<s>
Industry	B-Architecture
Standard	I-Architecture
Architecture	I-Architecture
(	O
ISA	O
)	O
is	O
the	O
16-bit	B-Device
internal	B-General_Concept
bus	I-General_Concept
of	O
IBM	B-Operating_System
PC/AT	I-Operating_System
and	O
similar	O
computers	O
based	O
on	O
the	O
Intel	B-General_Concept
80286	I-General_Concept
and	O
its	O
immediate	O
successors	O
during	O
the	O
1980s	O
.	O
</s>
<s>
The	O
bus	B-General_Concept
was	O
(	O
largely	O
)	O
backward	B-General_Concept
compatible	I-General_Concept
with	O
the	O
8-bit	O
bus	B-General_Concept
of	O
the	O
8088-based	O
IBM	B-Device
PC	I-Device
,	O
including	O
the	O
IBM	B-Device
PC/XT	I-Device
as	O
well	O
as	O
IBM	B-Device
PC	I-Device
compatibles	O
.	O
</s>
<s>
Originally	O
referred	O
to	O
as	O
the	O
PC	B-General_Concept
bus	I-General_Concept
(	O
8-bit	O
)	O
or	O
AT	B-Architecture
bus	I-Architecture
(	O
16-bit	B-Device
)	O
,	O
it	O
was	O
also	O
termed	O
I/O	O
Channel	O
by	O
IBM	O
.	O
</s>
<s>
The	O
ISA	O
term	O
was	O
coined	O
as	O
a	O
retronym	O
by	O
IBM	B-Device
PC	I-Device
clone	O
manufacturers	O
in	O
the	O
late	O
1980s	O
or	O
early	O
1990s	O
as	O
a	O
reaction	O
to	O
IBM	O
attempts	O
to	O
replace	O
the	O
AT-bus	O
with	O
its	O
new	O
and	O
incompatible	O
Micro	B-Device
Channel	I-Device
architecture	I-Device
.	O
</s>
<s>
The	O
16-bit	B-Device
ISA	B-Architecture
bus	I-Architecture
was	O
also	O
used	O
with	O
32-bit	O
processors	O
for	O
several	O
years	O
.	O
</s>
<s>
An	O
attempt	O
to	O
extend	O
it	O
to	O
32	O
bits	O
,	O
called	O
Extended	B-Device
Industry	I-Device
Standard	I-Device
Architecture	I-Device
(	O
EISA	B-Device
)	O
,	O
was	O
not	O
very	O
successful	O
,	O
however	O
.	O
</s>
<s>
Later	O
buses	O
such	O
as	O
VESA	O
Local	O
Bus	B-General_Concept
and	O
PCI	B-Protocol
were	O
used	O
instead	O
,	O
often	O
along	O
with	O
ISA	B-Architecture
slots	I-Architecture
on	O
the	O
same	O
mainboard	B-Device
.	O
</s>
<s>
Derivatives	O
of	O
the	O
AT	B-Architecture
bus	I-Architecture
structure	O
were	O
and	O
still	O
are	O
used	O
in	O
ATA/IDE	B-Protocol
,	O
the	O
PCMCIA	B-Architecture
standard	O
,	O
CompactFlash	B-Device
,	O
the	O
PC/104	B-Device
bus	B-General_Concept
,	O
and	O
internally	O
within	O
Super	B-Device
I/O	I-Device
chips	O
.	O
</s>
<s>
Even	O
though	O
ISA	O
disappeared	O
from	O
consumer	O
desktops	O
many	O
years	O
ago	O
,	O
it	O
is	O
still	O
used	O
in	O
industrial	B-Device
PCs	I-Device
,	O
where	O
certain	O
specialized	O
expansion	O
cards	O
that	O
never	O
transitioned	O
to	O
PCI	B-Protocol
and	O
PCI	B-Protocol
Express	O
are	O
used	O
.	O
</s>
<s>
The	O
original	O
PC	B-General_Concept
bus	I-General_Concept
was	O
developed	O
by	O
a	O
team	O
led	O
by	O
Mark	O
Dean	O
at	O
IBM	O
as	O
part	O
of	O
the	O
IBM	B-Device
PC	I-Device
project	O
in	O
1981	O
.	O
</s>
<s>
It	O
was	O
an	O
8-bit	O
bus	B-General_Concept
based	O
on	O
the	O
I/O	B-General_Concept
bus	I-General_Concept
of	O
the	O
IBM	B-Device
System/23	I-Device
Datamaster	I-Device
system	O
-	O
it	O
used	O
the	O
same	O
physical	O
connector	O
,	O
and	O
a	O
similar	O
signal	O
protocol	O
and	O
pinout	O
.	O
</s>
<s>
A	O
16-bit	B-Device
version	O
,	O
the	O
IBM	B-Operating_System
AT	I-Operating_System
bus	B-General_Concept
,	O
was	O
introduced	O
with	O
the	O
release	O
of	O
the	O
IBM	B-Operating_System
PC/AT	I-Operating_System
in	O
1984	O
.	O
</s>
<s>
The	O
AT	B-Architecture
bus	I-Architecture
was	O
a	O
mostly	O
backward	B-General_Concept
compatible	I-General_Concept
extension	O
of	O
the	O
PC	O
busthe	O
AT	B-Architecture
bus	I-Architecture
connector	O
was	O
a	O
