Why Does Linux Boot Faster from a USB Flash Drive Compared to an HDD?

A lot of live Linux systems are designed to be lightweight, meaning they skip loading many background processes you’d find in a full install. This doesn't just speed things up but reduces the data that needs to be read. Plus, access times on USB drives are generally way better than those of HDDs, which need time to spin up and seek the correct sectors. So while the HDD is reading, the flash drive might already be sending data to the system.

It's a matter of setup, too! Live USBs often use a compressed file system which allows them to boot faster because the system only needs to read essential files. If you were to install Linux on the USB and boot from it, you might see it performing more comparably to the HDD. Just keep in mind the physical differences — USBs don’t have moving parts which gives them an edge in reducing latency.

When it comes to booting, it's often about how data is accessed rather than just raw speeds. Flash drives excel in random reads, which means they can access small pieces of data quickly. Meanwhile, HDDs can be slower at random reads because the heads have to physically move to the right track. This difference in how data is retrieved can make USB drives seem quicker, even if they have lower overall read speeds.