The Compaq Portable was the first "real" IBM PC compatible, introduced in 1982.
The mainboard have 128KB RAM by default and was expandable to 256KB, enough for MS-DOS 1.1 (which was the version delivered with the computer) and the first MS-DOS applications. The Compaq Portable has expansion slots like the IBM PC, so you can upgrade it even with SCSI hard drives (if you want).
It's BIOS was a result of reverse engineering the original IBM PC BIOS, which gives ultimate compatibility. Even the first BASICA versions were running without problems.
My device have two full-height 40 track double density drives, not really exotic.
The weight is about 12Kg, not really portable (but the 9" green CRT is one reason).
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