AGP speed 2X,4x,8X: What it really means!

The speed difference between serial and parallel is; a byte needs to be
converted twice as often when its transmitted in parallel than when its
done serially. The main reason most things are done in parallel is
because its more cost effective and is easier to implement. Serial data
paths can't be too long because of resistance of the conductor which
causes data loss, thats why they use multiple shorter paths instead. The
main problem comes when there is too many of those shorter paths close
together and have "cross-talk" which causes data corruption. If any data
is lost or corrupt it needs to be re-sent and reduces throughput. This
happens more often with a parallel connection than serial, thats why
they needed the 80 conductor cables for IDE to support higher
throughput. Every other conductor is tied to ground to reduce cross-talk
between adjacent data lines. Hope this clears things up a bit.

Chris

It does thank you.

"PRIVATE1964" wrote in message
...

The speed difference between serial and parallel is; a byte needs to be
converted twice as often when its transmitted in parallel than when its
done serially. The main reason most things are done in parallel is
because its more cost effective and is easier to implement. Serial data
paths can't be too long because of resistance of the conductor which
causes data loss, thats why they use multiple shorter paths instead. The
main problem comes when there is too many of those shorter paths close
together and have "cross-talk" which causes data corruption. If any data
is lost or corrupt it needs to be re-sent and reduces throughput. This
happens more often with a parallel connection than serial, thats why
they needed the 80 conductor cables for IDE to support higher
throughput. Every other conductor is tied to ground to reduce cross-talk
between adjacent data lines. Hope this clears things up a bit.

Chris

It does thank you.

I think it's parallel communication that can't be used for long distances
rather than serial. With multiple lines of data, the signals start to skew
with long distances (where the data bits arrive at different times instead
the same time like they're supposed to). And if you try to clock it faster,
the skew becomes a big problem. With serial communication, the data bits
will arrive in the same order that you send them no matter how fast it's
going. I guess that's one reason why SATA came about.

Vu.

"Chris Madsen" wrote in message
...
Chip wrote:

The performance of PCI-express is not dramatically
better than AGP 8X. And since the performance increase you see when
going
from AGP 4x to AGP 8x is very very small, expect a similarly pathetic
performance boost moving to PCI-express. Its principle advantages are
for
Raid disk controllers and the like, because the old PCI standard has
become
a real bottleneck; AGP has not.
{snip}
With respect to graphics controllers, the only real advantages
PCI-Express
offers are that (A) it is bi-directional. This is beneficial in some
CAD
type modelling environments. and (B) the PCI-Express connector standard
can
carry more current than the PCI connector. Bottom line is PCI-express
is a
complete waste of time for gaming speed improvements. Anyone looking to
"upgrade" their graphics card specifically to take advantage of
PCI-Express
is going to be very disappointed.

I'm not sure about the CAD application benefits but the old PCI bus is
still fast enough for RAID as its capacity is 133MB/s and the best RAID
speed will only burst at ~85MB/s in real world.

That's just not true I am afraid. I agree that often it is the case, but
certainly its not always the case. 2 x 74GB Raptors will transfer 140MB/s
in real world tests. (And BTW the maximum you seem to be able to get
through PCI is only around 117MB/s: although the spec allows 133, that's not
really available in practice.) Also, you completely ignore multiple disk
Raid systems. Since - broadly speaking - 4 x 100GB is not much different in
price from 1 x 400GB, Raid 5 becomes a real possibility for even home PC's.
Why not buy 4 smaller disks instead of 1 large one? Its much faster than a
single disk and offers resiliance too. A Raid 5 setup like this just can't
work properly on PCI.

[snip]

Power shouldn't be much of an issue as most
hungry cards have connectors on them to get what they need directly from
the main supply anyway.

I agree its not much of an issue. But its a fudge, and its only been
brought about by the very limited power supply capability of the PCI slot.
The new PCI-Express standard aims to improve that. Certainly there will
always be some cards that will still need their own dedicated power supply,
but there will be many "mid-range" cards that won't need it on PCI-Express.
And this will help to keep the costs down and simplify wiring etc. I know
its not a big deal, but it is a marginal improvement.

