It's actually 8 bytes where I say 128bit on 128x8 cause 8 bytes is 64bit and 128bit doesn't exist on main RAM with common systems. 128x4 is 1GBx1 sticks. There are still a couple more variants for 1x2GB though.
Why do all RAM makers intentionally make density specs unreliable? Is it to make money off markets even when the product isn't compatible? Kingston and Crucial memory finders, as are others, are infamous for reporting incompatible RAM all because of this.
128x8=8 128bit 128MB chips
128x8=8 64bit 128MB chips per side
128x64=16 128MB chips at 64bit each
128x4=4 128bit 512MB chips
256x64=8 256MB chips at 64bit each
FYI: I believe there are even more specs just for 1x2GB alone.