BIOS Settings - Advanced Features



This section usually contains more advanced features for 
controlling the behavior of your system. There are some settings 
here that you will want to adjust to ensure maximum performance 
from your system. There may also be some features you will need 
to enable or disable if your system is exhibiting 
problem behavior.


Virus Protection / Virus Warning

This setting has one of the most misleading names of all of the 
parameters in the BIOS. The system BIOS really has no way at all 
to tell which programs are viruses, and which are "wanted" 
programs. If enabled, what this setting does is to trap any and 
all writes to the hard disk's master boot record, and display a 
message to the screen each time asking if you are willing to 
allow the write. Since one common type of virus is the boot 
sector infector, this can indeed prevent the spread of 
these viruses.

However, this setting will also cause the BIOS to display its 
warning message for any legitimate access to the boot sector. So 
if you use any utilities that modify partitions, or even if you 
reformat your hard disk, this message will pop up rather 
unexpectedly. You can of course just "authorize" the BIOS, 
telling it to proceed with the write, but this can grow rather 
annoying if it happens often. It can also be quite confusing to 
someone who doesn't understand what this strange BIOS 
message means.

Some people prefer the safety of having this enabled, others find 
it annoying and turn it off. In fact, most people don't regularly 
run utilities that modify the boot sector. If you turn this 
setting off, you can probably find a similar feature, more 
elegantly implemented, in a memory-resident anti-virus program.


Internal Cache

This setting enables or disables the internal cache on your 
processor. This is also known as the L1 or level 1 cache. For 
486 or later processors this should be enabled; turning off the 
level one cache will lead to a major performance hit. Earlier 
processors don't have internal cache, and enabling this setting 
can possibly lead to problems. You should disable this setting 
only for testing purposes if you are trying to find a problem, 
or if you suspect a bad processor chip.

On some BIOSes you may see three choices: "Disabled", "Write 
Through" and "Write Back". These refer to the cache's write 
policy . The write back cache policy will produce the 
best performance.


External Cache

This setting enables or disables the external cache on your 
processor, also known as the L2 or level 2 cache. Most 486 or 
later motherboards include this cache memory. Like the internal 
cache setting, this should be enabled at all times unless you are 
disabling it for troubleshooting purposes. Disabling the external 
cache will cause your system to slow down dramatically, but you 
can use it if you are having system crashes and suspect a problem 
with the cache chips.

On some BIOSes you may see three choices: "Disabled", "Write 
Through" and "Write Back". These refer to the cache's write 
policy. The write back cache policy will produce the 
best performance. 

	Note: There are some motherboards out on the market, 
particular PCI-based 486 motherboards, that have fake level 2 
cache on the board. One way to test for this is to disable the 
external cache and see if there is a performance decrease in the 
system. If there isn't, you never had any level 2 cache to begin 
with. In addition, some systems will report (in the System 
Configuration Summary ) the presence of enabled level 2 cache 
even when it is disabled. This is a BIOS that has been "doctored" 
and is a sign of fake cache on the motherboard as well. Amazing 
the trouble people will go to to cheat someone out of a few 
bucks, isn't it?


Quick Power On Self Test / Quick Boot

Enabling this setting will cause the BIOS power-on self test 
routine to skip some of its tests during bootup. One of the key 
things this setting usually does when enabled is cause the POST 
to skip checking all of extended memory for errors.

Most people enable this setting to speed up the boot process, 
but you should realize that you do increase the chance of the 
POST missing an error if you use this. Fortunately (or 
unfortunately) the POST memory test is virtually useless to 
detect transient memory errors (as opposed to hard errors that 
you would discover the first time you powered up the machine 
with the new memory in it), so once your system is running and 
stable, you can in most cases enable this setting safely. It's 
still safest to leave it disabled, which is what I recommend 
unless you have truly monstrous amounts of RAM. After all, how 
often do you boot the system during normal use? 


Memory Test Tick Sound

When enabled, the POST memory test will make a tick sound as it 
counts up your system memory. Most people leave this enabled, 
others turn it off because they find the sound annoying. Many 
newer systems skip this option and turn the sound off entirely.

When building a system, it is recommended that you enable this, 
as the sound will act as a confirmation that your speaker is 
working, and that the POST is progressing normally. This is 
important during the first few boots of a system, and also if 
you are having video problems.


Boot Sequence

This setting controls the order that the BIOS uses to look for 
a boot device from which to load the operating system during the 
DOS boot process. Older machines do not have this setting; they 
look at the floppy drive first (A:) and then the hard drive (C:). 
Most systems will at least let you choose between "A:, C:" (the 
default) and "C:, A:". Newer systems will allow you to boot from 
the CD-ROM as well; in this case there will be six different 
combinations listed. The default will normally be "A:, C:, CD-ROM".

	Note: Booting off the second floppy disk, B:, has not 
been an option on any PC I've ever seen.

