| Those of you who have been around
personal computers for a while might remember plug in cards
slots referred to as ISA, EISA, Microchannel, and VESA Local
Bus. ISA, EISA, and Microchannel were replaced by PCI. VESA
Local bus was primarily for video cards, which was replaced
by PCI, then AGP slots. It was a fun time during these card
slot transitions because many times you could not use the plug
in cards from your old machine in your new computer or motherboard
or if you did it could slow down the entire system. Well guess
what, its time to do it all over again. Intel has come up with
a new slot standard PCI Express, which will start to
show up in computers/motherboards this spring.
 PCI
came out in 1992. Today these slots and its data bus technology
are used for things not envisioned when it was under development
over 12 years ago. PCI has its limitations and the PCI pro
slots never became popular. The limitations are coming to
the forefront in delivering multimedia content and Gigabit
Ethernet. Of course getting higher frame rates at higher resolution
and quality for video games also is an issue. PCI has been
evolving over time increasing its speed to five times the
original, but it has reached its limits of development. Many
say that stretching out the AGP to 8x speed might be pushing
at its limit too.
First let us look at the current PCI architecture you will
find on most motherboards. The CPU/Microprocessor communicates
with the first of two data bridges, normally referred to as
the Memory Bridge or Northbridge. The
Northbridge not only communicates with the CPU; but also communicates
to the AGP port, which is where your main graphics card is
(usually the only graphics card). It also communicates with
your RAM. The fourth thing it communicates with is the second
data bridge, known as the Input/Output (I/O) Bridge or Southbridge.
The Southbridge also communicates to your plug in slots/cards,
drive controllers, and USB, Fireware/1394, parallel. serial,
game, keyboard and mouse ports. The theoretical speed limit
of the Southbridge communication to I/O including the PCI
slots is 133 MB/second. All of the communications in the system
are parallel with none of the data having any priority over
any other. Blocks of data have to be sent one at a time and
cannot be done concurrently. Therefore the data is transferred
from one section of the motherboard to the next section based
on the order received, not the importance or whether a  piece
of data arriving by a certain time to its destination is critical.
PCI Express, instead of using a parallel bus architecture,
uses serial networking typology with only two wires for each
direction. At higher speeds, it allows concurrent transfer
of data while having a similar look and the same type of Northbridge/Southbridge
architecture as currently in desktops and laptops.
However, in servers the Southbridge is eliminated producing
greater data throughput. The PCI slots initially have a 250
MB/second throughput, but the scalable width technology (increasing
the number of wire pairs) enables slots and cards to communicate
at 32 times that speed in later implementations using longer
slots. But the typology can also use network switching type
technology, giving data priority and quality of service functions.
Hot plug/swap of components is a native part of the architecture.
 The
PCI Express Graphics Port, replacing the AGP Port,
will have a 4GB/second transfer rate in its initial configuration,
double that of the current 8x AGP ports. For laptops units
there will be a new plug-in card to replace PCMCIA called
ExpressCard. It will come  in
two forms, one that more looks like a PCMCIA card refereed
to at the 34 module form factor (34 x 75 x 5 mm) and a more
oversized L looking card called the 54 module form factor
(54 x 75 x 5 mm). This new architecture is compatible with
existing operating systems. Also the new PCI Express
slot is capable of being placed alongside current type PCI
slots so a choice can be made which type of card can be used
in a motherboard just like was done with ISA slots and current
PCI slots. The standard PCI Express slots being put
in motherboards this spring (1x) will be a lot shorter than
the standard PCI slots.
All of this will mean that a lot of issues having to do with
multimedia on desktop and laptop computers will have been
solved. It also opens wider use of Gigabit Ethernet on local
area networks. It also enables the prospects of new motherboard
form factors and computer case designs. As the transition
from ISA to PCI was an interesting transition with computer
buyers having to do more research and planning on their purchases,
the move from PCI to PCI Express will do the same.
However, as was with the previous transition, the performance
and capability increases of computers will be profound. Further
information on PCI Express can be found at www.express-lane.org.
Timothy Everingham is CEO
of Timothy Everingham Consulting in Azusa, California. He
is also Vice Chair of the Los Angeles Chapter of ACM SIGGRAPH,
the largest chapter of the Association for Computing Machinery's
(ACM) Special Interest Group on Computer Graphics and Interactive
Techniques and one of Southern California's significant professional
organizations within the entertainment and media industries.
He is also on the Management Information Systems Program Advisory
Board of California State University, Fullerton; which he
also graduated from with honors with the double majors of
Management Information Systems and Accounting. In addition
he is the Vice President of the Windows Media Users' Group
of Los Angeles. He is also part-time press in the areas of
high technology, computers, video, audio, and entertainment/media
and has had articles published throughout the United States
and Canada plus Australia, England, & Japan. He is a member
of TUGNET. Further information can be found at http://home.earthlink.net/~teveringham
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