Two great posts about interaction latency on the hardware and software side. First is from Ink & Switch:

There is a deep stack of technology that makes a modern computer interface respond to a user’s requests. Even something as simple as pressing a key on a keyboard and having the corresponding character appear in a text input box traverses a lengthy, complex gauntlet of steps, from the scan rate of the keyboard, through the OS and framework processing layers, through the graphics card rendering and display refresh rate.

There is reason for this complexity, and yet we feel sad that computer users trying to be productive with these devices are so often left waiting, watching spinners, or even just with the slight but still perceptible sense that their devices simply can’t keep up with them.

We believe fast software empowers users and makes them more productive. We know today’s software often lets users down by being slow, and we want to do better. We hope this material is helpful for you as you work on your own software.

I loved the slow-motion videos comparing what is normally impossible to notice:

Dan Luu has a complementary post digging a bit more into computer hardware latency from the 1970s to now:

I’ve had this nagging feeling that the computers I use today feel slower than the computers I used as a kid. As a rule, I don’t trust this kind of feeling because human perception has been shown to be unreliable in empirical studies, so I carried around a high-speed camera and measured the response latency of devices I’ve run into in the past few months.

I feel both of these essays are fantastic, and important to develop some sense of what are specific numeric thresholds separating fast and slow, also in the context of being able to have an informed conversation with a front-end engineer. (Luu subsequently links to even more articles in the “Other posts on latency measurement” section, if you are curious.)

Otherwise, from my observation, the two most quoted laws of user-facing latency are still Jakob Nielsen’s response time limits, and the Doherty Threshold. But the Jakob Nielsen 100/1000/10000ms rule is from 1993 and as far as I understand is concerned primarily with UX flows: reactions to clicking a button, responses to typing a command, and so on. And the Doherty Threshold is even older. Both are simply not enough, especially not for things related to typing, multitouch, or mousing, where for a great experience you have to go way below 100ms, occasionally even down to single-digit milliseconds.

(My internal yardstick is “10 for touch, 30 for mousing, 50 for typing.” Milliseconds, of course.)

At the end of his essay, Luu writes:

It’s not clear what force could cause a significant improvement in the default experience most users see.

Perhaps one challenge is that these posts are dense and informative, but only appeal to people who care? Maybe latency eradication needs a PR strategy, with a few memorable rules and – perhaps arbitrary, but well-informed – numbers that come with some great names attached? I know in the context of web loading some of the metric names like FCP (First Contentful Paint) broke through at least to some extent, but those still feel more on the nerdy side. Even Nielsen’s otherwise fun 2019 video about response time limits didn’t stick the landing – why focus on slowing down an arbitrary label appearing above the glass when the ping sound was right there for the taking?!

I can’t help but dream of interaction speed’s “enshittification” moment.