Columbia Data Products' MPC 1600 "Multi Personal Computer", the first IBM PC compatible system, had come out in June 1982.

[7][8][9] Unlike Compaq, many of these companies had previously released computers based on Zilog's Z80 and Digital Research's CP/M operating system.

Like Compaq, they recognized the replicability of the IBM PC's off-the-shelf parts, and saw that Microsoft retained the right to license MS-DOS to other companies.

Like the non-portable IBM PC, the Compaq Portable runs on power from an AC outlet only; it has no battery.

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.

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.

Starting in 1984, Compaq began offering a hard disk-equipped version, the Portable Plus, which also featured a single half-height floppy drive.

Its reviewer tested IBM PC DOS, CP/M-86, WordStar, SuperCalc, and several other software packages, and found that all worked except one game.

[12] PC Magazine also rated the Compaq Portable very highly for compatibility, reporting that all tested applications ran.

Independent computer stores were previously doing this upon request of users, and Compaq saw this as a lost revenue opportunity.