<s>
A	O
reed	B-Algorithm
relay	I-Algorithm
is	O
a	O
type	O
of	O
relay	O
that	O
uses	O
an	O
electromagnet	O
to	O
control	O
one	O
or	O
more	O
reed	O
switches	O
.	O
</s>
<s>
Compared	O
with	O
armature-based	O
relays	O
,	O
reed	B-Algorithm
relays	I-Algorithm
can	O
switch	O
much	O
faster	O
,	O
as	O
the	O
moving	O
parts	O
are	O
small	O
and	O
lightweight	O
,	O
although	O
switch	O
bounce	O
is	O
still	O
present	O
.	O
</s>
<s>
A	O
few	O
million	O
reed	B-Algorithm
relays	I-Algorithm
were	O
used	O
from	O
the	O
1930s	O
to	O
the	O
1960s	O
for	O
memory	O
functions	O
in	O
Bell	O
System	O
electromechanical	O
telephone	O
exchanges	O
.	O
</s>
<s>
Most	O
reed	B-Algorithm
relays	I-Algorithm
in	O
the	O
crossbar	O
switching	O
systems	O
of	O
the	O
1940s	O
through	O
the	O
1970s	O
were	O
packaged	O
in	O
groups	O
of	O
five	O
.	O
</s>
<s>
Such	O
a	O
"	O
reed	O
pack	O
"	O
was	O
able	O
to	O
store	O
one	O
decimal	O
digit	O
,	O
encoded	O
in	O
a	O
two-out-of-five	O
code	O
(	O
74210	O
code	O
variant	O
)	O
for	O
easy	O
validity	O
checking	O
by	O
wire	B-Algorithm
spring	I-Algorithm
relay	I-Algorithm
logic	O
.	O
</s>
<s>
Such	O
an	O
electrically	O
latching	O
reed	B-Algorithm
relay	I-Algorithm
requires	O
continuous	O
power	O
to	O
maintain	O
state	O
,	O
unlike	O
magnetically	O
latching	O
relays	O
,	O
such	O
as	O
ferreed	O
(	O
ferrite	O
and	O
reed	B-Algorithm
relay	I-Algorithm
)	O
or	O
the	O
later	O
remreed	O
(	O
remanent	O
reed	B-Algorithm
relay	I-Algorithm
)	O
.	O
</s>
<s>
In	O
the	O
Bell	O
System	O
Stored	B-Device
Program	I-Device
Control	I-Device
exchange	I-Device
systems	O
of	O
the	O
1970s	O
,	O
reed	B-Algorithm
relays	I-Algorithm
were	O
no	O
longer	O
needed	O
for	O
data	O
storage	O
,	O
but	O
tens	O
of	O
millions	O
of	O
them	O
were	O
packaged	O
in	O
arrays	O
for	O
voice	O
path	O
switching	O
.	O
</s>
<s>
In	O
the	O
1ESS	B-Device
switch	I-Device
,	O
the	O
cores	O
were	O
made	O
of	O
a	O
magnetically	O
remanent	O
alloy	O
,	O
so	O
the	O
relay	O
could	O
latch	O
magnetically	O
instead	O
of	O
latching	O
electrically	O
.	O
</s>
<s>
Thus	O
,	O
while	O
a	O
telephone	O
call	O
in	O
a	O
typical	O
crossbar	O
exchange	O
like	O
5XB	B-Device
passed	O
through	O
four	O
switches	O
,	O
a	O
call	O
in	O
a	O
reed	O
system	O
such	O
as	O
1ESS	B-Device
typically	O
passed	O
through	O
eight	O
.	O
</s>
<s>
In	O
the	O
later	O
1AESS	B-Device
,	O
the	O
reeds	O
were	O
of	O
remanent	O
magnetic	O
material	O
.	O
</s>
<s>
Reed	B-Algorithm
relays	I-Algorithm
were	O
extensively	O
used	O
in	O
the	O
British	O
TXE	B-Device
family	O
of	O
telephone	O
exchanges	O
.	O
</s>
<s>
Reed	O
arrays	O
passed	O
out	O
of	O
use	O
in	O
the	O
mid-1990s	O
,	O
being	O
unnecessary	O
in	O
digital	O
telephone	O
systems	O
such	O
as	O
DMS-100	B-Protocol
and	O
5ESS	B-Device
switch	I-Device
.	O
</s>
<s>
Reed	B-Algorithm
relays	I-Algorithm
have	O
continued	O
in	O
their	O
uses	O
outside	O
the	O
telephone	O
industry	O
,	O
such	O
as	O
for	O
automatic	O
test	O
equipment	O
and	O
electronic	O
instrumentation	O
due	O
to	O
their	O
hermetic	O
seal	O
,	O
fast	O
operate	O
time	O
,	O
extended	O
life	O
to	O
109	O
operations	O
and	O
highly	O
consistent	O
contact	O
performance	O
.	O
</s>
<s>
Reed	B-Algorithm
relays	I-Algorithm
have	O
also	O
found	O
numerous	O
applications	O
in	O
RF	O
and	O
microwave	O
switching	O
applications	O
.	O
</s>
