The signal path: five parts, two cables
On a GL.iNet Comet Pro, the target computer's HDMI output goes into the KVM's HD IN port. A USB cable runs from the KVM's USB Type-C port to the target's USB port [1], and the console's keyboard, mouse and virtual-media features reach the target over that link [2]. The KVM joins your network by Ethernet or by 2.4 GHz or 5 GHz Wi-Fi [1]. PiKVM V4 has the same layout: an HDMI video input, a USB 2.0 OTG connector to the computer, and a separate RJ45 port for its optional ATX board [8].
| Part | Cable to target | What the target thinks it has | What you get remotely |
|---|---|---|---|
| Video capture | HDMI from target to KVM [1] | A monitor, described by the KVM's EDID [2] | A live video stream in your browser [2][10] |
| Keyboard and mouse emulation | USB from KVM to target [1] | A USB keyboard and mouse [2][6] | Typing and clicking, including in BIOS |
| Mass-storage emulation | Same USB cable [2] | A USB drive or CD/DVD [2][5] | Boot an installer or copy files |
| Power control | Separate ATX board to the front-panel header [4] | Someone pressing the case's power button [4] | Power on, forced off, restart [2] |
| Network | None; the KVM has its own Ethernet or Wi-Fi [1] | Nothing | Access that does not depend on the target's OS |
Why it reaches the BIOS, and when it does not
Remote-desktop software runs inside the operating system. A KVM over IP sits outside it, on the cables, so it can show the power-on screen, the BIOS setup and an OS installer. That is the main reason to own one.
There are documented exceptions. GL.iNet explains that the BIOS usually outputs only to the primary monitor. On a laptop, the built-in screen is primary, so an external KVM cannot capture the BIOS. On desktops, most graphics cards and motherboards favor DisplayPort over HDMI at startup [3]. Its fixes are to connect the KVM to the primary output, or to duplicate that output with a 1-to-2 HDMI splitter [3]. PiKVM adds that some BIOSes do not support absolute mouse mode [7]. It also says mass storage may not be available in some motherboards' BIOS, and that there should be no USB hub between the KVM and the computer [8].
Video: capture, EDID and streaming
EDID is the data a monitor sends to describe the resolutions it supports. The KVM supplies its own EDID so the target picks a mode it can capture. GL.iNet says its default EDID suits most setups and generally does not need changing, and says to restart the target if the screen does not refresh after a change [2]. PiKVM's FAQ says that when video shows in the OS but not in the BIOS on some devices with its CSI bridge, the fix is changing the EDID [7].
Capture hardware sets a ceiling. PiKVM says its HDMI-CSI bridge lacks the bus bandwidth for more than 1080p50, and that 4K real-time video would not fit through the network anyway [7]. The captured picture is then compressed and streamed. The modes differ by vendor.
| Vendor | Stream modes | Documented trade-off |
|---|---|---|
| GL.iNet Comet Pro | WebRTC, WebRTC (FEC), WebRTC (Native), Direct [2] | Direct: lowest latency and lossless quality, but no audio [2] |
| PiKVM | WebRTC H.264 (default), Direct H.264 (experimental), legacy MJPEG [10] | MJPEG uses a huge amount of traffic; Direct is very stable on poor networks [10] |
Keyboard and mouse: emulated USB devices
To the target, the KVM's USB port looks like an ordinary keyboard and mouse. The mouse can run in two ways, and picking the wrong one is the most common reason a BIOS session feels broken. PiKVM's USB OTG port is USB 2.0, which its FAQ gives as limited to 455 Mbit/s [7].
- GL.iNet's Bad Link Mode sends each key as a quick press-and-release, to avoid stuck or repeated keys on a poor connection [2].
- GL.iNet also offers a virtual keyboard and a Swap Command and Ctrl option for macOS targets [2].
