PCIE. It's about throughput of information. Country roads. Town roads. Freeways. (Motorways in the UK eg. The M25.)
The wider those lanes? The less congested the traffic. (Allegedly...but people always use the available 'bandwidth' or road space in computers and on roads until it's choked and needs to be upgraded again.
Eg. On here. Some have mentioned the TB3 protocol not being sufficient for eGPUs. And, ultimately, it isn't.
The current 'Road' is PCIE 3 is 'fast enough.' But we're in a progress to the next road (which is wider) called PCIE 4. Probably more lanes and faster traffic allowed. Which will give an overall boost to system responsiveness and how fast devices can go on that system. Roads. Cars. How wide the roads. How fast the cars.
Apple may postpone using this protocol. (I note they omitted it with the Mac Pro...but came up with their own solution for the GPUs et al for now.) Because...PCIE5 is road the corner and will be warp speed compared to PCIE4 and make PCIE3 seem quaint.
The problem with PCIE 4 is that the PCIE5 protocol is right on it's heels in relative terms. And PCIE 5 (from what I've read and heard) buries it. Probably in the way that RDNA2 buries RDNA1.
So. Do we wait for PCIE5? In an Apple device it's probably years away. Same with PCIE4. Probably 2021 if we're lucky in Macs. And there's the Mac ARM transition too. Which may muddy how Apple supports things in Mac regarding TB, PCIE etc. And there's buying for peripherals for PCIE3...4...5...er...do I wait...do I buy now...do I wait...etc...then upgrade later...
In short, any iMac revision is going to put the current out of date one in the shade. Any move to RDNA2 will bury the current iMac and iMac Pro. PCIE3 will hold just fine for the next year. But the latest AMD mobos are supporting PCIE 4.
Unless you're running an eGPU, I wouldn't worry about it 'that much.' And similarly, for SSDs. Sure they get a substantial boost with PCIE 4...but honestly? Apple do pretty good with the speeds on SSDs right now. At least until the dust settles on PCIE4 vs 5.
Apple sometimes seems very conservative in adopting protocols until there is a true market consensus.
So it's about overall system responsiveness. You can have a very fast cpu and/or gpu. But if the road you're using is too narrow? The system can 'wait' to feed that information through. An example of one such bottle neck being fixed was the move from Hard Drive to SSD.
What is exciting on the PS5 is that Sony have gone the expensive route of super fast IO 'throughput' with a super fast SSD tech' to shuttle it through. It's the hardest and least common thing to do, it seems. CPUs and gpus get more attention. But ultimately it's about balancing each part of the system.
You can have the fastest cpu and gpu in the world. But if you're wait on the harddrive to feed the info through the IO system...you get a massive choke point. eg. Waiting for games to 'load.'
TB3. Let's give it a '40mph.' I was hoping TB4 would be an '80mph.' But instead of making the road faster, I think they've 'just' made it wider? And consolidated the branding as USB3, USB3.1 and what was and wasn't compatible with TB3 seemed head ache inducing...into TB4. One plug and one brand to rule them all. We hope. As it seemed messy. And is the licensing on it now 'free' as well to aid adoption?
Azrael.
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PCIE 4. I don't see it having any impact on iMac or iMac Pro this year. It isn't on the Mac Pro. So they probably aren't going to get it.
Somebody correct me if I'm wrong. But doesn't the iPad work in a more integrated way in terms of IO/Ram/SSD? And maybe this kind of tech' will come to Mac care of the Mac Arm Transition.
But the PS5 is going to get something even better than PCIE4 it seems. And therefore 'we'll' have open worlds that load instantly as opposed to corridor sequences whilst the main game data loads. So for a taste of what 'PCIE' means in terms of computers in the next few years, check out the PS5 launch and how games are going to change as a result of it's next level IO and SSD throughput.
Might take PCs (and certainly Macs) a couple of years to catch up.
Azrael.