The ECS Chipset…
The Enhanced Chip Set (ECS) was an incremental update to the original chipset (OCS), increasing screen resolution options when both AGNUS and DENISE chips are the ECS versions. It also allows software switching between the PAL and NTSC video standards.
The Amiga 3000 was the first machine to be available with the full ECS chipset, allowing higher resolution graphical output, as well as much more flexible options for video output.
Some machines, such as the Amiga 2000 and Amiga 500, came with the ECS version of the AGNUS chip, but with the OCS version of the DENISE Chip. Upgrading the DENISE Chip in these machines upgrades the machine to the full ECS specification and allows the higher resolutions and PAL/NTSC software switching functionality. Older machines that came with the OCS AGNUS chip, would require both the AGNUS and DENISE to be upgraded in order to gain the improvements in ECS, this was not always possible, as the Amiga 1000 and Amiga 2000-A machines had different sockets for the AGNUS chip – for more information please see the AGNUS page.