<s>
Processor	B-General_Concept
design	I-General_Concept
is	O
a	O
subfield	O
of	O
computer	O
engineering	O
and	O
electronics	O
engineering	O
(	O
fabrication	B-Architecture
)	O
that	O
deals	O
with	O
creating	O
a	O
processor	O
,	O
a	O
key	O
component	O
of	O
computer	B-Architecture
hardware	I-Architecture
.	O
</s>
<s>
The	O
design	O
process	O
involves	O
choosing	O
an	O
instruction	B-General_Concept
set	I-General_Concept
and	O
a	O
certain	O
execution	O
paradigm	O
(	O
e.g.	O
</s>
<s>
VLIW	B-General_Concept
or	O
RISC	B-Architecture
)	O
and	O
results	O
in	O
a	O
microarchitecture	B-General_Concept
,	O
which	O
might	O
be	O
described	O
in	O
e.g.	O
</s>
<s>
VHDL	B-Language
or	O
Verilog	B-Language
.	O
</s>
<s>
For	O
microprocessor	B-General_Concept
design	I-General_Concept
,	O
this	O
description	O
is	O
then	O
manufactured	O
employing	O
some	O
of	O
the	O
various	O
semiconductor	B-Architecture
device	I-Architecture
fabrication	I-Architecture
processes	O
,	O
resulting	O
in	O
a	O
die	O
which	O
is	O
bonded	O
onto	O
a	O
chip	B-Algorithm
carrier	I-Algorithm
.	O
</s>
<s>
This	O
chip	B-Algorithm
carrier	I-Algorithm
is	O
then	O
soldered	O
onto	O
,	O
or	O
inserted	O
into	O
a	O
socket	B-General_Concept
on	O
,	O
a	O
printed	O
circuit	O
board	O
(	O
PCB	O
)	O
.	O
</s>
<s>
Instructions	O
typically	O
include	O
those	O
to	O
compute	O
or	O
manipulate	O
data	O
values	O
using	O
registers	B-General_Concept
,	O
change	O
or	O
retrieve	O
values	O
in	O
read/write	O
memory	B-General_Concept
,	O
perform	O
relational	O
tests	O
between	O
data	O
values	O
and	O
to	O
control	O
program	O
flow	O
.	O
</s>
<s>
Processor	B-General_Concept
designs	I-General_Concept
are	O
often	O
tested	O
and	O
validated	O
on	O
one	O
or	O
several	O
FPGAs	B-Architecture
before	O
sending	O
the	O
design	O
of	O
the	O
processor	O
to	O
a	O
foundry	O
for	O
semiconductor	B-Architecture
fabrication	I-Architecture
.	O
</s>
<s>
CPU	B-General_Concept
design	I-General_Concept
is	O
divided	O
into	O
multiple	O
components	O
.	O
</s>
<s>
Information	O
is	O
transferred	O
through	O
datapaths	B-General_Concept
(	O
such	O
as	O
ALUs	B-General_Concept
and	O
pipelines	B-General_Concept
)	O
.	O
</s>
<s>
These	O
datapaths	B-General_Concept
are	O
controlled	O
through	O
logic	O
by	O
control	B-General_Concept
units	I-General_Concept
.	O
</s>
<s>
Memory	B-General_Concept
components	O
include	O
register	B-General_Concept
files	I-General_Concept
and	O
caches	B-General_Concept
to	O
retain	O
information	O
,	O
or	O
certain	O
actions	O
.	O
</s>
<s>
Control	O
logic	O
implementation	O
techniques	O
(	O
logic	O
synthesis	O
using	O
CAD	O
tools	O
)	O
can	O
be	O
used	O
to	O
implement	O
datapaths	B-General_Concept
,	O
register	B-General_Concept
files	I-General_Concept
,	O
and	O
