logic unit and has a 16-bit external data bus, so 32-bit computations are transparently handled as multiple 16-bit values at a performance cost. The later Amiga 2500 and the Amiga 3000 models use fully 32-bit, 68000 compatible, processors from Motorola improved performance and larger addressing capability. CPU upgrades were offered by both Commodore and third-party manufacturers. Most Amiga models can be upgraded either by direct CPU replacement or through expansion boards. Such boards often included faster and higher capacity memory interfaces and hard disk controllers. Towards the end of Commodore's time in charge of Amiga development, there were suggestions that Commodore intended to move away from the 68000 series to higher performance RISC processors, such as the PA-RISC. Those ideas were never developed before Commodore filed for bankruptcy. Despite this, third-party manufacturers designed upgrades featuring a combination of 68000 series and PowerPC processors along with a PowerPC native microkernel and software. Later Amiga clones featured PowerPC processors only. Custom chipset The custom chipset at the core of the Amiga design appeared in three distinct generations, with a large degree of backward-compatibility. The Original Chip Set (OCS) appeared with the launch of the A1000 in 1985. OCS was eventually followed by the modestly improved Enhanced Chip Set (ECS) in 1990 and finally by the partly 32-bit Advanced Graphics Architecture (AGA) in 1992. Each chipset consists of several coprocessors that handle graphics acceleration, digital audio, direct memory access and communication between various peripherals (e.g., CPU, memory and floppy disks). In addition, some models featured auxiliary custom chips that performed tasks such as SCSI control and display de-interlacing. Graphics All Amiga systems can display full-screen animated planar graphics with 2, 4, 8, 16, 32, 64 (EHB Mode), or 4096 colors (HAM Mode). Models with the AGA chipset (A1200 and A4000) also have non-EHB 64, 128, 256, and 262144 (HAM8 Mode) color modes and a palette expanded from 4096 to 16.8 million colors. The Amiga chipset can genlock, which is the ability to adjust its own screen refresh timing to match an incoming NTSC or PAL video signal. When combined with setting transparency, this allows an Amiga to overlay an external video source with graphics. This ability made the Amiga popular for many applications, and provides the ability to do character generation and CGI effects far more cheaply than earlier systems. This ability has been frequently utilized by wedding videographers, TV stations and their