<s>
U.2	B-Protocol
(	O
pronounced	O
'	O
u-dot-2	O
'	O
)	O
,	O
formerly	O
known	O
as	O
SFF-8639	O
,	O
is	O
a	O
computer	O
interface	O
standard	O
for	O
connecting	O
solid-state	B-Device
drives	I-Device
(	O
SSDs	B-Device
)	O
to	O
a	O
computer	O
.	O
</s>
<s>
The	O
Enterprise	O
SSD	B-Device
form	O
factor	O
was	O
developed	O
by	O
the	O
SSD	B-Device
Form	O
Factor	O
Working	O
Group	O
(	O
SFFWG	O
)	O
.	O
</s>
<s>
The	O
specification	O
was	O
released	O
on	O
December	O
20	O
,	O
2011	O
,	O
as	O
a	O
mechanism	O
for	O
providing	O
PCI	O
Express	O
connections	O
to	O
SSDs	B-Device
for	O
the	O
enterprise	O
market	O
.	O
</s>
<s>
Goals	O
included	O
being	O
usable	O
in	O
existing	O
2.5	O
"	O
and	O
3.5	O
"	O
mechanical	O
enclosures	O
,	O
to	O
be	O
hot	B-Device
swappable	I-Device
and	O
to	O
allow	O
legacy	O
SAS	O
and	O
SATA	O
drives	O
to	O
be	O
mixed	O
using	O
the	O
same	O
connector	O
family	O
.	O
</s>
<s>
In	O
June	O
2015	O
,	O
the	O
SFFWG	O
announced	O
that	O
the	O
connector	O
was	O
being	O
renamed	O
to	O
U.2	B-Protocol
.	O
</s>
<s>
The	O
U.2	B-Protocol
connector	O
is	O
mechanically	O
identical	O
to	O
the	O
SATA	O
Express	O
device	O
plug	O
,	O
but	O
provides	O
four	O
PCI	O
Express	O
lanes	O
through	O
a	O
different	O
usage	O
of	O
available	O
pins	O
.	O
</s>
<s>
U.2	B-Protocol
devices	O
may	O
be	O
connected	O
to	O
an	O
M.2	B-Protocol
port	O
using	O
an	O
adapter	O
.	O
</s>
<s>
In	O
November	O
2015	O
,	O
Intel	O
introduced	O
the	O
750	O
series	O
SSD	B-Device
which	O
is	O
available	O
in	O
both	O
PCI	O
Express	O
and	O
U.2	B-Protocol
variants	O
.	O
</s>
<s>
Since	O
then	O
,	O
U.2	B-Protocol
has	O
achieved	O
a	O
high	O
level	O
of	O
support	O
from	O
the	O
major	O
storage	O
vendors	O
and	O
storage	O
appliance	O
suppliers	O
.	O
</s>
<s>
U.2	B-Protocol
allows	O
hot-swap	B-Device
,	O
whereas	O
M.2	B-Protocol
does	O
not	O
.	O
</s>
<s>
U.2	B-Protocol
can	O
use	O
3.3V	O
or	O
12V	O
for	O
power	O
,	O
while	O
M.2	B-Protocol
only	O
supports	O
3.3V	O
.	O
</s>
<s>
While	O
the	O
U.2	B-Protocol
standard	O
does	O
not	O
imply	O
a	O
form	O
factor	O
of	O
the	O
device	O
that	O
uses	O
it	O
,	O
in	O
practice	O
U.2	B-Protocol
is	O
used	O
only	O
on	O
2.5	O
"	O
SSDs	B-Device
.	O
</s>
<s>
2.5	O
"	O
drives	O
are	O
typically	O
physically	O
larger	O
than	O
M.2	B-Protocol
drives	O
and	O
thus	O
typically	O
have	O
larger	O
capacities	O
.	O
</s>