clocks	O
.	O
</s>
<s>
Common	O
logic	O
styles	O
used	O
in	O
CPU	B-General_Concept
design	I-General_Concept
include	O
unstructured	O
random	O
logic	O
,	O
finite-state	B-Architecture
machines	I-Architecture
,	O
microprogramming	B-Device
(	O
common	O
from	O
1965	O
to	O
1985	O
)	O
,	O
and	O
Programmable	O
logic	O
arrays	O
(	O
common	O
in	O
the	O
1980s	O
,	O
no	O
longer	O
common	O
)	O
.	O
</s>
<s>
A	O
CPU	B-General_Concept
design	I-General_Concept
project	O
generally	O
has	O
these	O
major	O
tasks	O
:	O
</s>
<s>
High-level	B-General_Concept
synthesis	I-General_Concept
(	O
HLS	O
)	O
or	O
register	O
transfer	O
level	O
(	O
RTL	B-Application
,	O
e.g.	O
</s>
<s>
Re-designing	O
a	O
CPU	O
core	O
to	O
a	O
smaller	O
die	O
area	O
helps	O
to	O
shrink	O
everything	O
(	O
a	O
"	O
photomask	B-Algorithm
shrink	O
"	O
)	O
,	O
resulting	O
in	O
the	O
same	O
number	O
of	O
transistors	O
on	O
a	O
smaller	O
die	O
.	O
</s>
<s>
Releasing	O
a	O
CPU	O
on	O
the	O
same	O
size	O
die	O
,	O
but	O
with	O
a	O
smaller	O
CPU	O
core	O
,	O
keeps	O
the	O
cost	O
about	O
the	O
same	O
but	O
allows	O
higher	O
levels	O
of	O
integration	O
within	O
one	O
very-large-scale	O
integration	O
chip	O
(	O
additional	O
cache	B-General_Concept
,	O
multiple	O
CPUs	O
or	O
other	O
components	O
)	O
,	O
improving	O
performance	O
and	O
reducing	O
overall	O
system	O
cost	O
.	O
</s>
<s>
Key	O
CPU	O
architectural	O
innovations	O
include	O
index	B-General_Concept
register	I-General_Concept
,	O
cache	B-General_Concept
,	O
virtual	B-Architecture
memory	I-Architecture
,	O
instruction	B-General_Concept
pipelining	I-General_Concept
,	O
superscalar	B-General_Concept
,	O
CISC	B-Architecture
,	O
RISC	B-Architecture
,	O
virtual	B-Architecture
machine	I-Architecture
,	O
emulators	B-Application
,	O
microprogram	B-Device
,	O
and	O
stack	B-Application
.	O
</s>
<s>
A	O
variety	O
of	O
new	O
CPU	B-General_Concept
design	I-General_Concept
ideas	O
have	O
been	O
proposed	O
,	O
</s>
<s>
including	O
reconfigurable	B-Architecture
logic	I-Architecture
,	O
clockless	O
CPUs	O
,	O
computational	B-Architecture
RAM	I-Architecture
,	O
and	O
optical	O
computing	O
.	O
</s>
<s>
Examples	O
include	O
SPECint	O
and	O
SPECfp	O
,	O
developed	O
by	O
Standard	O
Performance	O
Evaluation	O
Corporation	O
,	O
and	O
ConsumerMark	O
developed	O
by	O
the	O
Embedded	B-Architecture
Microprocessor	I-Architecture
Benchmark	O
Consortium	O
EEMBC	O
.	O
</s>
<s>
Instructions	O
per	O
second	O
-	O
Most	O
consumers	O
pick	O
a	O
computer	O
architecture	O
(	O
normally	O
Intel	O
IA32	B-Device
architecture	O
)	O
to	O
be	O
able	O
to	O
run	O
a	O
large	O
base	O
of	O
pre-existing	O
pre-compiled	O
software	O
.	O
</s>
<s>
Performance	O
per	O
watt	O
-	O
System	O
designers	O
building	O
parallel	B-Operating_System
