Power users routinely punch into the BIOS in order to fine tune their system, but it can be an intimidating place to go exploring if you've never before burrowed beneath the surface. And just like in real life, poking around in unknown places can be a dangerous affair if you don't know what you're doing or where you're going. On the other hand, once you understand the inner workings of your PC's control center, a whole world of overclocking and troubleshooting suddenly opens up. But what exactly is the BIOS?
Every modern motherboard comes with an embedded Flash EEPROM module, otherwise known as the BIOS chip. Short for Basic Input Out System, this is the first bit of code executed when you boot your PC. The BIOS stores all kinds of essential information about your system, such as your CPU's clockspeed, the size and type of RAM you're running, the boot order of your media, what onboard devices are present, and much, much more. An improperly configured BIOS can prevent Windows (or Linux) from loading, while a finely tuned BIOS has the potential to significantly improve performance over that of a similarly spec'd machine.
Whatever your goal is, this is your go-to guide for everything you've ever wanted to know about the BIOS. We cover every setting -- even the obscure ones -- so you'll never feel lost or out of your element, no matter what motherboard you're rocking under the hood.
Whether from a cold boot or rebooting, getting into your BIOS is as easy as hitting the DEL key as soon as your system starts to POST. You might even see a Splash screen instructing you to hit DEL, but this isn't always the case. If mashing the DEL key doesn't do the trick (some OEM setups, notebooks, and older PCs use a different key), try punching F1, F10, or the ESC key. For really old PCs, you might even need to hit a combination of keystrokes, in which case your best bet is to consult your user manual or the modern day oracle known as Google for the correct sequence.
The overall layout will vary depending on your specific motherboard model and BIOS type, but every modern BIOS shares the same basic settings. We're going to cover those now while using a Gigabyte X58 as our test platform.
Exactly as the name implies, this is where the standard settings are located, including the date, time, and drive configuration.
Date and Time: You shouldn't need to configure the date and time more than once, but if it keeps getting knocked out of whack, it may be time to replace the CMOS battery. You can try leaving your PC on for an extended period of time to recharge the battery, but it's cheap enough to replace outright and a new one should last for years. Check your motherboard manual for the type of battery it uses, which will probably be a CR2032.
IDE Channels: Here is where you'll find what IDE drives you have connected to your PC. These are the ones that use those old school fat ribbon cables of yesteryear and require multiple drives on the same channel be configured as 'Master' and 'Slave.' Your drives should show up automatically, but if not, highlight the appropriate entry and hit the Enter key, which brings up another submenu.
- IDE HDD Auto-Detection: Use this to auto-detect a newly connected hard drive.
- Access Mode: Also known as the Translation Method, this setting relays the physical characteristics of your IDE drive to your system and how to define the disk size.
If you're still not seeing your drive(s) show up, check that the jumper on the back has been properly configured and that you remembered to plug in a Molex power connector.
SATA Channels: These are your SATA drives, though your motherboard may still label them as IDE. Because each SATA drive operates on its own channel, they do not contain 'Master' and 'Slave' settings. On a related note, only connect ONE power source, even if it has inputs for both a 4-pin Molex and SATA power connectors. Plugging these both in can ruin your HDD.
Drive A and B: Refers to the type (if any) of floppy drive you have installed, or plan to install. The most common today is 1.44M, 3.5 in. You can also set this to Disabled if you're not planning to rock out with your floppy out.
Floppy 3 Mode Support: Designates a special type of floppy drive that supports three different types of floppies. These were mainly used in Japan and never gained any major footing in the U.S.
Video: Some motherboards don't even include this setting anymore, but this allows you to designate what type of videocard you have installed. Unless you have a specialized configuration, this should read EGA/VGA' Set this to your primary videocard type, and not the secondary (if one is installed).
Halt On: Configure this setting to tell your BIOS which errors to ignore during POST.
In the Advanced menu, you'll begin to scratch beneath the surface and configure how various parts of your system operate. This might also be where you set the boot priority, though some motherboards -- like those Asus offers -- dedicate a separate submenu to this task.
Hard Disk Priority: When you have multiple hard drives installed, this setting tells your BIOS which order it should attempt to boot them. This can be handy for dual-booting OSes, with each OS -- like Windows and Linux -- installed on separate drives.
First and Subsequent Boot Device: This is where you'll determine what order your system should attempt to boot from. If installing Windows, for example, you'll want to designate your CD/DVD drive as the first boot device before your hard drive.
Password Check: If you set a password, you can instruct your BIOS to ask for it either when booting the PC or when attempting to enter the BIOS.
