Overlay (programming): Difference between revisions

Revision as of 09:46, 20 May 2022

Revision as of 13:00, 20 May 2022

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In the [[home computer]] era overlays were popular because the operating system and many of the computer systems it ran on lacked virtual memory and had very little RAM by current standards: the original [[IBM PC]] had between 16K and 64K, depending on configuration. Overlays were a popular technique in [[Commodore BASIC]] to load graphics screens.<ref name="Commodore"/> In order to detect when an overlay was already loaded, a [[flag (computing)|flag variable]] could be used.{{fact|date=May 2022}}

"Several DOS linkers in the 1980s supported [overlays] in a form nearly identical to that used 25 years earlier on mainframe computers."<ref name="Levine"/> [[Binary file]]s containing memory overlays had a de facto standard extension, '''.OVL'''. This file type was used among others by [[WordStar]], [[dBase]], and the ''Enable'' DOS office automation software package from [[Enable Software, Inc.]] The [[GFA BASIC]] compiler was able to produce .OVL files.