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Providing that what I've read in this article is true I'm wondering why it's faster to run Raspberry Pi 4b from microSD, than it is to run it from decent speed (200MB/s read) USB Flash Drive? Is the above statement true at all? I mean do you agree with the results outlined in this article - above all with the statement that operating system run from microSD card will be faster than the one run from USB flash drive?

It confuses me because I know that modern USB flash drives connected to the USB 3.0 port have around 100MB/s real life sustained read/transfer speeds, compared to 50MB/s real life sustained, class V30 microSD cards, read speed.

I also read this article but for unknown reasons, there's no real life read speeds provided for these microSD cards.

Currently I have Samsung Bar Plus 256GB (around 150MB/s real life read speed) and Lexar PLAY 256GB microSDXC UHS-I R150 (around 100MB/s declared real life read speed) and I'd like you to advise me which of these will give me better performance while watching hi-res youtube videos and 1920x1080, H.265/HEVC movies? I will use VLC player to watch these HD movies.

I've also read that the microSD card reader installed on Raspberry Pi 4b has only 50MB/s max transfer speed, so even if microSD card can go faster, it bottlenecks on the reader. Is that true.

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    Welcome. I don't think storage speed has much impact on boot time; the bottleneck there is the CPU. If you look at the RAM in use after boot, it's probably about 150 MiB (on a non-gui system). There's also processing of configurations and such stuff that's read but not retained, but I doubt that adds more than 10% to this number.
    – goldilocks ♦
    Feb 22 at 22:10
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    On what evidence do you base "it's faster to run Raspberry Pi 4b from microSD". sdio also used for on-board WiFi is very fast (at least for reading).
    – Milliways
    Feb 22 at 23:23
  • In this question I'm just asking if it's true that Raspberry Pi 4b works faster from microSD card then it does from USB flash drive. Because I intuitively thought that it should work faster from USB flash drive, just because these flash drives have 300MB/s manufacturer declared read speeds, so probably they can pull around 85-100MB/s in real life, which is much faster than microSD cards.
    – michal roesler
    Feb 23 at 10:54
  • I say there's an article here: tomshardware.com/news/raspberry-pi-4-ssd-test,39811.html - that claims it's faster to run Raspberry Pi 4b from microSD than from USB flash drive", that the apps are opening faster from microSD card and I'm asking people here, if they agree with this or not. I'm a new Raspberry Pi 4b user, so I don't have an opinion just yet.
    – michal roesler
    Feb 23 at 10:59
  • There's an easy way to test this. Write speed time (dd if=/dev/zero of=tmp bs=4096 count=32768; sync). That's 128 MiB, use more if you want (there's no limit on /dev/zero). Then read it back: time dd if=tmp of=/dev/null. In case it isn't clear, tmp is a file that will be written in your current directory. There are of course better more thorough methods but this at least gives you an idea of which device is faster and by how much.
    – goldilocks ♦
    Feb 23 at 15:09

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