HDD S.M.A.R.T. Monitor: Short for Smart Monitoring Analysis and Reporting Technology, this serves as a preventative diagnostic to help predict imminent hard drive failures. When enabled, supported hard drives will report any problems that could ultimately lead to outright failures.
Limit CPUID Max. to 3: The only ones who should have this setting enabled are those running a legacy OS with a Pentium 4 processor or higher. CPUID instructions are used to identify the type of processor installed, and the higher the number, the more information can be obtained and written to. Operating systems released before the Pentium 4 had trouble handling the additional CPUID parameters, which is where this limit comes into play. Vista, XP, and Windows 7 users can safely leave this option Enabled.
No-Execute Memory Protect: This safeguard prevents buffer overflow attacks and both AMD and Intel support this feature, it's just labeled differently. When enabled, certain areas of memory will be marked as non-executable, preventing the processor from executing potentially dangerous code in those areas.
Delay For HDD (Secs): Also known as a Hard Disk Pre-Delay, this feature mostly applies to older IDE hard drives. In some cases, older, slower HDDs were incapable of spinning up in time to be intialized, rendering them undectable. To resolve this, motherboard makers introduced a way for users to manually force a delay before this happens.
Full Screen Logo: Rather than display a drab -- and sometimes cryptic - POST screen, enabling this setting will instead display the motherboard manufacturer's boot logo, or Splash screen, if one is included. More than just window dressing, these Splash screens often display helpful tips, such as what button to press to get into the BIOS (most often the DEL key) and how to initialize the motherboard's BIOS update utility.
You only have a few seconds before the Splash screen disappears, and at that point, you can no longer get into the BIOS unless you reboot and try again. Alternately, you can usually whisk the Splash screen away by hitting the TAB key, which will then display the standard POST screen.
Init Display First: In ancient times somewhere around the year 9 BT (Before Twitter), gamer's evolved from using PCI-based videocards to those built for the then-emerging AGP standard. This setting allowed users to tell their systems which type of card they were using, and if improperly configured, could lead to a blank screen. This was mainly relevant when running two types of videocards in the same machine.
Today's gamers get their groove on with PCI-Express based videocards, or at least the serious ones do (it's going to be fun looking back at this comment a decade from now). Most modern motherboards give you the option of selecting PEG, which is your PCI-Express graphics port, or PCI. The latter comes in handy when troubleshooting a potentially bad videocard by sticking a PCI card in your system. If it's not automatically detected, change this setting to PCI.
Every motherboard comes with at least a handful of functionality embedded into the board itself. When installing a third party peripheral -- like a Creative X-Fi soundcard -- your first order of business should be to the disable your motherboard's onboard equivalent to prevent any conflicts, and this is the section where you'll find those options.
The other school of thought here is that by disabling unused peripherals and ports, you can recover additional resources for improved performance. And for a time, this might have been true. However, now that 2GB and over has become the standard, you're not likely to gain any significant advantages by disabling unused LAN and other dormant ports, but you do run the risk of forgetting you disabled a previously unused port in the BIOS, making you think you have a bad mobo. Keep that in mind before you go disabling everything in sight.
SATA RAID/AHCI Mode: You might not always find this setting under Integrated Peripherals, depending on the layout of your BIOS. It might also be labeled slightly differently, but the options are the same. Here are your three possible choices.
IDE: Often times the default option, this sets up your system so that your SATA drives run in IDE mode (see below).
AHCI: Short for Advanced Host Controller Interface, AHCI takes better advantage of SATA drives by enabling hot swapping and NCQ, but there's a caveat. If you've already installed Windows, suddenly switching from IDE mode to AHCI will quickly muck things up. On the other hand, it's a good way to see what a BSOD looks like if you've never seen one before. Otherwise, be prepared to start fresh with a new Windows installation.
RAID/IDE: As the name implies, choose this when you plan to run one or more drives in a RAID array using your motherboard's built-in RAID controller.
SATA Port 0-3 Native Mode: The most common solution, configuring SATA drives in native IDE mode is also the easiest, as it sports the most compatibility and a 'driver-less' install, at least in terms of not needing to go through the F6 dance. Disabling this option puts the SATA ports in Legacy IDE mode, which is used for pre-XP OSes like Win 9x/ME
USB 1.0 Controller: We don't know why anyone would choose to disable their motherboard's onboard USB controllers, but this would be the place to do it.
USB 2.0 Controller: Also known as EHCI, or Enhanced Host Controller Interface, you'll need to enable this setting to take full advantage of your motherboard's USB 2.0 ports and high-speed USB devices.
USB Keyboard Function: If you don't have this option enabled, it will be difficult (read: impossible) to get into your motherboard's BIOS without a legacy PS/2 keyboard.
