It is fairly obvious that Compaq’s Deskpro 386 changed the PC hardware and was probably one of the major reasons why we aren’t using PS/2 compatibles today. It may be less obvious that CEMM, an offshoot of the Deskpro 386 better known in its later incarnation as EMM386, also significantly shaped the PC software landscape.
When the Deskpro 386 appeared, it faced an interesting problem: There was no popular operating system capable of utilizing the advanced features of the i386 processor. Compaq marketed the Deskpro 386 simply as a very fast (and quite expensive) PC compatible designed for running DOS applications. Even after the first UNIX ports appeared, DOS was so popular and ubiquitous that users did not feel sufficiently enticed to switch. That was compounded by the fact that RAM was very expensive and systems with more memory than DOS could handle were rare around 1987.
CEMM/EMM386 ensured that DOS could handle quite a lot of memory. CEMM, or Compaq Expanded Memory Manager, was a very innovative piece of software. By utilizing the virtual 8086 (V86) mode of the i386, CEMM could provide 8086-compatible expanded memory (EMS) to existing DOS applications without requiring special hardware (as an 8086 would). Continue reading