Just 290 days for the iPod to go from idea to customer is crazy fast
First, they used physically larger 2.5" hard drives, making them larger and heavier. The small 1.8" HDD that the iPod used allowed it to be the size of a deck of cards, meaning it was much more portable.
Secondly, hard drives consume a large amount of power to operate, so HDD-based players had terrible battery life because it was always spinning up the disk to get the next song. The iPod solved this by just adding 32 MB of RAM as a cache, so when you started an album the system would just read in the next 15 minutes (or so? that's about 30 MB at 160 kbit) of songs and then power down the HDD until the cache was running out or the user changed albums/playlists/tracks.
It was also fast; using firewire to transfer songs restricted it to Mac users at first, but it meant that you could rip a new CD and put it on your iPod in a short amount of time, or, later, buy an album on iTunes and have it ready for your jog in ten minutes.
It's funny to think how many people saw the iPod as an obvious immediate failure. As the infamous Slashdot post[0] said, "No wireless. Less space than a Nomad. Lame."
[0] https://slashdot.org/story/01/10/23/1816257/apple-releases-i...
It's the manufacturing speed that astonishes me -- the sourcing as you say, the supply chains and the factory capacity. I'm also very curious about the manufacture of the scroll wheel -- was that something really new that had to be figured out (it seemed/felt like it) or was it a trivial combination of existing components?
That's not to knock the speed of the iPod's development but it wasn't built totally from scratch. Apple also wasn't a garage startup, peeling some hardware engineers off for the iPod wasn't going to cripple the iMac's continued development.