USB Mouse Function: Enables USB mouse support for use with OSes that don't support it natively.
Legacy USB Storage Detect: Some very old OSes -- like DOS -- don't play nice with USB storage devices. Enabling this setting can help through emulation.
Azalia Codec: Several onboard audio solutions exist and depending on which one your motherboard manufacture has chosen, so finding this setting might be obvious (Onboard Audio) or a bit obscure (Azalia Codec, AC97). Enable this if you plan to use the included audio chip, and disable this setting if you plan to get your groove on with a discrete soundcard, such as Creative's X-Fi series or Asus' Xonar, to name just a couple.
Onboard H/W 1394: Refers to your motherboard's Firewire port(s).
Onboard H/W LAN: Depending on how many LAN ports your motherboard comes with, you may see one or several different entries (LAN1, LAN2, etc). Keep these enabled if you plan to do any kind of wired networking, including connecting your PC to a DSL or cable modem.
Green LAN: A power saving feature, enabling this option tells your motherboard to disable the network socket and onboard LAN chip when it doesn't detect a connection.
SMART LAN: This performs a diagnostic on your motherboard's integrated LAN ports.
Onboard LAN Boot ROM: Contrary to what you might have guessed, this setting doesn't refer to booting your PC remotely via the LAN port. Instead, this is intended for newer Gigabit LAN ports to operate at their full 1Gbps speed when using an older OS by loading the LAN controller's boot ROM during boot.
Onboard SATA/IDE Device: Enables your motherboard's SATA ports. Go figure!
Onboard SATA/IDE Ctrl Mode: This is where you'll tell your motherboard to operate its SATA ports in IDE, AHCI, or RAID mode, as outlined above (see SATA RAID/AHCI Mode).
Onboard Serial Port: This setting allocates an address and IRQ for your motherboard's serial port. Unless you're experiencing any IRQ conflicts, you should leave this setting on Auto (if it's an option), or however it comes configured by default (typically 3F8/IRQ4). If you don't plan on using the serial port, you can safely disable this setting, freeing up an IRQ in the process.
Onboard Parallel Port: Same as above, use this setting to configure your parallel port, otherwise known as LPT1. Or better yet, retire that crusty dot matrix printer and finally make the jump to a USB-based inkjet printer and never bother with a parallel port again.
Parallel Port Mode: Settings here include SPP (Standard Parallel Port), EPP (Enhanced Parallel Port), and ECP (Extended Capabilities Port). EPP adds bi-directional communications support between the PC and connected devices, resulting in faster transfers and lower CPU usage. ECP supports even faster transfers and is useful for daisy-chaining multiple parallel port devices.
With the recent push towards reducing carbon footprints and going green, power management schemes have started garnering a lot of attention. Some basic power saving features have been included on most motherboards for some time now, and this is where you'll find them.
ACPI Suspend Type: Short for Advanced Configuration and Power Interface, this setting dictates what power saving state your system goes into. ACPI replaces the older Advanced Power Management (APM) scheme and requires a compatible OS, such as Windows 98 and up, along with several Linux distributions.
S1(POS): In an S1 state, the CPU stops processing cycles but it, along with the RAM, are still fed power.
S3(STR): Also referred to as Suspend to RAM, this options saves the data to RAM before putting the PC in a sleep state. In most cases, fans and all other devices will be powered down, so it appears as though the PC is actually turned off.
Soft-Off by PWR-BTTN: This lets you adjust how long you need to press the power button before your system turns off. Choosing Instant Off will power off the system instantly, whereas Delay 4 Sec configures it so you need to hold the power button for 4 seconds before powering down. With the latter option enabled, pressing the power button (as opposed to holding it) puts the PC in a suspend state, feeding a small amount of power to the system.
PME Event Wake Up: Short for Power Management Event, this redundantly-named entry is usually the culprit when you find that your PC has turned on during the middle the night even though you remember turning it off before going to bed. Also referred to as Wake on LAN (WoL), network activity or a stray electrical signal tells your PC to fire up if you have this setting enabled.
Power on by Ring: You might also see this entry labeled as Wake/Power Up on Ext. Modem. Enabling this setting tells the PC to turn itself on when a call comes in through a phone line connected to the modem.
Resume by Alarm: Used to specify a time and date of the month (or everyday) for the PC to turn on automatically. Some ITs find this handy for ensuring PCs are up and running on Microsoft's Patch Tuesday, and businesses find it useful for making sure PCs are up and running when employees start rolling in early morning. You might also see this entry labeled Resume by RTC (Real Time Clock) Alarm.
