ATEN CS1642A

Computers: 2, each with two displays

Video: dual-link DVI-I

Max resolution: 2560x1600 at 60Hz; 1920x1200 at 120Hz for 3D displays

Port selection: hotkey, pushbutton, mouse

Console: 2x DVI-I, 2x USB Type-A, mic and speaker jacks

USB hub: 2x Type-A (1 front, 1 rear)

Daisy chain: 1x RJ-45 to link a second CS1642A or CS1644A

Audio: 3.5mm mic and speakers, switched independently

Power: 5.3V DC, 3.77W

Size: 26.23 x 7.68 x 4.40cm, 0.56kg, plastic and metal

ATEN lists the switch, two KVM cables (dual-link DVI-D, USB and audio, 1.8m), two dual-link DVI-D cables (1.8m), a power adapter and instructions.

That covers every computer-side connection. Monitor cables are not listed, so bring two dual-link DVI cables for your screens if they are not already attached.

A small box, 26.23 x 7.68 x 4.40cm and 0.56kg, in plastic and metal. It draws 3.77W.

The front panel has three pushbuttons and separate LEDs for KVM, audio and USB link on each port. That matters here, because the three can point at different computers. The lights tell you at a glance where your keyboard, speakers and USB devices currently are.

One hub port is on the front, one on the rear. Put a flash drive on the front and a printer on the back.

ATEN quotes 2560x1600 at 60Hz over DVI. That number only works because the CS1642A is dual-link.

One DVI link tops out at a 165 MHz pixel clock. 1920x1200 at 60Hz with reduced blanking needs 154 MHz, so it fits on one link. 2560x1600 at 60Hz needs 268.5 MHz. That is beyond one link and inside the 330 MHz two links provide.

The 3D figure works the same way. 1920x1200 at 120Hz needs about 317 MHz, again dual-link territory.

The catch: every cable in the chain must be dual-link. One single-link cable and you drop to 1920x1200.

Your new PC probably has no DVI port. Most current graphics cards ship with DisplayPort and HDMI only.

Passive DisplayPort to DVI adapters carry single-link signals, which caps you at 1920x1200. Getting 2560x1600 from a DisplayPort card needs an active dual-link adapter for each output, four of them for two dual-monitor PCs.

If your machines and monitors are already DVI, none of this matters and the CS1642A is a tidy fit. If they are not, buy a DisplayPort switch.

ATEN lets you switch keyboard and mouse, USB and audio focus independently. Leave the speakers on one machine while typing on the other.

Power-on detection moves to the next powered computer automatically if one is switched off.

ATEN's Video DynaSync is meant to stop boot-up display problems. ATEN does not say whether the idle PC keeps seeing your monitors, so set Windows 11 to remember window positions: Settings, System, Display, Multiple displays, tick "Remember window locations based on monitor connection".

ATEN CS1944: two computers, two monitors, DisplayPort at 4K60. Winner for any PC built in the last few years.

ATEN CS1644A: the same dual-link DVI design with four computer ports. Winner if a third machine is likely.

Rose MEM-2U2V: 2-port dual-head DVI or VGA over CATx, 1920x1200 per head, up to 500ft extension per our catalog. Winner if the computers live in another room.

Adder AV4PRO-DVI-DUAL: 4-port dual-head DVI at 2560x1600 with mouse switching and an optional remote. Winner for buyers who want four ports from Adder.