<s>
Each	O
server	B-Application
offered	O
for	O
rental	O
is	O
a	O
distinct	O
physical	O
piece	O
of	O
hardware	O
that	O
is	O
a	O
functional	O
server	B-Application
on	O
its	O
own	O
.	O
</s>
<s>
They	O
are	O
not	O
virtual	B-General_Concept
servers	I-General_Concept
running	O
in	O
multiple	O
pieces	O
of	O
shared	O
hardware	O
.	O
</s>
<s>
The	O
term	O
is	O
used	O
for	O
distinguishing	O
between	O
servers	O
that	O
can	O
host	O
multiple	O
tenants	O
and	O
which	O
use	O
virtualisation	B-Architecture
and	O
cloud	B-Architecture
hosting	I-Architecture
.	O
</s>
<s>
Unlike	O
bare-metal	B-General_Concept
servers	I-General_Concept
,	O
cloud	B-General_Concept
servers	I-General_Concept
are	O
shared	O
between	O
multiple	O
tenants	O
.	O
</s>
<s>
Each	O
bare-metal	B-General_Concept
server	I-General_Concept
may	O
run	O
any	O
amount	O
of	O
work	O
for	O
a	O
user	O
,	O
or	O
have	O
multiple	O
simultaneous	O
users	O
,	O
but	O
they	O
are	O
dedicated	O
entirely	O
to	O
the	O
entity	O
who	O
is	O
renting	O
them	O
.	O
</s>
<s>
Hypervisors	B-Operating_System
provide	O
some	O
isolation	O
between	O
tenants	O
but	O
there	O
can	O
still	O
be	O
a	O
noisy	O
neighbour	O
effect	O
.	O
</s>
<s>
If	O
a	O
physical	O
server	B-Application
is	O
multi-tenanted	O
,	O
peaks	O
of	O
load	O
from	O
one	O
tenant	O
may	O
consume	O
enough	O
machine	O
resources	O
to	O
temporarily	O
affect	O
other	O
tenants	O
.	O
</s>
<s>
As	O
the	O
tenants	O
are	O
otherwise	O
isolated	O
,	O
it	O
is	O
also	O
hard	O
to	O
manage	O
or	O
load	B-Application
balance	I-Application
this	O
.	O
</s>
<s>
Bare-metal	B-General_Concept
servers	I-General_Concept
,	O
and	O
single	O
tenancy	O
,	O
can	O
avoid	O
this	O
.	O
</s>
<s>
In	O
addition	O
,	O
hypervisors	B-Operating_System
provide	O
weaker	O
isolation	O
and	O
are	O
much	O
more	O
risky	O
from	O
a	O
security	O
point-of-view	O
compared	O
to	O
using	O
separate	O
machines	O
.	O
</s>
<s>
Attackers	O
have	O
always	O
found	O
vulnerabilities	O
in	O
the	O
isolation	O
software	O
(	O
such	O
as	O
hypervisors	B-Operating_System
)	O
,	O
covert	O
channels	O
are	O
impractical	O
to	O
counter	O
without	O
physically	O
separate	O
machines	O
,	O
and	O
shared	O
hardware	O
is	O
vulnerable	O
to	O
defects	O
in	O
hardware	O
protection	O
mechanisms	O
such	O
as	O
Rowhammer	B-General_Concept
,	O
Spectre	B-Error_Name
,	O
and	O
Meltdown	B-Architecture
.	O
</s>
<s>
As	O
,	O
once	O
again	O
,	O
server	B-Application
costs	O
are	O
dropping	O
as	O
a	O
proportion	O
of	O
total	O
cost	O
of	O
ownership	O
against	O
their	O
administration	O
overhead	O
,	O
the	O
classic	O
solution	O
of	O
'	O
throwing	O
hardware	O
at	O
the	O
problem	O
 '	O
becomes	O
viable	O
again	O
.	O
</s>
<s>
Infrastructure	B-General_Concept
as	I-General_Concept
a	I-General_Concept
Service	I-General_Concept
,	O
particularly	O
through	O
Infrastructure	B-Architecture
as	I-Architecture
Code	I-Architecture
,	O
offers	O
many	O
advantages	O
to	O
make	O
hosting	O
conveniently	O
manageable	O
.	O
</s>
<s>
Combining	O
the	O
features	O
of	O
both	O
cloud	B-Architecture
hosting	I-Architecture
,	O
and	O
bare-metal	B-General_Concept
servers	I-General_Concept
,	O
offers	O
most	O
of	O
these	O
,	O
whilst	O
still	O
conveying	O