HPET Support: Short for High Precision Event Timer, Microsoft describes this as a "new system timer that is needed in chipsets to replace legacy timers and to meet the needs of time-sensitive applications." By enabling this feature, the company claims system performance is improved.
HPET Mode: You can set this to either 32-bit or 64-bit, depending on your operating system. If you're rolling with a 64-bit OS, choose the latter to take full advantage of HPET's 64-bit registers.
Power on by Mouse: Enables turning on the system with a double-click.
Power on by Keyboard: Enables turning on the system by pressing your keyboard's Power key. Additionally, some BIOSes allow you to setup a short password instead of pressing the Power button. If setting up a password, you'll need to mash the Enter key afterwards.
AC Back Function: Also referred to as AC Power Loss Restart, this setting dictates how your PC responds to an unexpected power loss once the power is restored.
Soft-Off: Leaves the PC turned off, even if it was turned on prior to losing power.
Full-On: Turns the PC back on following a power loss.
Memory: If the PC was turned on prior to losing power, it will boot back up once power is restored. But if the PC was off to begin with, it will remain turned off.
Gigabyte's latest boards clumps these entries together in a handy submenu, but depending on your make and model, you may find these settings spread out in different sections of your BIOS.
CPU Clock Ratio: Otherwise known as the multipler, this number multiplied by your CPU's base frequency determines your processors clockspeed. See chipset-specific BIOS options below.
Intel Turbo Boost Tech.: New to Nehalem (Core i7), enabling this feature will temporarily boost processor cores to run faster than their stock frequency depending on the current power, current, and temperature levels.
CPU Cores Enabled: Allows you to enable all or just some of your processor's cores.
CPU Multi-Threading: Enable this option to take advantage of Intel's HyperThreading technology.
CPU Enhanced Halt (C1E): A power saving feature in Intel chips, enabling C1E will allow the operating system to send a halt command to the CPU when inactive. This halt state reduces both the processor's voltage and multiplier so that it consumes less power and runs cooler. This doesn't affect performance, though some power users have noted better overclocking headroom when disabling this setting.
C3/C67/C7 State Support: Essentially a revised version of C1E, these higher-numbered halt states put the processor into an even lower power state when idle. Again, overclocking results may vary, but performance does not.
CPU Thermal Monitor: First introduced with the Pentium 4, current iterations take a somewhat different approach by dropping down the core clockspeed and voltage when things get a bit too hot under the collar.
CPU EIST Function: Short for Enhanced Intel SpeedStep, this power-saving setting allows Intel chips to dynamically change frequency and voltage levels in small increments based on need.
Virtualization Technology: Enabling this feature allows virtualization programs like VMWare and Virtual PC to tap into your processor's hardware virtualization support
Bi-Directional PROCHOT: Enabling this setting sends a bi-directional signal that indicates if the processor has exceeded its maximum temperature and whether or not it should activate the Thermal Control Circuit (TCC).
This is the section of the BIOS that deals with the PCI bus and Plug-and-Play settings, most notably IRQ mapping. Unless you're attempting to run legacy hardware or are running into troubleshooting issues with your PCI peripherals, you won't be spending much time, if any, in this section.
PCI1 and PCI2 IRQ Assignment: This lets you configure whether to let your PC dole out IRQ resources automatically or to let you configure them manually. Unless you're dealing with older hardware or niggling IRQ conflicts that are not resolved by moving PCI cards to a different PCI slot, you should leave this one on Auto.
On most Asus boards, this section will come labeled as a Hardware Monitor submenu in the Power section. MSI boards usually call this H/W Monitor accessible through the BIOS's main menu. In each case, this is where you'll find system vitals, such as current system and CPU temperatures, fan speeds, and various voltage levels. This is helpful when troubleshooting overheating issues or power issues, such as random reboots, but treat this as a starting point before digging deeper. Overheating due to a poorly installed heatsink, for example, might not manifest itself until you boot into Windows and encode a DVD or otherwise stress your CPU.
Recent Case Open Status: Only of use with compatible cases, this security feature can detect if your case has been opened and reset the status at the next boot.
CPU Warning Temperature: Sounds an alarm when a certain CPU temperature threshold is reached.
CPU Fan Fail Warning: Sounds an alarm should the CPU heatsink's fan stop spinning, or whichever fan you have plugged into your motherboard's CPU fan power header.
System Fan 2 Fail Warning: Sounds an alarm when the fan plugged into this header stops spinning.
Power Fan Fail Warning: Sounds an alarm when the fan plugged into this header stops spinning (seeing a pattern yet?).
System Fan 1 Fail Warning: Sounds an alarm when...you get the idea.
CPU Smart Fan Control: Disabling this setting allows the CPU heatsink's fan to run at full bore all the time. Enabling this setting will vary the fan speed depending on CPU temperature.
