Advanced CMOS Setup
Remember…
- May vary according to your system, BIOS
version and brand. Some functions may not be present
or the order and name may be different (particularly
for different BIOS brand). Know EXACTLY what you
are doing. Some configurations may keep your computer off
from booting. If that's the case: Switch the power
off. Turn your computer on WHILE keeping the DEL
key pressed. This is supposed to erase the BIOS memory.
If it still doesn't boot, consult your motherboard
manual. Look for a "forget CMOS RAM" jumper.
Set it. Try it again. If it still doesn't boot, ask a
friend or post to a computer hardware newsgroup. You are
permitted to panic.
- Typematic Rate
Programming: Disabled recommended. It enables the
typematic rate programming of the keyboard. Not all
keyboards support this! The following two entries specify
how the keyboard is programmed if enabled.
- Typematic Rate Delay (msec):
500 ns recommended. The initial delay before key
auto-repeat starts, that is how long you've got to press
a key before it starts repeating.
- Typematic Rate
(Chars/Sec): 15. It is the frequency of the
auto-repeat i.e. how fast a key repeats.
- Above 1 MB Memory
Test: If you want the system to check the memory
above 1 MB for errors. Disabled recommended for
faster boot sequence. The HIMEM.SYS driver for DOS 6.2
verifies the XMS (Extended Memory Specification), so this
test is redundant. It is thus preferable to use the XMS
test provided by HIMEM.SYS since it is operating in the
real environment (where user wait states and other are
operational).
- Memory Test Tick
Sound: Enabled recommended. It gives an audio
record that the boot sequence is working properly. Plus,
it is an aural confirmation of your CPU clock speed/Turbo
switch setting. An experimented user can hear if
something is wrong with the system just be the memory
test tick sound. Since systems have now much more memory
than before, this setting is not common anymore.
- Memory Parity
Error Check: Enabled recommended.
Additional feature to test bit errors in the memory. All
(or almost all) PCs are checking their memory during
operation.Every byte in memory has another ninth bit,
that with every write access is set in such way that the
parity of all bytes is odd. With every read access the
parity of a byte is checked for this odd parity. If a
parity error occurs, the NMI (Non Maskable Interrupt), an
interrupt you mostly cannot switch off, so the computer
stops his work and displays a RAM failure) becomes active
and forces the CPU to enter an interrupt handler, mostly
writing something like this on the screen: PARITY ERROR
AT 0AB5:00BE SYSTEM HALTED. On some motherboards you can
disable parity checking with standard memory. Enabled to
be sure data from memory are correct. Disable only if you
have 8-bit RAM, which some vendors use because it is 10%
cheaper. Also, this setting is no longer necessary on
recent computers since the quality and reliance of memory
chips has greatly been improved.
- About different memory speeds:
Be sure to have memory chips of the same speed installed.
It is not uncommon to have system crashes simply because
memory SIMMS are of different speed. Faster memory may
not adapt itself to the speed of slower memory. 60 ns and
80 ns SIMMS will surely make your system crash and
yourself wonder what is the problem (I know).
- Hard Disk Type 47
RAM Area: The BIOS has to place the HD type 47
data somewhere in memory. You can choose between DOS
memory or PC BIOS (or peripheral card) memory area 0:300.
DOS memory is valuable, you only have 640KB of it. So you
should try to use 0:300 memory area instead. There may be
some peripheral card which needs this area too (sound
card, network card, whatever). So if there are some fancy
cards in your PC, check the manuals if they're using the
0:300 area. But in most cases this will work without
checking. This is redundant if BIOS is shadowed (maybe
not in very old BIOSes). The RAM area can be verified by
checking address of int41h and int46h. These are fixed
disk parameters blocks. If they point to the BIOS area,
BIOS made modification of parameters before mapping RAM
there.
- Wait for
<F1> If Any Error: When the boot sequence
encounter an error it asks you to press F1. Only at
'non-fatal' errors. If disabled, the system prints a
warning and continues to boot without waiting for you to
press any keys. Enabled recommended. Disabled if you want
the system to operate as a server without a keyboard.
- System Boot Up Num
Lock: Specify if you want the Num Lock key to be
activated at boot up. Some like it, some do not. MS-DOS
(starting with 6.0, maybe earlier) allows a
"NUMLOCK=" directive in config.sys, too; if
someone turns the BIOS flag off but has NUMLOCK=ON in
their configuration file, they may be a bit perturbed.
- Numeric Processor
Test: Enabled if you have a math coprocessor
(built in for the 486DX, 486DX2, 486DX3 and Pentium - 586
- family). Disabled if you don't (386SX, 386DX, 486SX,
486SLC and 486DLC). If disabled, your FPU (Floating Point
Unit, if present) isn't recognized as present by the
system and will therefore significantly decrease the
performance of your system.