Some BIOSes are getting even more advanced in terms of the boot 
sequence options they will allow. Some systems will now allow you 
to boot off a different IDE hard disk than the primary master 
(C:), or let you boot from a SCSI device instead of IDE even 
when both are used in the same system (normally the IDE device 
gets preference ).

Changing the boot sequence to seek from the hard disk drive first 
instead of the floppy disk drive has some advantages, and also 
some disadvantages. There are two main advantages. First, if the 
floppy disk isn't bootable, you virtually eliminate the chance of 
a boot sector virus spreading to your hard disk from a floppy. 
Second, you have a measure of security and reliability since when 
the floppy disk is bootable, anyone can write their own system 
files and boot the PC with their floppy, bypassing the standard 
startup files on the hard disk.

The disadvantages of not having the floppy bootable all relate 
to convenience. First, if you ever do have a virus on your PC 
then you will normally need to boot from a clean floppy disk to 
disinfect your hard disk; you will have to go back into the BIOS 
and change the boot sequence, disinfect, and then change it back. 
Second, there are some software programs that require their own 
boot disks (though they are becoming quite rare). Third, if your 
hard disk ever fails, you won't have any way to boot the PC. Some 
viruses manifest themselves by making the hard disk disappear. 
Finally, if you are installing a new operating system, or 
building a PC, you really need to be able to boot from the 
floppy disk.

	Note: See also the "Floppy Drive Seek" setting.


S.M.A.R.T. for Hard Disks

Some BIOSes have a specific BIOS setting to enable monitoring 
of hard disks that support the SMART (Self-Monitoring And 
Reporting Technology) feature, which can allow the hard disk 
to report, under some circumstances, impending failures of the 
hard disk. . The normal default for this setting is "Disabled".


Power On Delay / Boot Delay

If you have the combination of a PC that boots up quickly, and a 
hard disk that takes a relatively long time to spin up, your BIOS 
may start trying to boot the operating system before the hard 
disk is read. A giveaway to this problem is the computer that 
won't boot when first powered on but will boot seconds later if 
the reset button is pressed.

If your BIOS has this option, you can specify a time in seconds 
to delay the boot process. This is normally disabled, and should 
be unless you are experiencing this problem.


Boot Up Numlock Status

This setting, when enabled, automatically turns on your NumLock 
key when the system is booted. Most systems default this to 
enabled. This item is a matter of personal taste.

	Tip: There is also a DOS command (NUMLOCK) that can be 
put in the CONFIG.SYS file to enable the NumLock key. This 
will override the BIOS setting at startup if used.


Swap Floppy Drives

A useful feature for those machines that use two floppy drives, 
when enabled this swaps the A: and B: drives. This enables you 
to change the bootable floppy without having to open the case 
and switch the cable. See here for details on multiple floppy 
drives and the floppy cable .

	Warning: Windows NT 4.0 does not properly support the 
floppy drive swap BIOS option; do not enable it if using NT. I 
have read reports of people getting stuck in the middle of NT 
installs because NT changed the floppy disk letters in the 
middle of the installation.


Floppy Drive Seek

Causes the BIOS to search for floppy disk drives at boot time. 
When enabled, the BIOS will activate the floppy disk drives 
during the boot process: the drive activity light will come 
on and the head will move back and forth once. First A: will be 
done and then B: if it exists. When disabled, this seek will 
not be done. Older PCs always did this seek; on newer machines 
it can be disabled to speed up the boot process. 

	Note: This setting will not affect the boot sequence, 
and vice-versa; if the boot sequence starts with A: the system 
will still try to boot from the floppy disk even if this is 
disabled, and if the boot sequence starts with C: the system 
will still look to C: even if floppy disk seek is enabled.


Boot Up System Speed

There aren't as many PCs that have this setting any more. 
Usually the options are "High" and "Low", where "High" is the 
normal system speed, and is the default setting. "Low" is for 
debugging only. Overall, this is a software equivalent of the 
good old "Turbo Switch" and on a modern system should be used 
the same way: that is, not at all.


Keyboard Installed

Some BIOSes let you specify explicitly if there is a keyboard in 
the system. The default is of course "Installed" (or "Yes", etc.) 
If you are using a PC without a keyboard (for example, for a file 
server or secured network PC) this will instruct the BIOS to skip 
the keyboard test during the POST. Also see the "Halt On" setting 
for a different way to accomplish this task.


Typematic Delay

This setting controls the automatic repeat capability of your 
keyboard. Usually specified in milliseconds, this controls how 
long a key must be held down before it begins automatically 
repeating. Typical settings are usually somewhere between 200 
and 1000 milliseconds. Use what feels comfortable. See also 
"Typematic Rate".

	Note: Some higher-end keyboards have the equivalent 
function built-in.

