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Software Engineers Handbook/Operating Systems/Forth

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The earliest versions of the Forth Programming Language (around 1970) ran on primitive minicomputers with no other OS or executive. Systems at the National Radio Astronomy Observatory's 11-meter radio telescope near Tucson, AZ, controlled precise movements of the telescope and dome as well as performing concurrent data acquisition and supporting analysis on a graphics terminal.

Mass storage (used for both program source and data) resided on 7- or 9-track magnetic tape, soon replaced by a drum and later by disks. Mass storage was addressed in "blocks" (typically 1024 bytes), and a block number was a function of its physical location on the media. This was an extremely simple and reliable approach. The entire system, including drivers for disk and terminal, command line interpreter, resident compiler and assembler, multitasker, and applications such as control of the telescope, was so small it could run without overlays in under 32K bytes of memory.

Because of Forth's unique ability to run efficiently in such a resource-constrained environment, it has always been most popular in embedded systems, particularly hand-held or battery-powered devices such as the package-tracking devices used by FedEx Corporation. It has also been used in numerous space applications by NASA and others.

Some companies, such as New Micros, Inc. sell inexpensive microprocessor boards with Forth already installed. Others, such as FORTH, Inc. and Microprocessor Engineering Ltd., provide cross-compilers for embedded systems in which the Forth OS runs on the target but the compiler and other development tools run on a conventional PC.

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