<s>
The	O
Atari	B-Device
Program	I-Device
Recorder	I-Device
is	O
Atari	O
's	O
dedicated	O
magnetic	B-Architecture
tape	I-Architecture
data	I-Architecture
storage	I-Architecture
device	O
for	O
the	O
Atari	B-Device
8-bit	I-Device
family	I-Device
of	O
home	O
computers	O
.	O
</s>
<s>
The	O
data	O
rate	O
was	O
nominally	O
600bps	O
,	O
but	O
the	O
simple	O
error	B-Error_Name
correction	I-Error_Name
and	O
short	O
gaps	O
between	O
the	O
resulting	O
packets	B-Protocol
lowered	O
this	O
somewhat	O
.	O
</s>
<s>
In	O
the	O
end	O
,	O
its	O
rate	O
was	O
roughly	O
double	O
that	O
of	O
the	O
formats	O
used	O
by	O
the	O
Commodore	B-Device
Datasette	I-Device
or	O
the	O
TI-99/4	B-Device
.	O
</s>
<s>
The	O
system	O
's	O
device	B-Application
driver	I-Application
supported	O
a	O
packet-based	O
format	O
with	O
checksums	B-Algorithm
for	O
error	B-Error_Name
detection	I-Error_Name
,	O
as	O
opposed	O
to	O
lacking	O
any	O
error	B-Error_Name
detection	I-Error_Name
or	O
using	O
whole-file	O
checksums	B-Algorithm
.	O
</s>
<s>
The	O
original	O
400	O
and	O
800	O
models	O
,	O
released	O
in	O
1979	O
,	O
were	O
housed	O
in	O
robust	O
beige	O
colored	O
plastic	O
cases	O
and	O
a	O
series	O
of	O
computer	B-Device
peripherals	I-Device
were	O
released	O
to	O
match	O
this	O
design	O
.	O
</s>
<s>
The	O
release	O
of	O
the	O
600XL	B-Device
and	O
800XL	B-Device
in	O
1983	O
led	O
to	O
the	O
system	O
being	O
repackaged	O
in	O
a	O
much	O
smaller	O
form	O
,	O
the	O
1010	O
.	O
</s>
<s>
Only	O
small	O
numbers	O
seem	O
to	O
have	O
been	O
produced	O
,	O
as	O
by	O
this	O
time	O
floppy	B-Device
disks	I-Device
were	O
now	O
almost	O
universal	O
in	O
the	O
US	O
and	O
most	O
of	O
Europe	O
.	O
</s>
<s>
Most	O
sets	O
from	O
this	O
era	O
are	O
variations	O
on	O
the	O
XC12	O
,	O
using	O
a	O
Phonemark	O
PM-4401A	O
mechanism	O
,	O
the	O
same	O
unit	O
as	O
the	O
Commodore	B-Device
Datasette	I-Device
.	O
</s>
<s>
The	O
Atari	B-Device
8-bit	I-Device
family	I-Device
machines	O
featured	O
an	O
advanced	O
(	O
for	O
the	O
era	O
)	O
input/output	B-General_Concept
system	O
,	O
Atari	B-Architecture
SIO	I-Architecture
.	O
</s>
<s>
Devices	O
normally	O
had	O
in	O
and	O
out	O
ports	O
that	O
allowed	O
a	O
number	O
of	O
devices	O
to	O
be	O
daisy-chained	B-Application
together	O
into	O
a	O
single	O
port	O
on	O
the	O
host	O
computer	O
.	O
</s>
<s>
For	O
instance	O
,	O
the	O
Atari	B-Device
810	I-Device
floppy	B-Device
disk	I-Device
drive	I-Device
included	O
a	O
MOS	B-General_Concept
6507	I-General_Concept
that	O
watched	O
for	O
commands	O
being	O
sent	O
to	O
a	O
device	O
number	O
selected	O
using	O
switches	O
on	O
the	O
back	O
of	O
the	O
drive	O
.	O
</s>
<s>
