Before anything can appear, the display adapter must be initialized. It must be set to the correct resolution and refresh rate. The hard disks must be powered up and come to operating speed. The keyboard and mouse ports are tested. Any problems are reported with multiple beeps and an error code or message on the screen.
RAM memory is installed in the machine as a row of SIMMs.
Memory comes in some number of megabytes. The gap is divided into three 128K areas. Each time the system is initialized, the POST program scans this area for initialization programs and runs any that it finds. Code on the SCSI card makes up to two SCSI disks visible and usable to DOS programs. Code on the LAN adapter will boot a diskless workstation from a LAN server.