Earlier rev board:

Later rev board:

Can anyone explain this difference?
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These are the data bus drivers/receivers. The earlier rev used 2 8T28s in a 16 pin package. Each chip supported 4 bits, requiring 2 chips for an 8 bit bus. The later revs, I believe that this started with the RFI version, used 1 8 bit DP8304 chip in a 20 pin package. Functionality is the essentially same, with the savings of one chip. This was most likely a cost cutting move, and nothing more.
Regards,
Mike Willegal
I am proud to report that my working Apple ][ (1978 non-plus) has all three chips