People did not compile the kernel back then. The kernel was supplied in a precompiled form as a collection of object (.o) files, and there was a kernel «generat

People did not compile the kernel back then. The kernel was supplied in a precompiled form as a collection of object (.o) files, and there was a kernel «generation» shell script that would ask questions about which parts of the kernel were required (e.g. which device drivers to link in), what to set certain kernel parameters to (e.g. the number and the size of I/O buffers for the page cache had not been invented yet and neither had been «sysctl»), and – after jumping through the hooves of the very detailed and thorough interview with the kernel generation script – it would link the /unix kernel a.out image. It took several hours to get the final product. The source code was distributed on a tape but it was not customary to compile the kernel from scratch every time.