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Compaq Portable
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=== Software === [[File:Compaq Portable and Wordperfect.JPG|thumb|Running WordPerfect 5.0]] Compaq's efforts were possible because IBM had used mostly [[Commercial off-the-shelf|off-the-shelf]] parts for the PC and published full technical documentation for it, and because [[Microsoft]] had kept the right to license [[MS-DOS]] to other computer manufacturers. The only difficulty was the BIOS, because it contained IBM's copyrighted code. Compaq solved this problem by producing a [[clean room design|clean room]] workalike that performed all documented functions of the IBM PC BIOS, but was completely written from scratch. Although numerous other companies soon also began selling PC compatibles, few matched Compaq's achievement of essentially-complete software compatibility with the IBM PC (typically reaching "[[PC compatible#Compatibility issues|95% compatibility]]" at best) until [[Phoenix Technologies]] and others began selling similarly reverse-engineered [[BIOS]]s on the open market.<ref name="alsop19940131">{{cite news | url=https://books.google.com/books?id=AzsEAAAAMBAJ&q=%22flight+simulator%22&pg=PT1 | title=A public Windows pane to make compatibility clearer | accessdate=February 28, 2011 | last=Alsop | first=Stewart | date=1994-01-31 | publisher=InfoWorld | pages=102}}</ref> The first Portables used Compaq DOS 1.10,{{Citation needed|date=November 2019}} essentially identical to PC DOS 1.10 except for having a standalone [[BASIC]] that did not require the IBM PC's [[read-only memory|ROM]] Cassette BASIC, but this was superseded in a few months by DOS 2.00 which added hard disk support and other advanced features. Aside from using DOS 1.x, the initial Portables are similar to the 16 KB β 64 KB models of the IBM PC in that the BIOS was limited to 544 KB of RAM and did not support expansion ROMs, thus making them unable to use [[Enhanced Graphics Adapter|EGA]]/[[VGA]] cards, hard disks, or similar hardware. After DOS 2.x and the [[IBM XT]] came out, Compaq upgraded the BIOS. Although the Portable was not offered with a factory hard disk, users commonly installed them. Starting in 1984, Compaq began offering a hard disk-equipped version, the Portable Plus, which also featured a single half-height floppy drive. The hard disk offered would be 10 to 21 megabytes, although [[bad sector]]s often reduced the space available for use. In 1985, Compaq introduced the Portable 286, but it was replaced by the more compact Portable II in a redesigned case within a few months. The Portable 286 featured a full-height hard disk, and the options of one half-height floppy drive, two half-height floppy drives, or a half-height floppy drive and a tape backup drive.
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