4 ms·

Can I just have a backplane? Pretty please?

by pshirshov 1y ago

colejohnson66 1y ago
Sockets (and especially backplanes) are absolutely atrocious for signal integrity.
- pshirshov 1y ago
  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.
  - namibj 1y ago
    Cables much better sadly, so much so that they started to use cables to jump across the server main board in places.
vFunct 1y ago
VMEBus for the win! (now VPX...)
- pezezin 1y ago
  The hot stuff nowadays is µTCA: https://www.picmg.org/openstandards/microtca/ https://www.picmg.org/openstandards/microtca/
  - crimony 1y ago
    If I remember correctly the military / aerospace shy away from this spec because the connector with the pins is on the backplane, with the sockets on the cards. So if you incorrectly insert a card and bend a pin you're in trouble. VPX has the sockets on the backplane so avoids this issue, if you bend pins you just grab another card from spares. This may have changed since I last looked at it. Telecoms industry definitely seem to favour TCA though.
    - pezezin 1y ago
      I don't know, I work in particle physics and here µTCA is all the rage nowadays.
theandrewbailey 1y ago
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.
- namibj 1y ago
  Those exist; they are used for risers ("vertical mount GPU brackets, for dual GPU" equivalent for servers, where they make the cards flat again).
- KeplerBoy 1y ago
  PCIe x 32 actually exists, at least in the specification. I have never seen a picture of a part using it.
- iszomer 1y ago
  Retimers.
guerrilla 1y ago
Yes, for fucks sake, this is the only way forward. It gives us the ultimate freedom to do whatever we want in the future. Just make everything a card on the bus and quit with all this hierarchy nonsense.

Can I just have a backplane? Pretty please?

colejohnson66 1y ago

Sockets (and especially backplanes) are absolutely atrocious for signal integrity.

pshirshov 1y ago
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.
- namibj 1y ago
  Cables much better sadly, so much so that they started to use cables to jump across the server main board in places.

vFunct 1y ago

VMEBus for the win! (now VPX...)

pezezin 1y ago
The hot stuff nowadays is µTCA: https://www.picmg.org/openstandards/microtca/ https://www.picmg.org/openstandards/microtca/
- crimony 1y ago
  If I remember correctly the military / aerospace shy away from this spec because the connector with the pins is on the backplane, with the sockets on the cards. So if you incorrectly insert a card and bend a pin you're in trouble. VPX has the sockets on the backplane so avoids this issue, if you bend pins you just grab another card from spares. This may have changed since I last looked at it. Telecoms industry definitely seem to favour TCA though.
  - pezezin 1y ago
    I don't know, I work in particle physics and here µTCA is all the rage nowadays.

theandrewbailey 1y ago

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.

namibj 1y ago
Those exist; they are used for risers ("vertical mount GPU brackets, for dual GPU" equivalent for servers, where they make the cards flat again).
KeplerBoy 1y ago
PCIe x 32 actually exists, at least in the specification. I have never seen a picture of a part using it.
iszomer 1y ago
Retimers.

guerrilla 1y ago

Yes, for fucks sake, this is the only way forward. It gives us the ultimate freedom to do whatever we want in the future. Just make everything a card on the bus and quit with all this hierarchy nonsense.