superset	O
of	O
the	O
PC	B-General_Concept
bus	I-General_Concept
connector	O
.	O
</s>
<s>
In	O
1988	O
,	O
the	O
32-bit	O
EISA	B-Device
standard	O
was	O
proposed	O
by	O
the	O
"	O
Gang	B-Device
of	I-Device
Nine	I-Device
"	O
group	O
of	O
PC-compatible	O
manufacturers	O
that	O
included	O
Compaq	O
.	O
</s>
<s>
Compaq	O
created	O
the	O
term	O
"	O
Industry	B-Architecture
Standard	I-Architecture
Architecture	I-Architecture
"	O
(	O
ISA	O
)	O
to	O
replace	O
"	O
PC	O
compatible	O
"	O
.	O
</s>
<s>
In	O
the	O
process	O
,	O
they	O
retroactively	O
renamed	O
the	O
AT	B-Architecture
bus	I-Architecture
to	O
"	O
ISA	O
"	O
to	O
avoid	O
infringing	O
IBM	O
's	O
trademark	O
on	O
its	O
PC	O
and	O
PC/AT	B-Operating_System
systems	O
(	O
and	O
to	O
avoid	O
giving	O
their	O
major	O
competitor	O
,	O
IBM	O
,	O
free	O
advertisement	O
)	O
.	O
</s>
<s>
IBM	O
designed	O
the	O
8-bit	O
version	O
as	O
a	O
buffered	O
interface	O
to	O
the	O
motherboard	B-Device
buses	O
of	O
the	O
Intel	B-Device
8088	I-Device
(	O
16/8	O
bit	O
)	O
CPU	B-General_Concept
in	O
the	O
IBM	B-Device
PC	I-Device
and	O
PC/XT	B-Device
,	O
augmented	O
with	O
prioritized	O
interrupts	O
and	O
DMA	B-General_Concept
channels	O
.	O
</s>
<s>
The	O
16-bit	B-Device
version	O
was	O
an	O
upgrade	O
for	O
the	O
motherboard	B-Device
buses	O
of	O
the	O
Intel	B-General_Concept
80286	I-General_Concept
CPU	B-General_Concept
(	O
and	O
expanded	O
interrupt	O
and	O
DMA	B-General_Concept
facilities	O
)	O
used	O
in	O
the	O
IBM	B-Operating_System
AT	I-Operating_System
,	O
with	O
improved	O
support	O
for	O
bus	B-Architecture
mastering	I-Architecture
.	O
</s>
<s>
The	O
ISA	B-Architecture
bus	I-Architecture
was	O
therefore	O
synchronous	O
with	O
the	O
CPU	B-General_Concept
clock	O
,	O
until	O
sophisticated	O
buffering	O
methods	O
were	O
implemented	O
by	O
chipsets	B-Device
to	O
interface	O
ISA	O
to	O
much	O
faster	O
CPUs	O
.	O
</s>
<s>
ISA	O
was	O
designed	O
to	O
connect	O
peripheral	O
cards	O
to	O
the	O
motherboard	B-Device
and	O
allows	O
for	O
bus	B-Architecture
mastering	I-Architecture
.	O
</s>
<s>
The	O
original	O
8-bit	O
bus	B-General_Concept
ran	O
from	O
the	O
4.77MHz	O
clock	O
of	O
the	O
8088	B-Device
CPU	B-General_Concept
in	O
the	O
IBM	B-Device
PC	I-Device
and	O
PC/XT	B-Device
.	O
</s>
<s>
The	O
original	O
16-bit	B-Device
bus	B-General_Concept
ran	O
from	O
the	O
CPU	B-General_Concept
clock	O
of	O
the	O
80286	B-General_Concept
in	O
IBM	B-Operating_System
PC/AT	I-Operating_System
computers	O
,	O
which	O
was	O
6MHz	O
in	O
the	O
first	O
models	O
and	O
8MHz	O
in	O
later	O
models	O
.	O
</s>
<s>
The	O
IBM	B-Device
RT	I-Device
PC	I-Device
also	O
used	O
the	O
16-bit	B-Device
bus	B-General_Concept
.	O
</s>
<s>
ISA	O
was	O
also	O
used	O
in	O
some	O
non-IBM	O
compatible	O
machines	O
such	O
as	O
Motorola	O
68k-based	O
Apollo	O
(	O
68020	O
)	O
and	O
Amiga	B-Device
3000	I-Device
(	O
68030	O
)	O
workstations	O
,	O
the	O
short-lived	O
AT&T	B-Application
Hobbit	I-Application
and	O
the	O
later	O
PowerPC-based	O
BeBox	B-Device
.	O
</s>
<s>
Companies	O
like	O
Dell	O
improved	O
the	O
AT	B-Architecture
bus	I-Architecture
's	O
performance	O
but	O
in	O
1987	O
,	O
IBM	O
replaced	O
the	O
AT	B-Architecture
bus	I-Architecture
with	O
its	O
proprietary	O
Micro	B-Device
Channel	I-Device
Architecture	I-Device
(	O
MCA	O
)	O
.	O
</s>
<s>
MCA	O
was	O
far	O
more	O
advanced	O
than	O
ISA	O
and	O
had	O
many	O
features	O
that	O
would	O
later	O
appear	O
in	O
PCI	B-Protocol
.	O
</s>
<s>
Computer	O
manufacturers	O
responded	O
to	O
MCA	O
by	O
developing	O
