The A580/A580+ memory expansion was put on marked in 1990 for Amiga 500 and Amiga 500+.
The mainboard on the two models are the similar, and holds 16 DIP sockets which accepts up to 2 MB RAM, in 256kx4 DIPs (70 - 80ns); these have to be added in sets of four.
The main difference between the A580 and A580+ is how the adapter board is connected:
The A580 adapter board connects to the Gary's Socket, and it can only use 1.8 MB RAM of it's mainboard.
Where A580 Plus connects to the 68000's socket, and can use all 2 MB of it's mainboard. It will require Fat Agnus 8372A. Further more the chip RAM size can be switched between 512kB and 1 MB
In 1992, the second generation came, called A580 II, this had 2 MB RAM (SIP). Like the A580 the adapter board was connected to the Gary's Socket.
All models have battery backed up clock, and an on/off switch, and the main board is connected to the trapdoor slot.