<s>
Extension	B-Operating_System
conflicts	I-Operating_System
were	O
sometimes	O
a	O
common	O
nuisance	O
on	O
Apple	B-Device
Macintosh	I-Device
computers	I-Device
running	O
the	O
classic	B-Application
Mac	I-Application
OS	I-Application
,	O
especially	O
System	B-Operating_System
7	I-Operating_System
.	O
</s>
<s>
Extensions	O
were	O
bundles	O
of	O
code	O
that	O
extended	O
the	O
operating	B-General_Concept
system	I-General_Concept
's	O
capabilities	O
by	O
directly	O
patching	O
OS	B-Operating_System
calls	I-Operating_System
,	O
thus	O
receiving	O
control	O
instead	O
of	O
the	O
operating	B-General_Concept
system	I-General_Concept
when	O
applications	B-Application
(	O
including	O
the	O
Finder	B-Application
)	O
made	O
system	B-Operating_System
calls	I-Operating_System
.	O
</s>
<s>
Generally	O
,	O
once	O
an	O
extension	B-Operating_System
completed	O
its	O
task	O
,	O
it	O
was	O
supposed	O
to	O
pass	O
on	O
the	O
(	O
possibly	O
modified	O
)	O
system	B-Operating_System
call	I-Operating_System
to	O
the	O
operating	B-General_Concept
system	I-General_Concept
's	O
routine	O
.	O
</s>
<s>
If	O
multiple	O
extensions	O
want	O
to	O
patch	O
the	O
same	O
system	B-Operating_System
call	I-Operating_System
,	O
they	O
end	O
up	O
receiving	O
the	O
call	O
in	O
a	O
chain	O
,	O
the	O
first	O
extension	B-Operating_System
in	O
line	O
passing	O
it	O
on	O
to	O
the	O
next	O
,	O
and	O
so	O
on	O
in	O
the	O
order	O
they	O
are	O
loaded	O
,	O
until	O
the	O
last	O
extension	B-Operating_System
passes	O
to	O
the	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
If	O
an	O
extension	B-Operating_System
does	O
not	O
hand	O
the	O
next	O
extension	B-Operating_System
in	O
line	O
what	O
it	O
is	O
expecting	O
,	O
problems	O
occur	O
;	O
ranging	O
from	O
unexpected	O
behavior	O
to	O
full	O
system	B-General_Concept
crashes	I-General_Concept
.	O
</s>
<s>
This	O
is	O
triggered	O
by	O
several	O
factors	O
such	O
as	O
carelessly	O
programmed	O
and	O
malicious	O
extensions	O
that	O
change	O
or	O
disrupt	O
the	O
way	O
part	O
of	O
the	O
system	B-Application
software	I-Application
works	O
.	O
</s>
<s>
In	O
addition	O
,	O
extensions	O
sometimes	O
competed	O
for	O
system	O
resources	O
with	O
applications	B-Application
,	O
utilities	O
and	O
other	O
extensions	O
,	O
leading	O
to	O
crashes	B-General_Concept
and	O
general	O
instability	O
.	O
</s>
<s>
Some	O
users	O
happily	O
loaded	O
every	O
extension	B-Operating_System
they	O
could	O
find	O
on	O
their	O
computer	O
,	O
with	O
little	O
or	O
no	O
impact	O
.	O
</s>
<s>
This	O
problem	O
increased	O
during	O
the	O
mid-1990s	O
as	O
resource-hungry	O
multimedia	O
technologies	O
such	O
as	O
QuickTime	B-Application
were	O
installed	O
as	O
extensions	O
.	O
</s>
<s>
In	O
addition	O
,	O
a	O
number	O
of	O
applications	B-Application
,	O
especially	O
Microsoft	B-Application
Office	I-Application
,	O
required	O
a	O
large	O
number	O
of	O
extensions	O
.	O
</s>
<s>
Many	O
Macintosh	B-Device
users	O
had	O
hundreds	O
of	O
extensions	O
running	O
on	O
their	O
systems	O
,	O
all	O
of	O
varying	O
age	O
and	O
quality	O
.	O
</s>
<s>
Buggy	B-Error_Name
,	O
damaged	O
and	O
outdated	O
extensions	O
were	O
the	O
most	O
common	O
cause	O
of	O
problems	O
.	O
</s>
<s>
Later	O
versions	O
of	O
System	B-Operating_System
7	I-Operating_System
included	O
the	O
Extensions	B-Operating_System
Manager	I-Operating_System