the	O
Extended	B-Device
Industry	I-Device
Standard	I-Device
Architecture	I-Device
(	O
EISA	B-Device
)	O
and	O
the	O
later	O
VESA	O
Local	O
Bus	B-General_Concept
(	O
VLB	O
)	O
.	O
</s>
<s>
Both	O
EISA	B-Device
and	O
VLB	O
were	O
backwards-compatible	B-General_Concept
expansions	O
of	O
the	O
AT	O
(	O
ISA	O
)	O
bus	B-General_Concept
.	O
</s>
<s>
While	O
a	O
handful	O
of	O
devices	O
were	O
essentially	O
"	O
plug-n-play	B-Device
"	O
,	O
this	O
was	O
rare	O
.	O
</s>
<s>
Users	O
frequently	O
had	O
to	O
configure	O
parameters	O
when	O
adding	O
a	O
new	O
device	O
,	O
such	O
as	O
the	O
IRQ	B-General_Concept
line	O
,	O
I/O	O
address	O
,	O
or	O
DMA	B-General_Concept
channel	O
.	O
</s>
<s>
MCA	O
had	O
done	O
away	O
with	O
this	O
complication	O
and	O
PCI	B-Protocol
actually	O
incorporated	O
many	O
of	O
the	O
ideas	O
first	O
explored	O
with	O
MCA	O
,	O
though	O
it	O
was	O
more	O
directly	O
descended	O
from	O
EISA	B-Device
.	O
</s>
<s>
This	O
trouble	O
with	O
configuration	O
eventually	O
led	O
to	O
the	O
creation	O
of	O
ISA	B-Device
PnP	I-Device
,	O
a	O
plug-n-play	B-Device
system	O
that	O
used	O
a	O
combination	O
of	O
modifications	O
to	O
hardware	O
,	O
the	O
system	B-Operating_System
BIOS	I-Operating_System
,	O
and	O
operating	B-General_Concept
system	I-General_Concept
software	O
to	O
automatically	O
manage	O
resource	O
allocations	O
.	O
</s>
<s>
In	O
reality	O
,	O
ISA	B-Device
PnP	I-Device
could	O
be	O
troublesome	O
and	O
did	O
not	O
become	O
well-supported	O
until	O
the	O
architecture	O
was	O
in	O
its	O
final	O
days	O
.	O
</s>
<s>
PCI	B-Protocol
slots	I-Protocol
were	O
the	O
first	O
physically-incompatible	O
expansion	O
ports	O
to	O
directly	O
squeeze	O
ISA	O
off	O
the	O
motherboard	B-Device
.	O
</s>
<s>
At	O
first	O
,	O
motherboards	B-Device
were	O
largely	O
ISA	O
,	O
including	O
a	O
few	O
PCI	B-Protocol
slots	I-Protocol
.	O
</s>
<s>
By	O
the	O
mid-1990s	O
,	O
the	O
two	O
slot	O
types	O
were	O
roughly	O
balanced	O
,	O
and	O
ISA	B-Architecture
slots	I-Architecture
soon	O
were	O
in	O
the	O
minority	O
of	O
consumer	O
systems	O
.	O
</s>
<s>
Microsoft	O
's	O
PC-99	O
specification	O
recommended	O
that	O
ISA	B-Architecture
slots	I-Architecture
be	O
removed	O
entirely	O
,	O
though	O
the	O
system	O
architecture	O
still	O
required	O
ISA	O
to	O
be	O
present	O
in	O
some	O
vestigial	O
way	O
internally	O
to	O
handle	O
the	O
floppy	B-Device
drive	I-Device
,	O
serial	B-Protocol
ports	I-Protocol
,	O
etc.	O
,	O
which	O
was	O
why	O
the	O
software	O
compatible	O
LPC	O
bus	B-General_Concept
was	O
created	O
.	O
</s>
<s>
ISA	B-Architecture
slots	I-Architecture
remained	O
for	O
a	O
few	O
more	O
years	O
,	O
and	O
towards	O
the	O
turn	O
of	O
the	O
century	O
it	O
was	O
common	O
to	O
see	O
systems	O
with	O
an	O
Accelerated	B-Architecture
Graphics	I-Architecture
Port	I-Architecture
(	O
AGP	O
)	O
sitting	O
near	O
the	O
central	B-General_Concept
processing	I-General_Concept
unit	I-General_Concept
,	O
an	O
array	O
of	O
PCI	B-Protocol
slots	I-Protocol
,	O
and	O
one	O
or	O
two	O
ISA	B-Architecture
slots	I-Architecture
near	O
the	O
end	O
.	O
</s>
<s>
In	O
late	O
2008	O
,	O
even	O
floppy	B-Device
disk	I-Device
drives	I-Device
and	O
serial	B-Protocol
ports	I-Protocol
were	O
disappearing	O
,	O
and	O
the	O
extinction	O
of	O
vestigial	O
ISA	O
(	O
by	O
then	O
the	O
LPC	O
bus	B-General_Concept
)	O
from	O
chipsets	B-Device
was	O
on	O
the	O
horizon	O
.	O
</s>
<s>
PCI	B-Protocol
slots	I-Protocol
are	O
"	O
rotated	O
"	O
compared	O
to	O
their	O
ISA	O
counterpartsPCI	O
cards	O
were	O
