Hardware Reference
In-Depth Information
increments for any other ROMs located on any other adapter cards (such as SCSI adapters). If
any ROMs are found, they are checksum-tested and executed. These adapter ROMs can alter
existing BIOS routines and establish new ones.
13.
Failure of a checksum test for any of these ROM modules causes the message
XXXX ROM Error
to appear, where the address
XXXX
indicates the segment address of the failed ROM module.
14.
The ROM BIOS checks the word value at memory location 0000:0472 to see whether this start
is a cold start or a warm start. A word value of 1234h in this location is a flag that indicates a
warm start, which causes the BIOS to skip the memory test portion of the POST. Any other
word value in this location indicates a cold start, and the BIOS performs the full POST
procedure. Some system BIOSs let you control various aspects of the POST procedure, making
it possible to skip the memory test, for example, which can be lengthy on a system with a lot of
RAM.
15.
If this is a cold start, the full POST executes; if this is a warm start, a mini-POST executes,
minus the RAM test. Any errors found during the POST are reported by a combination of audio
and displayed error messages. Successful completion of the POST is indicated by a single beep
(with the exception of some Compaq computers, which beep twice).
16.
The ROM BIOS searches for a boot record at cylinder 0, head 0, sector 1 (the very first sector)
on the default boot drive. At one time, the default boot drive was always the first floppy disk
(or A: drive). However, the BIOSs on today's systems often enable you to select the default
boot device and the order in which the BIOS will look for other devices to boot from if
necessary, using a floppy disk, hard disk, or even a CD-ROM drive in any order you choose.
This sector is loaded into memory at 0000:7C00 and tested.
If a disk is in the drive but the sector can't be read, or if no disk is present, the BIOS continues
with step 19.
Booting from Optical, USB, or Floppy
If you want to boot from an optical or USB drive, be sure the drive is listed before the hard
disk in the boot devices or sequence menu in your BIOS setup. If you have a floppy drive
installed, you can set that to come before the hard disk in the sequence as well. This enables
you to always be ready for an emergency. So long as you do not start up the system with a
bootable USB drive, floppy, or optical disc loaded, the BIOS bypasses them and boots from
the hard drive instead.
Refer to
Chapter 11
, “
Optical Storage
,
” for information on how to make a bootable disc.
17.
If you are booting from a floppy disk and the first byte of the volume boot record is less than
06h, or if the first byte is greater than or equal to 06h and the first nine words contain the same
data pattern, this error message appears and the system stops:
602-Diskette Boot Record Error
18.
If the volume boot record can't find or load the system files, or if a problem was encountered
loading them, one of the following messages appears:
