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> Let's remove 20% due to 8b/10 encoding Thunderbolt 3 uses 64b/66b encoding (unlike display port 1.2 alt mode), so there's more bandwidth left over for non-di
by fleventynine 3y ago
> Let's remove 20% due to 8b/10 encoding
Thunderbolt 3 uses 64b/66b encoding (unlike display port 1.2 alt mode), so there's more bandwidth left over for non-display protocols.
- dishsoap 3y agocame here to comment this
- fabiensanglard 3y agoThank you for pointing out this mistake. So the 40 Gbps value advertised by Intel is not the pre-encoding rate but post-encoding rate. This means TB3 pre-encoding rate is 40.25gbps. Minus encoding we get post-encoding = 40Gbps (before TB headers). This leads me to question my USB maths. E.g.: USB 3.2 Gen 1×1 advertised as 5,000 Mbps, but is that pre-encoding or post-encoding? Is it `5000 Gbps pre-encoding -> 8b/10b > 4000 Gbps` or `6250 Gbps pre-encoding -> 8b/10b > 5000 Gbps` Same question for USB 3.2 Gen 2×1 which uses 128b/132b (I double checked this time :P!).
- _kb 3y agoUSB 3.2 gen 1x1 is a 5Gbps data rate. With the 8b/10b coding that provides 500MB/s throughput. USB 3.2 gen 2x1 runs at 10Gbps. After the 128b/132b coding this provides 1212MB/s.
- Kirby64 3y agoUSB-IF defines their data rates in terms of link rate. So 5 Gbps after 8b10b encoding is 4 Gbps. Makes sense, since fastest transfers never exceed 500 MB/s over USB3. Same applies for the 128b/132b variant, except it's only a ~3% speed reduction, so it's much harder to see that in practical testing.