CPU Smart Fan Mode: If you enable CPU Smart Fan Control, you can then set the mode to Auto (controlled by the BIOS), Voltage (for use with 3-pin fans), or PWM (for use with 4-pin fans).
If your motherboard allows you to manually tweak your RAM's latency timings, you'll find them in the overclocking section. These will most often be labeled as MB Intelligent Tweaker (Gigabyte), Cell Menu (MSI), Advanced Chipset (Asus), or Genie BIOS Setting (DFI). Other overclocking options will also be available, but we'll focus on these in more detail later on.
Performance Enhance: Applicable to Gigabyte boards, this section tells the BIOS how aggressively to auto-tune your RAM's settings.
Extreme Memory Profile (X.M.P.): Short for eXtreme Memory Profile, X.M.P.-compatible RAM contain additional, pre-programmed settings tuned for both performance and overclocking.
System Memory Multiplier: Left on Auto, your BIOS will determine the safest multiplier, or FSB:DRAM ratio, and resulting memory frequency for your RAM based on its pre-programmed SPD settings. If overclocking or tuning for additional performance, you can manually set the multiplier.
DRAM Timing Selectable: You may see the letters SPD in this section. This stands for Serial Presence Detect and refers to the information programmed into your memory modules by the manufacturer, which tells the BIOS what latencies and voltage to use at any given clockspeed to ensure compatibility. If left on Auto, your RAM will run at its pre-programmed SPD settings when overclocking. Otherwise, you can change this to Manual (or disabled) to and set your own latency timings.
Channel A/B/C Timing Settings: Refers to your RAM's timings or latencies, separated by memory channel.
CAS Latency Time: Short for Column Address Strobe, this number dictates the number of clock cycles that pass before data can be read or written to from where it's stored in a column address. The lower the number, the faster this takes place. When shopping for memory modules, the CAS latency is typically the first of a set of four numbers (for example, 8-8-8-24).
tRCD: Also referred to as DRAM RAS# to CAS# Delay, this number represents the delay in clock cycles it takes to find the fow of a location in memory and finding the column. The lower the number, faster this takes place. When shopping for memory modules, RAS# to CAS# is typically the second number in a set of four (for example, 8-8-8-24).
tRP: Also referred to DRAM RAS# Precharge, the RAS precharge is how long it takes for the memory to stop accessing one row, build up a charge, and access another. The lower the number, the fast this takes place. When shopping for memory modules, RAS# Precharge is typically the third number in a set of four (for example, 8-8-8-24).
tRAS: Also referred to as Precharge Delay, this number represents the minimum number of cylces that pass between an active and precharge command. The lower the number, the faster the performance. When shopping for memory modules, the Precharge Delay is typically the last (and highest) number in a set of four (for example, 8-8-8-24).
Command Rate (CMD): The Command Rate is the delay, in clock cycles, from when a memory chip is selected to when the first active command can be sent. A 1T command rate offers better performance than 2T, but if you experience instability, you'll want to change this 2T.
Advanced Timing Control: Depending on your motherboard, you may find anywhere from a handful to a boatload of additional RAM timings. These refer to various other dealys and can be overwhelming to even experienced overclockers. Unless you're shooting for a record overclock or trying to get over a certain MHz bump, we recommend leaving these settings on Auto.
Channel A/B/C Turnaround Settings: These submenus control the read and write delay settings, again separated by channel.
If you're going to overclock, you first must understand the nomenclature that applies to your processor and motherboard chipset's architecture. To help you do this, we rounded up three different motherboards each one based on a different, recent architecture.
The settings below also apply to Intel's X38 and X48 chipsets, and in some form even date back several generations. We used an Asus Formula Maximus II for this section.
Ai Overclock Tuner: Many enthusiast motherboards come with some form of automatic overclocking, and Asus calls its version the Ai Overclock Tuner.
Manual: Just as it says, choose this option if you plan to manually overclock your system.
Auto: Somewhat misleading, this really should be called Disabled. But despite the goofy nomenclature, leaving this setting on Auto tells the BIOS not to automatically overclock your CPU.
CPU Level Up: This option will attempt to automatically overclock your processor to that of a higher end chip. Or in other words, level up. Get it?
Ratio CMOS Setting: Also known as the CPU clock ratio or, more commonly, the CPU multiplier, you'll find this setting on both AMD and Intel processors. The multiplier measures the ratio of an internal CPU clock rate to an externally supplied clock often called the frontside bus and is used to determine your CPU's clockspeed. For example, an E8400 processor ships with a 9X multiplier and a 333MHz base clockspeed. Multiplied together, you arrive at 3.0GHz (3,000MHz). Intel locks the multiplier on all but its Extreme Edition CPUs, which prevents end-users from increasing the multiplier, but not from decreasing it.
