IBM ThinkPad R61, R61E Motherboard Schematic Circuit Diagram
IBM ThinkPad R61, R61E Motherboard Schematic Circuit Diagram
After Clean-Room Approach PC Software
After duplicating the IBM PC's motherboard hardware and BIOS, all that was left was MSDOS to create a completely IBM-compatible machine. Reverse-engineering DOS appeared to be a difficult effort at the time, even with the clean-room technique, because it is considerably larger than the BIOS and has many more applications and functions. Furthermore, the OS has developed and altered more frequently than the BIOS, which has stayed relatively consistent in contrast. This meant that in the early 1980s, the only way to obtain DOS on an IBM compatible was to purchase a license. This is when Microsoft entered. Because IBM did not verify that its licensing deal with Microsoft was exclusive, Microsoft was allowed to offer the same DOS it built for IBM to anybody else who wanted it. The last component was in place with a licensed copy of MS-DOS, and the floodgates were opened for IBM-compatible systems to be created whether IBM wanted it or not.
MS-DOS was ultimately copied, with the first being DR-DOS, which was launched in 1988 by Digital Research (developers of CP/M). By all rights, DR-DOS was more than a clone; it had a number of capabilities not seen in MS-DOS at the time, prompting Microsoft to include comparable functionality in subsequent MS-DOS versions. Novell acquired DR-DOS in 1991, followed by Caldera in 1996 (which published a version of the source code under an open-source license), Lineo in 1998, and DR-DOS in 2002. The DR-DOS/OpenDOS Enhancement Project and the FreeDOS Project have both independently generated, improved, and maintained free and open-source DOS versions Know more about FreeDOS(www.freedos.org).
