LOSTCIRCUITS

The following article is meant to shed some light on the various parameters accessible in the mainboard BIOS through Setup. It is quite impossible to give specific recommendations for any system since the choice of entries strongly depends on the nature of the system components. It is the goal of this article, though, to explain the various entries in the different BIOS pages and to put things into perspective, not only from a functional standpoint but also in the context of how they evolved. The latter is important since BIOS engineers are as overworked as everyone else. That is, cut and paste is common practice and has led to BIOS configuration entries that have become obsolete or else have little to do with the name under which they are posted. Another problem with writing this article has been that different manufacturers are using different names, which hardly bear any resemblance to each other, for the same entries. In some cases, particularly within the fields of memory timing settings, the descriptions are counterintuitive, suggesting faster settings where, in fact, benchmarks prove the opposite. All in all, this write-up has involved a lot of detective work and consulting with chipset application engineers as well as reading a few dozen manuals and white pages to find the common denominators between the various layouts and descriptions. There is still no guarantee that I got it all correct but, at least, it is a start. Furthermore, omissions are neither random nor on purpose but simply unavoidable.

[an error occurred while processing this directive]
BIOS 1.01

How does a computer know what it is supposed to do, once you turn it on, even with no operating system loaded? In other words, what is the driving force behind the different processes that happen during the Power On Self Test or POST during which all the hardware is recognized and resources are funneled into the necessary channels? The answer is a four letter word: BIOS

If this is spelled out, it reads basic input output system and stands for software that is stored in the BIOS chip. The particular chip holding the BIOS is generally a flash EEPROM (electrically erasable programmable read only memory) that contains all vital information about the mainboard hardware. This includes: number of expansion slots, CPU interface, bus frequencies etc.

In 99% of all POSTs, the BIOS simply counts all devices present and gives them predefined operating parameters according to which they have to operate. At the end of the self test, the responses of the devices are summed up, put into a hexadecimal code (if they aren't already and compared against the checksum, that is, the number that the system expects. In most cases, only the last two digits are used for checking since any error will affect those with a probability of 1/(16 x 16) = 0.004, that erroneously the same checksum numbers will come up in a wrong configuration.

Some of the parameters defined by the BIOS are protected from the outside world as a measure to avoid corruption of vital system data, in most cases it is up to the discretion of the manufacturer, how much access they will allow the user. As a rule of thumb, OEM systems have very limited possibilities to interact with the BIOS. Retail mainboards, on the other hand primarily used by the do-it-yourself builder or overclocking community thrive on offering the ultimate access to performance enhancing measures.

Originally, the BIOS was invented by IBM as proprietary software. Phoenix, cracked the code and, consequently, offered BIOS versions of their own. After that, several other companies started to go into the BIOS business, American Megatrends Incorporated (AMI), Award and Mr. BIOS were just a few players. Phoenix was acquired by Award, while AMI stayed independent and these two companies are now the main providers of BIOS in the current PC world.

The typical BIOS is divided into several independent chapters or pages that are indexed usually in the Main menu.

next page:    => more BIOS settings =>