essentially	O
inserted	O
"	O
upside-down	O
,	O
"	O
allowing	O
ISA	O
and	O
PCI	B-Protocol
connectors	O
to	O
squeeze	O
together	O
on	O
the	O
motherboard	B-Device
.	O
</s>
<s>
The	O
AT	B-Protocol
Attachment	I-Protocol
(	O
ATA	B-Protocol
)	O
hard	B-Device
disk	I-Device
interface	O
is	O
directly	O
descended	O
from	O
the	O
16-bit	B-Device
ISA	O
of	O
the	O
PC/AT	B-Operating_System
.	O
</s>
<s>
ATA	B-Protocol
has	O
its	O
origins	O
in	O
the	O
IBM	B-Device
Personal	I-Device
Computer	I-Device
Fixed	B-Device
Disk	I-Device
and	O
Diskette	B-Device
Adapter	O
,	O
the	O
standard	O
dual-function	O
floppy	B-Device
disk	I-Device
controller	O
and	O
hard	B-General_Concept
disk	I-General_Concept
controller	I-General_Concept
card	O
for	O
the	O
IBM	B-Operating_System
PC	I-Operating_System
AT	I-Operating_System
;	O
the	O
fixed	B-Device
disk	I-Device
controller	O
on	O
this	O
card	O
implemented	O
the	O
register	O
set	O
and	O
the	O
basic	O
command	O
set	O
which	O
became	O
the	O
basis	O
of	O
the	O
ATA	B-Protocol
interface	O
(	O
and	O
which	O
differed	O
greatly	O
from	O
the	O
interface	O
of	O
IBM	O
's	O
fixed	B-Device
disk	I-Device
controller	O
card	O
for	O
the	O
PC	B-Device
XT	I-Device
)	O
.	O
</s>
<s>
Direct	O
precursors	O
to	O
ATA	B-Protocol
were	O
third-party	O
ISA	O
hardcards	B-Device
that	O
integrated	O
a	O
hard	B-Device
disk	I-Device
drive	I-Device
(	O
HDD	O
)	O
and	O
a	O
hard	B-General_Concept
disk	I-General_Concept
controller	I-General_Concept
(	O
HDC	O
)	O
onto	O
one	O
card	O
.	O
</s>
<s>
This	O
was	O
at	O
best	O
awkward	O
and	O
at	O
worst	O
damaging	O
to	O
the	O
motherboard	B-Device
,	O
as	O
ISA	B-Architecture
slots	I-Architecture
were	O
not	O
designed	O
to	O
support	O
such	O
heavy	O
devices	O
as	O
HDDs	O
.	O
</s>
<s>
The	O
next	O
generation	O
of	O
Integrated	B-Protocol
Drive	I-Protocol
Electronics	I-Protocol
drives	O
moved	O
both	O
the	O
drive	O
and	O
controller	O
to	O
a	O
drive	O
bay	O
and	O
used	O
a	O
ribbon	O
cable	O
and	O
a	O
very	O
simple	O
interface	O
board	O
to	O
connect	O
it	O
to	O
an	O
ISA	B-Architecture
slot	I-Architecture
.	O
</s>
<s>
ATA	B-Protocol
is	O
basically	O
a	O
standardization	O
of	O
this	O
arrangement	O
plus	O
a	O
uniform	O
command	O
structure	O
for	O
software	O
to	O
interface	O
with	O
the	O
HDC	O
within	O
the	O
drive	O
.	O
</s>
<s>
ATA	B-Protocol
has	O
since	O
been	O
separated	O
from	O
the	O
ISA	B-Architecture
bus	I-Architecture
and	O
connected	O
directly	O
to	O
the	O
local	O
bus	B-General_Concept
,	O
usually	O
by	O
integration	O
into	O
the	O
chipset	B-Device
,	O
for	O
much	O
higher	O
clock	O
rates	O
and	O
data	O
throughput	O
than	O
ISA	O
could	O
support	O
.	O
</s>
<s>
ATA	B-Protocol
has	O
clear	O
characteristics	O
of	O
16-bit	B-Device
ISA	O
,	O
such	O
as	O
a	O
16-bit	B-Device
transfer	O
size	O
,	O
signal	O
timing	O
in	O
the	O
PIO	O
modes	O
and	O
the	O
interrupt	O
and	O
DMA	B-General_Concept
mechanisms	O
.	O
</s>
<s>
The	O
PC/XT	B-Device
-bus	O
is	O
an	O
eight-bit	O
ISA	B-Architecture
bus	I-Architecture
used	O
by	O
Intel	B-General_Concept
8086	I-General_Concept
and	O
Intel	B-Device
8088	I-Device
systems	O
in	O
the	O
IBM	B-Device
PC	I-Device
and	O
IBM	B-Device
PC	I-Device
XT	I-Device
in	O
the	O
1980s	O
.	O
</s>
<s>
Among	O
its	O
62	O
pins	O
were	O
demultiplexed	O
and	O
electrically	O
buffered	O
versions	O
of	O
the	O
8	O
data	O
and	O
20	O
address	O
lines	O
of	O
the	O
8088	B-Device
processor	O
,	O
along	O
with	O
power	O
lines	O
,	O
clocks	O
,	O
read/write	O
strobes	O
,	O
interrupt	O
lines	O
,	O
etc	O
.	O
</s>
<s>
Power	O
lines	O
