static	O
image	O
,	O
because	O
a	O
soft	O
reset	O
did	O
not	O
clear	O
the	O
video	O
memory	B-Architecture
on	O
Hi-Res	O
images	O
.	O
</s>
<s>
Soon	O
after	O
the	O
introduction	O
of	O
the	O
Apple	B-Device
IIe	I-Device
,	O
the	O
Apple	O
engineers	O
realized	O
that	O
the	O
video	O
bandwidth	O
doubling	O
circuitry	O
used	O
to	O
implement	O
80-column	O
text	O
mode	O
could	O
be	O
easily	O
extended	O
to	O
include	O
the	O
machine	O
's	O
graphics	O
modes	O
.	O
</s>
<s>
Replacement	O
motherboards	O
(	O
called	O
the	O
Revision	O
B	O
motherboard	O
)	O
were	O
offered	O
free	O
of	O
charge	O
to	O
owners	O
of	O
the	O
Apple	B-Device
IIe	I-Device
to	O
upgrade	O
their	O
machines	O
with	O
double	O
resolution	O
graphics	O
capabilities	O
.	O
</s>
<s>
Subsequent	O
Apple	B-Device
II	I-Device
models	O
also	O
implement	O
the	O
double	O
resolution	O
graphics	O
modes	O
.	O
</s>
<s>
Under	O
Applesoft	B-Language
BASIC	I-Language
,	O
enabling	O
this	O
mode	O
required	O
three	O
steps	O
.	O
</s>
<s>
(	O
Only	O
the	O
Apple	O
IIc	O
and	O
IIgs	B-Device
supported	O
this	O
in	O
firmware	O
.	O
</s>
<s>
Using	O
Double	O
Lo-Res	O
mode	O
from	O
BASIC	O
on	O
a	O
IIe	B-Device
was	O
much	O
more	O
complicated	O
without	O
adding	O
an	O
&	O
command	O
extension	O
to	O
BASIC	O
.	O
)	O
</s>
<s>
Second	O
,	O
the	O
SCRN	O
(	O
pixel	B-Algorithm
read	O
)	O
function	O
did	O
not	O
work	O
properly	O
.	O
</s>
<s>
At	O
least	O
one	O
commercially	O
available	O
BASIC	O
compiler	B-Language
,	O
ZBASIC	B-Application
from	O
Zedcor	O
Systems	O
,	O
was	O
known	O
to	O
support	O
Double	O
Lo-Res	O
graphics	O
.	O
</s>
<s>
In	O
addition	O
to	O
the	O
64:1	O
interleaving	B-Application
,	O
the	O
pixels	B-Algorithm
in	O
the	O
individual	O
rows	O
are	O
stored	O
in	O
an	O
unusual	O
way	O
:	O
each	O
pixel	B-Algorithm
was	O
half	O
its	O
usual	O
width	O
and	O
each	O
byte	B-Application
of	O
pixels	B-Algorithm
alternated	O
between	O
the	O
first	O
and	O
second	O
bank	O
of	O
64KB	O
memory	B-Architecture
.	O
</s>
<s>
Where	O
three	O
consecutive	O
on	O
pixels	B-Algorithm
were	O
white	O
,	O
six	O
were	O
now	O
required	O
in	O
double	O
high-resolution	O
.	O
</s>
<s>
Effectively	O
,	O
all	O
pixel	B-Algorithm
patterns	O
used	O
to	O
make	O
color	O
in	O
Lo-Res	O
graphics	O
blocks	O
could	O
be	O
reproduced	O
in	O
Double	O
Hi-Res	O
graphics	O
.	O
</s>
<s>
The	O
ProDOS	B-Operating_System
implementation	O
of	O
its	O
RAM	B-Application
disk	I-Application
made	O
access	O
to	O
the	O
Double	O
Hi-Res	O
screen	O
easier	O
by	O
making	O
the	O
first	O
8	O
KB	O
file	O
saved	O
to	O
/RAM	O
store	O
its	O
data	O
at	O
0x012000	O
to	O
0x013fff	O
by	O
design	O
.	O
</s>
<s>
However	O
,	O
access	O
via	O
the	O
ProDOS	B-Operating_System
file	O
system	O
was	O
slow	O
and	O
not	O
well	O
suited	O
to	O
page-flipping	O
animation	O
in	O
Double	O
Hi-Res	O
,	O
beyond	O
the	O
memory	B-Architecture
requirements	O
.	O
</s>
<s>
Despite	O
the	O
complexities	O
involved	O
in	O
programming	B-General_Concept
and	O
using	O
this	O
mode	O
,	O
there	O
were	O
numerous	O
applications	O
which	O
made	O
use	O
of	O
it	O
.	O
</s>
<s>
The	O
Apple	O
version	O
of	O
GEOS	B-Device
used	O
Double	O
Hi-Res	O
,	O
as	O
did	O
Broderbund	O
's	O
paint	O
program	O
,	O
Dazzle	B-Application
Draw	I-Application
.	O
</s>
<s>
Beagle	O
Bros	O
provided	O
a	O
toolkit	O
,	O
Beagle	O
Graphics	O
,	O
with	O
routines	O
for	O
developing	O
Double	O
Hi-Res	O
graphics	O
in	O
AppleSoft	B-Language
BASIC	I-Language
.	O
</s>
<s>
Numerous	O
arcade	O
games	O
,	O
and	O
games	O
written	O
for	O
other	O
computers	O
,	O
were	O
ported	O
to	O
the	O
Apple	B-Device
II	I-Device
,	O
and	O
many	O
took	O
advantage	O
of	O
this	O
graphics	O
mode	O
.	O
</s>
<s>
In	O
addition	O
to	O
supporting	O
existing	O
modes	O
,	O
the	O
Apple	B-Device
IIGS	I-Device
adds	O
new	O
modes	O
similar	O
to	O
those	O
of	O
the	O
Atari	B-Device
ST	I-Device
and	O
Amiga	B-Device
.	O
</s>