CPU Clock Skew: At the blistering speed that today's components operate at, timing issues can rear their ugly heads when trying to communicate with each other and result in instability, particularly when overclocking. To keep the different parts working in sync, some motherboards -- such as this one -- allow you to introduce tiny delays in different subsystems of your PC. In this case, you're 'skewing' the speed of the CPU clock as measured in picoseconds (ps), or one trillionth of a second.
NB Clock Skew: Allows you to introduce a delay to the Northbridge controller.
FSB Strap to North Bridge: This setting determines what memory divider ratios will be made available. Since the DRAM's frequency is linked to the frontside bus, dividers can help you achieve a higher CPU overclock without taxing the memory. Dividers available by FSB Strap include:
DRAM Frequency: This determines the frequency of your RAM. The settings available will depend on what FSB Strap you selected (see above).
DRAM Clock Skew: Allows you to introduce a delay to the individual RAM slots to address timing issues. See CPU Clock Skew above.
DRAM Timing Control: Lets you select whether you want the BIOS to automatically set your RAM's timings or if you want to manually input them yourself. See DRAM Timing for more information.
DRAM Static Read Control: This setting influences the overall memory access latency. In theory, enabling this setting can increase memory bandwidth.
DRAM Read Training: Like the skew settings, this option supposedly optimizes DRAM timing.
Mem. OC Charger: Intended to improve signal quality and, as a result, improve overclocking potential, not all memory modules play nice with this setting. And for the ones that do, Asus cautions not to expect any miracles.
Ai Clock Twister: Used in conjunction with the Ai Overclock Tuner, this setting determines how aggressive the board will attempt to run your memory's latency timings.
Ai Transaction Booster: Also known as Performance Level, this setting automatically adjusts parameters of the chipset to improve performace. The lower the number, the better the performance.
CPU Voltage: No big mystery here. As the name suggests, this is where you can adjust how much voltage gets pumped into your processor. Safe amounts will vary by processor, and even by different steppings of the same CPU, so be sure to thoroughly research before mucking with this setting.
CPU PLL Voltage: Determines the voltage applied to the CPU's internal clock generators. Overvolting this setting is a quick way to send your processor to the grave.
FSB Termination Voltage: This controls the voltage at the end of the frontside bus on the termination buffers. Increasing this can help with overclocking, however it also can result in instability, higher temps, and damage to your CPU.
DRAM Voltage: Determines the voltage for your memory modules. Safe amounts will vary by make and model. Generally speaking, DDR2 starts to get pretty hot at 2.3V and above and may require active cooling. Do your research and consult your memory kit's specs before manually adjusting the voltage.
North Bridge Voltage: Controls the voltage for your board's Northbridge (minus 1,000 geek points if you couldn't guess this one).
South Bridge 1.5 Voltage: Controls the voltage for the 1.5V line in your board's Southbridge, which is tied to the PCI-E bus.
South Bridge 1.1 Voltage: Controls the voltage for the 1.1V line from the Southbridge to the Northbridge, otherwise known as the base chipset voltage.
CPU GTL Reference: These setting represent advanced voltage options for the CPU's Gunning Transceiver Logic (GTL), which is an open drain, low power switching circuit. You can read more than you probably want know about the GTL here.
NB GTL Reference: Same as above, only in regards to the Northbridge.
DDR2 ChA Reference Voltage: Allows you to individually tweak the voltage levels for each memory bank (not to be confused with each memory slot).
North Bridge DDR Reference: Provides a fixed voltage to the memory bus and can presumably help with stability.
Load Line Calibration: Enabling this setting stabilizes voltage levels during both idle and load, reducing or eliminating vdroop altogether.
PCIE Spread Spectrum: Limits the electrical interference so that it stays within the FCC limit.
Starting with the Athlon 64, AMD moved away from a traditional frontside bus architecture in favor of using an integrated memory controller and a HyperTransport bus. This meant learning new terms and new ways of overclocking. We used a Gigabyte Ga-MA790FX motherboard for this section.
Advanced Clock Calibration: Advanced Clock Calibration, or ACC, taps into previously unused pins on Phenom processors for use with the chipset's Southbridge. Through some sort of guarded voodoo magic, this unlocks higher overclocking potential and is exclusive to Phenom processors.
