If your desktop icons rearrange, your windows move to the wrong screen, or your monitor blanks for two seconds every time you flip your KVM switch, you do not have a bandwidth problem or a cable problem. You have an EDID problem.
It is the single most common complaint about KVM switches, and it is almost never described in those terms on the product listing.
What EDID Is
EDID stands for Extended Display Identification Data. It is a small block of data, 128 or 256 bytes, that every monitor stores and hands to whatever it is plugged into.
It contains the manufacturer and model, the native resolution, every supported resolution and refresh rate combination, colour characteristics, and the physical screen dimensions. Your PC reads it the moment a display connects, picks the best mode both ends agree on, and builds your desktop layout from it.
Nothing about this is optional. Without an EDID, the operating system does not know a display exists.
What Goes Wrong With a KVM Switch
A basic switch physically routes the video signal. When you switch to PC B, the video path from PC A is broken, and with it the connection to the EDID of the monitor.
From the point of view of PC A the monitor was unplugged. Windows responds exactly as it would if you had pulled the cable: it removes the display, collapses your desktop onto whatever is left, and moves every window that lived there. On a single monitor setup it falls back to a default like 1024x768.
Switch back, and the EDID appears again. Windows re-detects a monitor, renegotiates the mode, and restores the resolution but not your window positions. That is the two-second black screen and the shuffled desktop.
What Emulation Does
A switch with EDID emulation keeps a stored copy of the monitor descriptor and presents it continuously to every connected PC, whether or not that PC is the one currently displayed.
Both machines believe the monitor has never been disconnected. Nothing is re-detected, nothing renegotiates, no windows move. Switching becomes instant because there is no handshake to perform.
That is the entire feature, and it is the difference between a switch that feels like part of your desk and one that annoys you daily.
The Three Grades of Emulation
Not all emulation is equal, and listings rarely distinguish these.
| Grade | What it does | Problem |
|---|---|---|
| None | Passes the real EDID through only to the active port | Full disconnect behaviour on every switch |
| Fixed | Presents a generic built-in descriptor to all ports | May not advertise your native mode or top refresh rate |
| Learned | Reads your actual monitor once and replays that exact descriptor | The one you want |
Fixed emulation is the trap. It solves the disconnect problem and creates a new one, because the generic descriptor often tops out at 1080p 60Hz or omits your high refresh modes entirely. You stop losing your windows and start losing your refresh rate.
On a dual-head switch, check that emulation is per port and per head. One shared descriptor across two different monitors describes at least one of them wrongly.
Spec Block: How to Spot It on a Listing
- The words EDID emulation, EDID retention or EDID learning, stated explicitly
- Learned or copy EDID rather than built-in EDID
- A description of switching as instant or seamless, which usually implies emulation
- Per port and per head on multi-monitor models
- HDCP handling stated separately, since HDCP renegotiation causes similar symptoms on protected content
- A firmware or DIP switch option to re-learn the EDID if you change monitors
Why It Also Affects Laptops and Docks
The same mechanism explains a behaviour that looks unrelated. A laptop docked with the lid closed relies on the external display existing. Switch a non-emulating KVM away from it and the laptop sees zero displays, which on many machines triggers a suspend.
It is the same root cause, and the same fix.
Winner
Buy learned, per-port EDID emulation and treat it as non-negotiable rather than a premium feature. It costs a little more than a passive switch and it is the single specification that determines whether you enjoy using the thing.
If a listing does not mention EDID at all, assume it has none.
Pros and Cons
Pros: Instant switching, no window rearrangement, no resolution renegotiation, and it fixes lid-closed laptop suspends as a side effect.
Cons: Fixed emulation can cap your resolution or refresh rate while appearing to work, learned emulation may need re-learning if you change monitors, and the feature is inconsistently named across brands so comparing listings is harder than it should be.
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