BIOS Setup
By Gabriel Torres on July 2, 2004


Setup is a configuration program found in every PC, which is burned on ROM (which in turn is placed in the motherboard). Usually, to call the setup you must press Del key during memory counting.

PC configuration is stored in a special memory called configuration memory. As this memory is built with CMOS technology, most guys refer to it just as CMOS memory. As this is a RAM type memory, its data are erased when PC is turned off. To avoid that, there is a battery that holds power to it, such that stored data won't be lost when mains is turned off. This battery is also responsible for powering the PC real time clock (RTC) circuitry for the same reason. Every PC has this clock built in and that's what keeps date and time updated.

In setup we alter the parameters stored in configuration memory, as shown in the picture. There is a general misconception about setup operation, though. As it is stored in PC's ROM memory, many guys think that setup and BIOS are just the same thing, which is not true. Inside ROM three different programs are stored (actually burned). The Basic Input and Output System (BIOS) that is responsible for teaching the main processor how to deal with basic devices, such as floppy unit, hard disk or video in text mode; the Power On Self Test (POST) which is the program in charge of the self test that is executed every time PC is powered up (like memory counting, for instance); and the Setup which is the program that allows the alteration of the parameters stored in the configuration memory (CMOS).

Another common misconception is to think that the configuration altered by setup program is stored in BIOS. As BIOS is a ROM type memory, it just can't allow its data to be altered. All information handled and altered by setup are stored solely in the configuration memory (CMOS).

Therefore when we run setup we don't enter BIOS nor do we alter BIOS values, as some guys say it by mistake. Actually we enter in setup and alter the values in the configuration memory.


Figure 1: Motherboard ROM memory chip. BIOS, POST and Setup softwares are written in this chip.

South Bridge

Figure 2: Example of a south bridge chip. The CMOS memory and the Real Time Clock (RTC) are both embedded in this chip nowadays.


Figure 3: This battery is connected to the south bridge chip, to power both CMOS memory and RTC circuits.

Main Menu

In order to call the setup you must press Del key during memory counting. In some computers (like those from IBM) the key may be another one, and you must pay attention to the instructions displayed on screen during the memory counting in order to have access to the setup.

Once inside setup, browsing is normally done using the keyboard arrows to moving around the options, the Enter key to select a menu, the Esc key to return to previous menu, and the Page Up and Page Down keys to modify an existing option.

It is very important to note that the changes done when you're inside setup are not automatically saved in CMOS configuration memory. Therefore you save the changes before leaving setup, choosing the Save and Exit option.

When entering setup you'll see the main menu displaying options for calling other setup menus. Those options are basically the ones listed below (don't worry, we'll discuss all of them in detail).

Basic CMOS Setup

Basic setup doesn't present any difficulties in its setup There you must find:

That's it. Some setups may display some additional options:

Naturally some computers may display some additional basic setup information like installed RAM size. But the options you'll find out in all setups are those we discussed today.

Advanced CMOS Setup

As referred by the name itself, the Advanced CMOS Setup displays the computer configuration advanced options. However, most advanced setup options are set according to user preferences as you'll see. Below we'll discuss the most common advanced options, indicating our setup options, though you'll don't have to take them literally, because, as we mentioned, several options are configured according to user's taste.

It is worth noting that your computer setup may not have all options discussed here, just as it can eventually display options that were not discussed.

Advanced CMOS Setup (Cont.)

Advanced CMOS Setup (Cont.)

Advanced Chipset Setup

Next we'll discuss the main options available in the Advanced Chipset Setup. Most options of this menu refer to RAM memory access setup. Therefore take care when changing any option as a wrong configuration can cause a computer freezing. In case computer freezer after this option is enabled, just reset computer and undo the setup changes in order to function properly. Though sometimes we will suggest to enable some functions, it may happen your computer doesn't support that function enabled, and keeps freezing.

Advanced Chipset Setup (Cont.)

Most Advanced Chipset Setup configurations are restricted to a standard configuration and you can only change these configurations if you disable the existing Auto Configuration or Auto Config. This happens because the configurations of this menu involve the time base and all sort of configurations of this kind may freeze the computer if wrongly set.

Therefore, if you don't want to take any risks, the safest is to enable automatic configuration and not changing any of the configurations that may have been far from optimum.

Among the several options involving time base options are the wait states configurations. Wait states are clock pulses that are added to the memory reading or writing cycles in order to match the processor speed with RAM memory speed, as RAM is much slower than processor. During the wait state clock pulses processor doesn't do absolutely nothing, it stays waiting for RAM memory to be ready to receive or send data. Therefore wait states decreases computer performance. However processor can't access RAM directly, without using wait states.

But the less wait states the processor uses, the better. This means that you can try to reduce the number of wait states to get a little more computer performance. The Automatic Configuration doesn't rate the best wait state values, but rather it sets values that safely won't freeze the computer. Therefore there is a chance to decrease the number of wait states keep computer from freezing.

If you decide to decrease the wait states, disable the Auto Config option and decrease the number of wait states used for each option, one at a time. For example imagine that CAS Read Wait State option is set as 4 - that is, using 4 wait states. You can decrease this value to 3, save the changes and try to use the computer to check if it won't freeze. If it freezes, you must restart the computer enter setup and undo the last change done. In case the computer doesn't freeze you must try to decrease even more this number, repeating all process until the ideal number is found, which is always one before computer freezes.

But do not try to change lots of options simultaneously, because if computer freezes you will not know which of the options is freezing the computer. The wait states final adjustments must be done individually for each existing option. It is a lengthy process, but it can bring an extra performance to the computer.

