History of Device Configuration
In the beginnings of data processing technology, the hardware was just a collection of modules, and the functions of those modules had to be linked to accommodate different calculating operations. This linking was usually done by connecting some wires between modules and disconnecting others. For many mechanical data processing machines, such as the IBM punched card accounting machines, their calculating operations were directed by the use of a quick-swap control panel wired to route signals between module sockets.
As general purpose computing devices developed, these connections and disconnections were instead used to specify locations in the system address space where an expansion device should appear, in order for the device to be accessible by the central processing unit. If two or more of the same type of device were installed in one computer, it would be necessary to assign the second device to a separate, non-overlapping region of the system address space so that both could be accessible at the same time.
Some early microcomputing devices such as the Apple II sometimes required the end-user to physically cut some wires and solder others together to make configuration changes. The changes were intended to be largely permanent for the life of the hardware.
As computers became more accessible to the general public, the need developed for more frequent changes to be made by computer users unskilled with using soldering irons. Rather than cutting and soldering connections, configuration was accomplished by jumpers or DIP switches.
| Left: Jumper blocks of various sizes, Right: a slide-style DIP switch with 8 switches | |
However, the process of configuring devices manually using jumpers or DIP switches could be quite difficult, and there was usually no forgiveness for technical inexperience. Incorrect settings could render either the whole system or just the expansion device completely or partially inoperable. Some settings such as for interrupts (IRQ) or direct memory access (DMA) required knowledge of what configuration had been previously manually assigned to other devices, as well as what settings the main system itself may be using. The system might still seem to work properly with an incorrect setting, until the IRQ or DMA is actually needed and the entire system suddenly freezes and must be reset.
Read more about this topic: Plug And Play
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