When man first booted the PC, he saw the BIOS screen: a jumble of monochromatic numbers that made about as much sense as the binary language of load lifters. Sadly, not much about the BIOS has changed since the DeLorean and skinny ties were cool. Decades later, in our modern, visual-based world, we’re still greeted with a screen full of text from machines 1,000 times faster than those that were around when the ol’ BIOS was born.

Most PC lightweights simply ignore the BIOS and wait for their OSes to take over. Power users, however, know that the BIOS can be a friendly and rewarding place to go spelunking.

So just what the hell is the BIOS? Short for Basic Input Output System, the BIOS is a tiny bit of software embedded in your motherboard that gets executed when your PC is turned on. The BIOS is responsible for chores such as sizing up the amount of available RAM, detecting the hard drives, and setting the CPU speed. Once the system house-cleaning is done, the BIOS boots the OS from the hard drive and hands over control.

Even though there are only two BIOS makers for consumer desktops today, AMI and Award/Phoenix, a multitude of BIOS variants exists. In fact, a Gigabyte board using an Award BIOS can bear little resemblance to an Asus board using an Award BIOS.

In motherboards designed for enthusiasts, board makers typically unmask as many controls as possible. Unfortunately, the dizzying array of options includes both safe and unsafe tweaks. While some tweaks will just leave you with a system that refuses to boot, others can do long-term harm.

So if you feel the least bit uneasy about even changing the boot order of your rig’s drives, you may not want to muck around too much in the BIOS. If, however, you’re comfortable with the prospect of a little trial and error, it’s time you dive in and discover the many secrets your BIOS holds.

How do you get into your BIOS? Reboot the system and then hit DEL, F1, or F2 within a few seconds of the machine POSTing. If your machine has a splash screen that doesn’t show anything, try hitting Escape, which should reveal the ugly DOS-looking screen underneath. Only Intel-branded boards still require jumpers to be thrown to access all of the BIOS features. Power down, look for the BIOS Setup Configuration Jumper, set it to 2-3, and power up.

Tweaking Your Memory

The days of just selecting your RAM speed are gone. A modern BIOS exposes enough RAM controls to give even the most seasoned hobbyist a headache. For the die-hard enthusiast though, those knobs and switches also mean something good: control.

Timing Is Everything

Poke around the BIOS of a budget board or an OEM machine and you’ll find it as easy to understand as “The Pet Goat.” Heck, even an enthusiast board from three years ago could be understood by most advanced users, as the memory options were as simple as DDR333 or DDR400. Today, we’re not even sure that the engineers who write BIOSes fully understand all of the options available. Take, for example, DQS Drive Strength or Process On-die Term B. Huh? Both actually relate to the ability to tweak and tune your RAM to higher frequencies, but for the most part, you can ignore them unless you really want to spend an entire afternoon setting, crashing, and resetting your machine.

Fortunately, the fundamentals are still as valid today as they were a couple of years ago: Column Access Strobe Latency (tCL), Row Access Strobe to Column Access Strobe Delay (tRCD), Row Access Strobe Precharge (tRP), Row Access Strobe Precharge and Precharge Delay (tRAS), and Command Rate or Command Per Clock (CMD). In the BIOS, you’re able to tweak the timing for each of these settings to affect RAM performance.

If you think of RAM as a collection of books in a public library, each timing setting relates to an element of the librarian fulfilling your request for a particular tome. The timing is described in clock cycles, so a lower number equals a faster time.

The tRCD setting, for example, describes how much time the librarian has to get to a certain row on a shelving column. Set it too low, and she can’t get to the row where your desired book resides.

Say she reaches the row; the tRAS determines the time the librarian can linger there finding your book. tRP is how much time the librarian has to get from the row she was at to the bottom of the ladder.

tCL is how much time she has to move between the different shelves of books. Setting it too low would be like asking her to push a 30-foot rolling ladder 100 yards in 2 seconds. tRAS is basically how much time the overall operation takes to climb the ladder, get the book, and get off the ladder.

CMD describes the amount of time between one request and the next.

You often have to set performance RAM manually for it to hit its rated speed and timing.

There are two approaches to setting these values: The first is to match them with the timings on your RAM (assuming your RAM provides those settings—commodity RAM doesn’t always list specs). If you paid extra for those fancy high-performance modules, you’re getting more than just a shiny aluminum heat spreader, you’re also getting RAM that’s been tested and binned to run at optimal speeds. If you peer at the label of most enthusiast RAM, you’ll see timing settings of 5-5-5-15-2T.

Translated for your BIOS, that means a tCL of 5, a tRCD of 5, a tRP of 5, a tRAS of 15, and a CMD of 2T. The other method is to let the chipset determine the settings automatically. For example, you could enable SLI memory mode on nForce boards, which would give you optimum settings if the modules support Nvidia’s Enhanced Performance Profiles (EPP). Intel has a similar feature call XMP.

There’s more to getting your high-performance RAM to run at its rated speed though. The RAM manufacturer specs for timing require the RAM to run at its rated clock speed (see below) and at a certain voltage (see page 62).

Watching the Clock

Nvidia’s SLI Memory (also called EPP and EPP 2.0) as well as Intel’s XMP profiles
let the BIOS set many of the overclocking modes for you automatically.

To make sure your RAM is set to the correct clock speed in the BIOS, you’ll need to first know your RAM’s overall bandwidth rating. If it’s expressed as PC3200 or PC6400, you can find out your RAM’s clock speed by dividing by eight. So 3200 becomes 400, or 400MHz, and 6400 becomes 800, or 800MHz. Most memory vendors will actually list the module’s overall bandwidth—say, PC8500—along with the rated clock speed—1066MHz, in this case. When it comes to manually setting your RAM’s clock speed in the BIOS, you’ll find the process differs among chipset vendors. On Intel chipsets, where the memory controller is still in the chipset and RAM is tied to the front-side bus, it gets a bit confusing: If you overclock your CPU’s front-side bus, your RAM’s clock speed will be automatically overclocked along with it. This could cause problems if the RAM’s speed is set beyond its rating. (See the North Bridge Strap section on this page to learn how to compensate for this issue.)

With Nvidia’s nForce series chipsets, you can actually unlink the FSB from the RAM. This lets you independently set the clock speed for the front-side bus to, say, 1066MHz, and the RAM to 800MHz. The nForce also lets you run the two in linked mode using traditional ratios of 1:1, 5:4, 3:2, and sync. These set the RAM speed based on a ratio related to the speed of the front-side bus. If you’re running a 1066MHz FSB CPU and a 1:1 ratio, your RAM would run at 1066. At 5:4, the RAM is 853, and at 3:2 it’s 711. Sync would set the RAM at 533. Various vendors pitch linked mode as the best way to set RAM, but we’ve come to settle on getting the highest reliable front-side bus speed with the RAM speed that works best for you. Remember:

Just because your RAM is rated to run at, say, 1100MHz, doesn’t guarantee best results at that speed. Since the interaction between memory, chipset, and CPU will greatly depend on what you’re doing, there is no one-size-fits-all answer. Get out the game or application you use the most and tweak the memory settings until you find the optimal solution.

Next: Unstrapping your RAM from your FSB

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how_to, bios, tweaks, features, ami, award/phoenix

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