This article is from the comp.sys.acorn FAQ, by Paul Vigay with numerous contributions by others.
I've now decided to restrict this section of the FAQ to detailing currently available models. For the graphics capabilities of older machines, please visit my Acorn History page at http://www.vigay.com/riscos/acorn.html
- Iyonix machines
The most notable difference in the graphics capability of the Iyonix is that it now incorporates a 'standard' graphics card, namely the nVidia GeForce 2MX. This gives much higher resolutions and colour depths than previous 'Acorn' machines, but also sacrifices 2 & 4 bit colour depths (ie. 4 and 16 colour screen modes).
Rather than give an exhaustive list of all 'modes', it will suffice to say that it can display resolutions from 320x200 up to 2048x1536 pixels, each in either 256, 32 thousand or 16 million colours (8, 16 or 24 bit).
- Risc PC machines
his covers all Risc PC in the Risc PC 600, Risc PC 700, A7000 & A7000+ machines. Here the newer VIDC20 chip has been used and the display capabilities are somewhat extended. Namely :-
X res. Y res. Colours 160 256 4,16,256 320 256 2,4,16,256 640 200 2,4,16,256 640 250 4,16 640 256 2,4,16,256 640 352 2,4,16,256 640 480 2,4,16,256 640 512 2,4,16,256 768 288 2,4,16,256 800 600 2,4,16,256,32k*,16M** 896 352 2,4,16,256 1024 768 16,256*,32k** 1056 250 16 1056 256 16,256 1152 896 2 1280 1024 4,16*,256** 1600 1200 16*,256**
* Requires 1 MB of VRAM
** Requires 2 MB of VRAM
With the addition of Video RAM (VRAM) to the Risc PC the base capabilities are a touch variable, thus the note next to some of entries. All other modes are available with standard DRAM, and these the only modes the A7000 can access. The A7000+, thanks to it's faster memory speeds, functions equivalently to a RiscPC with 1 Mb of VRAM even though it doesn't have any VRAM itself.
Furthermore the new VIDC20 has 256 palette registers, compared to the VIDC1a's 16, and a palette range of 16 million colours. Exactly how the colour mapping in 32,000 modes is handled is not yet clear. Again these are just standard screen modes provided, and even perhaps not all of them - the Risc PC is completely configurable in display resolutions and capabilities.
However each monitor type must have a mode definition file set up for it, to allow you to take advantage of this flexability. A library of common monitor definition files can be found at http://acorn.cybervillage.co.uk/monitors/
It must be stressed again that these are merely the resolutions and colour depths defined by the machines operating systems. In all of the machines cases there are both hardware and software extensions that alter and increase the list.