CMOS is a small amount of random access memory in your PC. This memory stores certain important settings of the motherboard. The CMOS is refreshed by the CMOS battery even when the system is turned off. The information in the CMOS Ram is not wiped off, unless the battery stops functioning. You might think that your only need to know about CMOS if your are learning how to build a computer however, this article can also help you if you already own a computer, but want it to perform faster.

If the CMOS battery stops, it can be replaced easily and the CMOS settings can be restored. The information in the CMOS setup is read by the BIOS during the system boot up process.

You can access the CMOS setup by pressing a certain key combination or the delete key. This depends on the type of BIOS you have in your PC. Watch you boot screen and it should indicate the correct way to access CMOS.

Most CMOS setups consist of menu selections. This Article gives a general idea of how to perform CMOS setup. Different CMOS setups exist in different PC’s and if you want more information on the setup for your motherboard, you can always obtain it from the motherboard manual.

Menu Selections :

1) Configuring Standard CMOS setup.

Most of the configuration in this part of CMOS setup is done automatically.

1) IDE drive is automatically detected when Enter is pressed.
2) Floppy drive is to be selected as per the drive connected to your PC – 1.44 M, 3.5 in
3) Video is set to VGA
4) Internal memory is automatically detected.
5) Date and time can be set through the CMOS setup as well as through the operating
     system.

2) Configuring Advanced CMOS setup.

Advance CMOS settings configure the boot characteristics, the memory and cache.

Typical entries are :

? Virus warning 
? CPU level 1 Cache, CPU level 2 Cache
? Quick power on self test
? First boot device, Second boot device, Third boot device.
? Boot other device
? Swap Floppy drive
? IDE block mode
? Typematic rate setting , Typematic rate , Typematic delay
? Security option 

The Advance CMOS settings allow you to enable or disable the CPU caches.
First boot device allows you to set the device from which your system will boot. If you want to boot from the hard disk, as is mostly the case, then set this to HDD0. If you want to boot from CD Rom, as when you are installing a new hard disk and operating system, set it to CDRom.

If your system is not able to boot from the First boot device than it will search for operating system in the Second boot device and boot the PC from there.

If typematic rate is enabled, you can set the typematic rate for your keyboard.

If Quick power on self test is enabled your PC will boot faster, and the BIOS will skip many of the hardware tests.

3) Configuring Advanced Chipset setup.

In this section you will find the parameters that can be configured to optimize the performance of your chipset. This has to be done carefully, otherwise it may result in lowering the performance of your PC, instead of enhancing it. This section contains entries for the memory operations, memory refresh options, data bus performance, cache enhancements etc

As every BIOS is not similar, the motherboard manual can give you a better idea of how to configure the chipset settings.

Some of the entries in this section  are the following.

? Sdram RAS to CAS delay , Sdram RAS precharge time
? Dram read burst, Dram write burst
? System BIOS Cacheable, Video BIOS Cacheable
? Video RAM Cacheable
? 8 bit I/O recovery time, 16 bit I/O recovery time
? Passive Release etc.

The above settings can be either enabled or disabled to enhance the chipset performance.
For example, enabling video BIOS cacheable will improve the video performance, though it may not be of much help for some latest video devices.

4) Configuring PCI and Plug and Play setup.

This section contains entries for configuring the PCI slots and Plug and Play behavior of your PC. Some BIOS’s have the option to automatically configure the PCI slots and Plug and Play. If this is enabled the Interrupt requests will be automatically assigned to the devices you connect to the PC.

The Interrupt requests for particular devices can also be set manually using the respective entries in the CMOS setup.

5) Configuring Integrated peripherals.

This section contains CMOS setup entries for the external IDE devices connected to the motherboard.

Besides the IDE devices, you can also configure the serial ports, parallel ports etc

There are also options to enable and disable the Infra red and the USB ports.

Some of the entries are the following :

? IDE HDD Block mode, IDE PIO mode
? On chip PCI IDE , PCI slot IDE 2nd channel
? On board serial port – allows you to select a the address for the serial ports
? On board parallel port – allows you to select the address for parallel printer port.
? Parallel port mode
? Infrared duplex type – keep enabled if your system has infra red devices.
? USB controller – keep enabled if your system has USB ports and devices connected to them.

6) Configuring Power Management.

This section contains CMOS setup power management functions. The Power consumption in modern PCs is reduced due to use of efficient components. However, PCs have to remain on for a long time and power may be wasted. The CMOS settings allow you to configure your PC so that the power can be saved.

Here are some of the CMOS settings you can use to save power.

Doze timer : This setting determines the time  before which the idle PC system will reduce itself to 80% of its activity. (set to 10 to 20 minutes)

Green timer: This setting determines the time before a CPU of an idle system will shut down.

HDD Standby Timer : This setting determines the time before which the idle hard disk will shut down.

Standby timer : This setting sets the delay before which the  idle PC system will reduce itself to 92% of its activity. (set to 30 to 40 mins)

Suspend timer : This setting sets the time after which the system goes into the most inactive state possible (99%) (set to 30 to 45 mins)

System slow down : This setting will slow the CPU clock dramatically after the timer has elapsed.

What is Auto-configuration.

Motherboards now provide Auto-configuration option, which allows the technician to set the BIOS defaults and the power on defaults. Hence, if the Auto-configuration setting is enabled the BIOS will work fine and booting will take place smoothly. Hence, there is actually no need for the technician to setup the CMOS. However, this does not ensure optimization of the system, which will have to be carried out manually.

BIOS defaults

Turning on BIOS defaults does not ensure that the machine is fully optimized. If your CMOS settings are totally messed up and your system does not boot, BIOS defaults will restore the setting to acceptable values for booting your system.

Power on defaults

When powering up the system, the system may not enter the CMOS setup. Setting Power on default ensures that you can always enter the CMOS setup.

Understanding of CMOS settings is useful for optimizing your system. If you want to run your system faster and smoother, or you want to upgrade the devices, or connect new adapters because the onboard adapters have gone faulty, it is essential to have good knowledge of CMOS settings.