[HN Gopher] PCIe 8.0 announced by the PCI-Sig will double throug...
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PCIe 8.0 announced by the PCI-Sig will double throughput again
Author : rbanffy
Score : 85 points
Date : 2025-08-09 22:41 UTC (4 days ago)
(HTM) web link (www.servethehome.com)
(TXT) w3m dump (www.servethehome.com)
| SlightlyLeftPad wrote:
| Any EEs that can comment on at what point do we just flip the
| architecture over so the GPU pcb is the motherboard and the
| cpu/memory lives on a PCIe slot? It seems like that would also
| have some power delivery advantages.
| vincheezel wrote:
| Good to see I'm not the only person that's been thinking about
| this. Wedging gargantuan GPUs onto boards and into cases,
| sometimes needing support struts even, and pumping hundreds of
| watts through a power cable makes little sense to me. The CPU,
| RAM, these should be modules or cards on the GPU. Imagine that!
| CPU cards might be back..
| ksec wrote:
| It is not like CPU aren't getting higher wattage as well.
| Both AMD and Intel have roadmap for 800W CPU.
|
| At 50-100W for IO, this only leaves 11W per Core on a 64 Core
| CPU.
| linotype wrote:
| 800 watt CPU with a 600 watt GPU, I mean at a certain point
| people are going to need different wiring for outlets
| right?
| jchw wrote:
| At least with U.S. wiring we have 15 amps at 120 volts.
| For continuous power draw I know you'd want an 80% margin
| of safety, so let's say you have 1440 Watts of AC power
| you can safely draw continuously. Power supplies built on
| MOSFETs seem to peak at around 90% efficiency, but you
| could consider something like the Corsair AX1600i using
| gallium nitride transistors, which supposedly can handle
| up to 1600 watts at 94% efficiency.
|
| Apparently we still have room, as long as you don't run
| anything else on the same circuit. :)
| cosmic_cheese wrote:
| Where things get hairy are old houses with wiring that's
| somewhere between shaky and a housefire waiting to
| happen, which are numerous.
| kube-system wrote:
| Yeah, but it ain't nothing that microwaves, space
| heaters, and hair dryers haven't already given a run for
| their money.
| jchw wrote:
| Hair dryers and microwaves only run for a few minutes, so
| even if you do have too much resistance this probably
| won't immediately reveal a problem. A space heater might,
| but most space heaters I've come across actually seem to
| draw not much over 1,000 watts.
|
| And even then, even if you _do_ run something 24 /7 at
| max wattage, it's definitely not guaranteed to start a
| fire even if the wiring is bad. Like, as long as it's not
| egregiously bad, I'd expect that there's enough margin to
| cover up less severe issues in most cases. I'm guessing
| the most danger would come when it's particularly hot
| outside (especially since then you'll probably have a lot
| of heat exchangers running.)
| jchw wrote:
| As an old house owner, I can attest to that for sure. In
| fairness though, I suspect most of the atrocities occur
| in wall and work boxes, as long as your house is new
| enough to at least have NM sheathed wiring instead of
| ancient weird stuff like knob and tube. That's still bad
| but it's a solvable problem.
|
| I've definitely seen my share of scary things. I have a
| lighting circuit that is incomprehensibly wired and seems
| to kill LED bulbs randomly during a power outage; I have
| zero clue what is going on with that one. Also, often
| times opening up wall boxes I will see backstabs that
| were not properly inserted or wire nuts that are just
| covering hand-twisted wires and not actually threaded at
| all (and not even the right size in some cases...)
| Needless to say, I should really get an electrician in
| here, but at least with a thermal camera you can look for
| signs of serious problems.
| atonse wrote:
| You can always have an electrician install a larger
| breaker for a particular circuit. I did that with my
| "server" area in my study, which was overkill cuz I
| barely pull 100w on it. But it cost nearly zero extra
| since he was doing a bunch of other things around the
| house anyway.
| davrosthedalek wrote:
| Larger breaker and thicker wires!
| atonse wrote:
| I thought you only needed thicker wires for higher amps?
