The System Basic InputOutput Services

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The System Basic Input/Output Services

The system Basic Input/Output Service (BIOS) is made up of a group of tiny programs that control input and output services to devices internal to the computer. The BIOS itself is usually stored on a ROM chip that is usually soldered onto the motherboard. Newer BIOSs come in the form of flash ROM, which is ROM that can be changed. The major manufacturers of BIOS are Phoenix, Award, and AMI. You may have seen one of their names flash by on the computer screen as the BIOS carries out instructions during boot. From time to time, a user may want to upgrade, or flash, the current version of BIOS with software updates from the manufacturer. It is important to know the make and model of the motherboard for BIOS updates, and it is also very important to document system configuration settings before upgrading the BIOS.

When a computer is booted, instructions are first available to the system from the ROM BIOS. The main functions of the BIOS are to carry out boot operations and to act as an intermediary between peripheral devices, software applications, and operating systems. As mentioned earlier, the BIOS is permanently stored on ROM chips. The next section describes some types of BIOS chips.

Programmable Read-Only Memory (PROM) Chips

A Programmable ROM (PROM) is a BIOS chip that cannot be changed. Data can only be stored on it once. A device known as a ROM burner is used to record information into the chip. If the PROM chip goes bad or loses its information, there is no way to reprogram it. The user has no choice but to get another chip from the manufacturer.

Erasable Programmable Read-Only Memory (EPROM) Chips

Erasable PROM (EPROM) BIOS chips look almost identical to PROM chips, with the exception of a little window that is used to shine an ultraviolet light through to erase their contents. Many BIOS chips in the past were EPROM chips. This was great for upgrading the BIOS if you had a tool to erase the chip's contents. They were easily identified on the motherboard by the shiny label on the top of the chip that usually contained the manufacturer's name and the version of the chip.

Electronically Erasable Programmable Read-Only Memory (EEPROM)

By applying a higher voltage to one of the pins on the Electronically Erasable PROM (EEPROM) chip, the program on the chip is erased. A new program or set of instructions can then be electronically written to the chip. EEPROM is also known as flash ROM.



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A+ Complete Study Guide, Third Edition (220-301 and 220-302)
The A+ Exams Guide: (Exam 220-301), (Exam 220-302) (TestTakers Guides)
ISBN: 1584503076
EAN: 2147483647
Year: 2003
Pages: 237

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