Until the early 1980’s most monitors were terminals. They were boxy video display terminals (VDT’s) combined with an attached keyboard. A terminal could be configured to work with just about any computer on the market. (Not that there was a wide selection of personal computers for you to choose from.)

Terminals were attached to computers by a serial interface. In those days, the VDT was commonly referred to as a CRT (Cathode Ray Tube).

earlier DOS, the dominant operating system (OS) for 8 bit computers was CP/M (Control Program for Microprocessors). Early CP/M machines were originally designed to use separate memory-mapped video display devices and discrete keyboards that plugged into the machines – not unlike video display cards used later. The most well known was the VDM-1. Terminal manufacturers recognized this “lost market “and began to market mainframe and ministyle terminals to the CP/M community. The sales pitch of “just like a real (mainframe at the time) computer" paid off. CP/M computers soon used terminals almost exclusively.

Apple II computers and the early game machines (such as those made by Atari, Coleco or Nintendo) hooked to a monitor not a terminal. (The Apple II was built with a keyboard as part of the system. All that was missing was a monitor once the Apple II was plugged in).

These monitors – unlike terminals – looked like television sets without the tuner. In couple cases they actually were television sets. (Many early computers – such as the Commodores Vic 20, 64 and 128, could be used with any television set with a special RF adapter that hooked to the antenna of the TV).

Then IBM came out with PC-DOS computers, which were dubbed “threepiece computers.’ One explanation according to a prominent used car dealer Moonie Bronstein was that many of the early marketers / hucksters advising the techies of the early computer era ,had their start in the competitive world of auto sales where such terms as “ 3 piecers “ and “ 4 piecers" were popular marketing and sales terms. Other explanations for this marketing term was because the computers included three main components i.e. – the monitor, the keyboard and the CPU “box".

Ironically, when the IBM PCDOS computers arrived on the scene with separate monitor and keyboard – the monitor connected directly to the computer. Just like the earliest personal computers) through a display device connection. These new monitors used video cards that were either IBM monochrome (MDA), IBM color graphics cards9 CGA), or Hercules (the first third party ad on cards).