| Should go without saying, but I am not a certified
| electrician :-)
|
| I only have a PhD from YouTube (Electroboom)
| jchw wrote:
| The voltage is always going to be the same because the
| voltage is determined by the transformers leading to your
| service panel. The breakers break when you hit a certain
| amperage for a certain amount of time, so by installing a
| bigger breaker, you allow more amperage.
|
| If you actually had an electrician do it, I doubt they
| would've installed a breaker if they thought the wiring
| wasn't sufficient. Truth is that you can indeed get away
| with a 20A circuit on 14 AWG wire if the run is short
| enough, though 12 AWG is recommended. The reason for this
| is voltage drop; the thinner gauge wire has more
| resistance, which causes more heat and voltage drop
| across the wire over the length of it, which can cause a
| fire if it gets sufficiently hot. I'm not sure how much
| risk you would put yourself in if you were out-of-spec a
| bit, but I wouldn't chance it personally.
| bangaladore wrote:
| Could you not just run a 240 volt outlet on existing
| wiring built for 110v? Just send l1 and l2 on the
| existing hot/neutral?
| bri3d wrote:
| You can, 240V on normal 12/2 Romex is fine. The neutral
| needs to be "re-labeled" with tape at all junctions to
| signify that it's hot, and then this practice is
| (generally) even code compliant.
|
| However! This strategy only works if the outlet was the
| only one on the circuit, and _that_ isn't particularly
| common.
| viraptor wrote:
| > You can always have an electrician install ...
|
| If you own the house, sure. Many people don't.
| chronogram wrote:
| That's still not much for wiring in most countries. A
| small IKEA consumer oven is only 230V16A=3860W. Those
| GPUs and CPUs only consume that much at max usage anyway.
| And those CPUs are uninteresting for consumers, you only
| need a few Watts for a single good core, like a Mac Mini
| has.
| dv_dt wrote:
| So Europe ends up with an incidental/accidental advantage
| in the AI race?
| buckle8017 wrote:
| In residential power delivery? yes
|
| In power cost? no
|
| I'm literally any other way? also no
| kube-system wrote:
| Consumers with desktop computers are not winning any AI
| race anywhere.
| atonse wrote:
| All American households get mains power at 240v (I'm
| missing some nuance here about poles and phases, so the
| electrical people can correct my terminology).
|
| It's often used for things like ACs, Clothes Dryers,
| Stoves, EV Chargers.
|
| So it's pretty simple for a certified electrician to just
| make a 240v outlet if needed. It's just not the default
| that comes out of a wall.
| kube-system wrote:
| To get technical -- US homes get two phases of 120v that
| are 180 degrees out of phase with the neutral. Using
| either phase and the neutral gives you 120v. Using the
| two out of phase 120v phases together gives you a
| difference of 240v.
|
| https://appliantology.org/uploads/monthly_2016_06/large.5
| 758...
| ender341341 wrote:
| Even more technical, we don't have two phases, we have
| 1-phase that's split in half. I hate it cause it makes it
| confusing.
|
| Two phase power is not the same as split phase (There's
| basically only weird older installations of 2 phase in
| use anymore).
| kube-system wrote:
| Yeah that's right. The grid is three phases (as it is
| basically everywhere in the world), and the transformer
| at the pole splits one of those in half. Although, what
| are technically half-phases are usually just called
| "phases" when they're inside of a home.
| voxadam wrote:
| Relevant video from _Technology Connections_ :
|
| "The US electrical system is not 120V"
| https://youtu.be/jMmUoZh3Hq4
| atonse wrote:
| That's such a great video, like most of his stuff.
| dv_dt wrote:
| Well yes its possible but often $500-1000 to run a new
| 240v outlet, and that's to a garage for an ev charger. If
| you want an outlet in the house I dont know how much wall
| people want to tear up and extra time and cost.
| atonse wrote:
| Sure yeah, I was just clarifying that if the issue is
| 240v, etc, US houses have the feed coming in.
| Infrastructure-wise it's not an issue at all.
| ender341341 wrote:
| > So it's pretty simple for a certified electrician to
| just make a 240v outlet if needed. It's just not the
| default that comes out of a wall.
