PCI Express 6.0 Reaches Version 0.5 Ahead Of Finalization Next Year

[coder]

I am not a fan of inflating price levels due to higher costs from build materials and using retimers. The engineers should have come up with something more clever than that.

Like cables? Twin-axial cables are pretty much the only alternative, AFAIK.

[coder]

maybe enterprise will take care of costs this time around and it will be affordable once we need it in a PC.

1. You won't need it in a (desktop) PC. Desktops don't currently "need" PCIe 4.0, even if some synthetic SSD and GPU benchmarks can show a slight benefit.
2. Enterprise will not "take care of costs". It will probably always be expensive and exotic, like 100+ Gigabit networking.

[coder]

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.

From what I understand, doubling the clock frequency of PCIe 5.0 is not just more expensive, it's completely infeasible.

[coder]

There are motherboard options with passive cooling.

No, there won't be for PCIe 5.0+.

Even the few X570 (Ryzen 3000-series) boards that don't have active chipset coolers will still require a fair amount of airflow.

[zxy_thf]

There are motherboard options with passive cooling.

In addition, Epyc is SOC and no chipset on motherboard. I'm hoping next TR follows this.

[torsionbar28]

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

Meanwhile, Intel will still be stuck at PCIe 3.0 and 14 nm CPU's, lol.

[brouhaha]

This depends on if your two levels are [0,1] or [1,-1]. The latter obviously is the same as phase inversion, i.e. BPSK.

Thanks, you're obviously correct. I hadn't considered the [+1, -1] case.

[brouhaha]

In radio modulation PAM generally means Phase Angle Modulation.

Interesting. While I've heard of "phase angle modulation", I've never seen it abbreivated "PAM". All of the phase-only modulation techniques I've seen for radio have been called PSK or PM, or variants thereof. I've only ever seen "PAM" used for Pulse Amplitude Modulation, which is the kind of PAM used in PCIe 6.

[StefanBruens]

I may be nitpicking a bit here, but that's not quite correct, because PAM is amplitude modulation, not phase modulation (or phase keying). The radio equivalent of PAM-2 is OOK (on-off keying), which is used by many remote controls but not for high-data-rate communication. There is no commonly used radio modulation equivalent to PAM-3 or higher; high-data-rate wireless uses QAM, which modulates both amplitude and phase, or OFDM, which is multiple QAM carriers, as used by e.g. WiFi and LTE.

This depends on if your two levels are [0,1] or [1,-1]. The latter obviously is the same as phase inversion, i.e. BPSK. So OOK is another PAM-2 modulation, while ASK (Amplitude Shift Keying) would be a third one. For BPSK you obviously need to decode/recover the phase of the signal, while for OOK/ASK a trivial envelope/power detector is sufficient. If you want to go dirt cheap, use OOK/ASK.

There is actually no difference between Amplitude/Phase and Quadrature modulation if you just look at the radio signal, these are just different coordinate systems - polar vs carthesian. You can not tell QPSK and QAM-4 apart. SDR receivers are typically build as quadrature receivers, and if the signal of interest uses phase shift keying the phase is computed from the quadrature signals.

In wired communication, both [0,1] and [1,-1] are used. RS232 signals use e.g. +5/-5 volts, TTL signals are 0V/+5V.

[willmore]

I may be nitpicking a bit here, but that's not quite correct, because PAM is amplitude modulation, not phase modulation (or phase keying). The radio equivalent of PAM-2 is OOK (on-off keying), which is used by many remote controls but not for high-data-rate communication. There is no commonly used radio modulation equivalent to PAM-3 or higher; high-data-rate wireless uses QAM, which modulates both amplitude and phase, or OFDM, which is multiple QAM carriers, as used by e.g. WiFi and LTE.

In radio modulation PAM generally means Phase Angle Modulation. It's the class of modulations of which BPSK is but one. PAM-2 would be BPSK (0 and 180 degrees). PAM-4 would be QPSK (0, 90, 180, 270 degrees). I've seen PAM-8 and 16 used before. Generally beyond that, more complex modulations are used like QAM--which varies the phase and amplitude of the modulated signal. PAM has the property that the signal it generates is phase coherent which lets it be amplified by non-linear amplifiers--which are cheaper to design and can be more efficient.