	Warning: Setting this too low can cause the keyboard to 
repeat keys during normal typing, which can appear to be 
"keyboard bounce" and imply a hardware problem with the 
keyboard to the casual user.


Typematic Rate

This setting controls the repeat rate for the keyboard when the 
typematic feature is activated. It is usually expressed in 
characters per second. Use what feels comfortable, but don't go 
too high or you may feed the characters faster than the system 
can deal with them, which can cause beeping or even system lockups.

	Tip: Some higher-end keyboards have the ability to set 
this parameter built-in; sometimes it is called "Key Repeat" or 
"Repeat Rate".


Fast A20 / A20 Gate Option

In order to fully understand this setting you need to understand 
what the A20 line (21st address line) is and what its 
significance is. In a nutshell, the A20 line is used to control 
access to the high memory area, the first 64 KB or so of extended 
memory. This line is normally controlled by the keyboard 
controller . To improve performance, newer systems have this 
control function built into the chipset as well.

To have the chipset control the A20 line and improve performance, 
enable this option. This setting is normally enabled by default. 
There is rarely any reason to disable this.


Video BIOS Shadow

This parameter, when enabled, turns on BIOS ROM shadowing for the 
block of memory normally used for standard VGA video ROM code, 
which is C0000 to C7FFF (32K). See here for a full description 
of what ROM shadowing does ; in short, it speeds up your system 
by copying the contents of your video BIOS code from the slow 
ROM in which it resides into faster RAM.

The default for this setting depends on the particular system 
a great deal.. Enabling it will increase performance. Disable 
it if it causes system problems, particularly those related to 
the video subsystem.

	Note: On some systems the video BIOS shadow setting is 
named for the address range the video BIOS occupies, 
C0000-C7FFFh, instead of being specifically called 
"Video BIOS Shadow".


System BIOS Shadow

When enabled, this parameter turns on BIOS ROM shadowing for the 
block of memory that contains your system BIOS. This is normally 
F0000 to FFFFF (64K). See here for a full description of what 
ROM shadowing does ; in short, it speeds up your system by 
copying the contents of your system BIOS code from the slow ROM 
in which it resides into faster RAM.

This setting normally defaults to "Enabled". Since the system 
BIOS code is used so extensively, shadowing it can cause a great 
deal of system performance improvement.


C8000-CBFFF Shadow

When enabled, turns on adapter ROM shadowing for this 16K block 
of memory. See here for a full description of what ROM shadowing 
does ; in short, it speeds up your system by copying the contents 
of any BIOS code found in adapters using this memory space, from 
the slow ROM in which it resides into faster RAM.

The areas of memory from C8000 to DFFFFh are normally used by 
expansion cards such as network adapters. Turning on shadowing 
would speed these adapters up in the same way that shadowing 
the system BIOS speeds up the system BIOS code. However, things 
are much more tricky here, because some adapters use RAM as well 
as ROM, and map this RAM into this address space as well. If they 
do, and you enable shadowing, the adapter will malfunction 
because shadowing write-protects the RAM it uses (since it 
thinks it is emulating a ROM only, which cannot be rewritten). 
This can cause spurious results when using these cards, and can 
be very difficult to diagnose. In addition, normally unused areas 
of memory in this region are used as UMBs for loading drivers 
via the EMM386 driver, and enabling shadowing will cause this 
to malfunction.

For this reason, the default for shadowing these adapter ROM 
areas is normally "Disabled" and I recommend that it be left that 
way in most cases. If you know all the details on the card whose 
ROM you are trying to shadow, enabling this can in theory 
increase performance, but it is not going to be anything very 
substantial in most cases. Incidentally, on most IDE/ATA systems, 
the block from C8000 to CBFFFh is reserved by the IDE hard 
disk BIOS.

	Note: Some systems have settings for ROM shadowing in 32K 
blocks instead of 16K, so you will see "C8000-CFFFF" instead of 
"C8000-CBFFF" and "CC000-CFFFF".

	Note: Some systems leave off the last digit, calling the 
block "C800-CBFF". It's the same thing.


CC000-CFFFF Shadow

When enabled, turns on adapter ROM shadowing for this 16K block 
of memory. See under "C8000-CBFFF Shadow" for a full description.


D0000-D3FFF Shadow

When enabled, turns on adapter ROM shadowing for this 16K block 
of memory. See under "C8000-CBFFF Shadow" for a full description.


D4000-D7FFF Shadow

When enabled, turns on adapter ROM shadowing for this 16K block 
of memory. See under "C8000-CBFFF Shadow" for a full description.


D8000-DBFFF Shadow

When enabled, turns on adapter ROM shadowing for this 16K block 
of memory. See under "C8000-CBFFF Shadow" for a full description.


DC000-DFFFF Shadow

When enabled, turns on adapter ROM shadowing for this 16K block 
of memory. See under "C8000-CBFFF Shadow" for a full description.