|
| It'd be all new wire run (120 is split at the panel, we
| aren't running 240v all over the house) and currently
| electricians are at a premium so it'd likely end up
| costing a thousand+ to run that if you're using an
| electrician, more if there's not clear access from an
| attic/basement/crawlspace.
|
| Though I think it's unlikely we'll see an actual need for
| it at home, I imaging a 800w cpu is going to be for
| server class CPUs and rare-ish to see in home
| environments.
| vel0city wrote:
| I don't think many people would want some 2kW+ system
| sitting on their desk at home anyways. That's quite a
| space heater to sit next to.
| bonzini wrote:
| Also the noise from the fans.
| com2kid wrote:
| > and currently electricians are at a premium so it'd
| likely end up costing a thousand+
|
| I got a quote for over 2 thousand to run a 24v line
| literally 9 feet from my electrical panel across my
| garage to put a EV charger in.
|
| Opening up an actual wall and running it to another room?
| I can only imagine the insane quotes that'd get.
| the8472 wrote:
| If we're counting all the phases then european homes get
| 400V 3-phase, not 240V split-phase. Not that typical
| residential connections matter to highend servers.
| bonzini wrote:
| It depends on the country, in many places independent
| houses get a single 230V phase only.
| carlhjerpe wrote:
| In the Nordics we're on 10A for standard wall outlets so
| we're stuck on 2300W without rewiring (or verifying
| wiring) to 2.5mm2.
|
| We rarely use 16A but it exists. All buildings are
| connected to three phases so we can get the real juice
| when needed (apartments are often single phase).
|
| I'm confident personal computers won't reach 2300W
| anytime soon though
| bonzini wrote:
| In Italy we also have 10A and 16A (single phase). In
| practice almost all wires running in the walls are 2.5
| mm^2, so that you can use them for either one 16A plug or
| two adjacent 10A plugs.
| rbanffy wrote:
| > And those CPUs are uninteresting for consumers, you
| only need a few Watts for a single good core, like a Mac
| Mini has.
|
| Speak for yourself. I'd love to have that much computer
| at my disposal. Not sure what I'd do with it. Probably
| open Slack and Teams at the same time.
| orra wrote:
| Laughs in 230V (sorry).
| tracker1 wrote:
| There already are different outlets for these higher
| power draw beasts in data centers. The amount of energy
| used in a 4u "AI" box is what an entire rack used to
| draw. Data centers themselves are having to rework/rewire
| areas in order to support these higher power systems.
| t0mas88 wrote:
| A simple kitchen top water cooker is 2000W, so a 1500W PC
| sounds like no big deal.
| kube-system wrote:
| Kettles in the US are usually 1500W, as the smallest
| branch circuits in US homes support 15A at 120V and the
| general rule for continuous loads is to be 80% of the
| maximum.
| linotype wrote:
| True but kettles rarely run for very long.
| kube-system wrote:
| But computers do, which was why I included that context.
| You don't really want to build consumer PC >1500W in the
| US or you'd need to start changing the plug to patterns
| that require larger branch circuits.
| CyberDildonics wrote:
| Kettles and microwaves are usually 1100 watts and lower,
| but space heaters and car chargers can be 1500 watts and
| run for long periods of time.
| triknomeister wrote:
| And cooling. Look here: https://www.fz-
| juelich.de/en/news/archive/press-release/2025...
|
| Especially a special PDU: https://www.fz-
| juelich.de/en/newsroom-jupiter/images-isc-202...
|
| And cooling: https://www.fz-juelich.de/en/newsroom-
| jupiter/images-isc-202...
| avgeek23 wrote:
| And the memory should be a onboard module on the cpu card
| intel/amd should replicate what apple did with a unified same
| ringbus sort of memory modules. Lower latency,higher
| throughput.
|
| Would push performance further. Although companies like intel
| would bleed the consumer dry with, a certain i5-whatever cpu
| with onboard memory of 16 gigs could be insanely priced
| compared to what you'd pay for addon memory.
| 0x457 wrote:
| That would pretty much make both intel and amd to start
| market segmentation by CPU Core + Memory combination. I
| absolutely do not want that.
