<s>
A	O
desk	B-Application
accessory	I-Application
(	O
DA	O
)	O
in	O
computing	O
is	O
a	O
small	O
transient	B-General_Concept
or	I-General_Concept
auxiliary	I-General_Concept
application	I-General_Concept
that	O
can	O
be	O
run	O
concurrently	O
in	O
a	O
desktop	O
environment	O
with	O
any	O
other	O
application	O
on	O
the	O
system	O
.	O
</s>
<s>
Early	O
examples	O
,	O
such	O
as	O
Sidekick	B-Application
and	O
Macintosh	B-Device
desk	B-Application
accessories	I-Application
,	O
used	O
special	O
programming	O
models	O
to	O
provide	O
a	O
small	O
degree	O
of	O
multitasking	B-Operating_System
on	O
systems	O
that	O
initially	O
did	O
not	O
have	O
any	O
other	O
multitasking	B-Operating_System
ability	O
.	O
</s>
<s>
Early	O
personal	O
information	O
managers	O
,	O
such	O
as	O
Norton	O
Desktop	O
and	O
Borland	O
's	O
Sidekick	B-Application
,	O
provided	O
pop-up	O
calculator	O
,	O
alarm	O
,	O
calendar	O
and	O
other	O
functions	O
for	O
single-tasking	O
operating	O
systems	O
like	O
MS-DOS	O
using	O
terminate-and-stay-resident	O
techniques	O
.	O
</s>
<s>
Introduced	O
in	O
1984	O
as	O
part	O
of	O
the	B-Application
operating	I-Application
system	I-Application
for	O
the	O
Apple	B-Device
Macintosh	I-Device
computer	I-Device
,	O
a	O
Desk	B-Application
Accessory	I-Application
(	O
DA	O
)	O
was	O
a	O
piece	O
of	O
software	O
written	O
as	O
a	O
device	B-Application
driver	I-Application
,	O
conforming	O
to	O
a	O
particular	O
programming	O
model	O
.	O
</s>
<s>
This	O
provided	O
a	O
small	O
degree	O
of	O
multitasking	B-Operating_System
on	O
a	O
system	O
that	O
initially	O
did	O
not	O
have	O
any	O
other	O
multitasking	B-Operating_System
ability	O
.	O
</s>
<s>
DAs	O
were	O
implemented	O
as	O
a	O
special	O
class	O
of	O
driver	B-Application
.	O
</s>
<s>
It	O
was	O
installed	O
in	O
the	O
driver	B-Application
queue	O
,	O
and	O
given	O
time	O
periodically	O
and	O
co-operatively	O
as	O
a	O
result	O
of	O
the	O
host	O
application	O
calling	O
SystemTask( )	O
within	O
its	O
main	B-General_Concept
loop	I-General_Concept
.	O
</s>
<s>
The	O
control	B-Operating_System
panel	I-Operating_System
,	O
Chooser	B-Operating_System
,	O
and	O
Scrapbook	B-Application
were	O
initially	O
implemented	O
as	O
DAs	O
.	O
</s>
<s>
However	O
,	O
since	O
on	O
the	O
early	O
Mac	B-Application
OS	I-Application
drivers	O
did	O
not	O
have	O
any	O
special	O
privileges	O
,	O
writing	O
a	O
DA	O
was	O
,	O
with	O
practice	O
,	O
no	O
more	O
difficult	O
than	O
any	O
other	O
application	O
.	O
</s>
<s>
A	O
special	O
Font/DA	B-Application
Mover	I-Application
utility	O
was	O
used	O
to	O
change	O
the	O
configuration	O
of	O
DAs	O
.	O
</s>
<s>
They	O
resided	O
in	O
the	O
System	O
file	O
's	O
'	O
DRVR	O
 '	O
resources	B-Operating_System
,	O
like	O
actual	O
drivers	O
,	O
though	O
they	O
could	O
be	O
installed	O
in	O
any	O
file	O
whose	O
resources	B-Operating_System
were	O
loaded	O
into	O
the	O
memory	O
,	O
and	O
were	O
stored	O
in	O
"	O
suitcases	O
"	O
when	O
not	O
installed	O
in	O
the	O
system	O
file	O
.	O
</s>
<s>
That	O
is	O
,	O
a	O
desk	B-Application
accessory	I-Application
installed	O
as	O
a	O
resource	O
within	O
an	O
application	O
would	O
appear	O
on	O
the	O
Apple	O
menu	O
as	O
a	O
desk	B-Application
accessory	I-Application
only	O
when	O
