<s>
The	O
Berkeley	O
Network	O
,	O
or	O
Berknet	B-Operating_System
,	O
was	O
an	O
early	O
wide	O
area	O
network	O
,	O
developed	O
at	O
the	O
University	O
of	O
California	O
,	O
Berkeley	O
in	O
1978	O
,	O
primarily	O
by	O
Eric	O
Schmidt	O
as	O
part	O
of	O
his	O
master	O
's	O
thesis	O
work	O
.	O
</s>
<s>
The	O
network	O
continuously	O
connected	O
about	O
a	O
dozen	O
computers	O
running	O
BSD	B-Operating_System
and	O
provided	O
email	O
,	O
file	B-Protocol
transfer	I-Protocol
,	O
printing	O
and	O
remote	B-Protocol
command	I-Protocol
execution	I-Protocol
services	O
to	O
its	O
users	O
,	O
and	O
it	O
connected	O
to	O
the	O
two	O
other	O
major	O
networks	O
in	O
use	O
at	O
the	O
time	O
,	O
the	O
ARPANET	O
and	O
UUCPNET	O
.	O
</s>
<s>
The	O
network	O
operated	O
using	O
what	O
were	O
then	O
high-speed	O
serial	B-Protocol
links	I-Protocol
,	O
1200bps	O
in	O
the	O
initial	O
system	O
.	O
</s>
<s>
Its	O
software	O
implementation	O
shipped	O
with	O
the	O
Berkeley	B-Operating_System
Software	I-Operating_System
Distribution	I-Operating_System
from	O
version	O
2.0	O
onwards	O
.	O
</s>
<s>
It	O
consisted	O
of	O
a	O
line	B-Operating_System
discipline	I-Operating_System
within	O
the	O
Unix	B-Application
kernel	B-Operating_System
,	O
a	O
set	O
of	O
daemons	B-Operating_System
that	O
managed	O
queues	O
of	O
commands	O
to	O
be	O
sent	O
across	O
machines	O
,	O
and	O
a	O
set	O
of	O
user-level	O
programs	O
that	O
enqueued	O
the	O
actual	O
commands	O
.	O
</s>
<s>
The	O
release	O
of	O
UUCP	B-Protocol
as	O
part	O
of	O
Version	B-Operating_System
7	I-Operating_System
Unix	I-Operating_System
in	O
1979	O
led	O
to	O
little	O
external	O
interest	O
in	O
the	O
system	O
;	O
</s>
<s>
Mary	O
Ann	O
Horton	O
noted	O
in	O
1984	O
that	O
"	O
Berknets	B-Operating_System
are	O
gone	O
now	O
"	O
.	O
</s>
<s>
Support	O
for	O
Berknet	B-Operating_System
's	O
custom	O
email	O
addressing	O
scheme	O
was	O
provided	O
in	O
the	O
Sendmail	B-Application
program	O
until	O
1993	O
.	O
</s>
<s>
The	O
development	O
of	O
what	O
became	O
Berknet	B-Operating_System
began	O
with	O
an	O
initial	O
concept	O
developed	O
by	O
Bob	O
Fabry	O
,	O
Eric	O
Schmidt	O
's	O
advisor	O
.	O
</s>
<s>
The	O
system	O
was	O
initially	O
designed	O
to	O
connect	O
only	O
two	O
machines	O
,	O
known	O
as	O
A	O
and	O
Q	O
,	O
both	O
PDP-11	B-Device
machines	O
running	O
Unix	B-Application
.	O
</s>
<s>
Dealing	O
with	O
this	O
problem	O
was	O
initially	O
handled	O
by	O
having	O
dedicated	O
"	O
free	O
"	O
accounts	O
on	O
both	O
machines	O
that	O
was	O
used	O
by	O
Berknet	B-Operating_System
,	O
along	O
with	O
using	O
the	O
file	O
to	O
automatically	O
log	O
into	O
them	O
when	O
needed	O
.	O
</s>
<s>
While	O
he	O
was	O
away	O
,	O
the	O
Computing	O
Center	O
made	O
several	O
changes	O
to	O
the	O
system	O
,	O
and	O
this	O
led	O
to	O
several	O
incompatible	O
versions	O
of	O
Berknet	B-Operating_System
emerging	O
,	O
and	O
periodic	O
breakage	O
of	O
the	O
system	O
,	O
including	O
the	O
sendmail	B-Application
system	O
not	O
working	O
.	O
</s>
<s>
By	O
the	O
time	O
Schmidt	O
returned	O
to	O
the	O
system	O
in	O
October	O
,	O
a	O
VAX	O
11/780	O
machine	O
had	O
been	O
added	O
,	O
bringing	O
the	O
total	O
to	O
three	O
different	O
versions	O
of	O
Unix	B-Application
being	O
supported	O
.	O
</s>
<s>
make	B-Application
was	O
then	O
used	O
to	O
build	O
and	O