| sitkack wrote:
| https://en.wikipedia.org/wiki/Compute_Express_Link
| derefr wrote:
| But all of the most-ridiculous hyperscale deployments, where
| bandwidth + latency most matter, have multiple GPUs per CPU,
| with the CPU responsible for splitting/packing/scheduling
| models and inference workloads across its own direct-attached
| GPUs, providing the network the abstraction of a single GPU
| with more (NUMA) VRAM than is possible for any single
| physical GPU to have.
|
| How do you do that, if each GPU expects to be its own
| backplane? One CPU daughterboard per GPU, and then the CPU
| daughterboards get SLIed together into one big CPU using
| NVLink? :P
| wmf wrote:
| GPU as motherboard really only makes sense for gaming PCs.
| Even there SXM might be easier.
| mensetmanusman wrote:
| It's always going to be a back and forth on how you attach
| stuff.
|
| Maybe the GPU becomes the motherboard and the CPU plugs into
| it.
| verall wrote:
| If you look at a any of the nvidia DGX boards it's already
| pretty close.
|
| PCIe is a standard/commodity so that multiple vendors can
| compete and customers can save money. But at 8.0 speeds I'm not
| sure how many vendors will really be supplying, there's already
| only a few doing serdes this fast...
| MurkyLabs wrote:
| Yes I agree, let's bring back the SECC style CPU's from the
| Pentium Era, I've still got my Pentium II (with MMX technology)
| Razengan wrote:
| Isn't that what has kinda sorta basically happened with Apple
| Silicon?
| MBCook wrote:
| GPU + CPU on the same die, RAM on the same package.
|
| A total computer all-in-one. Just no interface to the world
| without the motherboard.
| trenchpilgrim wrote:
| And AMD Strix Halo.
| Dylan16807 wrote:
| And limit yourself to only one GPU?
|
| Also CPUs are able to make use of more space for memory, both
| horizontally and vertically.
|
| I don't really see the power delivery advantages, either way
| you're running a bunch of EPS12V or similar cables around.
| burnt-resistor wrote:
| Figure out how much RAM, L1-3|4 cache, integer, vector,
| graphics, and AI horsepower is needed for a use-case ahead-of-
| time and cram them all into one huge socket with intensive
| power rails and cooling. The internal RAM bus doesn't have to
| be DDRn/X either. An integrated northbridge would deliver PCIe,
| etc.
| kvemkon wrote:
| > at what point do we just flip the architecture over so the
| GPU pcb is the motherboard and the cpu/memory
|
| Actually the RapsberryPi (appeared 2012) was based on a SoC
| with a big and powerful GPU and small weak supporting CPU. The
| board booted the GPU first.
| LeoPanthera wrote:
| Bring back the S100 bus and put literally everything on a card.
| Your motherboard is just a dumb bus backplane.
| MBCook wrote:
| We were moving that way, sorta, with Slot 1 and Slot A.
|
| Then that became unnecessary when L2 cache went on-die.
| leoapagano wrote:
| One possible advantage of this approach that no one here has
| mentioned yet is that it would allow us to put RAM on the CPU
| die (allowing for us to take advantage of the greater memory
| bandwidth) while also allowing for upgradable RAM.
| pshirshov wrote:
| Can I just have a backplane? Pretty please?
| colejohnson66 wrote:
| Sockets (and especially backplanes) are absolutely atrocious
| for signal integrity.
| pshirshov wrote:
| I guess if it's possible to have 30cm PCIe 5 riser cables,
| it should be possible to have a backplane with traces of
| similar length.
| vFunct wrote:
| VMEBus for the win! (now VPX...)
| theandrewbailey wrote:
| I've wondered why there hasn't been a desktop with a CPU+RAM
| card that slots into a PCIe x32 slot (if such a thing could
| exist), or maybe dual x16 slots, and the motherboard could be
| a dumb backplane that only connected the other slots and
| distributed power, and probably be much smaller.