- Weitek Coprocessor:
If you have Weitek FPU, enable. If you have not, disable.
This high performance FPU has 2-3 times the performance
of the Intel FPU. Weitek uses some RAM address space, so
memory from this region must be remapped somewhere else.
This setting is normally found on 386 motherboards.
- Floppy Drive Seek
at Boot: Power up your A: floppy drive at boot. Disabled
recommended for faster boot sequence and for reduced
damage to heads. Disabling the floppy drive,
changing the system boot sequence and setting a BIOS
password are good techniques for adding some security to
a PC.
- System Boot Sequence:
What drive the system checks first for an operating
system. C:, A: recommended for faster boot
sequence, or to not allow any user to enter your
system by booting from the FDD if your autoexec.bat
starts with a login procedure. A:, C: if the person who
uses the computer is someone who don't knows how to setup
CMOS. Because if something fails and a boot floppy won't
work, many users won't know what to do next. However, be
careful. You had better know this setting is turned on
and be prepared to turn it off if your hard disk boot
track becomes corrupted, but not obviously absent, since
you otherwise won't be able to boot from floppy. Also,
it's easy to fool yourself into thinking you booted from
a known virus-free floppy when it actually booted from
the (virus-infested) hard drive.
- System Boot Up CPU
speed: Specify at what processor speed the system
will boot from. Usual settings are HIGH and LOW. HIGH
recommended. If you encounter booting problems,
you may try LOW. You may also change the CPU speed with
Ctrl-Alt +.
- External Cache Memory:
Enabled if you have external cache memory (better
known as L2 cache memory). This is a frequent
error in CMOS setup as if Disabled when you have cache
memory, the system performance decreases significantly.
Most systems have from 64K to 512K of external cache. It
is a cache between the CPU and the system bus. Different
operating systems may address different levels of cache
memory. For instance, DOS and Windows can address up to
64K at one time while Windows 95, OS/2 and Windows NT can
address larger memory spaces. So, don't buy 256K of cache
is you are using a DOS environment with less than 8MB of
memory. It will not improve much the performance of your
system. If Enabled when the system does not have cache
memory, the system will freeze most of the time.
- Internal Cache Memory:
Enable or disable the internal cache memory of the CPU (better
known as L1 cache memory). Disabled for 386 and
Enabled for 486 (1 to 8KB of internal CPU cache). If the
CPU does not have internal cache, the system may freeze
if enabled.
- In many AMI and AWARD BIOSes, the two
previous options are implemented either as separate
Internal and External Enable/Disable options, or as a
single option (Cache Memory :
Disabled/Internal/Both).
- CPU Internal Cache:
same as above.
- Fast Gate A20 Option:
Enabled recommended. A20 refers to the first 64KB of
extended memory (A0 to A19) known as the "high
memory area". This option uses the fast gate A20
line, supported in some chipsets, to access memory above
1 MB. Normally all RAM access above 1 MB is handled
through the keyboard controller chip (8042 or 8742).
Using this option will make the access faster than the
normal method. This option is very useful in networking
and multitasking operating systems.
- Turbo Switch Function:
Enables or disables the turbo switch. Disabled
recommended. This setting is now removed since there are
no need to switch from normal to turbo modes.
- Shadow Memory
Cacheable: You increase speed by copying ROM to
RAM. Do you want to increase it by cacheing it? Yes or no
- see Video BIOS Area cacheable. Yes recommended for
MS-DOS and OS/2. Linux and other Unix-like operating
systems will not use the cached ROMs and will benefit
from the additional available memory if they are not
cached.
- Password Checking
Option: Setup password to have access to the
system and / or to the setup menu. Good if the computer
is to be shared with several persons and you don't want
anyone (friends, sister, etc.) to mess up with the BIOS.
Default password: AMI (if you have AMI BIOS). Award:
BIOSTAR or AWARD_SW for newer versions (Note: I even know
a computer store that kept standard AWARD BIOS
configuration with their systems because they didn't know
what the default password was!).
- Video ROM Shadow
C000, 32K: Memory hidden under the "I/O
hole" from 0x0A0000 to 0x0FFFFF may be used to
"shadow" ROM (Read-Only Memory). Doing so, the
contents of the ROM are copied into the RAM and the RAM
is used instead, which is obviously faster. Video BIOS is
stored in slow EPROM (Erasable Programmable Read-Only
Memory) chips (120 to 150ns of access time). Also, ROM is
8 or 16 bit while RAM 32 bit wide access. With Shadow on,
the EPROM content is copied to RAM (60 to 80ns of access
time with 32 bit wide access). Therefore performance
increases significantly. Only sensible on EGA/VGA
systems. Enabled recommended. If you have flash
BIOS (EEPROM), you can disable it. Flash BIOS enables
access at speeds similar to memory access so you can use
the memory elsewhere. However, flash BIOS is still only
accessing it at the speed of the bus (ISA, EISA or VLB).