When	O
being	O
used	O
to	O
write	O
data	O
,	O
the	O
POKEY	B-Device
chip	O
was	O
set	O
up	O
with	O
one	O
of	O
its	O
four	O
channels	O
producing	O
5327Hz	O
for	O
mark	O
and	O
another	O
to	O
3995Hz	O
for	O
space	O
,	O
while	O
a	O
third	O
channel	O
was	O
set	O
to	O
600Hz	O
and	O
used	O
as	O
a	O
clock	O
.	O
</s>
<s>
Data	O
sent	O
to	O
the	O
cassette	O
device	B-Application
driver	I-Application
toggled	O
which	O
of	O
the	O
two	O
tones	O
was	O
played	O
to	O
DATAOUT	O
while	O
being	O
timed	O
by	O
the	O
clock	O
.	O
</s>
<s>
During	O
playback	O
,	O
the	O
two	O
outputs	O
would	O
toggle	O
DATAIN	O
on	O
and	O
off	O
,	O
which	O
was	O
automatically	O
interpreted	O
by	O
the	O
POKEY	B-Device
and	O
reformed	O
into	O
a	O
series	O
of	O
bytes	O
for	O
storage	O
.	O
</s>
<s>
While	O
most	O
systems	O
of	O
the	O
era	O
wrote	O
bytes	O
of	O
data	O
with	O
no	O
particular	O
overall	O
format	O
,	O
Atari	O
's	O
driver	O
used	O
a	O
simple	O
packetized	B-Protocol
format	O
to	O
aid	O
in	O
error	B-Error_Name
detection	I-Error_Name
.	O
</s>
<s>
Data	O
was	O
split	O
into	O
packets	B-Protocol
of	O
128	O
bytes	O
and	O
then	O
sent	O
to	O
the	O
tape	O
with	O
three	O
header	O
bytes	O
and	O
a	O
single	O
checksum	B-Algorithm
byte	O
at	O
the	O
end	O
,	O
so	O
the	O
overall	O
packet	B-Protocol
was	O
132	O
bytes	O
long	O
.	O
</s>
<s>
The	O
first	O
two	O
bytes	O
were	O
01010101	O
01010101	O
,	O
used	O
for	O
clock	O
recovery	O
by	O
the	O
POKEY	B-Device
to	O
address	O
tape	O
stretch	O
and	O
other	O
common	O
problems	O
in	O
cassette	O
systems	O
.	O
</s>
<s>
The	O
next	O
byte	O
,	O
the	O
control	O
byte	O
,	O
specified	O
if	O
the	O
packet	B-Protocol
had	O
a	O
complete	O
128	O
bytes	O
of	O
data	O
,	O
less	O
than	O
that	O
,	O
or	O
was	O
a	O
special	O
end-of-file	O
(	O
EOF	O
)	O
marker	O
.	O
</s>
<s>
Only	O
the	O
packet	B-Protocol
immediately	O
preceding	O
the	O
EOF	O
could	O
be	O
in	O
the	O
shorter	O
format	O
,	O
with	O
the	O
number	O
of	O
used	O
bytes	O
placed	O
in	O
the	O
byte	O
preceding	O
end-of-packet	O
checksum	B-Algorithm
.	O
</s>
<s>
Both	O
the	O
short	O
packet	B-Protocol
and	O
EOF	O
packet	B-Protocol
were	O
padded	O
out	O
to	O
a	O
full	O
132	O
bytes	O
long	O
.	O
</s>
<s>
Between	O
packets	B-Protocol
,	O
the	O
system	O
played	O
the	O
mark	O
tone	O
continually	O
,	O
with	O
a	O
short	O
Pre-Record	O
Write	O
Tone	O
and	O
a	O
variable	O
length	O
Post-Record	O
Gap	O
,	O
the	O
two	O
combined	O
known	O
as	O
the	O
InterRecord	O
Gap	O
(	O
IRG	O
)	O
.	O
</s>
<s>
This	O
mode	O
was	O
used	O
for	O
most	O
transfers	O
,	O
leaving	O
just	O
enough	O
time	O
for	O
the	O
computer	O
to	O
calculate	O
the	O
checksum	B-Algorithm
and	O
potentially	O