included	O
−5V	O
and	O
±12V	O
in	O
order	O
to	O
directly	O
support	O
pMOS	B-Algorithm
and	O
enhancement	O
mode	O
nMOS	B-Algorithm
circuits	O
such	O
as	O
dynamic	O
RAMs	O
among	O
other	O
things	O
.	O
</s>
<s>
The	O
XT	B-Architecture
bus	I-Architecture
architecture	I-Architecture
uses	O
a	O
single	O
Intel	B-Device
8259	I-Device
PIC	B-Architecture
,	O
giving	O
eight	O
vectorized	O
and	O
prioritized	O
interrupt	O
lines	O
.	O
</s>
<s>
It	O
has	O
four	O
DMA	B-General_Concept
channels	O
originally	O
provided	O
by	O
the	O
Intel	B-Device
8237	I-Device
.	O
</s>
<s>
Three	O
of	O
the	O
DMA	B-General_Concept
channels	O
are	O
brought	O
out	O
to	O
the	O
XT	B-Architecture
bus	I-Architecture
expansion	O
slots	O
;	O
of	O
these	O
,	O
2	O
are	O
normally	O
already	O
allocated	O
to	O
machine	O
functions	O
(	O
diskette	B-Device
drive	O
and	O
hard	B-General_Concept
disk	I-General_Concept
controller	I-General_Concept
)	O
:	O
</s>
<s>
The	O
PC/AT	B-Operating_System
-bus	O
,	O
a	O
16-bit	B-Device
(	O
or	O
80286	B-General_Concept
-	O
)	O
version	O
of	O
the	O
PC/XT	B-Device
bus	B-General_Concept
,	O
was	O
introduced	O
with	O
the	O
IBM	B-Operating_System
PC/AT	I-Operating_System
.	O
</s>
<s>
This	O
bus	B-General_Concept
was	O
officially	O
termed	O
I/O	O
Channel	O
by	O
IBM	O
.	O
</s>
<s>
It	O
extends	O
the	O
XT-bus	O
by	O
adding	O
a	O
second	O
shorter	O
edge	O
connector	O
in-line	O
with	O
the	O
eight-bit	O
XT-bus	O
connector	O
,	O
which	O
is	O
unchanged	O
,	O
retaining	O
compatibility	O
with	O
most	O
8-bit	O
cards	O
.	O
</s>
<s>
It	O
also	O
adds	O
new	O
interrupt	O
lines	O
connected	O
to	O
a	O
second	O
8259	B-Device
PIC	I-Device
(	O
connected	O
to	O
one	O
of	O
the	O
lines	O
of	O
the	O
first	O
)	O
and	O
4	O
×	O
16-bit	B-Device
DMA	B-General_Concept
channels	O
,	O
as	O
well	O
as	O
control	O
lines	O
to	O
select	O
8	O
-	O
or	O
16-bit	B-Device
transfers	O
.	O
</s>
<s>
The	O
16-bit	B-Device
AT	B-Architecture
bus	I-Architecture
slot	O
originally	O
used	O
two	O
standard	O
edge	O
connector	O
sockets	O
in	O
early	O
IBM	B-Operating_System
PC/AT	I-Operating_System
machines	O
.	O
</s>
<s>
However	O
,	O
with	O
the	O
popularity	O
of	O
the	O
AT-architecture	O
and	O
the	O
16-bit	B-Device
ISA	B-Architecture
bus	I-Architecture
,	O
manufacturers	O
introduced	O
specialized	O
98-pin	O
connectors	O
that	O
integrated	O
the	O
two	O
sockets	O
into	O
one	O
unit	O
.	O
</s>
<s>
The	O
ISA	B-Architecture
slot	I-Architecture
connector	O
is	O
typically	O
black	O
(	O
distinguishing	O
it	O
from	O
the	O
brown	O
EISA	B-Device
connectors	O
and	O
white	O
PCI	B-Protocol
connectors	O
)	O
.	O
</s>
<s>
Motherboard	B-Device
devices	O
have	O
dedicated	O
IRQs	B-General_Concept
(	O
not	O
present	O
in	O
the	O
slots	O
)	O
.	O
</s>
<s>
16-bit	B-Device
devices	O
can	O
use	O
either	O
PC-bus	O
or	O
PC/AT	B-Operating_System
-bus	O
IRQs	B-General_Concept
.	O
</s>
<s>
It	O
is	O
therefore	O
possible	O
to	O
connect	O
up	O
to	O
6	O
devices	O
that	O
use	O
one	O
8-bit	O
IRQ	B-General_Concept
each	O
and	O
up	O
to	O
5	O
devices	O
that	O
use	O
one	O
16-bit	B-Device
IRQ	B-General_Concept
each	O
.	O
</s>
<s>
At	O
the	O
same	O
time	O
,	O
up	O
to	O
4	O
devices	O
may	O
use	O
one	O
8-bit	O
DMA	B-General_Concept
channel	O
each	O
,	O
while	O
up	O
to	O
3	O
devices	O
can	O
use	O
one	O
16-bit	B-Device
DMA	B-General_Concept
channel	O
each	O
.	O
</s>
<s>
Originally	O
,	O
the	O
bus	B-General_Concept
clock	O
was	O
synchronous	O
with	O
the	O
CPU	B-General_Concept
clock	O
,	O
resulting	O
in	O
varying	O
bus	B-General_Concept
clock	O
