A printed circuit board (PCB) is a component of a computer on which chips, transistors, and other electronics are mounted. Text on a PCB often gives a clue to the manufacturer.
"ASSY" numbers are often found in components of Commodore computers, such as the Commodore 64.
Serial numbers beginning with "820" are usually associated with Apple computers like the Apple II or Apple Macintosh.
"Z-80", "Z 80", or "Z-80A" indicates a Zilog Z80 processor; which was commonly used in home computers like the Sinclair ZX Spectrum.
The manufacturer code "MITS" indicates hardware from Micro Instrumentation and Telemetry Systems, like the Altair 8800.