The follow-up to the TRS-80, the CoCo is actually incompatible with its precursor's hardware due to a completely different processor (Motorola 6809E vs. the Zilog Z80). This processor was actually more powerful than that used in many machines, which led to a higher price-tag and a correspondingly smaller user base.
The CoCo went through three revisions, taking it from the start of the 1980s through to the start of the 1990s. Impressively, each version had a high level of backwards compatibility with the software of previous revisions.
The CoCo line ultimately succumbed to the rise of the IBM PC Clone.
The CoCo 1 and 2 are largely identical under the hood, consisting of five LSI chips:
- MPU: An MC6809E Microprocessor Unit that acted as the machine's brain.
- SAM: A MC6883/SN74LS783/SN74LS785 Synchronous Address Multiplexor that controls the DRAM, clock synchronization and a bunch of other tiny little things.
- VDG: A MC6847 Video Display Generator, capable of drawing graphics in up to nine colours to a 256x192 resolution display, supporting 16 lines of 32 characters on screen at once.
- PIA: Two Peripheral Interface Adapters, either MC6821 or MC6822 chips, handing I/O operations for cassete decks, the keyboard, and other things that plug into the machine.
The CoCo 3 made a few more significant changes:
- ACVC: A new ASIC-manufactured VLSI, dubbed the Advanced Color Video Chip, that integrated the capabilities of SAM AND VDG while enhancing their capabilities (for example, adding support for lower-case characters and 40-80 character displays).
- MPU: Bumped up to a MC68B09E.
- PIA: Bumped up to MC68B21s.