If you don't feel inclined for such patient jobs or if don't have the necessary time to do it, don't worry: just enable the Auto Configuration option and forget about this story of wait states adjustments.

The main wait state adjustment options are:

Advanced Chipset Setup (Cont.)

Generally, options related to the time base must be set up in the same way as the wait states - the shorter the time, the higher the performance. But, in order to do that, you must find the precise setup value as we discussed previously. The following options may be set up similarly to the wait states:

We will discuss below other common options to be found in the chipset advanced setup.

Advanced Chipset Setup (Cont.)

Today we will discuss other important options available in the advanced machine setup. The options below increase the PC performance when enabled, therefore we suggest you enable them. However not all PCs are fully compatible with those options, and some PCs may not boot after having enabled some of them. If that happens, one must disable the option that is causing the problem.

Below are some other options available in the advanced setup:

Power Management Setup

Now that we've seen the major advanced setup options, we will discuss the PC advanced power management setup, which is performed by means of the setup Power Management menu.

The PC has several sleep modes in order to save electrical power. This is obtained in several different ways, as for instance, reducing the processor clock frequency or turning off the hard disk. Naturally the PC only goes into sleep mode after a determined inactive time period, that is, without executing any task at all. It is right in the power management menu that you set up the appropriated inactivity time needed before the PC goes into the sleep mode.

There are three sleep modes: Doze, Standby and Suspend. The difference between them is the sleeping "deepness". The deeper the sleep, the more energy you'll save. The Doze mode is the most superficial and the Suspend mode is the deepest.

At setup you set the inactivity time needed before PC goes into those sleeping modes. Additionally you'll set up the length of the inactivity period of time before the hard disk is turned off (IDE Power Control or HDD Power Down Time options) and you may even set up the option to turn off the processor fan when it goes into sleeping mode (CPU Fan Off option). As the processor clock is reduced in that mode, the fan may be turned off, as the processor will not heat as much.

You may also set up the activity type allowed to wake up the PC. Modem is a good example. It is quite common to use the modem as a fax and let the PC on throughout the day waiting for fax calls. In order to save energy, you can set up the PC to stay in sleeping mode and to wake up at the reception of a fax call, then going back into sleeping mode after an inactivity period. This facility is called Wake-up On Ring.

Most setups show an option where an interruption request (IRQ) wakes up the PC. This means that any activity in the device using that IRQ will wake up the PC. The keyboard, for instance, uses interruption 1 (IRQ1). Consequently if you set that IRQ1 wakes the PC up, that is to say that any keyboard activity will wake up the PC. The same happens with any device connected to the PC as for instance, the serial mouse, which usually uses IRQ4 (that is setting IRQ4 to wake the PC up, it jumps out of sleeping mode whenever you move the mouse). You can get a complete list of the relations between devices and IRQ in your computer by means of the Device Manager (an icon in the Control Panel System), selecting Computer and clicking in the Properties box.

When power management is enabled, Windows 98 displays a new option in the Start menu: Suspend. This options puts the PC immediately into Suspend Mode and no programmed inactivity time needs to be timed out.

Occasionally your PC may display many other options in the power management menu, but we expect that you will be able to set them up intuitively grounded on today's discussions.

PCI/Plug and Play Setup

There is in the setup a menu for the setting of the PCI bus and of the ISA Plug and Play devices, usually called PCI/Plug and Play Setup (or PNP/PCI Configuration). The proper menu setting is important in order to avoid interruptions or DMA conflicts in your computer, specially when you have an old peripheral device installed as for instance a sound board.

Usually when two or more peripheral devices are configured to share the same facility, they don't work appropriately. When two Plug and Play devices are installed using same facility (same interruption line or DMA channel) the operating system itself may automatically reconfigure the devices in order to solve the facilities conflict.

Old Plug and Play devices are not Plug and Play therefore there is no way to change their settings by means of the operational system (in those type of peripherals the setup is changed by means of jumpers). If a Plug and Play device consistently uses same interruption or DMA channel as a legacy non Plug and Play device, it may happen that the system is unable to manage this conflict permitting that peripheral devices conflict and therefore don't operate.

Therefore in the computer setup there is how to manually set which interruptions (IRQ) and DMA channels are being used by legacy non plug and play devices. In that way such facilities are set apart by the system and no Plug and Play device may use them.

If you have any legacy non plug and play device installed in the computer - as a sound board or fax modem - you must perform this procedure. Sound boards normally use IRQ5, DMA1, and DMA5 while fax modem uses IRQ3.

The set up is done by means of options such as "IRQ x Available To" and "DMA x Available To". There are two configuration possibilities: "PCI/PnP" in case the facility is being used by a Plug and Play PCI or PCI device, or "ISA/EISA" (or "Legacy ISA") when the facility is being used by a non Plug and Play device.

If you have a legacy sound board in your computer, you will have to set "IRQ5 Available To", DMA1 Available To", and DMA5 Available To" as "Legacy ISA", while other options should stay in "PCI/PnP".

In case you don't have legacy boards installed, you can just set the option "Resources Controlled By" in Auto to inform all peripherals in your computer are Plug and Play. In case there is at least an installed legacy non Plug and Play board, you must leave this option in Manual and execute the discussed setup.

The existing "PnP OS installed" option must be enabled if you are using Windows 9x.

Peripheral Setup

Now we will discuss the Peripheral Setup (or Integrated Peripherals) which configure all peripherals integrated in the motherboard (onboard), including the serial ports, the parallel port the IDE port and the floppy drive controller.

The most frequent options found in this menu are:

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