The MOS Tech 8568 VDU was the "Visual" (or "Video") "Display Unit" controller chip responsible for the secondary ("80-column" or "RGBI") display on the Commodore 128 personal computer.
The Commodore 128 had two video display modes, which were usually used singularly, but could be used simultaneously. The VIC-II chip, also found in the Commodore 64, was mapped directly into main memory - that is, the video memory and main CPU's (the 8502 and Z80A processors) shared a common 128KiB RAM, and the VIC-II control registers were accessed as memory locations.
The secondary display, the VDU, had a smaller set of control registers which were accessed via memory locations, and were only available when the computer was in "native" mode (and not in the "GO64" Commodore 64 emulation mode). The VDU, similar in programming to early IBM MDA, CGA, and EGA boards, had its own dedicated video RAM. Depending on the date of manufacture of the particular machine, this could be either 16KiB RAM or 64KiB RAM. Text or graphics to be displayed is loaded into the VDU memory byte-by-byte through the control registers, similar to the "IN" and "OUT" instructions for IBM PC video boards.
In Commodore 128 terminology, the VIC-II display was called the "40 column" display, and the VDU, "80 column," due to the number of columns of fixed-pitch text that could be natively displayed.
The MOSTechnology 6502 is an 8-bit microprocessor designed by MOSTechnology in 1975.
When it was introduced it was the least expensive full featured CPU on the market by far, at about 1/6th the price, or less, of competing designs from larger companies such as Motorola and Intel.
Motorola sued immediately, and although today the case would have been dismissed out of hand, the damage to MOS was enough for them to agree to stop producing the 6501.
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