VirtualAcorn Technical support:
Screen resolutions above 1920 x 1080 - StrongARM VirtualRPC Only

The maximum resolution that a VirtualRPC can normally display is full HD (1920 x 1080). The worldwide adoption of 'HD' resolution monitor panels means that they are made in vast numbers and as a result are cheap. However there are larger resolution monitors in use. Lets suppose that one needed to edit full HD video on a computer. A full HD (1920 x 1080) monitor could display the video, but not the video and an editing environment without having to scale the video resolution down.

So, in order to edit HD video a new resolution was required, one that was greater than 'Full HD'. This new resolution is 2560 x 1440. As more people edit 'Full HD video' the more customers there are for this resolution monitor and so the prices have fallen. In 2014 you could purchase an excellent 2560 x 1440 monitor for less than Acorn charged for a bad 14" screen 20 years ago. Technology really has moved on.

If you are running a StrongARM VirtualRPC you have the choice of three processor models, the ARM710, StrongARM and ARM7500. They might all look like they behave the same, but they don't. The ARM710 and StrongARM models have an 8MB VRAM (Video RAM) limitation which is 4 times the size of VRAM on a real RiscPC and can handle full HD at 16 million colours.

The ARM7500 model on the other hand doesn't have any dedicated VRAM, instead video memory is taken from main memory up to a practical limit of 16MB.

RISC OS is a very screen centric system, everything hangs on the refresh of the screen. On a 'real' Acorn computer you could see the system slow down as the screen resolution increased, because the CPU did most of the work and the more processing the screen needs the less processing is left over for other tasks. The 2MB of VRAM on a RiscPC may have been restrictive, but even a screen mode that took up 1.8 MB placed a very heavy load on the CPU.

The same is true when RISC OS is running inside a VirtualRPC, bigger screen modes mean more work for the processor. However a modern PC has much more power and it's now possible to push resolutions far beyond what a 'real' Acorn machine could have even dreamed of.

So, if you have a powerful PC (Intel Corei5 or better) and a StrongARM RiscPC you can push past the 8MB VRAM limit and up to 2560 x 1440. As long as your monitor supports it. Reproduced below is the MDF (Monitor Definition File) that you will need for this super size resolution. You will need to copy and paste the definition, as plain text, into your 'monitors' file inside the !Boot sequence. This can normally be found at:

   !Boot.Resources.Configure.Monitors.VirtualAcorn

The super size MDF is:

   # For display in the Windows desktop
   # 2560 x 1440 (51hz)
   startmode
   mode_name:2560x1440
   x_res:2560
   y_res:1440
   pixel_rate:192600
   h_timings:10,10,16,2560,0,0
   v_timings:10,0,0,1440,0,0
   sync_pol:0
   endmode

We would like to thank T.O.M.S. for their work testing and refining RISC OS screen resolutions. Without their support this article would not have been possible.

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 Copyright (c) 2017 3QD Developments Ltd. All rights reserved. All trademarks are acknowledged. All details are correct at the time of publication, E & OE.
Last Edit Date 01/11/17
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