Our Amigas can basically only display three different resolutions and there are only two for the OCS Amigas. The graphics chip changes the image output at a certain base clock, that is the pixel clock. In LowRes it is 140 ns for each pixel, in HiRes it is 70 ns and with the exception of OCS there is SHiRes with 35 ns.
This clock specifies how fast the image data in the beam can change. This beam is steered over the screen with a fixed speed. This cannot be changed, what can be changed is the position where the beam starts its image buildup, where it jumps to the next line or starts the next frame. With the interlace trick you can additionally double the number of horizontal lines, but this will then halve the lifetime of our eyes.
However, the Amiga needs time to transmit the change to the beam during frame building. The required time results from the connection of the graphics chip to the RAM, this connection has a data width of 16Bit. The AGA chipset has an additional 32Bit and burst access to the ChipMem, so the ChipSet can process four times as much data from the memory as ECS or OCS.
At that time, the developers divided the additional data volume into higher color count and higher resolution. With an OCS Hires 70ns image, the beam has access to a maximum of 4 bitplanes, so 16 colors out of 4096 colors are possible there. With AGA we can change the beam twice as fast with 35 ns and additionally process the double number with 8 bitplanes, which makes 256 colors out of 16777216 possible.
Now we come to the special feature with the ECS chipset. This was introduced with the Amiga3000 and it was advertised at that time, that the ChipMem with 32Bit is faster integrated in the architecture. This is true, but only for the connection of the processor to the RAM. If you consider the ChipMem with its memory connection as an autarkic subsystem, the old structure with internal 16 bit accesses is still given here. What did the designers do to at least increase the resolution, i.e. the speed for changing the beam? Exactly, they took the necessary data volume at the color depth and the maximum number of bitplanes. Under ECS, the beam can be changed in SHiRes at 35ns, but this only gives access to a maximum of 2 BitPlanes, which means 4 colors out of 64.
Starting from Workbench 2.0 there are freely programmed image formats, which all fall back to the three speeds of the beam and change only start and end of the image line and the whole image. There are still little things like overscan, if I describe them here it will get too complicated, let's just say you can still use a main switch, where I take the power from the beam gun and it still continues to move across the screen, but can't paint a picture. After this small introduction "how do I build my own chipset tomorrow or the day after tomorrow" I can now explain how SuperPlus works and why the ECS chipset can handle a resolution of 800x600 pixels with 16 out of 4096 colors.
To do this, I stretched the length of the horizontal line to be painted from 736 (overscan) to 800 pixels, and finished the complete image at 300 painted lines (600 in interlace) instead of 240 lines (NTSC overscan). In doing so, I fed the beam with HiRes (70ns). We remember, HiRes means 16 out of 4096 colors. Since the beam now has to travel longer across the screen than with NTSC or PAL, the number of painted frames drops from 60/50 to 48 frames per second.
The Amiga developers decided at that time for a different way and set the resolution to SHiRes (35ns) and at the same time reduced the horizontal distance of the beam. This resulted in Super72, which uses 4 out of 64 colors to show a resolution of 800x600 at 72 frames per second. This was more important than a high number of colors at that time, because the AtariST and the Mac were not notable for their monochrome display, but for the frame rate used. Today, thanks to modern flickerfixers, all common formats can be converted and used without flickering. Usually the SuperPlus mode is also displayed without any problems by normal Amiga displays, like 1081, 1084 or Philips CM8833.
Another special feature of SuperPlus mode is that it is the only mode where the image area is stretched, so the beam travels a longer distance. All other ECS/AGA modes reduce the path length. This also manifests itself in a special feature of the memory structure. The ChipSet takes care of the data transfer between the individual components. In Productivity mode, for example, twice as much data can be pumped to the sound chip as in normal NTSC/PAL. With SuperPlus, on the other hand, the DMA interface is already pushed to the limit, even longer image lines then even lead to data loss and crashes.