frequencies	O
among	O
the	O
many	O
different	O
IBM	O
"	O
clones	O
"	O
on	O
the	O
market	O
(	O
sometimes	O
as	O
high	O
as	O
16	O
or	O
20MHz	O
)	O
,	O
leading	O
to	O
software	O
or	O
electrical	O
timing	O
problems	O
for	O
certain	O
ISA	B-Architecture
cards	I-Architecture
at	B-Architecture
bus	I-Architecture
speeds	O
they	O
were	O
not	O
designed	O
for	O
.	O
</s>
<s>
Later	O
motherboards	B-Device
or	O
integrated	O
chipsets	B-Device
used	O
a	O
separate	O
clock	O
generator	O
,	O
or	O
a	O
clock	O
divider	O
which	O
either	O
fixed	O
the	O
ISA	B-Architecture
bus	I-Architecture
frequency	O
at	O
4	O
,	O
6	O
,	O
or	O
8MHz	O
or	O
allowed	O
the	O
user	O
to	O
adjust	O
the	O
frequency	O
via	O
the	O
BIOS	B-Operating_System
setup	O
.	O
</s>
<s>
When	O
used	O
at	O
a	O
higher	O
bus	B-General_Concept
frequency	O
,	O
some	O
ISA	B-Architecture
cards	I-Architecture
(	O
certain	O
Hercules-compatible	B-Device
video	O
cards	O
,	O
for	O
instance	O
)	O
,	O
could	O
show	O
significant	O
performance	O
improvements	O
.	O
</s>
<s>
Memory	O
address	O
decoding	O
for	O
the	O
selection	O
of	O
8	O
or	O
16-bit	B-Device
transfer	O
mode	O
was	O
limited	O
to	O
128KiB	O
sections	O
,	O
leading	O
to	O
problems	O
when	O
mixing	O
8	O
-	O
and	O
16-bit	B-Device
cards	O
as	O
they	O
could	O
not	O
co-exist	O
in	O
the	O
same	O
128KiB	O
area	O
.	O
</s>
<s>
In	O
2008	O
IEI	O
Technologies	O
released	O
a	O
modern	O
motherboard	B-Device
for	O
Intel	O
Core	O
2	O
Duo	O
processors	O
which	O
,	O
in	O
addition	O
to	O
other	O
special	O
I/O	O
features	O
,	O
is	O
equipped	O
with	O
two	O
ISA	B-Architecture
slots	I-Architecture
.	O
</s>
<s>
It	O
is	O
marketed	O
to	O
industrial	O
and	O
military	O
users	O
who	O
have	O
invested	O
in	O
expensive	O
specialized	O
ISA	B-Architecture
bus	I-Architecture
adaptors	O
,	O
which	O
are	O
not	O
available	O
in	O
PCI	B-Protocol
bus	I-Protocol
versions	O
.	O
</s>
<s>
Similarly	O
,	O
ADEK	O
Industrial	B-Device
Computers	I-Device
is	O
releasing	O
a	O
motherboard	B-Device
in	O
early	O
2013	O
for	O
Intel	O
Core	O
i3/i5/i7	O
processors	O
,	O
which	O
contains	O
one	O
(	O
non-DMA	O
)	O
ISA	B-Architecture
slot	I-Architecture
.	O
</s>
<s>
The	O
PC/104	B-Device
bus	B-General_Concept
,	O
used	O
in	O
industrial	O
and	O
embedded	O
applications	O
,	O
is	O
a	O
derivative	O
of	O
the	O
ISA	B-Architecture
bus	I-Architecture
,	O
utilizing	O
the	O
same	O
signal	O
lines	O
with	O
different	O
connectors	O
.	O
</s>
<s>
The	O
LPC	O
bus	B-General_Concept
has	O
replaced	O
the	O
ISA	B-Architecture
bus	I-Architecture
as	O
the	O
connection	O
to	O
the	O
legacy	O
I/O	O
devices	O
on	O
recent	O
motherboards	B-Device
;	O
while	O
physically	O
quite	O
different	O
,	O
LPC	O
looks	O
just	O
like	O
ISA	O
to	O
software	O
,	O
so	O
that	O
the	O
peculiarities	O
of	O
ISA	O
such	O
as	O
the	O
16	O
MiB	O
DMA	B-General_Concept
limit	O
(	O
which	O
corresponds	O
to	O
the	O
full	O
address	O
space	O
of	O
the	O
Intel	B-General_Concept
80286	I-General_Concept
CPU	B-General_Concept
used	O
in	O
the	O
original	O
IBM	B-Operating_System
AT	I-Operating_System
)	O
are	O
likely	O
to	O
stick	O
around	O
for	O
a	O
while	O
.	O
</s>
<s>
As	O
explained	O
in	O
the	O
History	O
section	O
,	O
ISA	O
was	O
the	O
basis	O
for	O
development	O
of	O
the	O
ATA	B-Protocol
interface	O
,	O
used	O
for	O
ATA	B-Protocol
(	O
a.k.a.	O
</s>
<s>
IDE	O
)	O
hard	B-Device
disks	I-Device
.	O
</s>
<s>
Physically	O
,	O
ATA	B-Protocol
is	O
essentially	O
a	O
simple	O
subset	O
of	O
ISA	O
,	O
with	O
16	O
data	O
bits	O
,	O
support	O
for	O
exactly	O
one	O
IRQ	B-General_Concept