computers	I-Operating_System
,	O
such	O
as	O
Google	O
,	O
pick	O
CPUs	O
based	O
on	O
their	O
speed	O
per	O
watt	O
of	O
power	O
,	O
because	O
the	O
cost	O
of	O
powering	O
the	O
CPU	O
outweighs	O
the	O
cost	O
of	O
the	O
CPU	O
itself	O
.	O
</s>
<s>
Some	O
system	O
designers	O
building	O
parallel	B-Operating_System
computers	I-Operating_System
pick	O
CPUs	O
based	O
on	O
the	O
speed	O
per	O
dollar	O
.	O
</s>
<s>
System	O
designers	O
building	O
real-time	B-General_Concept
computing	I-General_Concept
systems	O
want	O
to	O
guarantee	O
worst-case	O
response	O
.	O
</s>
<s>
That	O
is	O
easier	O
to	O
do	O
when	O
the	O
CPU	O
has	O
low	O
interrupt	B-General_Concept
latency	I-General_Concept
and	O
when	O
it	O
has	O
deterministic	O
response	O
.	O
</s>
<s>
Computer	O
programmers	O
who	O
program	O
directly	O
in	O
assembly	O
language	O
want	O
a	O
CPU	O
to	O
support	O
a	O
full	O
featured	O
instruction	B-General_Concept
set	I-General_Concept
.	O
</s>
<s>
In	O
this	O
market	O
,	O
the	O
Intel	B-Device
IA-32	I-Device
and	O
the	O
64-bit	O
version	O
x86-64	B-Device
architecture	O
dominate	O
the	O
market	O
,	O
with	O
its	O
rivals	O
PowerPC	B-Architecture
and	O
SPARC	B-Architecture
maintaining	O
much	O
smaller	O
customer	O
bases	O
.	O
</s>
<s>
Yearly	O
,	O
hundreds	O
of	O
millions	O
of	O
IA-32	B-Device
architecture	O
CPUs	O
are	O
used	O
by	O
this	O
market	O
.	O
</s>
<s>
Since	O
these	O
devices	O
are	O
used	O
to	O
run	O
countless	O
different	O
types	O
of	O
programs	O
,	O
these	O
CPU	B-General_Concept
designs	I-General_Concept
are	O
not	O
specifically	O
targeted	O
at	O
one	O
type	O
of	O
application	O
or	O
one	O
function	O
.	O
</s>
<s>
The	O
demands	O
of	O
being	O
able	O
to	O
run	O
a	O
wide	O
range	O
of	O
programs	O
efficiently	O
has	O
made	O
these	O
CPU	B-General_Concept
designs	I-General_Concept
among	O
the	O
more	O
advanced	O
technically	O
,	O
along	O
with	O
some	O
disadvantages	O
of	O
being	O
relatively	O
costly	O
,	O
and	O
having	O
high	O
power	O
consumption	O
.	O
</s>
<s>
Before	O
1990	O
,	O
CPU	B-General_Concept
design	I-General_Concept
was	O
often	O
done	O
for	O
this	O
market	O
,	O
but	O
mass	O
market	O
CPUs	O
organized	O
into	O
large	O
clusters	O
have	O
proven	O
to	O
be	O
more	O
affordable	O
.	O
</s>
<s>
The	O
main	O
remaining	O
area	O
of	O
active	O
hardware	B-General_Concept
design	I-General_Concept
and	O
research	O
for	O
scientific	O
computing	O
is	O
for	O
high-speed	O
data	O
transmission	O
systems	O
to	O
connect	O
mass	O
market	O
CPUs	O
.	O
</s>
<s>
When	O
the	O
only	O
allowed	O
program	B-Device
memory	I-Device
is	O
ROM	B-Device
,	O
the	O
device	O
is	O
known	O
as	O
a	O
microcontroller	B-Architecture
.	O
</s>
<s>
For	O
many	O
embedded	O
applications	O
,	O
interrupt	B-General_Concept