On systems where the BIOS automatically steals 384K of
RAM anyway, it shouldn't hurt to enable shadowing even on
flash ROM. One side effect is that you will not be able
to modify the contents of flash ROM when the chip is
shadowed. If you reconfigure an adapter which you think
might have flash ROM, and your changes are ignored, or of
course if it gives you an error message when you try to
change them, you'll need to temporarily disable shadowing
that adapter. On (S)VGA you should enable both video
shadows. Some video cards maybe using different addresses
than C000 and C400. If it is the case, you should use
supplied utilities that will shadow the video BIOS, in
which case you should disable this setting in the CMOS.
Video BIOS shadowing can cause software like XFree86 (the
free X Window System) to hang. They should be probably be
disabled if you run any of the 386 unixes.
- Some cards map BIOS or other memory not only
in the usual a0000-fffff address range, but also just
below the 16MB border or at other places. The BIOS (for
PCI buses only?) now allows to create a hole in the
address range where the card sits. The hole may be
enabled by giving an address, then a size is requested in
power of 2, 64k - 1MB.
- Adaptor ROM Shadow
C800,16K: Disabled. Those addresses (C800 to EC00)
are for special cards, e.g. network and controllers.
Enable only if you've got an adapter card with ROM in one
of these areas. It is a BAD idea to use shadow RAM for
memory areas that aren't really ROM, e.g. network card
buffers and other memory-mapped devices. This may
interfere with the card's operation. To intelligently set
these options you need to know what cards use what
addresses. Most secondary display cards (like MDA and
Hercules) use the ROM C800 address. Since they are slow,
shadowing this address would improve their performance.
An advanced tip: in some setups it is possible to enable
shadow RAM without write-protecting it; with a
small driver (UMM) it is then possible to use this
'shadow RAM' as UMB (Upper Memory Block) space. This has
speed advantages over UMB space provided by EMM386. Some
BIOSes have three options per 16KB/32KB/64KB block; e.g.
disable - shadow ROM - shadow RAM or disable - shadow/WP
- shadow (WP = write protect) the third option is for
upper memory.
- Adaptor ROM Shadow CC00,16K: Disabled. Some hard
drive adapters use that address.
- Adaptor ROM Shadow D000,16K: Disabled. D000 is the
default Address for most Network Interface Cards.
- Adaptor ROM Shadow D400,16K: Disabled. Some
special controllers for four floppy drives have a BIOS
ROM at D400..D7FF.
- Adaptor ROM Shadow D800,16K: Disabled
- Adaptor ROM Shadow DC00,16K: Disabled
- Adaptor ROM Shadow E000,16K: Disabled. E000 is a
good "out of the way" place to put the EMS page
frame. If necessary.
- Adaptor ROM Shadow E400,16K: Disabled
- Adaptor ROM Shadow E800,16K: Disabled
- Adaptor ROM Shadow EC00,16K: Disabled. SCSI
controller cards with their own BIOS could be accelerated
by using Shadow RAM. Some SCSI controllers do have some
RAM areas too, so it depends on the brand.
- Some SCSI adapters do not use I/O-Addresses.
The BIOS address range contains writable addresses, which
in fact are the I/O-ports. This means this address must
not be shadowed and even not be cached.
- System ROM Shadow
F000, 64K: Same thing as Video shadow, but according
to the system BIOS (main computer BIOS). Enabled
recommended for improved performance. System BIOS
shadowing and caching should be disabled to run anything
but DOS (Windows).
- On older BIOS versions the shadow choices
are in 400(hex)-byte increments. For instance, instead of
one Video ROM Shadow segment of 32K, you will have two
16K segments (C400 and C800). Same thing for Adaptor ROM
Shadow segments.
- BootSector Virus
Protection: It is not exactly a virus
protection. All it does is whenever your boot sector
is accessed for writing, it gives a warning to the screen
allowing you to disable the access or to continue.
Extremely annoying if you use something like OS/2 Boot
Manager that needs to write to it. It is completely
useless for SCSI or ESDI (Enhanced Small Device
Interface) drives as they use their own BIOS on the
controller. Disabled recommended. If you want
virus protection, use a TSR (Terminate and Stay Resident)
virus detection (Norton, Central Point, etc...). Viruscan by Macfee is
also a good idea since it is a shareware.