A quick survey of computers available today shows that BIOS POST time averages about 30 seconds. The next step in improving system boot speed is to improve BIOS POST time. Both system BIOS POST time and the POST time of option ROMs in add-on cards must be improved. As with the original IBM PC XT, computers spend time counting through memory, even though memory failures are rare today on most systems. Disk Spin Up.
Hard drives are mechanical devices that can take several seconds to come up to full speed.
System BIOSs and option ROMs perform a number of diagnostics at every boot, despite the fact that most hardware is high quality and doesn't require such frequent testing. SCSI adapters enumerate the entire SCSI bus, which can take more than 1 minute. Boot Delays for Logos. Many vendors who show their logos at boot time add delays to make sure the user sees them. Floppy Disk Check.