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Q about KVM



 
 
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  #1  
Old November 5th 18, 03:59 PM posted to alt.comp.hardware
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Posts: 42
Default Q about KVM

I am looking at KVMs on EBAY - will choose DVI this time. I notice
the pics show only one USB to support mouse and keyboard. How do they
get away with that? My mouse and keyboard each has its own USB
connector. and right now needed two ports on my defunct IOGEAR VGA KVM
is why I ask.
Thanks
Al
  #3  
Old November 5th 18, 09:02 PM posted to alt.comp.hardware
VanguardLH[_2_]
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Posts: 1,286
Default Q about KVM

Turing wrote:

I am looking at KVMs on EBAY - will choose DVI this time. I notice
the pics show only one USB to support mouse and keyboard. How do they
get away with that?


Multiple devices can connect to the same USB port. That is how, for
example, passive USB hubs work: many ports to one port. The USB port
can only support a fixed amount of power, so how many USB devices you
can connect to the port depends on whether they are low- or high-power
USB devices. Keyboards and mice are low-power USB devices. A single
USB controller can manage up to 127 devices (7 bit address = 2^7
addresses = 128 addresses, but the host controller gets one). To get
that many chained together means having to use powered USB hubs (they
have their own source of power, like an A/C adapter). A hub itself
counts as a device. While I've seen 10-, 20-, and 30-port powered USB
hubs that you could chain together (four 30-port hub + one address for
each hub = 124 addresses) at newegg.com which get pretty pricey, I
didn't bother hunting around for one with 126 ports (126 ports + 1 for
itself for the 127-port maximum). I did happen to find the following:

97-port USB hub
https://www.youtube.com/watch?v=4OS6L80Fe3Q
16 7-port powered USB hubs = 112 ports minus 16 ports to chain them
together = 96 ports, so I don't know how they get a count of 97 unless
they're counting the downstream port+cable to the computer. Whether
such a frankenjob works on your computer depends on its USB host
controller's capabilities. As the video show, plug-n-play detects takes
a long time to discover all those ports.

Remember those old movies showing a telephone switchboard manned by many
telephone operators? Large-numbered USB ports chained together would
make the same mess. You'd probably want Bluetooth or wi-fi devices
instead of the cost of such a hugh-ported USB hub and all those USB
cables and the space for it all.

You didn't give a URL to the KVM with just one USB port for both
keyboard and mouse. Perhaps in its description is listed a Y-adapter
cable: 2 USB ports to 1 USB port. Those have been around a long time.
I remember using one for an external USB HDD that needed to use 2 ports
because the drive needed more power than one port could deliver. In
that case, I was using 2 USB ports for 1 device. In your case, the
Y-adapter would go the other way: 2 devices to 1 port. Maybe the KVM
comes with a passive or powered hub that lets you connect more than 2
input USB devices to the KVM. We don't know because you didn't show us
(by giving a URL). Tough to explain something that is vague.
  #4  
Old November 5th 18, 09:10 PM posted to alt.comp.hardware
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Default Q about KVM

On Mon, 5 Nov 2018 11:43:46 -0500, John McGaw wrote:

On 11/5/2018 9:59 AM, wrote:
I am looking at KVMs on EBAY - will choose DVI this time. I notice
the pics show only one USB to support mouse and keyboard. How do they
get away with that? My mouse and keyboard each has its own USB
connector. and right now needed two ports on my defunct IOGEAR VGA KVM
is why I ask.
Thanks
Al

Which one are you looking at, specifically? Mine has a single USB on the
front and two on the back for keyboard and mouse

There are many. One is:
https://www.ebay.com/itm/KVM-Cable-f...0~:rk:197:pf:0
I guess I am confused.
You see my present, now defunct, KVM is VGA, and the VGA cables
connecting each PC to the KVM connect the mouse and keyboard
capability with USB attachments on said cables to both (plus sound
cables). And of course, the mouse and keyboard themselves connect to
the KVM too. That's how the mouse and keyboard reach each PC. So far
I do not see that on the DVI models. I think I see (on the DVI) just
one cable, printer on one end, USB on the other. Also sound cables
tho. So I have no idea how the mouse and keyboard each reach the PCs
via a DVI KVM. Unless it is thru the DVI itself?
Thanks for your response.
Al

  #5  
Old November 5th 18, 09:46 PM posted to alt.comp.hardware
VanguardLH[_2_]
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Posts: 1,286
Default Q about KVM

wrote:

