The operating system - so it can load it into memory. It searches according to the path laid down in the config.sys file.
The POST (Power On Self Test).
POST
The first step in the booting process is POST (power-on self-test).
Post
POST stands for power on self test it does basic hardware checks on the computer
A "POST card."
POST
BIOS boot sequence option.
No post, fails start up tests, No boot pass's POST tests but wont load os. (answer A on dell exam)
Monitor not plugged in. Won't boot without it
A POST test card monitors the boot process and reports errors typically as coded numbers on a small LED panel. The majority of POST test cards plug directly into an expansion slot although some do connect via serial or parallel connection.
Quickboot in relation to the CMOS startup procedure simply performs the process faster because it skips a check of the memory. If you disabled quick boot, POST checks RAM and the process takes longer. So disabling quick boot would allow a check of RAM.