latency	I-General_Concept
will	O
be	O
more	O
critical	O
than	O
in	O
some	O
general-purpose	O
processors	O
.	O
</s>
<s>
The	O
embedded	O
CPU	O
family	O
with	O
the	O
largest	O
number	O
of	O
total	O
units	O
shipped	O
is	O
the	O
8051	B-Architecture
,	O
averaging	O
nearly	O
a	O
billion	O
units	O
per	O
year	O
.	O
</s>
<s>
The	O
8051	B-Architecture
is	O
widely	O
used	O
because	O
it	O
is	O
very	O
inexpensive	O
.	O
</s>
<s>
It	O
is	O
now	O
often	O
embedded	O
as	O
a	O
small	O
part	O
of	O
a	O
larger	O
system	B-Architecture
on	I-Architecture
a	I-Architecture
chip	I-Architecture
.	O
</s>
<s>
The	O
silicon	O
cost	O
of	O
an	O
8051	B-Architecture
is	O
now	O
as	O
low	O
as	O
US	O
$0.001	O
,	O
because	O
some	O
implementations	O
use	O
as	O
few	O
as	O
2,200	O
logic	O
gates	O
and	O
take	O
0.4730	O
square	O
millimeters	O
of	O
silicon	O
.	O
</s>
<s>
As	O
of	O
2009	O
,	O
more	O
CPUs	O
are	O
produced	O
using	O
the	O
ARM	B-Architecture
architecture	I-Architecture
family	I-Architecture
instruction	B-General_Concept
sets	I-General_Concept
than	O
any	O
other	O
32-bit	O
instruction	B-General_Concept
set	I-General_Concept
.	O
</s>
<s>
The	O
ARM	B-Architecture
architecture	I-Architecture
and	O
the	O
first	O
ARM	B-Architecture
chip	I-Architecture
were	O
designed	O
in	O
about	O
one	O
and	O
a	O
half	O
years	O
and	O
5	O
human	O
years	O
of	O
work	O
time	O
.	O
</s>
<s>
The	O
32-bit	O
Parallax	B-Architecture
Propeller	I-Architecture
microcontroller	B-Architecture
architecture	O
and	O
the	O
first	O
chip	O
were	O
designed	O
by	O
two	O
people	O
in	O
about	O
10	O
human	O
years	O
of	O
work	O
time	O
.	O
</s>
<s>
The	O
8-bit	O
AVR	B-Architecture
architecture	I-Architecture
and	O
first	O
AVR	B-Architecture
microcontroller	I-Architecture
was	O
conceived	O
and	O
designed	O
by	O
two	O
students	O
at	O
the	O
Norwegian	O
Institute	O
of	O
Technology	O
.	O
</s>
<s>
The	O
8-bit	O
6502	B-General_Concept
architecture	O
and	O
the	O
first	O
MOS	B-General_Concept
Technology	I-General_Concept
6502	I-General_Concept
chip	O
were	O
designed	O
in	O
13	O
months	O
by	O
a	O
group	O
of	O
about	O
9	O
people	O
.	O
</s>
<s>
The	O
32-bit	O
Berkeley	B-General_Concept
RISC	I-General_Concept
I	O
and	O
RISC	B-Architecture
II	O
processors	O
were	O
mostly	O
designed	O
by	O
a	O
series	O
of	O
students	O
as	O
part	O
of	O
a	O
four	O
quarter	O
sequence	O
of	O
graduate	O
courses	O
.	O
</s>
<s>
This	O
design	O
became	O
the	O
basis	O
of	O
the	O
commercial	O
SPARC	B-Architecture
processor	B-General_Concept
design	I-General_Concept
.	O
</s>
<s>
Some	O
undergraduate	O
courses	O
require	O
a	O
team	O
of	O
2	O
to	O
5	O
students	O
to	O
design	O
,	O
implement	O
,	O
and	O
test	O
a	O
simple	O
CPU	O
in	O
a	O
FPGA	B-Architecture
in	O
a	O
single	O
15-week	O
semester	O
.	O
</s>
