of the Xerox NoteTaker, a prototype computer developed at Xerox PARC in 1976. Other portable "work-alikes", that were not PC compatible clones include the Seequa Chameleon, and Corona Data Systems' Model PPC-400, and Eagle Computer's Eagle Spirit Portable. They were all short-lived competitors. IBM responded to the Compaq Portable with the IBM Portable, developed because its sales force needed a comparable computer to sell against Compaq. Design The Compaq Portable has basically the same off-the-self hardware as an IBM PC, transplanted into a luggable case (specifically designed to fit as carry-on luggage on an airplane), with Compaq's BIOS instead of IBM's. All Portables shipped with 128k of RAM and 1-2 double-sided double-density 360 KB disk drives. The machine uses a unique hybrid of the IBM MDA and CGA which supports the latter's graphics modes, but contains both cards' text fonts in ROM. When using the internal monochrome monitor the 9x14 font is used, and the 8x8 one when an external monitor is used (the user switches between internal and external monitors by pressing ). The user can use both IBM video standards, for graphics capabilities and high-resolution text. With a larger external monitor, the graphics hardware is also used in the original Compaq Deskpro desktop computer. Compaq used a “foam and foil” keyboard from Keytronics, with contact mylar pads that were also featured in the Tandy TRS-80, Apple Lisa 1 and 2, Compaq Deskpro 286 AT, some mainframe terminals, SUN Type 4, and some Wang keyboards. The foam pads the keyboards used to make contact with the circuit board when pressed disintegrate over time, due to both the wear of normal use and natural wear. The CRT display also suffered from a low refresh rate and heavy ghosting. Software Compaq's efforts were possible because IBM had used mostly 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 main difficulty was the BIOS, because it contained IBM's copyrighted code. Compaq solved this problem by producing a 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 "95% compatibility" at best).Then Phoenix Technologies and others began selling similarly reverse-engineered BIOSs on