CPU Clock Ratio: Also known as the Ratio CMOS Setting (P45 chipset) or, more commonly, the CPU multiplier, you'll find this setting on both AMD and Intel processors. The multiplier measures the ratio of an internal CPU clock rate to an externally supplied clock often called the frontside bus and is used to determine your CPU's clockspeed. For example, a Phenom 955 processor ships with a 16X multiplier and a 200MHz HyperTransport reference clockspeed. Multiplied together, you arrive at 3.2GHz (3,200MHz).
CPU Northbridge Frequency: Contains multiplier settings for the Northbridge frequency. This number multiplied by the HT reference clock equals the Northbridge frequency.
CPU Host Clock Control: It's a shame motherboard makers don't label their BIOSes more intelligently. If they did, this option would simply be labeled 'Do You Wish to Overclock Manually?' By enabling the CPU Host Clock Control, you're answering 'Yes' to that question and the appropriate settings are then unlocked.
CPU Frequency: Otherwise known as the base frequency or HT frequency, this number multiplied by the CPU multiplier gives you the processor's clockspeed.
PCIE Clock (MHz): Allows you to set the clockspeed for (and overclock) your PCI-E graphics port.
HT Link Width: This is where you designate the width of the HyperTransport interconnects, which directly affects the maximum theoretical bandwidth. The Link Width is bi-directional.
HT Link Frequency: Don't let the nomenclature fool you - this is really the HT Link multiplier. When multiplied by the HT reference clock, you arrive at the HT Link clockspeed.
DRAM Configuration: Inside this submenu sits all the options for tweaking and overclocking your memory. Let's take a look at some of the less obvious entries.
DCTs Mode: Unofficially short for Dual-Channel Type, you have two choices: Ganged and Unganged. A common misconception is that Unganged operates in single-channel mode, but this isn't the case. In Ganged mode, each memory subsystem is treated as a single 128-bit dual-channel bus, whereas Unganged treats each memory subsystem as two independent 64-bit dual-channel buses. In most cases, Unganged offers better bandwidth and performance.
Set Memory Clock: This is where you either tell the BIOS to automatically configure your RAM's clockspeed or to let you manually adjust it.
DCT Channel Interleave: Describes whether or not memory is accessed as a single, large block to act as a single module (Enabled).
System Voltage Control: Enable this setting if you plan on manually inputting your system's different voltages.
DDR3 Voltage Control: Allows you to adjust your RAM's voltage level. Consult your kit's rated specs, as pumping too much voltage can kill your memory.
SB/HT Voltage Control: Voltage settings for the Southbridge and HyperTransport.
NB/PCIe/PLL Voltage Control: Voltage settings for the chipsets' power regulation circuits all inconveniently bundled together.
CPU PLL Voltage Control: Determines the voltage applied to the CPU's internal clock generators. Overvolting this setting is a quick way to send your processor to the grave.
DDR VTT Voltage Control: Determines the termination voltage for your system's RAM. Raising the VTT increases the current flow and can help increase stability.
NB Voltage Control: Voltage settings for the Northbridge chipset.
CPU NB VID Control: Voltage settings for the memory controller on the CPU. This can help with stability when overclocking.
CPU Voltage Control: Voltage settings for the processor.
With the introduction of Nehalem -- now better known as Core i7 -- Intel moved away from a traditional frontside bus architecture in favor of an integrated memory controller, somewhat similar to what AMD had been using for years. This also meant that old hats at overclocking suddenly were forced to learn new terms. For this section, we used an Asus Rampage II motherboard.
Ai Overclock Tuner: As previously stated (see Intel P45 Chipset), this is Asus' implementation of automatic overclocking.
OC From CPU Level Up: This option will attempt to automatically overclock your processor to that of a higher end chip. Or in other words, level up.
OC From Memory Level Up: This option will attempt to automatically overclock your memory to that of a higher end kit. Or in other words, level up.
CPU Ratio Setting (MSI - Adjust CPU Ratio, Gigabyte - CPU Clock Ratio): Also known as the CPU Clock Ratio or, more commonly, the CPU multiplier, you'll find this setting on both AMD and Intel processors. The multiplier measures the ratio of an internal CPU clock rate to an externally supplied clock often called the frontside bus and is used to determine your CPU's clockspeed. For example, a Core i7 920 processor ships with a 20X multiplier and a 133MHz base clockspeed. Multiplied together, you arrive at 2.67GHz (2,667MHz). Intel locks the multiplier on all but its Extreme Edition CPUs, which prevents end-users from increasing the multiplier, but not from decreasing it.
CPU Turbo Power Limit: Enabling this setting prevents the Turbo mode ratio from changing based on CPU load. For this to work, both C1E and TM functions must also be disabled.
