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A20 line - Definition and Overview |
| Related Words: L, Mo, Zeitgeist, Accommodation, Accompaniment, Accord, Aceldama, Acknowledgment, Acquire, Action, Activity, Adaptation, Affiliation, Aftermath, Agreement, Aim |
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In the x86 architecture (Intel 80286 CPU and above), the A20 line is a control line (typically stored in the keyboard controller) that, when enabled, turns off memory wrap-around above the 1-megabyte mark.
When disabled, the memory locations 0000:0000 (the first byte of memory), and ffff:0010 (the first byte above the 1MB mark) refer to the same byte of memory. This is switched off by default in order to maintain backwards compatibility with the XT architecture, which has a dependence on this memory wrap around feature. Thus, without special measures to enable this line, the processor mimics the wrap-around these programs expect.
Enabling the A20 line is one of the first steps an operating system does in the bootup process, often before control has been passed onto the kernel from the bootstrap (in the case of Linux, for example).
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Example Usage of line |
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BrooketheDancer: If you don't like crowds, and have no patience then for god's sakes do your holiday shopping on line! Don't hit me in the butt with a cart! |
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CarrieSkinner: @Gabriella_PRowl if its any consolation, I once thought there was a line in Frankie by Sister Sledge that said take me to the Taliban |
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helpdeskdave: RT @DavidStockwell: The line of law enforcement vehicles on I-5 in Tacoma this AM is amazing. Saw 10 motorcycle officers braving the cold. |
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