the	O
performance	O
advantages	O
.	O
</s>
<s>
Some	O
bare-metal	O
cloud	B-General_Concept
servers	I-General_Concept
may	O
run	O
a	O
hypervisor	B-Operating_System
or	O
containers	O
,	O
e.g.	O
,	O
to	O
simplify	O
maintenance	O
or	O
provide	O
additional	O
layers	O
of	O
isolation	O
.	O
</s>
<s>
Note	O
that	O
the	O
distinction	O
between	O
these	O
services	O
and	O
the	O
traditional	O
dedicated	O
server	B-Application
offerings	O
is	O
the	O
user	O
's	O
ability	O
to	O
provision	O
infrastructures	O
composed	O
out	O
of	O
multiple	O
servers	O
,	O
a	O
complex	O
network	O
and	O
storage	O
setup	O
rather	O
than	O
servers	O
in	O
isolation	O
.	O
</s>
<s>
BMaaS	O
software	O
typically	O
takes	O
over	O
the	O
lifecycle	O
management	O
of	O
the	O
equipment	O
in	O
a	O
datacenter	B-Operating_System
(	O
Compute	O
,	O
Storage	O
and	O
Network	O
Switches	O
,	O
Firewalls	O
,	O
Loadbalancers	O
and	O
others	O
.	O
</s>
<s>
It	O
enables	O
datacenter	B-Operating_System
operators	O
to	O
offload	O
much	O
of	O
the	O
manual	O
work	O
typically	O
associated	O
with	O
deploying	O
hardware	O
.	O
</s>
<s>
BMaaS	O
Software	O
has	O
a	O
similar	O
objective	O
to	O
Composable	B-Architecture
disaggregated	I-Architecture
infrastructure	I-Architecture
in	O
that	O
it	O
aims	O
to	O
offer	O
the	O
user	O
the	O
ability	O
to	O
"	O
compose	O
"	O
the	O
desired	O
compute	O
unit	O
defined	O
as	O
a	O
set	O
of	O
resources	O
(	O
such	O
as	O
Compute	O
or	O
Storage	O
)	O
.	O
</s>
<s>
The	O
distinction	O
is	O
that	O
the	O
storage	O
and	O
compute	O
need	O
not	O
be	O
"	O
dissagregated	O
"	O
(	O
accessed	O
from	O
outside	O
the	O
server	B-Application
unit	O
)	O
as	O
this	O
often	O
requires	O
specialized	O
hardware	O
.	O
</s>
<s>
Instead	O
,	O
the	O
same	O
result	O
is	O
achieved	O
with	O
off-the-shelf	O
hardware	O
by	O
selecting	O
a	O
matching	O
server	B-Application
that	O
matches	O
the	O
desired	O
characteristics	O
(	O
RAM	O
,	O
CPU	O
Cores	O
,	O
Local	O
Disk	O
capacity	O
,	O
GPU	O
,	O
FPGA	O
,	O
SmartNICs	O
)	O
from	O
a	O
pool	O
of	O
servers	O
and	O
reconfiguring	O
the	O
network	O
so	O
that	O
the	O
server	B-Application
joins	O
the	O
others	O
that	O
a	O
tenant	O
has	O
deployed	O
.	O
</s>
<s>
Note	O
that	O
in	O
some	O
implementations	O
,	O
the	O
storage	O
component	O
is	O
external	O
to	O
the	O
systems	O
using	O
iSCSI	B-Protocol
blurring	O
the	O
lines	O
between	O
BMaaS	O
and	O
Composable	O
infrastructure	O
.	O
</s>
<s>
This	O
allows	O
the	O
user	O
to	O
choose	O
the	O
size	O
and	O
performance	O
of	O
the	O
node	O
's	O
storage	O
in	O
a	O
manner	O
similar	O
to	O
classical	O
virtualized	O
Infrastructure	B-General_Concept
as	I-General_Concept
a	I-General_Concept
Service	I-General_Concept
offerings	O
.	O
</s>
<s>
As	O
new	O
workloads	O
such	O
as	O
Augmented	B-General_Concept
reality	I-General_Concept
,	O
Mixed	B-General_Concept
Reality	I-General_Concept
,	O
Connected	O
cars	O
,	O
Telerobotics	O
are	O
gaining	O
ground	O
so	O
is	O
the	O
demand	O
for	O
low	O
latency	O
cloud	B-Architecture
services	I-Architecture
so	O
does	O
demand	O
for	O
Edge	B-Device
Computing	I-Device
.	O
</s>
<s>
Bare	O
Metal	O
and	O
the	O
BMaaS	O
automation	O
software	O
is	O
used	O
for	O
Edge	B-Device
