Why Modern Computers Struggle to Match the Input Latency of an Apple IIe

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Update (5/25/2020): This report is various a long time outdated, but it’s one of my favorites and one of the most intriguing matters we’ve talked about. There’s an outdated stating: “What hardware engineers create, software package engineers choose away.” Which is not the fairest way to glimpse at the scenario — modern desktops can do considerably extra than outdated types — but the wrestle to hold methods responding quickly whilst ramping up their complexity is not a series of unbroken triumphs. Even top rated-stop PCs wrestle to offer you the latency of devices that available a fraction of their functionality.

Initial story proceeds beneath:

Evaluating the input latency of a modern Laptop with a method that’s 30-40 a long time outdated appears preposterous on the confront of it. Even if the computer system on your desk or lap isn’t particularly new or really rapid, it’s still clocked a thousand or extra occasions a lot quicker than the slicing-edge engineering of the 1980s, with several CPU cores, specialized decoder blocks, and guidance for online video resolutions and detail degrees on par with what science fiction of the period experienced dreamed up. In small, you’d consider the comparison would be a one-sided blowout. In lots of cases, it is, but not with the winners you’d assume.

Engineer Dan Luu a short while ago received curious about how different equipment look at in phrases of input latency. He carried a large-velocity digicam close to to measure input lag on some of them because this is the kind of brilliant factor engineers at times do. What he identified is alternatively placing, as shown by the table beneath:


Data and chart by Dan Luu

The method with the lowest input latency — the quantity of time amongst when you strike a critical and that keystroke appears on the computer system — is the Apple IIe, at 30ms. A respectable 3rd-place goes to a Haswell-E method with a 165Hz keep an eye on. #T refers to the range of transistors in every chip the color-coding shows that chips with bigger quantities of transistors are likely to be in methods with extra latency, and a lot quicker methods are likely to be older than slower types.

Improving keep an eye on refresh charge clearly can help the identical Haswell-E rig has 90ms much less input latency on a 165Hz exhibit in contrast to a 24Hz exhibit. If you have at any time made use of a exhibit with a 30Hz refresh charge, you have most likely seen this the big difference amongst 30Hz and 60Hz is effortlessly noticeable to the bare eye. But it clearly doesn’t make the overall big difference in and of itself.

Luu has been accomplishing an in-depth discussion of latency from various angles and we’d recommend his articles on keyboard and mouse latency if you want to abide by up. In some cases, it’s practically unachievable for a method to offer you lower latency than an Apple IIe because the keyboard’s latency by itself may perhaps be bigger than the Apple method. Also, gaming keyboards may perhaps not be a lot quicker than typical keyboards, and even if they are, median keyboard latency is large adequate that 3.5ms doesn’t make improvements to the whole input latency really considerably.

Why Modern day Devices Wrestle to Match Outdated Types

This boils down to a solitary phrase: Complexity. For the applications of this comparison, it doesn’t make a difference if you use macOS, Linux, or Windows. An Apple IIe with an open terminal window and nothing at all else is sitting there, waiting for input. Its keyboard is wired for an helpful polling charge of 556Hz and a tailor made chip for keyboard input as opposed to polling the keyboard with a microcontroller. This online video, from Microsoft’s Used Sciences Team, discusses why very low latency input is important.

An Apple IIe isn’t handling refined multi-tasking commands. It isn’t juggling history threads, or dealing with several apps that aren’t built to be conscious (or thorough) of one another. It isn’t polling a massive array of equipment that range from audio and community controllers to discrete GPUs and storage. The Apple IIe OS doesn’t use a compositing window supervisor, which adds latency. This report, by Pavel Fatin, is an in-depth breakdown of latency processing and discusses how considerably delay every action in a modern method adds, from keyboard scan to last output.


I ran this examination in SublimeText 2, not PowerShell, so really don’t look at it against the final results higher than. One particular factor it illustrates? Refresh rates genuinely make a difference. The initial two final results are @60Hz, the 3rd is at 24Hz.

It really should also be pointed out that the velocity of text input can change from terminal to terminal. PowerShell is now the default terminal of Windows 10, and text input velocity in PowerShell is… terrible. I create my tales by default in SublimeText, which has little-to-no observable lag. PowerShell, in distinction, is so laggy, you can perceive a gap amongst what you are typing and when it appears (even though not a particularly large one).

Either way, this report is an intriguing example of how, despite myriad innovations, very low-latency input continues to be hard. Complexity is often a really good factor, but we pay back a functionality penalty for it.

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