PCI Express 6.0 Reaches Version 0.5 Ahead Of Finalization Next Year

[phoronix]

Phoronix: PCI Express 6.0 Reaches Version 0.5 Ahead Of Finalization Next Year

Following the PCI Express 6.0 announcement from last summer that called for 64 GT/s transfer rates, version 0.5 of the PCIe 6.0 specification is now out for evaluation...

http://www.phoronix.com/scan.php?page=news_item&px=PCI-Express-6.0-v0.5

[FireBurn]

Michael what's PAM-4 encoding?

[Danny3]

Does the chipset still comes with a fan?
I don't want any moving parts on the motherboard which makes it less reliable.
And I don't want any noise coming from the motherboard. I want to make the computer as silent as possible.
I assume the power consumption is even higher which I don't like also.
So, with all these anti-features, I think I will say again no thanks and buy an older motherboard instead.

[ix900]

Michael what's PAM-4 encoding?

I'm not him but,

pam-4 is a modulation technique. I don't think it really matters in knowing about it though. There's also for example pam-8. All we really need to know is that PCI-E 6 > 4 and eventually if you need new hardware you will have to go with 6 or greater at some point.

https://www.neophotonics.com/pam-4-key-solution-next-generation-short-haul-optical-fiber-links/

[jo-erlend]

Does the chipset still comes with a fan?
I don't want any moving parts on the motherboard which makes it less reliable.
And I don't want any noise coming from the motherboard. I want to make the computer as silent as possible.
I assume the power consumption is even higher which I don't like also.
So, with all these anti-features, I think I will say again no thanks and buy an older motherboard instead.

You can always use passive cooling, you know.

[nomadewolf]

Does the chipset still comes with a fan?
I don't want any moving parts on the motherboard which makes it less reliable.
And I don't want any noise coming from the motherboard. I want to make the computer as silent as possible.
I assume the power consumption is even higher which I don't like also.
So, with all these anti-features, I think I will say again no thanks and buy an older motherboard instead.

There are motherboard options with passive cooling.

[StefanBruens]

Michael what's PAM-4 encoding?

PAM - Pulse Amplitude Modulation

Binary would be PAM-2, two different voltages or currents. Current ethernet (twisted pair, 1G) uses PAM-5. Current SSDs use multple levels as well, so you could call it PAM-4 ("MLC", multi level), PAM-8 ("TLC", triple, more correctly 2^3) or even PAM-16, though the PAM term is typically only used for transmissions.

For wireless communications, PAM-2 is called BPSK (Binary Phase Shift Keying), two points on a unit circle spaced 180 degrees apart, which happen two lie on a straight line through the circle center. For higher bitrates the first step is two add a second, same frequency but orthogonal carrier (sine and cosine), which gives you QAM. If each of the carriers has two levels, you have QAM-4 (though thats called QPSK), with 4 levels each ("PAM-4") you have QAM-16. Most current WIFI uses up to QAM-1024, i.e. up to 32 different levels per carrier.

The win of using higher modulation is higher data rates without using more spectrum. The downside is each valid level has less distance to its other valid neighbours, so it can't tolerate as much noise. Also the hardware implementation becomes more complex - the receiver now essentially needs an ADC running at several GSample/s, though only with a few bits.

[tg--]

Michael what's PAM-4 encoding?

To provide a slightly simpler explaination than StefanBruens, in addition:
The signal lines to PCIe ports are not purely digital (on, off/1, 0), they carry a defined voltage.
What PAM does is add the possibility to decode partial voltages in steps (PAM-4 is 4 steps), which increases the datarate.
In PAM-4 the voltage between 0 and 1 is divided in 4 steps, so every cycle encodes 2 bits (2^2 is 4 steps), thus doubling the data rate.

[bug77]

To provide a slightly simpler explaination than StefanBruens, in addition:
The signal lines to PCIe ports are not purely digital (on, off/1, 0), they carry a defined voltage.
What PAM does is add the possibility to decode partial voltages in steps (PAM-4 is 4 steps), which increases the datarate.
In PAM-4 the voltage between 0 and 1 is divided in 4 steps, so every cycle encodes 2 bits (2^2 is 4 steps), thus doubling the data rate.

And dividing the acceptable noise levels by 3. This is going to work wonders for signal integrity/reach.
Though I'm sure the engineers working on the spec are more aware of this than I am.

[tg--]

And dividing the acceptable noise levels by 3. This is going to work wonders for signal integrity/reach.
Though I'm sure the engineers working on the spec are more aware of this than I am.

There is always a tradeoff to be made, nothing comes for free.
Usually higher-order modulation works better than doubling the clock, which comes with its own set of downsides.
To achieve acceptable robustness, PCIe 6.0 will very likely also add Forward-Error-Correction, which will decrease the net-throughput.

Most importantly, PAM-4 is a very very simple modulation, which makes it reasonably cheap. Doubling the clock would require quite a bit more expensive hardware.