Taken from there:

Motherboard revisions

revision 3
512 kB Chip RAM on motherboard as 16 chips
Kickstart 1.2 ROM

revision 5
Fat Agnus 8370 (NTSC) or 8371 (PAL)

revision 6
Fat Agnus 8372A (part of the ECS chip set) supports 1 MB Chip RAM
Agnus is rotated 90° counter clockwise
512 kB Chip RAM on motherboard as 4 chips
empty places for other 4 chips giving 1 MB RAM on the motherboard
Kickstart 1.3 ROM

revision 7
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revision 8
Kickstart 2.04 ROMs and ECS chip set: Fat Agnus (8375), Super Denise (8373)
A500:
512 kB Chip RAM on the motherboard
battery and clock circuit is missing
A500 Plus:
1 MB Chip RAM on the motherboard
battery backed up real time clock