Optical PCIe 7.0 connection hits 128 GT/s

An once that becomes generally available operating systems will eat the bandwidth in an instance and any speed-up to be gained on a desktop will be completely negated.

It seems like we're stuck at a pre-set level of latency, which is just within what people tolerate. I was watching a video of someone running Windows 3.11 and notice that the windows closes instantly, which on Windows 10 and 11 I've never seen there NOT be a small delay between the user clicking close and the window disappearing.

> It seems like we're stuck at a pre-set level of latency,

Bandwidth isn't latency, and PCIe 7.0 running as fast as 128 GT/s is no statement at all about its latency. I remember this great analogy from university: a truck carrying a full load of backup tapes across a country has amazing bandwidth but atrocious latency.

(I still agree with your sentiment, just PCIe is not one of the problems in this regard. The connection between bandwidth becoming available and being eaten up vs. latency is a red herring; it's all about properly engineering software for responsitivity.)

GT/s is a measure of latency (not total system latency, but the bus itself is only adding 128 billionth of a second). In fact it does not say anything about bandwidth if you don't know how many bits in a transfer.

I'm sorry, but you're multiply wrong. First, a "transfer" is not a term in the PCIe spec; if anything, there's "transaction". But GT/s does not refer to transactions as you seem to be implying, and in fact "GT" does not have an assigned long form in the PCIe base specification. The term is introduced / defined like this:

| The primary Link attributes for PCI Express Link are:

| · The basic Link – PCI Express Link consists of dual unidirectional differential Links, implemented as a Transmit pair and a Receive pair. A data clock is embedded using an encoding scheme (see Chapter 4) to achieve very high data rates.

| · Signaling rate – Once initialized, each Link must only operate at one of the supported signaling levels. For the first generation of PCI Express technology, there is only one signaling rate defined, which provides an effective 2.5 Gigabits/second/Lane/direction of raw bandwidth. The second generation provides an effective 5.0 Gigabits/second/Lane/direction of raw bandwidth. The third generation provides an effective 8.0 Gigabits/second/Lane/direction of raw bandwidth. The data rate is expected to increase with technology advances in the future.

| · Lanes – A Link must support at least one Lane – each Lane represents a set of differential signal pairs (one pair for transmission, one pair for reception). To scale bandwidth, a Link may aggregate multiple Lanes denoted by xN where N may be any of the supported Link widths. A x8 Link operating at the 2.5 GT/s data rate represents an aggregate bandwidth of 20 Gigabits/second of raw bandwidth in each direction. This specification describes operations for x1, x2, x4, x8, x12, x16, and x32 Lane widths.

(from PCIe 4.0 base specification)

So, GT/s is used to be less ambiguous on multi-lane links.

Next,

> the bus itself is only adding 128 billionth of a second).

no, the bus does actually add more latency since almost all receivers need to reassemble the whole transaction (generally tens to hundreds of bytes) to checksum validate and then dispatch further to continue. This latency can show up multiple times if you have PCIe switches, but (unlike endpoints) these are frequently cut-through.

However, that latency is seriously negligible compared to anything else in your system.

> In fact it does not say anything about bandwidth if you don't know how many bits in a transfer.

How many bits are in a transaction does in fact influence that latency mentioned right above, but has no impact on bandwidth. What does have an impact on available end-user bandwidth is how small you chunk longer transactions since each of them has per-transaction overhead.

And finally —

> GT/s is a measure of latency

— absolutely not. It is a measure of raw bandwidth. It indirectly influences minimum and maximum latency, but those are complicated relationships especially on multi-lane links, and especially maximum latency depends on a whole host of factors from hardware capabilities, to BIOS and OS settings in PCIe config, to driver behavior.

I do totally agree about the relative merits of bandwidth vs latency. However, I also still think GT/s is generally accepted as an abbreviation for gigatransfers per second and that the PCIe spec is assuming it as such. I also note you have had to pull in lots of additional specifications to describe the bandwidth of the complete Link supporting my assertion it is not a pure function of the GT/s.