BCLK Frequency (MSI - Base Clock, Gigabyte - Base Clock Control): Intel's new architecture whisked away the traditional frontside bus so many Intel fans had grown up on, and replaced it with a base clock, or bclock (or in this case, BCLK). You may also see this referred to as a host clock or reference clock. Core i7 processors come with a base clock of 133MHz, and the easiest way to overclock is by pushing this frequency higher. However, you'll also be overclocking other subsystems, such as the RAM and uncore.
PCIE Frequency: Allows you to set the clockspeed for (and overclock) your PCI-E graphics port.
DRAM Frequency (MSI - Memory Frequency, Gigabyte - System Memory Frequency): As you might have guessed, this is the your RAM's frequency. As you increase the base clock, so too will your DRAM frequency increase.
UCLK Frequency (MSI - Uncore Ratio, Gigabyte - UnCore & QPI Features): This setting controls the speed of the uncore, which describes the areas outside of the Core i7's processor core (integrated memory controller, L3 cache, Quick Path Interconnect).
QPI Link Data Rate (MSI - QPI Configuration, Gigabyte - QPI Link Speed): Short for Quick Path Interconnect, this is the high-speed interface that connects the processor to the chipset. You'll need to keep an eye on this when overclocking, as just like the HyperTransport bus, if the QPI is set too high, you'll find yourself running head first into an overclocking wall of defeat.
EPU II Phase Control: A power saving feature built into some Asus boards, the Energy Processing Unit (EPU) dynamically adjusts voltages based on load, and can also hinder potential overclocks.
CPU Differential Amplitude: Some Asus boards allow you to increase the amplitude of the differential clock signals making them less susceptible to noise. Asus claims this can also help achieve a higher base clock frequency.
Extreme OV: Not for the faint of heart, enabling this setting allows you to 'OverVolt' higher than you would normally be able to. Air cooling aficionados need not apply.
IOH Voltage: For overvolting the Northbridge.
IOH PCIE Voltage: For overvolting the PCI-E bus.
ICH Voltage: For overvolting the Southbridge.
DRAM Bus Voltage: For overvolting the memory bus.
Updating or flashing the BIOS carries a certain amount of risk, but the potential rewards make it worth the effort. Motherboard makers are contstantly enhanching the BIOS firmware and the end result can be significantly improved performance, less buggy behavior, additional functionality, improved overclocking performance, and much more.
BIOS updates can also be minor and only address a specific function, such as adding native support for higher frequency RAM or a new CPU stepping. If the added functionality isn't something that affects your setup, you needn't worry about updating your BIOS. The general rule of thumb is if it isn't broken, well, you know the rest.
We recommend checking your vendor's website every few months to see if any new BIOS versions have been released, and if so, what changes they bring. Then make a determination on whether or not you should flash your BIOS.
You've heard of Murphy's Law, and it definitely applies here. While BIOS flashes have become orders of magnitude easier and less risky in recent years, the one time you attempt to update your BIOS unprepared will inevitably be the time something goes wrong.
Standard housekeeping applies - backup any important data. A BIOS flash won't nuke your hard drive, but if done incorrectly, it could kill your motherboard. Plus, you should have a routine backup plan in place anyway.
Next, tune your system for stability. If you're overclocking, revert back to default clockspeeds and voltage levels. The reason for this is because if there's an underlying instability issue -- even one you're not aware of -- your system could suddenly reboot during the middle of a BIOS flash, rendering your BIOS chip corrupt and your motherboard a rather bulky keychain.
Finally, make a note of any pertinent BIOS settings that you've changed from their default values. Sometimes when updating the BIOS, all settings are reverted back to default. Did you disable onboard sound? You may need to do so again.
Most motherboard manufacturers offer some kind of handy Windows utility with a snazzy GUI for updating your BIOS. If at all possible, avoid using these, particularly if you're updating your BIOS because of instability. Should your Windows installation suddenly freeze or restart, you could be in a world of trouble.
There are several alternative methods to updating your BIOS, the simpliest being from a USB key. Some motherboard manufacturers implement a built-in utility for updating the BIOS during POST. Gigabyte boards, for example, come with a Q-Flash utility. To use it, you would first go to your motherboard's product page and download the latest BIOS file (when updating a BIOS, you don't need to go in order - you can skip straight to the latest BIOS version) and copy it to your USB key. Next, reboot your PC and hit the End key during post or F8 from within the BIOS. This brings up the Q-Flash utility. Follow the GUI prompts to locate and load the BIOS on your USB key and sit back while the new firmware is written. Be sure not to power down or reset your system.
If you own an older or proprietary system, you may need to kick it old school and update your BIOS with a floppy disk using one of several utilities. Reference your motherboard maker's website to see which utilities your motherboard supports (see here, for example).