distribute	O
the	O
code	O
to	O
the	O
machines	O
,	O
including	O
using	O
the	O
older	O
version	O
of	O
the	O
code	O
to	O
bootstrap	O
the	O
Cory	O
machine	O
,	O
which	O
ran	O
Unix	B-Application
Version	O
6	O
while	O
the	O
others	O
ran	O
7	O
.	O
</s>
<s>
The	O
system	O
had	O
some	O
resemblance	O
to	O
UUCP	B-Protocol
in	O
that	O
it	O
used	O
a	O
batch	B-General_Concept
mode	I-General_Concept
file	B-Protocol
transfer	I-Protocol
system	O
based	O
on	O
a	O
Unix	B-Operating_System
daemon	I-Operating_System
that	O
performed	O
the	O
actual	O
transfers	O
,	O
as	O
well	O
as	O
defining	O
a	O
suitable	O
simple	O
network	O
protocol	O
to	O
move	O
the	O
data	O
over	O
the	O
telephone-based	O
links	O
.	O
</s>
<s>
When	O
a	O
file	O
appears	O
,	O
starts	O
a	O
terminal	O
connection	O
to	O
the	O
selected	O
remote	O
machine	O
,	O
issues	O
commands	O
and	O
performs	O
file	B-Protocol
transfers	I-Protocol
,	O
and	O
then	O
disconnects	O
and	O
deletes	O
the	O
local	O
file	O
if	O
it	O
was	O
a	O
success	O
.	O
</s>
<s>
From	O
a	O
user	O
's	O
perspective	O
,	O
there	O
are	O
a	O
number	O
of	O
separate	O
applications	O
that	O
make	B-Application
up	O
the	O
system	O
,	O
ones	O
for	O
reading	O
and	O
writing	O
mail	O
,	O
one	O
for	O
moving	O
files	O
between	O
machines	O
,	O
etc	O
.	O
</s>
<s>
Paths	O
were	O
a	O
combination	O
of	O
a	O
machine	O
name	O
followed	O
by	O
a	O
colon	O
,	O
and	O
then	O
a	O
normal	O
Unix	B-Application
slash-separated	O
path	O
.	O
</s>
<s>
The	O
uppermost	O
was	O
the	O
command	O
protocol	O
,	O
which	O
defined	O
the	O
overall	O
file	O
structure	O
,	O
below	O
this	O
was	O
the	O
stream	O
protocol	O
,	O
which	O
broke	O
the	O
file	O
into	O
multiple	O
packets	O
,	O
and	O
at	O
the	O
bottom	O
was	O
the	O
hardware	O
layer	O
using	O
the	O
serial	B-Protocol
ports	I-Protocol
.	O
</s>
<s>
The	O
header	O
data	O
is	O
written	O
as	O
normal	O
ASCII	B-Protocol
text	I-Protocol
with	O
the	O
fields	O
separated	O
by	O
colons	O
.	O
</s>
<s>
During	O
a	O
transfer	O
,	O
the	O
file	O
is	O
broken	O
into	O
packets	O
for	O
error	B-Error_Name
correction	I-Error_Name
purposes	O
.	O
</s>
<s>
The	O
packets	O
have	O
a	O
header	O
consisting	O
of	O
a	O
length	O
byte	O
that	O
allows	O
up	O
to	O
255	O
bytes	O
in	O
a	O
packet	O
,	O
followed	O
by	O
a	O
two-byte	O
packet	O
number	O
,	O
a	O
one-byte	O
type	O
indicator	O
,	O
a	O
one-byte	O
checksum	B-Algorithm
,	O
and	O
then	O
the	O
data	O
.	O
</s>
<s>
The	O
checksum	B-Algorithm
is	O
placed	O
at	O
the	O
front	O
because	O
the	O
packets	O
are	O
variable	O
length	O
,	O
and	O
this	O
simplified	O
the	O
code	O
.	O
</s>
<s>
The	O
protocol	O
was	O
very	O
similar	O
to	O
XMODEM	B-Protocol
in	O
complexity	O
,	O
lacking	O
sliding	O
windows	O
or	O
streaming	O
acknowledgement	O
,	O
features	O
that	O
were	O
considered	O
important	O
to	O
add	O
to	O
future	O
versions	O
.	O
</s>
<s>
At	O
the	O
hardware	O
level	O
,	O
the	O
system	O
was	O
simply	O
a	O
serial	B-Protocol
port	I-Protocol
connecting	O
two	O
machines	O
.	O
</s>
<s>
However	O
,	O
the	O
existing	O
Unix	B-Application
systems	I-Application
could	O
not	O
directly	O
process	O
8-bit	O
ASCII	B-Protocol
data	O
without	O
considerable	O
overhead	O
,	O
so	O
the	O
data	O
being	O
sent	O
is	O
encoded	O
with	O
three	O
8-bit	O
bytes	O
packaged	O
into	O
four	O
6-bit	O
characters	O
in	O
the	O
printable	O
range	O
.	O
</s>
