Intermec 6100 Reference Guide

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In its simplest form, the basic input/output system (BIOS) is composed of softĆ

ware that allows the operating system (in this case, DOS) to interact with the

PC hardware.  The BIOS may also be known as firmware" or system software.

The BIOS, in most desktop PCs, is typically contained on ROM chips.  In the

PEN*KEY 6000 Series Computer, the BIOS is programmed into flash memory to

allow you to periodically update the system, without physically opening the unit

to replace any of the chips.

The BIOS manages the system through the use of interrupts, which are basically

signals generated by the hardware to indicate that they need the attention of the

CPU.  For example, when you type characters at the keyboard, your key presses

are changed into binary strings and sent to the BIOS.  When the BIOS receives

the string, it sets an interrupt to alert the CPU that it has data to be processed.

All of this happens in just a fraction of a second.
From the software's point of view, BIOS is sometimes referred to as a Hardware

Abstraction Layer (HAL).  HAL is an important concept, in view of the fact that,

an application that is written for a computer with HAL can be easily moved to

another computer where the hardware is different.  For those peripherals that

are supported directly by BIOS, software developers need not be concerned about

differences between hardware from various manufacturers.  Hard drives are one

example, since all these devices look the same upstream of BIOS.  Between BIOS

and the hardware, using the hardware device is often a matter of setting paramĆ

eters for BIOS.  This is commonly the case with hard drives, where the user

must first set parameters in BIOS before the hard drive can be seen" by DOS.

Hardware that is not directly supported by BIOS, such as a PC Card drive, must

be supported by a BIOS extension (known as a DOS device driver).

DOS device drivers tell the operating system about specific PC hardware compoĆ

nents that are not directly supported by BIOS.  Device drivers are loaded into

memory at boot time; and they enable peripherals such as CDĆROM drive or

memory above 1 megabyte.  The PEN*KEY 6000 Series Computer requires at

least one device driver, HIMEM.SYS, to control access to the high memory area

(HMA); the first 64K RAM above the 1Ćmegabyte boundary.  Other DOS device

drivers may be loaded, depending on the requirements of attached peripherals.

DOS device drivers are always loaded into memory from the CONFIG.SYS file,

which is located in the root directory of the default boot drive.