and	O
one	O
DMA	B-General_Concept
channel	O
,	O
and	O
3	O
address	O
bits	O
.	O
</s>
<s>
To	O
this	O
ISA	O
subset	O
,	O
ATA	B-Protocol
adds	O
two	O
IDE	O
address	O
select	O
(	O
"	O
chip	O
select	O
"	O
)	O
lines	O
(	O
i.e.	O
</s>
<s>
address	O
decodes	O
,	O
effectively	O
equivalent	O
to	O
address	O
bits	O
)	O
and	O
a	O
few	O
unique	O
signal	O
lines	O
specific	O
to	O
ATA/IDE	B-Protocol
hard	B-Device
disks	I-Device
(	O
such	O
as	O
the	O
Cable	O
Select/Spindle	O
Sync	O
.	O
</s>
<s>
In	O
addition	O
to	O
the	O
physical	O
interface	O
channel	O
,	O
ATA	B-Protocol
goes	O
beyond	O
and	O
far	O
outside	O
the	O
scope	O
of	O
ISA	O
by	O
also	O
specifying	O
a	O
set	O
of	O
physical	O
device	O
registers	O
to	O
be	O
implemented	O
on	O
every	O
ATA	B-Protocol
(	O
IDE	O
)	O
drive	O
and	O
a	O
full	O
set	O
of	O
protocols	O
and	O
device	O
commands	O
for	O
controlling	O
fixed	B-Device
disk	I-Device
drives	I-Device
using	O
these	O
registers	O
.	O
</s>
<s>
The	O
ATA	B-Protocol
device	O
registers	O
are	O
accessed	O
using	O
the	O
address	O
bits	O
and	O
address	O
select	O
signals	O
in	O
the	O
ATA	B-Protocol
physical	O
interface	O
channel	O
,	O
and	O
all	O
operations	O
of	O
ATA	B-Protocol
hard	B-Device
disks	I-Device
are	O
performed	O
using	O
the	O
ATA-specified	O
protocols	O
through	O
the	O
ATA	B-Protocol
command	I-Protocol
set	I-Protocol
.	O
</s>
<s>
The	O
earliest	O
versions	O
of	O
the	O
ATA	B-Protocol
standard	O
featured	O
a	O
few	O
simple	O
protocols	O
and	O
a	O
basic	O
command	O
set	O
comparable	O
to	O
the	O
command	O
sets	O
of	O
MFM	O
and	O
RLL	O
controllers	O
(	O
which	O
preceded	O
ATA	B-Protocol
controllers	O
)	O
,	O
but	O
the	O
latest	O
ATA	B-Protocol
standards	O
have	O
much	O
more	O
complex	O
protocols	O
and	O
instruction	O
sets	O
that	O
include	O
optional	O
commands	O
and	O
protocols	O
providing	O
such	O
advanced	O
optional-use	O
features	O
as	O
sizable	O
hidden	O
system	O
storage	O
areas	O
,	O
password	O
security	O
locking	O
,	O
and	O
programmable	O
geometry	O
translation	O
.	O
</s>
<s>
A	O
further	O
deviation	O
between	O
ISA	O
and	O
ATA	B-Protocol
is	O
that	O
while	O
the	O
ISA	B-Architecture
bus	I-Architecture
remained	O
locked	O
into	O
a	O
single	O
standard	O
clock	O
rate	O
(	O
for	O
backward	O
hardware	O
compatibility	O
)	O
,	O
the	O
ATA	B-Protocol
interface	O
offered	O
many	O
different	O
speed	O
modes	O
,	O
could	O
select	O
among	O
them	O
to	O
match	O
the	O
maximum	O
speed	O
supported	O
by	O
the	O
attached	O
drives	O
,	O
and	O
kept	O
adding	O
faster	O
speeds	O
with	O
later	O
versions	O
of	O
the	O
ATA	B-Protocol
standard	O
(	O
up	O
to	O
133	O
MB/s	O
for	O
ATA-6	B-Protocol
,	O
the	O
latest	O
.	O
)	O
</s>
<s>
In	O
most	O
forms	O
,	O
ATA	B-Protocol
ran	O
much	O
faster	O
than	O
ISA	O
,	O
provided	O
it	O
was	O
connected	O
directly	O
to	O
a	O
local	O
bus	B-General_Concept
(	O
e.g.	O
</s>
<s>
southbridge-integrated	O
IDE	O
interfaces	O
)	O
faster	O
than	O
the	O
ISA	B-Architecture
bus	I-Architecture
.	O
</s>
<s>
Before	O
the	O
16-bit	B-Device
ATA/IDE	B-Protocol
interface	O
,	O
there	O
was	O
an	O
8-bit	O
XT-IDE	O
(	O
also	O
known	O
as	O
XTA	O
)	O
interface	O
for	O
hard	B-Device
disks	I-Device
.	O
</s>
<s>
It	O
was	O
not	O
nearly	O
as	O
popular	O
as	O
ATA	B-Protocol
has	O
become	O
,	O
and	O
XT-IDE	O
hardware	O
is	O
now	O
fairly	O
hard	O
to	O
find	O
.	O
</s>
<s>
Some	O
XT-IDE	O
adapters	O
were	O
available	O
as	O
8-bit	O
ISA	B-Architecture
cards	I-Architecture
,	O
and	O
XTA	O
sockets	O
were	O
also	O
present	O
on	O
the	O
motherboards	B-Device
of	O
