> The first Unix distributions I used, you had to build the OS yourself, hand compiling in, or out different options. I built a bunch of DNS servers, FTP servers, SMTP servers... sync sync reboot
The first unix distributions, back at Bell Labs, were tapes that you booted. These tapes had programs to initialize the disk, copy files from the tape that were disk images to the disk and/or restore other partitions from tar or its predecessors. These date back to V1 on the system which had you set the system console switches to a certain magic value to do the install. You didn't have to recompile anything, though you often did recompile the kernel to tune it to your system rather than run a generic version (most tapes had a generic version, and several copies of that with different major/minor numbers plugged into it so that different disks could be root). BSD improved this a bit by having a RAM disk that you'd copy to the swap partition and run out of that to do the initialization (fewer stand alone programs to run).
The first Linux distributions were not nearly this nice. You had a boot floppy that you could use for format the hard disk and a few other floppies that had other programs on them that you'd basically tar off (though early on the concept of floppy sets arose that was basically a multi-volume tar file under a different name). It took a couple of years before the CD isos appeared which made it a lot easier and the install process to get going....
So things have come a long way since then, but we're not longer installing this stuff on 4-8MB 386DX computers with 50-100MB hard drives either...