Chip

PRIVATE1964 wrote:


The speed difference between serial and parallel is; a byte needs to be
converted twice as often when its transmitted in parallel than when its
done serially. The main reason most things are done in parallel is
because its more cost effective and is easier to implement. Serial data
paths can't be too long because of resistance of the conductor which
causes data loss, thats why they use multiple shorter paths instead. The
main problem comes when there is too many of those shorter paths close
together and have "cross-talk" which causes data corruption. If any data
is lost or corrupt it needs to be re-sent and reduces throughput. This
happens more often with a parallel connection than serial, thats why
they needed the 80 conductor cables for IDE to support higher
throughput. Every other conductor is tied to ground to reduce cross-talk
between adjacent data lines. Hope this clears things up a bit.

Chris

It does thank you.

Except that it makes no sense.

--
--John
Reply to jclarke at ae tee tee global dot net
(was jclarke at eye bee em dot net)

Chris Madsen wrote:

PRIVATE1964 wrote:
"serial" connection not "parallel"


I really don't understand that concept. How can data be faster moving
down a single path? Is it because the path can be run at a much higher
clock speed?

Got it in one.

What happens with parrallel does the data get corrupted
easier?

It can if the circuit is badly designed.

The real purpose of PCI Express though is to make money for Intel. There
are alternatives that give the same performance and allow the use of
existing PCI boards in the same slots that take the higher performance
boards. But that would mean that people didn't have to throw away there
entire investment in older hardware to use the new technology.

The speed difference between serial and parallel is; a byte needs to be
converted twice as often when its transmitted in parallel than when its
done serially.

"Converted"? From what to what? And why would serial take fewer
"conversions" than parallel?

The main reason most things are done in parallel is
because its more cost effective and is easier to implement.

"Most things"? Such as?

Serial data
paths can't be too long because of resistance of the conductor which
causes data loss, thats why they use multiple shorter paths instead.

So how does using parallel data paths gain you anything over serial if the
parallel paths are shorter? And it's possible to transfer about the same
amount of over 100 meters of CAT5 cable using gigabit Ethernet as over the
few inches of parallel circuit trace that makes up the PCI bus, so what's
wrong with your picture?

The
main problem comes when there is too many of those shorter paths close
together and have "cross-talk" which causes data corruption. If any data
is lost or corrupt it needs to be re-sent and reduces throughput.

I see, so what mechanism on the PCI bus resends corrupted data?

This
happens more often with a parallel connection than serial,

All else being equal it does. It's debatable whether running a serial
connection 16 times faster gives any real improvement in reliability
though.

thats why
they needed the 80 conductor cables for IDE to support higher
throughput. Every other conductor is tied to ground to reduce cross-talk
between adjacent data lines.

The first part that you've gotten unambiguously right.

Hope this clears things up a bit.

Chris

--
--John
Reply to jclarke at ae tee tee global dot net
(was jclarke at eye bee em dot net)

Except that it makes no sense.

It makes sense.

PRIVATE1964 wrote:

Except that it makes no sense.

It makes sense.

Only if you don't try to apply logic to it.

--
--John
Reply to jclarke at ae tee tee global dot net
(was jclarke at eye bee em dot net)

"PRIVATE1964" wrote in message
...
Except that it makes no sense.

It makes sense.

Sorry Private, I am with J Clark on this one. I think you have some useful
concepts, but some of it is not quite right. For example this "byte needs
to be converted twice..." stuff. That's complete nonsense. The data is
parallel in the first pace. The CPU reads and writes words, not bits, or
even bytes. Its very easy for a parallel controller to read data in
parallel and output it in parallel. Ironically, to do it serially takes
more work.

Chip.

It makes sense.

I meant it makes sense in a general way.

Like the extra 40 conductors in an EIDE cable which help keep crosstalk down.
That's accurate. Length of cable also. EIDE is maxed at 18" I believe but the
serial cable could be longer and run faster because of less chance of cross
talk. It's a lot easier to shield a single cable then to shield a large number
of cables like with EIDE.

That's all I know and I'm sticking by it. : )

Like the extra 40 conductors in an EIDE cable which help keep crosstalk down.
That's accurate. Length of cable also. EIDE is maxed at 18" I believe but the
serial cable could be longer and run faster because of less chance of cross
talk. It's a lot easier to shield a single cable then to shield a large number
of cables like with EIDE.

That's all I know and I'm sticking by it. : )

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I'm running a hard drive on a 36" round IDE cable with no problems. I needed it
because it's a full tower case so the cable will reach. DOUG