Amstrad	O
's	O
later	O
XT	B-Device
clones	I-Device
as	O
well	O
as	O
a	O
short-lived	O
line	O
of	O
Philips	O
units	O
.	O
</s>
<s>
The	O
XTA	O
pinout	O
was	O
very	O
similar	O
to	O
ATA	B-Protocol
,	O
but	O
only	O
eight	O
data	O
lines	O
and	O
two	O
address	O
lines	O
were	O
used	O
,	O
and	O
the	O
physical	O
device	O
registers	O
had	O
completely	O
different	O
meanings	O
.	O
</s>
<s>
A	O
few	O
hard	B-Device
drives	I-Device
(	O
such	O
as	O
the	O
Seagate	O
ST351A/X	O
)	O
could	O
support	O
either	O
type	O
of	O
interface	O
,	O
selected	O
with	O
a	O
jumper	O
.	O
</s>
<s>
Many	O
later	O
AT	O
(	O
and	O
AT	O
successor	O
)	O
motherboards	B-Device
had	O
no	O
integrated	O
hard	B-Device
drive	I-Device
interface	O
but	O
relied	O
on	O
a	O
separate	O
hard	B-Device
drive	I-Device
interface	O
plugged	O
into	O
an	O
ISA/EISA/VLB	O
slot	O
.	O
</s>
<s>
Commodore	O
built	O
the	O
XT-IDE	O
based	O
peripheral	O
hard	B-Device
drive	I-Device
/	O
memory	O
expansion	O
unit	O
A590	O
for	O
their	O
Amiga	B-Device
500	I-Device
and	O
500+	O
computers	O
that	O
also	O
supported	O
a	O
SCSI	B-Architecture
drive	O
.	O
</s>
<s>
Later	O
models	O
–	O
the	O
A600	B-Device
,	O
A1200	B-Application
,	O
and	O
the	O
Amiga	B-Device
4000	I-Device
series	O
–	O
use	O
AT-IDE	O
drives	O
.	O
</s>
<s>
The	O
PCMCIA	B-Architecture
specification	O
can	O
be	O
seen	O
as	O
a	O
superset	O
of	O
ATA	B-Protocol
.	O
</s>
<s>
The	O
standard	O
for	O
PCMCIA	B-Architecture
hard	B-Device
disk	I-Device
interfaces	I-Device
,	O
which	O
included	O
PCMCIA	B-Architecture
flash	O
drives	O
,	O
allows	O
for	O
the	O
mutual	O
configuration	O
of	O
the	O
port	O
and	O
the	O
drive	O
in	O
an	O
ATA	B-Protocol
mode	O
.	O
</s>
<s>
As	O
a	O
de	O
facto	O
extension	O
,	O
most	O
PCMCIA	B-Architecture
flash	O
drives	O
additionally	O
allow	O
for	O
a	O
simple	O
ATA	B-Protocol
mode	O
that	O
is	O
enabled	O
by	O
pulling	O
a	O
single	O
pin	O
low	O
,	O
so	O
that	O
PCMCIA	B-Architecture
hardware	O
and	O
firmware	O
are	O
unnecessary	O
to	O
use	O
them	O
as	O
an	O
ATA	B-Protocol
drive	I-Protocol
connected	O
to	O
an	O
ATA	B-Protocol
port	O
.	O
</s>
<s>
PCMCIA	B-Architecture
flash	O
drive	O
to	O
ATA	B-Protocol
adapters	O
are	O
thus	O
simple	O
and	O
inexpensive	O
,	O
but	O
are	O
not	O
guaranteed	O
to	O
work	O
with	O
any	O
and	O
every	O
standard	O
PCMCIA	B-Architecture
flash	O
drive	O
.	O
</s>
<s>
Further	O
,	O
such	O
adapters	O
cannot	O
be	O
used	O
as	O
generic	O
PCMCIA	B-Architecture
ports	O
,	O
as	O
the	O
PCMCIA	B-Architecture
interface	O
is	O
much	O
more	O
complex	O
than	O
ATA	B-Protocol
.	O
</s>
<s>
Although	O
most	O
modern	O
computers	O
do	O
not	O
have	O
physical	O
ISA	O
buses	O
,	O
almost	O
all	O
PCs	O
—	O
x86-32	B-Device
,	O
and	O
x86-64	B-Device
—	O
have	O
ISA	O
buses	O
allocated	O
in	O
physical	O
address	O
space	O
.	O
</s>
<s>
some	O
Southbridges	B-Device
and	O
some	O
CPUs	O
themselves	O
provide	O
services	O
such	O
as	O
temperature	O
monitoring	O
and	O
voltage	O
readings	O
through	O
ISA	O
buses	O
as	O
ISA	O
devices	O
.	O
</s>
<s>
IEEE	O
started	O
a	O
standardization	O
of	O
the	O
ISA	B-Architecture
bus	I-Architecture
in	O
1985	O
,	O
called	O
the	O
P996	O
specification	O
.	O
</s>
<s>
There	O
still	O
is	O
an	O
existing	O
user	O
base	O
with	O
old	O
computers	O
,	O
so	O
some	O
ISA	B-Architecture
cards	I-Architecture
are	O
still	O
manufactured	O
,	O
e.g.	O
</s>
<s>
with	O
USB	B-Protocol
ports	I-Protocol
or	O
complete	O
single-board	B-Device
computers	I-Device
based	O
on	O
modern	O
processors	O
,	O
USB	B-Protocol
3.0	O
,	O
and	O
SATA	O
.	O
</s>
