Talk:PCI Express/Archive 2023

PCIe Gen 5 page

I am new editor, and I realized that there is no PCIe Gen 5 page. I am really bad at writing, so I could not do this. Thank you for reading this, by the way! Intel Lover (talk) 00:14, 28 February 2023 (UTC)

PCIe 5.0, 6.0, and 7.0 can be found under the History and Revisions section of this page, did you miss these sections? 134.134.137.81 (talk) 22:18, 23 March 2023 (UTC)

Yes. I am so sorry about that. 2600:1702:3FC0:4590:113C:F289:9CBA:577C (talk) 22:56, 23 March 2023 (UTC)

Note iii on PCI Express Link Performance

Note iii specifies: "Throughput indicates the unencoded bandwidth (without 8b/10b, 128b/130b, or 242B/256B encoding overhead). The PCIe 1.0 transfer rate of 2.5 GT/s per lane means a 2.5 Gbit/s serial bit rate corresponding to a throughput of 2.0 Gbit/s or 250 MB/s prior to 8b/10b encoding." However, the conversion from 2.5Gbit/s serial bit rate corresponding to a throughput of 2.0Gbit/s or 250MB/s is a result of 8b/10b encoding, is it not? I ran the numbers on the throughput of the 128/130b encoded versions as well and they are also accounting for encoding losses, so I would propose altering Note iii as follows: "Throughput indicates the encoded bandwidth (with 8b/10b, 128b/130b, or 242B/256B encoding overhead). The PCIe 1.0 transfer rate of 2.5 GT/s per lane means a 2.5 Gbit/s serial bit rate corresponding to a throughput of 2.0 Gbit/s or 250 MB/s when accounting for 80% bandwidth efficiency of 8b/10b encoding." 134.134.137.81 (talk) 22:14, 23 March 2023 (UTC)

To me, "unencoded" means pure user data (ignoring any overhead) and "encoded" includes the line-code overhead. I understand your logic as "encoded" meaning "to be encoded" but I think most readers don't see it that way. Perhaps it's better to rephrase "Throughput indicates the usable bandwidth without 8b/10b, [...] encoding overhead." --Zac67 (talk) 08:23, 24 March 2023 (UTC)

slot size

The size of compatible cards is listed but not the size of the slot. 46.131.26.213 (talk) 14:29, 4 May 2023 (UTC)

Overhead calculation (in chapter "PCI Express 1.0a")

To me the sentence "PCIe 1.x uses an 8b/10b encoding scheme, resulting in a 20% (= 2/10) overhead on the raw channel bandwidth." would appear not ok, as "overhead" in form of a ratio would typically be regarded as the result of "(gross - net) / net". Hence in my view it should rather be an overhead of 25 % (= 2 bit / 8 bit).

Greetings from Munich/Bavaria!

Manfred / lini — Preceding unsigned comment added by 62.216.209.208 (talk) 02:08, 21 June 2023 (UTC)

That's not correct. Overhead is defined as the portion of data that is transmitted "in vain" in proportion to the total transmitted data: (total - payload)/total. --Zac67 (talk) 14:57, 21 June 2023 (UTC)

Sorry, but in my view that would be just one possible way to define overhead in form a ratio (or respectively a fraction) - and the less logical or respectively intuitive or natural one at that. Because the "over-" in the word "overhead" already indicates an extra on top of something, namely the net content (or the payload, to use your term) in this case. And hence the more logical (intuitive, natural...) choice as reference (denominator) for an overhead in form of a ratio would be the net (payload) rather than the gross (total). And examples of that sort of usage can also easily be found - e.g. the at least 33 (1/3) % overhead caused by Base64 encoding, or this example from the example section of the Wikipedia page about "Overhead (engineering)": "The date and time "2011-07-12 07:18:47" can be expressed as Unix time with the 32-bit signed integer 1310447927, consuming only 4 bytes. Represented as ISO 8601 formatted UTF-8 encoded string 2011-07-12 07:18:47 the date would consume 19 bytes, a size overhead of 375% over the binary integer representation."

Greetings from Munich!

Manfred / lini — Preceding unsigned comment added by 62.216.209.247 (talk) 02:46, 23 June 2023 (UTC)

Of course, that's an alternative way – the more common one is the one above. Please discuss your view on the appropriate page. --Zac67 (talk) 06:15, 23 June 2023 (UTC)