Configurability of Hardware and Software

Both hardware and software are produced for use in a wide range of situations. In most cases, to be commercially viable software must be usable on a number of systems and it must be able to adapt to whatever printers, VDU's and other peripherals are available.

Similarly when an item of hardware - such as a CD ROM drive - is added to an existing system it must be possible to install it in a way that does not conflict with existing peripherals.

This means that when new software or hardware is installed it must be adapted to suit the environment it to work in. The manufacturer leaves certain options open that can be set when the item is installed. The process of setting these options is called configuring the hardware or software for the system.

Hardware is configured in one of three ways. Some devices have small switches (called DIP switches) which are used to set various options. An example of this would be setting a device number for a SCSI device. Each device on a SCSI bus must have a unique identity number. The manufacturer will not know what number will be required for his device in a particular system since it depends on what other SCSI devices are attached to the bus. The person installing the device for a particular system will set the device number using DIP switches on the device.

A second way of configuring hardware is use a configuration program to set the required options. When the options are as required the settings are stored in battery backed up memory within the device itself. Some network boards are configured like this but a more common example is the configuration for the CPU of a PC. The CPU needs detailed information about the hard disk drive and the other hardware that makes up the particular system that it is working in. This information is stored in the BIOS settings. The PC can be configured using a special set up program and the settings saved in battery powered memory. If the battery fails then the settings are lost and the PC must be reconfigured when the battery is eventually replaced.

A third way of configuring hardware is for the manufacturer to provide a special program called a device driver. This driver program is used by the operating system when it needs to communicate with the associated hardware. In a PC device drivers are used, sometimes in conjunction with the previous two methods, to configure peripherals. The main function of the driver however is to handle communication between the Operating System and the device.

The device driver can be thought of as a virtual device. The operating system 'sees' the driver as though it were the real device. The driver for an output device takes the output from the operating system in operating system format and passes it to the real device in the specific format needed by the physical device. A PC would need device drivers for the VDU, the keyboard, the mouse, the sound card, the printer, in fact for any peripheral that was connected to the computer.

As mentioned before, the device driver acts as a translator from operating system format to device format, but it can also be used to configure the device. For example the sound card driver program can be used to set the input and output levels. The printer driver can be used to set default paper size, orientation and source.

Since different device drivers, possibly from different manufacturers, are responsible for communicating with the peripherals it is sometimes the case that peripherals that should produce identical output do not. One example of this is the occasional mismatch between screen output and printer output. This mismatch may be the result of limitations of the hardware due to different resolution or different size of the output as when a line that prints as very fine on a laser printer is shown normal thickness on the screen. It may be due to an incorrect configuration such as when the printer is expecting a line feed signal at the end of each line and the software is expecting the printer to automatically feed each new line or when red on the screen is printed as purple on the printer.

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