upgradesor provided chainable expansions that extended the bus as they were addedas there is only one side expansion slot. Expansions are configured automatically by AutoConfig software, so multiple pieces of hardware did not conflict with each other. Diagnostics When the computer is powered on a self-diagnostic test is run that will indicates failure with a specific colour: Medium green means no chip RAM found or is damaged. Red means bad kickstart-ROM. Yellow means the CPU has crashed (no trap routine or trying to run bad code) or a bad Zorro expansion card. Blue means a custom chip problem (Denise, Paula, or Agnus). Light green means CIA problem. Light gray means that the CIA might be defective. mean there is a ROM or CIA problem. Black-only (no video) means there is no video output. The keyboard LED uses blink codes: One blink means the keyboard ROM has a checksum error. Two blinks means RAM failure. Three blinks means watchdog timer failure. Trap-door expansion 501 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 RAM configured by default as "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. 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 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. Software Each time the Amiga 500 is booted, it executes code from the Kickstart ROM. The Amiga 500 initially came shipped with AmigaOS 1.2, but units since October 1988 had version 1.3 installed. Reception and sales The Amiga 500 was the best-selling model in the Amiga family of computers. The German computer magazine Chip awarded the model the annual "Home Computer of the Year" title three consecutive times. At the European Computer Trade Show 1991, it also won the Leisure Award for the similar "Home Computer of the Year" title. Owing to the inexpensive cost of the Amiga