Editing Amiga 500 (section)

== Trap-door expansion 501 ==
{{Unsourced section|date=June 2023}}
[[File:RAM 512K for Amiga 500 ubt.jpeg|thumb|An A501 compatible expansion]]

A popular expansion for the Amiga 500 was the Amiga 501 circuit board that can be installed underneath the computer behind a plastic cover. The expansion contains {{nowrap|512 KB}} RAM configured by default as "[[Amiga Chip RAM#Fast RAM|Slow RAM]]" or "trap-door RAM" and a battery-backed [[real-time clock]] (RTC).

The 512 KB trap-door RAM and 512 KB of original chip RAM will result in 1 MB of total memory.{{efn|name=binpre}} The added memory is known as "Slow RAM", as its access is impacted by chip-bus bandwidth contention, while the chipset is not actually able to address it.

Later revisions of the motherboard provide solder-jumpers to relocate the trap-door RAM to the chip memory pool, given the [[MOS Technology Agnus|Agnus]] chip is the newer ECS version, shipped in later A500 motherboards. Newest (rev 8) A500s would share motherboard with A500+, and configure the expansion memory as CHIP by default.