| dylan604 wrote:
| Wouldn't that mean an complete mobo replacement to upgrade the
| GPU? GPU upgrades seem much more rapid and substantial compared
| to CPU/RAM. Each upgrade would now mean taking out the CPU/RAM
| and other cards vs just replacing the GPU
| p1esk wrote:
| GPUs completely dominate the cost of a server, so a GPU
| upgrade typically means new servers.
| BobbyTables2 wrote:
| Agree - newer GPU likely will need faster PCIe speeds too.
|
| Kinda like RAM - almost useless in terms of "upgrade" if
| one waits a few years. (Seems like DDR4 didn't last long!)
| zkms wrote:
| My reaction to PCIe gen 8 is essentially "Huh? No, retro data
| buses are like ISA, PCI, and AGP, right? PCIe Gen 3 and SATA are
| still pretty new...".
|
| I wonder what modulation order / RF bandwidth they'll be using on
| the PHY for Gen8. I think Gen7 used 32GHz, which is ridiculously
| high.
| eqvinox wrote:
| I'd highly advise against using GHz here (without further
| context, at least), a 32Gbaud / 32Gsym/s NRZ signal toggling at
| full rate is only a 16GHz square wave.
|
| baud seems out of fashion, sym/s is pretty clear & unambiguous.
|
| (And if you're talking channel bandwidth, that needs
| clarification)
| kvemkon wrote:
| > > I think Gen7 used 32GHz, which is ridiculously high.
|
| > 16GHz square wave
|
| Is it for PCIe 5.0? PCIe 6.0 should operate on the same
| frequency and doubling the bandwidth by using PAM4. If PCIe
| 7.0 doubled the bandwidth and is still PAM4, what is the
| underlying frequency?
| eqvinox wrote:
| PCIe 7 = 128 GT/s = 64 Gbaud x PAM-4 = 32 "GHz" (if you
| alternate extremes on each symbol)
|
| for gen6, halve all numbers
| Dylan16807 wrote:
| Is it me or are they using the term GigaTransfers wrong?
| They're counting a single PAM4 pulse as two "transfers".
| eqvinox wrote:
| They kinda are and kinda aren't, they're just using their
| own definition...
|
| (I'm accepting it because "Transfers"/"T" as unit is
| quite rare outside of PCIe)
| zamalek wrote:
| GT/s is also gaining ground for system RAM in order to
| clear up the ambiguity that DDR causes for end-consumers.
| Dylan16807 wrote:
| And it's a good way to remove the ambiguity of things
| like DDR, but ugh "transfers" is not the best word here.
|
| Looking at some documents from Micron I don't see them
| using GT/s anywhere. And in particular if I go look at
| their GDDR6X resources because those chips use PAM4, it's
| all about gigabits per second [per pin]. So for example
| 6GHz data clock, 12Gbaud, 24Gb/s/pin.
| guerrilla wrote:
| > baud seems out of fashion, sym/s is pretty clear &
| unambiguous.
|
| Huh? Baud is sym/s.
| eqvinox wrote:
| Yes, that was the implication, but I've been getting the
| impression that using baud is kinda unpopular compared to
| using sym/s.
| throwway120385 wrote:
| A lot of people think that baud rate represents bits per
| second, which it only does in systems where the symbol
| set is binary. People got it from RS232.
| rbanffy wrote:
| IIRC, modems never went much beyond 2400 baud. Everything
| past that was clever modulation packing more bits onto a
| single symbol.
| Dylan16807 wrote:
| > PCIe Gen 3 and SATA are still pretty new...
|
| That's an interesting thought to look at. PCIe 3 was a while
| ago, but SATA was nearly a decade before _that_.
|
| > I wonder what modulation order / RF bandwidth they'll be
| using on the PHY for Gen8. I think Gen7 used 32GHz, which is
| ridiculously high.
|
| Wikipedia says it's planned to be PAM4 just like 6 and 7.
|
| Gen 5 and 6 were 32 gigabaud. If 8 is PAM4 it'll be 128
| gigabaud...
| weinzierl wrote:
| Don't forget VESA Local Bus.
| bhouston wrote:
| I love the PCIe standard is 3 generations ahead of what is
| actually released. Gen5 is the live version, but the team behind
| it is so well organized that they have a roadmap of 3 additional
| versions now. Love it.
