<s>
PackIt	B-Operating_System
is	O
a	O
software	O
data	B-General_Concept
compression	I-General_Concept
utility	O
for	O
archiving	O
and	O
compressing	O
files	O
on	O
the	O
Apple	B-Device
Macintosh	I-Device
platform	O
.	O
</s>
<s>
It	O
was	O
the	O
first	O
such	O
program	O
to	O
see	O
widespread	O
use	O
on	O
the	O
Mac	B-Device
,	O
and	O
most	O
Mac	B-Device
software	O
archives	O
accepted	O
uploads	O
only	O
in	O
PackIt	B-Operating_System
format	O
for	O
some	O
time	O
.	O
</s>
<s>
StuffIt	B-Application
,	O
introduced	O
in	O
the	O
summer	O
of	O
1987	O
,	O
offered	O
much	O
improved	O
compression	O
,	O
and	O
PackIt	B-Operating_System
quickly	O
disappeared	O
.	O
</s>
<s>
PackIt	B-Operating_System
was	O
written	O
by	O
Harry	O
Chesley	O
to	O
support	O
an	O
online	O
magazine	O
he	O
was	O
writing	O
for	O
at	O
the	O
time	O
,	O
MacDeveloper	O
.	O
</s>
<s>
In	O
the	O
original	O
version	O
this	O
was	O
done	O
in	O
a	O
simple	O
manner	O
,	O
simply	O
placing	O
the	O
Finder	O
file	B-Operating_System
information	O
,	O
data	B-Operating_System
fork	I-Operating_System
and	O
resource	B-Operating_System
fork	I-Operating_System
,	O
if	O
present	O
,	O
in	O
a	O
single	O
stream	O
and	O
placing	O
the	O
resulting	O
"	O
block	O
"	O
in	O
the	O
archive	O
.	O
</s>
<s>
No	O
compression	O
was	O
used	O
,	O
the	O
program	O
was	O
purely	O
an	O
archiver	O
,	O
similar	O
to	O
the	O
Unix	B-Application
tar	B-Application
utility	O
in	O
concept	O
.	O
</s>
<s>
Like	O
tar	B-Application
,	O
the	O
format	O
did	O
not	O
include	O
an	O
archive	O
header	O
of	O
any	O
sort	O
.	O
</s>
<s>
To	O
extract	O
the	O
nth	O
file	B-Operating_System
,	O
PackIt	B-Operating_System
had	O
to	O
read	O
past	O
all	O
of	O
the	O
n-1	O
files	O
first	O
.	O
</s>
<s>
PackIt	B-Operating_System
II	O
was	O
released	O
in	O
early	O
1986	O
and	O
added	O
Huffman	B-General_Concept
encoding	I-General_Concept
.	O
</s>
<s>
However	O
the	O
encoding	O
was	O
applied	O
after	O
the	O
file	B-Operating_System
had	O
already	O
been	O
"	O
grouped	O
"	O
together	O
,	O
meaning	O
that	O
the	O
compressor	O
had	O
to	O
work	O
on	O
the	O
file	B-Operating_System
as	O
a	O
whole	O
,	O
or	O
not	O
at	O
all	O
.	O
</s>
<s>
Since	O
Mac	B-Device
files	O
often	O
consisted	O
of	O
text	O
in	O
the	O
data	B-Operating_System
fork	I-Operating_System
and	O
binary	O
data	O
in	O
the	O
resource	B-Operating_System
fork	I-Operating_System
,	O
compressing	O
these	O
separately	O
and	O
then	O
joining	O
them	O
together	O
would	O
likely	O
offer	O
better	O
compression	O
overall	O
.	O
</s>
<s>
PackIt	B-Operating_System
III	O
,	O
released	O
in	O
mid-1986	O
,	O
added	O
DES	B-Algorithm
encryption	I-Algorithm
.	O
</s>
<s>
According	O
to	O
Chesley	O
this	O
option	O
was	O
not	O
widely	O
used	O
,	O
but	O
nevertheless	O
PackIt	B-Operating_System
III	O
became	O
the	O
de	O
facto	O
standard	O
compression/archiving	O
system	O
on	O
the	O
Mac	B-Device
through	O
this	O
period	O
.	O
</s>
<s>
In	O
December	O
1986	O
he	O
joined	O
Apple	O
Computer	O
,	O
and	O
work	O
on	O
PackIt	B-Operating_System
ended	O
.	O
</s>
<s>
In	O
comparison	O
,	O
StuffIt	B-Application
supported	O
the	O
newer	O
LZW-type	O
compression	O
system	O
and	O
compressed	O
the	O
data	O
and	O
resource	B-Operating_System
forks	I-Operating_System
separately	O
.	O
</s>
<s>
The	O
files	O
were	O
then	O
stored	O
with	O
a	O
single	O
universal	O
header	O
,	O
allowing	O
the	O
program	O
to	O
quickly	O
list	O
the	O
archive	O
contents	O
,	O
as	O
well	O
as	O
uncompress	O
a	O
single	O
file	B-Operating_System
,	O
without	O
having	O
to	O
"	O
scan	O
"	O
through	O
the	O
archive	O
.	O
</s>
<s>
This	O
made	O
StuffIt	B-Application
much	O
easier	O
and	O
faster	O
to	O
use	O
in	O
practice	O
.	O
</s>
<s>
Archives	O
created	O
with	O
PackIt	B-Operating_System
used	O
the	O
file	B-Operating_System
extension	O
.	O
</s>
<s>
File	B-Operating_System
extensions	O
are	O
not	O
normally	O
needed	O
on	O
the	O
Mac	B-Device
,	O
but	O
were	O
commonly	O
used	O
on	O
archives	O
because	O
they	O
would	O
typically	O
be	O
stored	O
on	O
some	O
other	O
system	O
that	O
would	O
require	O
them	O
(	O
PC	O
's	O
for	O
instance	O
)	O
.	O
</s>
<s>
These	O
files	O
were	O
generally	O
stored	O
in	O
MacBinary	B-General_Concept
format	O
on	O
such	O
machines	O
,	O
however	O
,	O
making	O
the	O
extension	O
somewhat	O
superfluous	O
.	O
</s>
<s>
Later	O
versions	O
of	O
PackIt	B-Operating_System
would	O
recognize	O
a	O
MacBinary	B-General_Concept
header	O
if	O
it	O
had	O
been	O
left	O
on	O
,	O
and	O
strip	O
it	O
off	O
automatically	O
.	O
</s>
