Its main differences were support for more I/O devices (floppy disk drives, IEEE-488, RS-232) and a character set (EBCDIC) which was compatible with other IBM machines.

However, in 1981 Hal Prewitt, founder of Core International, Inc invented and marketing the world's first and only hard disk subsystems and "CoreNet", a LAN used to share programs and data for the IBM 5110 and 5120 systems.

Citing the easy use of his new system, Jeff Grube, vice president of Punxsutawney Electric Repair (who received the first IBM 5110 on February 2, 1978), said: "If you can type and use a hand-held calculator, you have all the skills necessary to operate a 5110."

In 1984, Core International, Inc introduced PC51, software that allowed 5100 Series computer programs written in BASIC to run unmodified on the IBM PC and compatibles under PC DOS and share programs and data on CoreNet, the LAN for all these models.

However, companies such as Core International, Inc designed and supported a wide assortment of application programs.