- On PiKVM V4, dual mouse mode (switching between absolute and relative without reloading) is on by default [6].
| Mouse mode | What is sent | Best for |
|---|---|---|
| Absolute | Exact screen coordinates (X,Y) [6] | Everyday use in a modern OS; GL.iNet notes some network delay may occur [2] |
| Relative | Movement offsets (dX,dY); cursor locked to the remote window [6][2] | BIOS, older systems and embedded devices [2]; not supported in mobile browsers on PiKVM [6] |
Virtual media: a USB drive that lives on the KVM
Mass-storage emulation lets the KVM present a file as a drive. GL.iNet offers two forms: File Sharing, a read-write USB drive named GLKVM, and Image Mounting, a read-only CD/DVD for BIOS/UEFI use that needs an ISO-mountable file [2]. Its OS-install tutorial has you upload the ISO, mount it, enter the BIOS and set Glinet Flash Drive 1.00 as the first boot option [11].
PiKVM can emulate a CD/DVD or a flash drive. The media type is set when the image is connected, and images are stored on a memory-card partition [5]. Images can also come from HTTP(S), SMB, SFTP, NFS or NBD sources so they do not use card space [5]. Two warnings from its docs: never cut power while an image is uploading, and each emulated USB device uses limited endpoints, so only one or two extra USB devices fit by default [5].
Power control: the part that needs extra hardware
Video and USB cannot press a power button. GL.iNet's GL-ATXPC board sits between the case's front-panel wires and the motherboard's F_PANEL header and simulates the physical power button. Wiring examples cover 10-1, 20-5 and 20-8 pin headers, and polarity varies by case [4]. It has no HDD LED. One board works with Comet, Comet PoE, Comet Pro and Comet 5G, up to four work with Comet X, and Comet Q is not supported [4]. Comet Pro's console offers short press, long press for forced shutdown, and restart [2].
PiKVM's ATX board page states that Apple Macs lack the needed ATX headers and that the board is only for PC servers and desktops [12]. For other machines, GL.iNet lists Wake-on-LAN and its Fingerbot, a small device that physically presses a button, as alternatives [9].
Questions before you decide
Why can a KVM see the BIOS when remote desktop cannot?
Remote-desktop software runs inside the operating system, so it is not there before the OS boots. A KVM sits on the HDMI and USB cables, so the target just sees a display and a keyboard. GL.iNet notes one limit: the BIOS usually outputs only to the primary display, so the KVM must be on that output.
Why does the mouse not move in the BIOS?
PiKVM's FAQ says some BIOSes do not support absolute mouse mode, which PiKVM prefers, and suggests relative or dual mode. GL.iNet's console guide likewise recommends Relative mode for BIOS, older systems and embedded devices.
Can a KVM over IP turn the computer on?
Only with extra hardware or Wake-on-LAN. GL.iNet's ATX board connects to the motherboard's front-panel header and simulates the power button; Comet Q does not support it. PiKVM's ATX board page says Macs lack the needed ATX headers and the board is only for PC servers and desktops.
Does virtual media work as a boot drive?
Usually. GL.iNet's image mounting presents an ISO as a read-only CD/DVD for BIOS/UEFI use. PiKVM notes that mass storage may be unavailable in some BIOSes, and that a few buggy BIOSes dislike keyboard, mouse and storage sharing one USB device.
Sources & verification
Product details and prices can change. Check the linked provider before buying.
- GL.iNet KVM Docs: Comet Pro (GL-RM10) quick setup guide Accessed 30 Oct 2026
- GL.iNet KVM Docs: Comet Pro (GL-RM10) console guide Accessed 30 Oct 2026
- GL.iNet KVM Docs: Remote screen does not show the BIOS interface Accessed 30 Oct 2026
- GL.iNet KVM Docs: GL-ATXPC ATX board Accessed 30 Oct 2026
- PiKVM Handbook: Mass Storage Drive Accessed 30 Oct 2026
- PiKVM Handbook: Mouse Accessed 30 Oct 2026
- PiKVM Handbook: FAQ Accessed 30 Oct 2026
- PiKVM Handbook: PiKVM V4 Accessed 30 Oct 2026
- GL.iNet KVM Docs: Quick FAQs about GL.iNet KVM Accessed 30 Oct 2026
- PiKVM Handbook: Video modes Accessed 30 Oct 2026
- GL.iNet KVM Docs: How to install an OS remotely Accessed 30 Oct 2026
- PiKVM Handbook: ATX board Accessed 30 Oct 2026
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