2

The main question is:

Defined by maximum allowable height from the surface of the PCB on both sides (soldered pins and components), or whatever metric experts think would be most useful in decoding an undefined "card height" measurement in inches as outlined below, what is the maximum vertical height/thickness of a PCIe card in a single slot?

<< Background >>

I'm trying to work this out since GPUs (namely the just-released, ludicrously huge nVidia 4090) are now being listed in vertical inches instead of PCIe slots taken up, which seems both avoidant to me (not just lazy, as you'll see) and completely unhelpful to any consumer at any level of computer knowledge.

Searching for PCIe card thickness gets me lots of results on the PCB thickness (no SMDs/components) and height usually gets results on full-height vs half-height cards (a "height" moving out from the PCIe connector, perpendicular to the board the connector is mounted on). As such, it'd be good to get this question answered as an authoritative reference for others on this path.

<< Alternate Explanation | Reason This Matters >>

While I realize measuring in vertical inches could help people with unconventional (usually vertical or case-mod) mounting clearance concerns, that's a rare exception and it still seems like an attempt to obscure the information somewhat as, save for engineers designing cards, I've never seen vertical inches used.

Normally, a card either fits in X number of slots or not, which builders and enthusiasts need to know when planning a card addition/move to ensure the cards fit next to each other and within the spacing/slot layout of the motherboard. Basic stuff for even novice techies and the reason why we have a standard that simplifies it so we're not left manually measuring fractional inches of clearance with calipers, fearing shorting out neighboring cards if we don't get the clearance right.

<< Examples of Cards Listed by Vertical Inches >>

To get back to my example, listings for 4090s are now showing thicknesses in mm or in, on both retailer and manufacturer sites, which seems to rule out simple listing laziness on retailer sites (i.e. "they'll check the mfg site if they care"). The consistency of this varies a bit, but seem to lean towards not listing slots used, the main concern here, though there are certainly exceptions. As noted under the Suprim below, it does appear, in my 4090-only sample size, that mfgs are more sheepish/forgetful when it goes over 3 slots.

This is not an exhaustive search by any means, but the further I look the more it seems to be a trend, hence why it warrants an opposite (inches-to-slots) conversion reference. I'd link to cards directly, but that will not help keep this question self-contained as these are listings on retailer sites and mfgs, so I'll just list some cards and where I'm seeing the thicknesses:

  1. Gigabyte RTX 4090 Windforce 24G (gigabyte.com) -> "Card size L=331 W=150 H=70 mm" (no slot count listed)

  2. PNY RTX 4090 VCG409024TFXXPB1 (bestbuy.com) -> "Product height: 2.63in" (no slot count listed -- pny.com shows 3.5 slots so listing laziness on this one?)

  3. MSI RTX 4090 Suprim Liquid X 24G (bestbuy.com) -> "Slot size: Dual slot" (This points to an interesting exception, as it seems like slot count is only listed when it's 3 slots or lower as only 2x other cards have slot count listed on bestbuy.com.)

  4. MSI RTS 4090 GAMING TRIO 24G (msi.com) -> Nothing at all under [rather sparse] specifications page or datasheet. Nothing shown on bestbuy.com or newegg.com listings for this or other MSI cards.

  5. ASUS RTX 4090 TUF-RTX4090-O24G-GAMING (msi.com/newegg.com) -> Shows 3.65 slots, which was shown as "3.65 in" on other sites, so this was probably a listing error and is a counterexample when listed properly.

Rook
  • 184
  • 1
  • 6
  • 2
    (Nominal slot pitch is .8 inches - have you consulted the PCI-SIG documents?) – greybeard Dec 26 '22 at 06:11
  • I found other StackExchange questions and answers in forums that basically said the OP of those threads should check the PCI SIG documents, but then acknowledged that they are apparently partly or only accessible to partners. I didn't check myself to see if this was true. – Rook Dec 26 '22 at 06:55
  • And thank you for using a better term. I should have probably said "slot spacing" as it's effectively the same difference but doesn't account for clearance. Slot pitch avoids all other issues, albeit a quick search shows it also doesn't bring up [*EDIT: "many results relevant to this question"], oddly enough, so I guess it's just a very obscure measurement, at least on Google, for whatever reason, or there's a closer or more common term for what I'm looking for.. – Rook Dec 26 '22 at 06:59
  • 1
    Anyone can buy copies of PCI standards, but they are quite expensive. – Peter Green Dec 27 '22 at 06:37

1 Answers1

4

According to the "PCI express card electromechnical specification" the PCB itself is shown as 1.57 mm thick with 14.47mm available on the front side and 2.67mm available on the back side that adds up to 18.71 mm.

According to the ATX specification, PC expansion slots have a pitch of 0.8 inches which translates to 20.32mm.

Presumablly the difference of around 1.6mm between the allowed thickness for a PCIe card and the slot pitch was intended to allow for some clearance between cards for ventilation and to prevent short circuits.

Peter Green
  • 21,158
  • 1
  • 38
  • 76
  • Thank you very much. Answered as completely as I could have wanted, from all angles. – Rook Dec 28 '22 at 01:27