Windows 10 | Multiple Monitor 4k | Full Screen

[TugBoat_SunK]

Here is the problem: With "full screen mode" on more than the first three monitors, one at 1920x1080, one at 2560x1600 (2k) and the third at 4096x2160 (4k), a Windows 10 guest cannot display full resolution on all of them (See picture below entitled "five_monitors_with_black_edges.jpg").

Example of the reduced resolution

five_monitors_with_black_edges.jpg (38.83 KiB) Viewed 2112 times

Here is the kicker: it has worked for years on a Windows 7 guest.

Six Monitors, one 2k and one 4k

Six_monitor_setup_five_portrait.jpg (101.27 KiB) Viewed 2112 times

I have a six monitor system with four 1920x1080px (3,5,6,4 in the screenshot above), one 2k (#2) and one 4k monitor (#1), driven by three graphics cards on a Windows 10 host running the latest version of Virtual Box (v5.1.18). When I enable five of the monitors including the 2K and 4K inside a Windows 7 Guest, it works gloriously with full resolution on all five screens. Windows 7 also reports the correct amount of VRAM at 256 MB.

When I upgraded the same Windows 7 image to Windows 10, it can handle a maximum of three monitors at full resolution, one 1080p, the 2k and 4k (and reports 1638MB of VRAM?). For every extra monitor added, it reduces the resolution on the 4k monitor, until five monitors and Windows 10 starts to reduce the resolution on the other monitors as well. If I revert back to three monitors in the Windows 10 guest, they all immediately go back to full resolution when the view is in "Full-screen Mode". Of note, the extra monitors can be added by Virtual Box but not enabled in Windows 10, and it still exhibits the same behaviour, reduced resolution on the other monitors. Also of note, the Windows 10 Host has no problem handling the six monitors, so the limiting factor is because of some interplay between VirtualBox and Windows 10.

Here is what I think the problem is : Windows 10 needs more than 256MB of VRAM to render more than 14 million pixels (1920x1080+2560x1600+4096x2160) where as Windows 7 did not.

Here is what I have tried with no luck:

• * Yes, guest extensions are installed and at the latest version (v5.1.18)
  * Video RAM is at 256Mb (And tried hard coding >256MB but that only crashes the VM)
  * Even when I bump up the monitor count to 5, there is just a little sliver of green left on the VRAM bar (However, I don't think they are counting a 2k and 4k resolution).
  * "Auto-resize Guest Display" is checked
  * Used vboxmanage to
  • * force a CustomVideoMode1
    * change the maxresolution
    * change the guest resolution hint.
  * Used 3D Acceleration - should it not be using VRAM from the graphics card? It doesn't make any difference and I am guessing it only works for 3D rendering.
  * Turned off 2D Acceleration
  * Read all the forum postings about multiple monitors
  * Read all the google searches I could find on Windows 10, multiple monitors and Virtual Box
  * I googled for a registry edit I could do on Windows 10 that might revert it's graphic engine back to Windows 7 or increase some video handler limit

I ran VMware for five years and have been on VirtualBox for at least as long and would consider myself an advanced user. I upgraded Windows 7 to 10 almost a year ago and immediately ran in to the problem but waited to see if future revisions of Virtual Box fixed the problem. I decided to take another crack at it this weekend and have gotten no where.

I suspect the answer is some kind of Windows 10 resolution limit due to the 256 MB of VRAM, which has probably already been noted in a bug report somewhere. I thought someone else might have run into a similar problem and gotten farther then I have in figuring out a work around.

[TugBoat_SunK]

In the off chance someone else had the same unique set of circumstances I did, here is an update:

It fixed itself.

A couple days ago, I replaced the four monitors on the left (#'s 3,4,5,6) in the screen shot above from the previous post with a single 55" 4K Vizio (4:4:4 chromake0y baby!). The end result is that Windows 10 guests now stretch properly across all the monitors.

Two 4K Monitors and one 2k monitor running Virtualbox

IMG_6935.jpg (96.3 KiB) Viewed 1529 times

The strange thing is that the number of pixels did not change. The four portrait monitors were at 1920x1080 pixels and with four of them, that meant (1920 H x (1080 x 4)W) which equals 8,294,400 pixels. My new 4K monitor runs at 3840x2160 or 8,294,400 which is exactly the same number of pixels.

The Virtualbox guest display restriction as related to Windows 10 must have something to do with the number of monitors and not specifically with the video memory.

Yah, I can finally move into Windows 10!