I find it hard to believe disk was snappy compared to modern devices, since original comment mentioned IO. Cpu/memory are down to program behavior in addition to hw. Disk, more size and hw. And HW improvements have dwarfed size increases (rather, facilitating them to some degree).
Depends on what sort of disk I/O you have in mind. Floppy disks were never snappy, but HDD disks were fine for the most part until the OS started using them for virtual memory. Keep in mind that things were much smaller these days - i remember thinking that my 2GB HDD would never fill up :-P.
Also in the last few years disk I/O optimization took a massive nosedive, especially under Windows. My 2013 laptop has a ~5400rpm HDD was so unusable with Windows 10 that even the login screen crossfade animation stuttered from disk I/O and updates took literally hours. Meanwhile Windows 8, released only a few years prior, was able to boot my older 2008 laptop from power on to desktop in ~22 seconds (i was so impressed at the time that i uploaded a video of the boot process [0]).
If you are used to the recent awful I/O performance it can be hard to imagine things not always being like that.
Besides you can also check a bunch of YouTube videos with old computers running Win95, here is a short one i found that goes through the bootup process and clicks around the OS for a bit.[1] The computer in the video is actually slower than the one i personally had too.