stop	O
the	O
drive	O
if	O
the	O
checksum	B-Algorithm
failed	O
.	O
</s>
<s>
The	O
other	O
mode	O
,	O
Normal	O
IRG	O
,	O
played	O
a	O
3second	O
gap	O
between	O
packets	B-Protocol
.	O
</s>
<s>
This	O
time	O
was	O
selected	O
to	O
ensure	O
that	O
the	O
drive	O
could	O
be	O
stopped	O
and	O
restarted	O
without	O
it	O
having	O
advanced	O
past	O
the	O
next	O
packet	B-Protocol
.	O
</s>
<s>
Normal	O
IRG	O
was	O
not	O
widely	O
used	O
,	O
the	O
only	O
known	O
examples	O
being	O
assembler	B-Language
language	I-Language
programs	O
be	O
loaded	O
in	O
ATASCII	B-Protocol
format	O
,	O
and	O
the	O
much	O
more	O
rarely	O
used	O
ability	O
to	O
load	O
and	O
store	O
BASIC	B-Language
programming	I-Language
language	I-Language
as	O
text	O
.	O
</s>
<s>
This	O
consisted	O
of	O
a	O
single	O
extra	O
packet	B-Protocol
at	O
the	O
start	O
of	O
the	O
file	O
,	O
using	O
only	O
the	O
first	O
six	O
bytes	O
of	O
the	O
payload	O
and	O
filling	O
the	O
rest	O
of	O
the	O
packet	B-Protocol
with	O
zeros	O
.	O
</s>
<s>
The	O
second	O
byte	O
held	O
the	O
number	O
of	O
packets	B-Protocol
in	O
the	O
file	O
,	O
allowing	O
up	O
to	O
255	O
packets	B-Protocol
,	O
or	O
32kB	O
of	O
data	O
.	O
</s>
<s>
The	O
system	O
would	O
then	O
assert	O
the	O
MOTOR	O
line	O
to	O
begin	O
playback	O
,	O
reading	O
from	O
the	O
tape	O
for	O
up	O
to	O
35	O
seconds	O
looking	O
for	O
the	O
header	O
packet	B-Protocol
.	O
</s>
<s>
If	O
it	O
was	O
not	O
found	O
,	O
or	O
some	O
other	O
type	O
of	O
packet	B-Protocol
was	O
found	O
,	O
an	O
error	O
was	O
reported	O
.	O
</s>
<s>
Another	O
feature	O
of	O
the	O
Atari	B-Architecture
SIO	I-Architecture
port	O
was	O
the	O
AUDIOIN	O
pin	O
,	O
which	O
was	O
connected	O
to	O
the	O
left	O
channel	O
of	O
the	O
cassette	O
.	O
</s>
<s>
The	O
associated	O
program	O
would	O
then	O
turn	O
on	O
the	O
MOTOR	O
line	O
to	O
begin	O
playback	O
and	O
then	O
read	O
data	O
until	O
it	O
saw	O
a	O
series	O
of	O
ones	O
on	O
the	O
POKEY	B-Device
.	O
</s>
<s>
The	O
basic	O
signaling	O
rate	O
of	O
the	O
system	O
was	O
600bps	O
,	O
but	O
there	O
was	O
some	O
additional	O
overhead	O
due	O
to	O
the	O
inter-record	O
gaps	O
and	O
the	O
packet	B-Protocol
structure	O
.	O
</s>
<s>
This	O
compares	O
favorably	O
to	O
similar	O
systems	O
of	O
the	O
era	O
,	O
like	O
the	O
300bps	O
Kansas	B-Device
City	I-Device
Standard	I-Device
or	O
the	O
formats	O
used	O
on	O
the	O
TI-99/4	B-Device
or	O
Commodore	B-Device
Datasette	I-Device
,	O
which	O
had	O
similar	O
signaling	O
rates	O
as	O
Atari	O
but	O
wrote	O
all	O
data	O
twice	O
as	O
an	O
error	B-Error_Name
correction	I-Error_Name
mechanism	O
and	O
thus	O
had	O
effective	O
rates	O
closer	O
to	O
300bps	O
.	O
</s>