Cloud	I-Device
implementations	O
,	O
where	O
large	O
numbers	O
of	O
small	O
data-centers	B-Operating_System
need	O
to	O
be	O
automated	O
and	O
then	O
consumed	O
as	O
a	O
service	O
and	O
where	O
the	O
service	O
needs	O
to	O
offer	O
the	O
lowest	O
latency	O
possible	O
.	O
</s>
<s>
At	O
one	O
time	O
,	O
all	O
servers	O
were	O
bare-metal	B-General_Concept
servers	I-General_Concept
.	O
</s>
<s>
Servers	O
were	O
kept	O
on-premises	B-General_Concept
and	O
often	O
belonged	O
to	O
the	O
organisation	O
using	O
and	O
operating	O
them	O
.	O
</s>
<s>
Operating	B-General_Concept
systems	I-General_Concept
developed	O
very	O
early	O
on	O
(	O
early	O
1960s	O
)	O
to	O
allow	O
time-sharing	B-General_Concept
.	O
</s>
<s>
Single	O
large	B-Architecture
computers	I-Architecture
,	O
mainframes	B-Architecture
or	O
minis	O
,	O
were	O
commonly	O
housed	O
in	O
centralised	O
locations	O
and	O
their	O
services	O
shared	O
through	O
a	O
bureau	B-General_Concept
.	O
</s>
<s>
Popular	O
growth	O
of	O
the	O
internet	O
,	O
and	O
particularly	O
the	O
web	O
,	O
in	O
the	O
1990s	O
encouraged	O
the	O
practice	O
of	O
hosting	O
in	O
data	B-Operating_System
centres	I-Operating_System
,	O
where	O
many	O
customers	O
shared	O
the	O
facilities	O
of	O
single	O
servers	O
.	O
</s>
<s>
Small	O
web	B-Application
servers	I-Application
at	O
this	O
time	O
often	O
cost	O
more	O
for	O
their	O
connectivity	O
than	O
their	O
hardware	O
cost	O
,	O
encouraging	O
this	O
centralisation	O
.	O
</s>
<s>
HTTP	B-Protocol
1.1	I-Protocol
'	O
s	O
ability	O
for	O
virtual	O
hosting	O
also	O
made	O
it	O
easy	O
to	O
co-host	O
many	O
web	O
sites	O
on	O
the	O
same	O
server	B-Application
.	O
</s>
<s>
From	O
around	O
2000	O
,	O
or	O
2005	O
in	O
commercially	O
practical	O
terms	O
,	O
interest	O
grew	O
in	O
the	O
use	O
of	O
virtual	B-General_Concept
servers	I-General_Concept
and	O
then	O
cloud	B-Architecture
hosting	I-Architecture
,	O
where	O
Infrastructure	B-General_Concept
as	I-General_Concept
a	I-General_Concept
Service	I-General_Concept
made	O
the	O
computing	O
service	O
the	O
fungible	O
commodity	O
,	O
rather	O
than	O
the	O
server	B-Application
hardware	O
.	O
</s>
<s>
Hypervisors	B-Operating_System
were	O
developed	O
which	O
could	O
offer	O
many	O
virtual	B-Architecture
machines	I-Architecture
hosted	O
on	O
larger	O
physical	O
servers	O
.	O
</s>
<s>
The	O
load	O
pattern	O
of	O
multiple	O
users	O
has	O
long	O
been	O
recognised	O
as	O
being	O
smoother	O
overall	O
than	O
individual	O
users	O
,	O
so	O
these	O
virtual	B-Architecture
machines	I-Architecture
could	O
make	O
more	O
efficient	O
use	O
of	O
the	O
physical	O
hardware	O
and	O
its	O
costs	O
,	O
whilst	O
also	O
appearing	O
to	O
have	O
higher	O
individual	O
performance	O
than	O
a	O
simple	O
cost-share	O
would	O
suggest	O
.	O
</s>
<s>
One	O
of	O
the	O
forefathers	O
of	O
bare	O
metal	O
provisioning	O
is	O
Cobbler	B-Device
(	O
software	O
)	O
that	O
appeared	O
in	O
the	O
1990s	O
and	O
was	O
using	O
the	O
Preboot	B-Device
Execution	I-Device
Environment	I-Device
(	O
PXE	O
)	O
protocol	O
.	O
</s>
<s>
April	O
2015	O
OpenStack	B-Application
Ironic	O
component	O
was	O
launched	O
as	O
part	O
of	O
the	O
Kilo	O
release	O
.	O
</s>