| ThatMedicIsASpy wrote:
| Gen6 is in use look at Nvidia ConnectX-8
| drewg123 wrote:
| What hosts support Gen6? AFAIK, Gen5 is the most recent
| standard that's actually deployed. Eg, what can you plug a
| CX8 into that will link up at Gen6?
| triknomeister wrote:
| Custom Nvidia network cards I guess.
| my123 wrote:
| Blackwell DC (B200/B300)
| tails4e wrote:
| It takes a long time to get form standard to silicon, so I bet
| there are design teams working on pcie7 right now, which won't
| see products for 2 or more years
| Seattle3503 wrote:
| Is there an advantage of getting so far ahead of
| implementations? It seems like it would be more difficult to
| incorporate lessons.
| kvemkon wrote:
| When AMD introduces a new Desktop CPU series IIRC they claim
| the next generation design is (almost) finished (including
| layout?) and they start with the next-next-gen design. And
| I'm also asking the same question. But more than a half a
| year before the CPU becomes available to the public it is
| already being tested by partners (mainboard manufacturers and
| ?).
| Phelinofist wrote:
| So we can skip 6 and 7 and go directly to 8, right?
| ThatMedicIsASpy wrote:
| I'll take it if my consumer mb chipset supports giving me 48
| PCIe7 lanes if future desktops still would only come with 24 gen
| 8 lanes
| richwater wrote:
| Meanwhile paying a premium for a Gen5 motherboard may net you
| somewhere in the realm of 4% improvements in gaming if you're
| lucky.
|
| Obviously PCI is not just about gaming but...
| simoncion wrote:
| From what I've seen, the faster PCI-E bus is important when you
| need to shuffle things in and out of VRAM. In a video game, the
| faster bus reduces the duration of stutters caused by pushing
| more data into the graphics card.
|
| If you're using a new video card with only 8GB of onboard RAM
| and are turning on all the heavily-advertised bells and
| whistles on new games, you're going to be running out of VRAM
| very, very frequently. The faster bus isn't really important
| for higher frame rate, it makes the worst-case situations less
| bad.
|
| I get the impression that many reviewers aren't equipped to do
| the sort of review that asks questions like "What's the
| intensity and frequency of the stuttering in the game?" because
| that's a bit harder than just looking at average, peak, and 90%
| frame rates. The question "How often do textures load at
| reduced resolution, or not at all?" probably _requires_ a human
| in the loop to look at the rendered output to notice those
| sorts of errors... which is time consuming, attention-demanding
| work.
| Dylan16807 wrote:
| There's a good amount of reviewers showing 1% lows and 0.1%
| lows, which should capture stuttering pretty well.
|
| I don't know how many games are even capable of using lower
| resolutions to avoid stutter. I'd be interested in an
| analysis.
| rbanffy wrote:
| I'm sure Windows performance counters can track the volume of
| data going between CPU memory and VRAM over the PCIe bus.
| jeffbee wrote:
| By an overwhelming margin, most computers are not in gamers'
| basements.
| checker659 wrote:
| No matter the leaps in bandwidth, the latency remains the same.
| Also, with PCIe switches used in AI servers, the latency (and
| jitter) is even pronounced.
| LeoPanthera wrote:
| I thought we were only just up to 5? Did we skip 6 and 7?
| pkaye wrote:
| Some of the newer ones maybe more for data centers.
| robotnikman wrote:
| I know very little about electronics design, so I always find it
| amazing that they keep managing to double PCIe throughput over
| and over. Its also probably the longest lived expansion bus at
| the moment.
| wmf wrote:
| It's less surprising if you realize that PCIe is behind
| Ethernet (per lane).
| rbanffy wrote:
| I'm sure you can get some VMEbus boards.
| pshirshov wrote:
| Yeah, such a shame I've just upgraded to a 7.0 motherboard for my
| socket AM7 CPU.
|
| Being less sarcastic, I would ask if 6.0 mobos are on the
| horizon.
| wmf wrote:
| I guess Venice, Diamond Rapids, and Vera will have 6.0.
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