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Experiences with KVM switches

Posted 04-17-2015 at 11:16 AM by flshope

I have four computers at the moment sharing one keyboard, video, and mouse using a KVM switch ("KVM"= Keyboard Video Mouse). As my machine count has grown over the years, I have acquired new switches to accommodate additional machines and new port requirements (PS2 vs USB).

My current KVM switch is an IOGEAR GCS1724 4-port box-type. Of the five KVM switches I have used since 2003, my current IOGEAR GCS1724 is by far the one I would recommend (depending on machine requirements). The input and output connectors include both USB and PS2 as well as VGA. There are no other options for the monitor cable on this unit. The machine "focus" (in the user manual's terminology) can be switched with front panel buttons or hot keys. The default hot-key sequence is "Scroll Lock" "Scroll Lock" followed by a machine number (1-2-3-4) and then "Enter". Front panel lights indicate which machines are powered up and which one is selected. The switch includes four integral cables, each containing cables for keyboard, video, and mouse. Both the keyboard and mouse outputs include PS2 and USB connectors. These special cables connect to the KVM switch with a modified VGA connector, so it is necessary to use only the IOGEAR cables. The cables are four feet long. There is no software to install on the machines for using the KVM switching function; however, there is Windows-specific software to accomplish firmware upgrades, should that be necessary. This KVM has a unique feature that allows dumping the configuration settings to a text file.

One of the machines, an HP-2133 Mini-Note PC laptop running Ubuntu 14.04, is giving me some trouble during boot. The problem is that sometimes the machine will boot with a blank screen if the external monitor is connected. Fortunately, I still have keyboard control and can do a ctrl-alt-F1 to a shell for a graceful restart. Other times it will boot satisfactorily, but I get different results without any obvious changes from the previous boot. I had no such trouble under Ubuntu 12.04 with a previous IOGEAR KVM switch, but 14.04 changed the video driver. The boot problems began with 14.04 before I installed the current KVM switch. So far, the only repeatable boot procedure is to boot the machine without the external video connection and then to plug in the external video after the machine is up and running with its built-in monitor. When the external display is active, the built-in display is blank, and the mirror option in Ubuntu's system settings for the display is deactivated. I had no such limitation with 12.04. I am not sure this problem has anything to do with the KVM switch, but the switch certainly added additional variables to the initial conditions.

Before the GCS1724, I was using an IOGEAR GCS24U. This is a squid-like KVM switch. I say "squid-like" because it has a central body with the four cable sets coming out one side. Input cables go in the opposite side. I hung it on a wall to get the cable mess off my computer table. It operates only by manual switch, which is a little single-button box on a cable several feet long that lays nicely beside the console. The button box is about the size of a thumbnail. I purchased the GCS24U when I finally got tired of dealing with the ConnectGear's control hot key interference (see concerns list below). The GCS24U itself worked well enough, but I could never get the USB keyboard and mouse to work with my ancient (1996) Dell, which pre-dates USB connectors and has only PS2-type input. USB-to-PS2 adapters didn't work. The new GCS1724 works fine with the Dell.

Manufacturer user manuals are available on line for all of the KVM switches listed below. If you are considering your first switch, be aware that there are more choices than I have discussed here. I have seen 8-port switches, and there are switches that allow more modern video cables, such as DVI and HDMI.

Some concerns in selecting a KVM switch:

- Some KVM switches use hot keys (keyboard sequences) to accomplish the switching. Two of my retired ConnectGear switches (MG2 and MG4) in particular use the control key as a hot key (can also use buttons). This, of course, causes problems when the control key is used as part of a software shortcut (e.g., ctrl-c, ctrl-v, ...). I contacted ConnectGear about this. I was told there is no way to disable the hot key sequence and that I should use the software menus instead (yeah ... right ... thanks a lot ). This feature is not made clear in any literature or on-line product descriptions that I could find.
- Cable lengths for the ConnectGear KVMs are 6 feet, 4 feet for the IOGEAR KVMs.
- A KVM switch with USB connectors for the keyboard and mouse may not work with USB-to-PS2 adapters.
- Not all keyboards are compatible with a given KVM switch.
- Laptops may have quirks to deal with.


The machines I have on the IOGEAR GCS1724 KVM switch are the following:

Pogo2011: Pogo Linux Altura M3, AMD Athlon II X3, 1.3 Ghz, USB connectors, Ubuntu 14.04
Pogo2003: Pogo Linux Altura, AMD Athlon XP 1.3 Ghz, PS2 and USB connectors, Debian 7.7
Dell1996: Dell Dimension Pentium 133C/XPS 133 Mhz, PS2 connectors, Windows 95
HP2008: HP 2133 Mini-Note PC (laptop), VIA C7-M 1.2 Ghz, USB connectors, Ubuntu 14.04

My current shared peripherals are the following:

Keyboard: Logitech K120 wired
Video: Dell UltraSharp UZ2315H 23-in., VGA in use
Mouse: Logitech 3-button optical wired

KVM switches

Belkin F1DK102P 2-port squid-type, hot key only, PS2 connectors
Connect Gear MG2 2-port box-type, push-button and hot key, PS2 connectors
Connect Gear MG4 4-port box-type, push-button and hot key, PS2 connectors
IOGEAR GCS24U 4-port squid-type, push-button only, USB connectors
IOGEAR GCS1724 4-port box-type, push-button and hot key, PS2 and USB connectors

KVM switch summary chart (displays best in full-screen mode)

Manufacturer       Belkin       ConnectGear  ConnectGear  IOGEAR   IOGEAR
Model              F1DK102P     MG2          MG4          GCS24U   GCS1724
Type               Squid        Box          Box          Squid    Box
Ports              2            2            4            4        4 
Switching          Hot keys     Hot keys     Hot keys     Button   Hot keys
                                Buttons      Buttons               Buttons
Connectors in      PS2,VGA      PS2,VGA      PS2,VGA      USB,VGA  USB/PS2,VGA
Connectors out     PS2,VGA      PS2,VGA      PS2,VGA      USB,VGA  USB/PS2,VGA
Hot keys           Scroll-lock  Scroll-lock  Scroll-lock  --       Scroll-lock
                                Ctrl(1)      Ctrl(1)      --       Ctrl(2)
Software           None         None         None         None     upgrade only
Ext power supply   No           Yes          Yes          No       Optional
Cable length       6-ft         6-ft         6-ft         4-ft     4-ft
Cost (3)           $50          $43          $70          $48      $109
Purchase date      2003         2007         2011         2012     2015
(1) Cannot be disabled
(2) Disabled by default, key sequence to enable
(3) Not including shipping or tax
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