that	O
application	O
was	O
active	O
.	O
</s>
<s>
(	O
Similarly	O
,	O
the	O
FKEY	O
resources	B-Operating_System
could	O
be	O
installed	O
either	O
within	O
the	O
System	O
so	O
as	O
to	O
be	O
universally	O
available	O
,	O
or	O
within	O
an	O
application	O
so	O
as	O
to	O
be	O
available	O
only	O
when	O
that	O
application	O
was	O
active	O
)	O
.	O
</s>
<s>
As	O
a	O
resource	O
numbering	O
scheme	O
was	O
implemented	O
for	O
marking	O
resources	B-Operating_System
as	O
belonging	O
to	O
another	O
resource	O
of	O
some	O
particular	O
type	O
and	O
number	O
in	O
the	O
same	O
file	O
,	O
such	O
as	O
a	O
DA	O
( 	O
 '	O
DRVR	O
 '	O
)	O
,	O
it	O
was	O
possible	O
for	O
desk	B-Application
accessories	I-Application
to	O
have	O
a	O
limited	O
"	O
resource	B-Operating_System
fork	I-Operating_System
"	O
of	O
their	O
own	O
within	O
the	O
file	O
they	O
were	O
contained	O
in	O
;	O
the	O
mover	O
utility	O
recognised	O
such	O
resources	B-Operating_System
and	O
moved	O
them	O
along	O
with	O
the	O
actual	O
DA	O
code	O
resource	O
they	O
were	O
associated	O
with	O
.	O
</s>
<s>
With	O
the	O
advent	O
of	O
System	B-Operating_System
7	I-Operating_System
,	O
which	O
included	O
a	O
standard	O
cooperative	B-Operating_System
multitasking	I-Operating_System
feature	O
,	O
the	O
need	O
for	O
DAs	O
diminished	O
greatly	O
,	O
and	O
developers	O
were	O
encouraged	O
to	O
develop	O
small	O
applications	O
instead	O
.	O
</s>
<s>
Under	O
System	B-Operating_System
7	I-Operating_System
and	O
later	O
,	O
DAs	O
could	O
be	O
moved	O
and	O
renamed	O
using	O
the	O
Finder	O
like	O
normal	O
applications	O
,	O
removing	O
the	O
need	O
for	O
Font/DA	B-Application
Mover	I-Application
and	O
confining	O
suitcases	O
to	O
font	O
management	O
.	O
</s>
<s>
When	O
a	O
DA	O
was	O
run	O
under	O
System	B-Operating_System
7	I-Operating_System
,	O
it	O
always	O
executed	O
in	O
the	O
Finder	O
's	O
address	B-General_Concept
space	I-General_Concept
.	O
</s>
<s>
The	O
icon	O
for	O
a	O
desk	B-Application
accessory	I-Application
program	O
under	O
System	B-Operating_System
7	I-Operating_System
and	O
later	O
is	O
roughly	O
a	O
reversed	O
version	O
of	O
the	O
application	O
icon	O
,	O
with	O
the	O
writing	O
hand	O
on	O
the	O
left	O
side	O
instead	O
of	O
the	O
right	O
.	O
</s>
<s>
A	O
similar	O
mechanism	O
to	O
allow	O
small	O
utility	O
programs	O
to	O
run	O
along	O
with	O
regular	O
applications	O
was	O
also	O
present	O
in	O
the	B-Application
operating	I-Application
system	I-Application
for	O
the	O
Apple	B-Device
IIGS	I-Device
and	O
Apple	B-Device
IIe	I-Device
.	O
</s>
<s>
GEM	B-Application
resembled	O
the	O
Macintosh	B-Device
closely	O
in	O
many	O
respects	O
.	O
</s>
<s>
One	O
example	O
was	O
the	O
presence	O
of	O
desk	B-Application
accessories	I-Application
,	O
for	O
the	O
same	O
reason	O
:	O
to	O
allow	O
multiple	O
programs	O
to	O
be	O
used	O
in	O
a	O
system	O
that	O
only	O
supported	O
one	O
full	O
application	O
at	O
a	O
time	O
(	O
although	O
GEM	B-Application
desk	B-Application
accessories	I-Application
used	O
task	B-Operating_System
switching	I-Operating_System
and	O
not	O
cooperative	B-Operating_System
multitasking	I-Operating_System
like	O
the	O
Macintosh	B-Device
.	O
)	O
</s>
<s>
From	O
a	O
programming	O
point	O
of	O
view	O
,	O
desk	B-Application