,	O
which	O
allowed	O
users	O
to	O
disable	O
specific	O
extensions	O
or	O
groups	O
of	O
extensions	O
at	O
startup	O
when	O
troubleshooting	O
the	O
conflict	O
by	O
pressing	O
the	O
spacebar	O
while	O
the	O
computer	O
boots	O
.	O
</s>
<s>
This	O
tool	O
was	O
also	O
accessible	O
by	O
opening	O
the	O
Extensions	O
CDEV	O
in	O
the	O
Control	B-Operating_System
Panels	I-Operating_System
found	O
in	O
the	O
Apple	O
menu	O
.	O
</s>
<s>
Conflict	B-Application
Catcher	I-Application
and	O
Now	O
Startup	O
Manager	O
were	O
third	O
party	O
utilities	O
that	O
automatically	O
detected	O
conflicts	O
and	O
problematic	O
extensions	O
and	O
other	O
software	O
executing	O
at	O
boot	O
,	O
otherwise	O
a	O
time-consuming	O
task	O
that	O
required	O
users	O
to	O
turn	O
off	O
extensions	O
in	O
sets	O
until	O
they	O
found	O
the	O
conflict	O
,	O
as	O
well	O
as	O
allowing	O
load	O
order	O
to	O
be	O
altered	O
without	O
renaming	O
items	O
.	O
</s>
<s>
The	O
most	O
common	O
time	O
for	O
extension	B-Operating_System
conflicts	I-Operating_System
to	O
start	O
was	O
the	O
release	O
of	O
a	O
new	O
version	O
of	O
the	O
operating	B-General_Concept
system	I-General_Concept
,	O
followed	O
closely	O
by	O
the	O
installation	O
of	O
a	O
complex	O
new	O
application	O
that	O
either	O
conflicted	O
with	O
existing	O
extensions	O
,	O
or	O
installed	O
extensions	O
that	O
conflicted	O
with	O
the	O
existing	O
set	O
.	O
</s>
<s>
All	O
of	O
this	O
was	O
mitigated	O
by	O
the	O
ease	O
with	O
which	O
extensions	O
and	O
the	O
operating	B-General_Concept
system	I-General_Concept
itself	O
could	O
be	O
swapped	O
in	O
and	O
out	O
:	O
Instead	O
of	O
modifying	O
configuration	O
files	O
as	O
on	O
other	O
operating	B-General_Concept
systems	I-General_Concept
,	O
extensions	O
and	O
other	O
automatically	O
run	O
software	O
simply	O
had	O
to	O
reside	O
in	O
a	O
particular	O
subfolder	O
of	O
the	O
System	O
Folder	O
to	O
be	O
picked	O
up	O
.	O
</s>
<s>
And	O
load	O
their	O
order	O
could	O
be	O
altered	O
by	O
renaming	O
items	O
in	O
the	O
Finder	B-Application
,	O
based	O
on	O
descending	O
ASCIIbetical	O
order	O
for	O
each	O
System	O
subfolder	O
.	O
</s>
<s>
In	O
addition	O
,	O
the	O
Mac	B-Device
was	O
perfectly	O
happy	O
to	O
have	O
two	O
(	O
or	O
more	O
)	O
System	O
Folders	O
present	O
on	O
a	O
hard	O
drive	O
.	O
</s>
<s>
So	O
,	O
when	O
a	O
new	O
version	O
of	O
the	O
operating	B-General_Concept
system	I-General_Concept
was	O
to	O
be	O
installed	O
,	O
or	O
a	O
new	O
application	O
,	O
the	O
user	O
could	O
easily	O
duplicate	O
the	O
system	O
folder	O
,	O
perform	O
the	O
install	O
,	O
and	O
then	O
fall	O
back	O
if	O
a	O
problem	O
resulted	O
.	O
</s>
<s>
Extension	B-Operating_System
conflicts	I-Operating_System
came	O
to	O
an	O
end	O
with	O
the	O
release	O
of	O
Mac	B-Application
OS	I-Application
X	I-Application
,	O
which	O
uses	O
a	O
different	O
extension	B-Operating_System
mechanism	O
.	O
</s>
<s>
Software	O
can	O
still	O
add	O
new	O
features	O
to	O
the	O
Mac	B-Device
but	O
instead	O
of	O
requiring	O
a	O
kernel	O
extension	B-Operating_System
,	O
the	O
new	O
method	O
has	O
allowed	O
Apple	O
to	O
push	O
more	O
and	O
more	O
extensions	O
into	O
user	B-Operating_System
space	I-Operating_System
,	O
which	O
is	O
a	O
safer	O
and	O
more	O
organized	O
approach	O
that	O
cannot	O
destabilize	O
the	O
entire	O
machine	O
.	O
</s>