On Mon, 5 Nov 2018 11:43:46 -0500, John McGaw wrote:

On 11/5/2018 9:59 AM,
wrote:
I am looking at KVMs on EBAY - will choose DVI this time. I notice
the pics show only one USB to support mouse and keyboard. How do they
get away with that? My mouse and keyboard each has its own USB
connector. and right now needed two ports on my defunct IOGEAR VGA KVM
is why I ask.
Thanks
Al

Which one are you looking at, specifically? Mine has a single USB on the
front and two on the back for keyboard and mouse

There are many. One is:
https://www.ebay.com/itm/KVM-Cable-f...0~:rk:197:pf:0
I guess I am confused.
You see my present, now defunct, KVM is VGA, and the VGA cables
connecting each PC to the KVM connect the mouse and keyboard
capability with USB attachments on said cables to both (plus sound
cables). And of course, the mouse and keyboard themselves connect to
the KVM too. That's how the mouse and keyboard reach each PC. So far
I do not see that on the DVI models. I think I see (on the DVI) just
one cable, printer on one end, USB on the other. Also sound cables
tho. So I have no idea how the mouse and keyboard each reach the PCs
via a DVI KVM. Unless it is thru the DVI itself?
Thanks for your response.
Al


Cables aren't a KVM. With cables, YOU will have to do the switching
between input devices (keyboard and mouse) and the computers. I thought
you wanted a KVM.

From what I can tell in the eBay auction, that is just the cable that
goes between the computer and the KVM as just one host on the KVM. You
need the same cable for each host. If the KVM has 5 hosts it can switch
between and you have 5 hosts for the KVM, you will need 5 sets of those
cables.

As mentioned in my other reply, multiple USB devices can go to one USB
port. Just because you've been physically connecting the keyboard to
one USB port and the mouse to another USB port on a computer (to use up
2 USB ports) doesn't mean it must be that way. You could hook up both
the keyboard and mouse to one USB port on your computer. I suspect the
cables you pointed at has the KVM with 2 USB ports on the front or
separately on the back for the keyboard and mouse (2 USB ports for 2
input USB devices) but hubs those 2 input devices to 1 USB port to the
computer.

There is no need to use up more USB ports on the computer than just one
for both the keyboard and mouse. Physically each device has its own
cable but that doesn't mandate you must use the same number of USB ports
at the computer. You don't even need a KVM to share multiple USB
devices to one USB computer port. A passive or powered USB hub could
run both your keyboard, mouse, tablet, trackball, flash drive, USB HDD,
and lots of USB devices to just 1 USB port on the computer. A KVM can
have its own USB hub to do the same. There's no need to run N USB
cables from the KVM to the computer for N USB devices connected to the
KVM. You can connect N USB devices (however many the KVM allows)
through a hub to *one* USB cable to *one* USB port on the computer.
There is no restriction of just 1 device per USB host controller (the
USB port in your computer).

You pointed at "KVM cables for blah blah blah". Show us the *KVM* in
which you are interested, not cables that might be used with it.
  #6  
Old November 5th 18, 10:22 PM posted to alt.comp.hardware
John McGaw
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Posts: 666
Default Q about KVM

On 11/5/2018 9:59 AM, wrote:
I am looking at KVMs on EBAY - will choose DVI this time. I notice
the pics show only one USB to support mouse and keyboard. How do they
get away with that? My mouse and keyboard each has its own USB
connector. and right now needed two ports on my defunct IOGEAR VGA KVM
is why I ask.
Thanks
Al


If you look up a picture of the back of "IOGEAR 4-Port DVI KVMP Switch with
Cables, TAA Compliant, GCS1104" (the one that I have and which is
definitely no an economy buy) you will see that there is a pair of USB
"type A" ports designated "console" which go to the keyboard and mouse. The
hydra cables that go to each computer have only a single "Type B" that
serves to connect the keyboard, mouse, and whatever is connected to the
auxiliary USB device and it does this via an internal USB hub function. Of
course there are also the audio and DVI connectors but I don't think those
are part of the question unless one is seeking "double link" DVI rather
than the more common "single". So far as I know the hydra cables are pretty
much standard items, at least so far as IOGEAR is concerned. The cable
description can be found by searching out "IOGEAR Single Link DVI-D USB KVM
Cable, 6 Feet, G2L7D02U". One end of this cable has a "type A" connector
which plugs into the computer and a "type B" connector which plugs into the
KVM.

Hope that clarifies rather than confuses the situation.
 




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