accessories	I-Application
were	O
implemented	O
,	O
like	O
other	O
GEM	B-Application
applications	O
,	O
as	O
DOS	O
.EXE	O
files	O
,	O
with	O
names	O
ending	O
with	O
.ACC	B-Application
(	O
Accessory	O
)	O
rather	O
than	O
.APP	B-Application
(	O
Application	O
)	O
.	O
</s>
<s>
Each	O
.ACC	B-Application
file	O
could	O
support	O
multiple	O
accessories	O
;	O
all	O
three	O
of	O
the	O
standard	O
GEM	B-Application
accessories	O
(	O
Calculator	O
,	O
Clock	O
and	O
Print	O
Spooler	O
)	O
were	O
provided	O
by	O
CALCLOCK.ACC	B-Application
.	O
</s>
<s>
Installation	O
was	O
simply	O
a	O
matter	O
of	O
placing	O
the	O
.ACC	B-Application
in	O
the	O
correct	O
directory	O
-	O
\GEMBOOT	O
in	O
earlier	O
versions	O
,	O
and	O
\GEMAPPS\GEMSYS	O
in	O
GEM/3	O
and	O
later	O
.	O
</s>
<s>
Since	O
each	O
desk	B-Application
accessory	I-Application
loaded	O
reduced	O
the	O
amount	O
of	O
memory	O
available	O
for	O
programs	O
,	O
one	O
technique	O
for	O
temporarily	O
increasing	O
available	O
space	O
was	O
to	O
rename	O
one	O
or	O
more	O
.ACC	B-Application
files	O
to	O
have	O
a	O
different	O
suffix	O
(	O
usually	O
.ACX	O
)	O
and	O
restart	O
GEM	B-Application
.	O
</s>
<s>
On	O
the	O
Amstrad	O
PC-1512	O
,	O
for	O
example	O
,	O
the	O
Snapshot	O
accessory	O
was	O
shipped	O
as	O
SNAPSHOT.ACX	O
and	O
had	O
to	O
be	O
renamed	O
to	O
.ACC	B-Application
prior	O
to	O
use	O
.	O
</s>
<s>
Desk	B-Application
accessories	I-Application
continued	O
to	O
be	O
supported	O
in	O
ViewMAX	B-Application
,	O
the	O
DR-DOS	B-Application
file	O
manager	O
,	O
which	O
was	O
supplied	O
with	O
almost	O
unchanged	O
versions	O
of	O
Calculator	O
and	O
Clock	O
.	O
</s>
<s>
For	O
much	O
the	O
same	O
reason	O
as	O
desk	B-Application
accessories	I-Application
were	O
used	O
in	O
Mac	B-Application
OS	I-Application
and	O
in	O
GEM	B-Application
,	O
namely	O
to	O
allow	O
more	O
than	O
one	O
simultaneous	O
program	O
on	O
a	O
system	O
which	O
did	O
not	O
support	O
multitasking	B-Operating_System
,	O
the	O
concept	O
of	O
desk	B-Application
accessories	I-Application
was	O
extended	O
to	O
Palm	O
OS	O
by	O
third-party	O
developers	O
.	O
</s>
<s>
The	O
DA	O
launcher	O
may	O
watch	O
for	O
keystrokes	O
or	O
other	O
system	O
events	O
and	O
pop	O
up	O
a	O
predefined	O
desk	B-Application
accessory	I-Application
.	O
</s>
<s>
A	O
desk	B-Application
accessory	I-Application
program	O
is	O
a	O
Palm	O
resource	O
database	O
of	O
type	O
'	O
DAcc	O
 '	O
,	O
specified	O
to	O
include	O
a	O
single	O
'	O
code	O
 '	O
#1000	O
resource	O
that	O
contains	O
the	O
binary	O
code	O
implementing	O
the	O
desk	B-Application
accessory	I-Application
.	O
</s>
<s>
It	O
is	O
possible	O
for	O
a	O
DA	O
to	O
have	O
user	O
interface	O
resources	B-Operating_System
in	O
its	O
database	O
.	O
</s>
<s>
The	O
desk	B-Application
accessory	I-Application
launcher	O
transfers	O
execution	O
to	O
the	O
first	O
byte	O
of	O
the	O
'	O
code	O
 '	O
#1000	O
resource	O
.	O
</s>
<s>
DAs	O
provide	O
a	O
modicum	O
of	O
multitasking	B-Operating_System
.	O
</s>
<s>
However	O
,	O
unlike	O
in	O
Mac	B-Application
OS	I-Application
and	O
GEM	B-Application
,	O
after	O
the	O
user	O
is	O
done	O
working	O
with	O
the	O
DA	O
,	O
it	O
must	O
be	O
closed	O
to	O
return	O
to	O
the	O
underlying	O
application	O
.	O
</s>
