screens, from a palette of 4096 colours. Two special graphics modes are also included: Extra HalfBrite (EHB), which uses a 6th bitplane as a mask that halved the brightness of any colour seen Hold-And-Modify (HAM), which allows all 4096 colours on screen at once. HAM makes it possible to use over a wide span. This works by letting each pixel position use the previous RGB value and modify one of the red, green or blue values to a new 4-bit value. This will cause some negligible colour artifacts however. Memory Using various expansion techniques, the A500's total RAM can reach up to 138 MB – 2 MB Chip RAM, 8 MB 16-bit Fast RAM, and 128 MB 32-bit Fast RAM. Chip RAM The stock 512 KB Chip RAM can be complemented by 512 KB using a "trapdoor" expansion (Commodore A501 or compatible). While that expansion memory is connected to the chip bus, hardware limitations of early stock Agnus chip revisions prevent its use as Chip RAM, only the CPU can access it. Suffering from the same contention limitations as Chip RAM, that memory is known as "Slow RAM" or "Pseudo-fast RAM". Agnus revisions shipped with late A500 are ECS and allow use of trapdoor RAM as real Chip RAM for a total 1 MB. after changing the memory-layout jumper allows use of trapdoor RAM as real Chip RAM for a total 1 MB. Additionally, several third-party expansions exist with up to 2 MB on the trapdoor board. Using a Gary adapter, that memory will be mapped as either split on Chip RAM and Slow RAM or fully as Slow RAM, depending on configuration. Furthermore, using an A3000 Agnus on an adapter board, it is possible to expand the Chip RAM to 2 MB, matching the A500+. Fast RAM "Fast" RAM is located on the CPU-side bus. Its access is exclusive to the CPU and not slowed by any chipset access. The side expansion port allows for up to 8 MB of Zorro-style expansion RAM. Alternatively, a CPU adapter allows for internal expansion. Accelerator RAM Internal or external CPU accelerators often include their own expansion memory. 16-bit CPUs are limited by the 24-bit address space but they can repurpose otherwise unused memory space for their included RAM. 32-bit CPU accelerators aren't limited by 24-bit addressing and can include up to 128 MB of Fast RAM (and potentially more). Memory map Connectors