Re: Two computers in one: two users each with their own accounts, monitor, and keyboard?

[Stan Hoeppner <stan@hardwarefreak.com>]

Albretch Mueller put forth on 1/12/2010 12:06 PM:

>  In a friendly and technically honest way, what the f#ck are you
> taking about? I would like to understand you because I am not
> primarily a hardware guy. Why would you need "CAT5 to support USB"?

From:  http://www.usb.org/developers/usbfaq/#cab1

The USB cable length limit is 5 meters, or 16.4 ft.  To go 100 ft with USB
requires a USB balun.  Read about baluns:  http://en.wikipedia.org/wiki/Balun

Cables and Long-Haul Solutions

1.   Why are there cable length limits, and what are they?

A:   The cable length was limited by a cable delay spec of 26ns to allow for
reflections to settle at the transmitter before the next bit was sent. Since USB
uses source termination and voltage-mode drivers, this has to be the case,
otherwise reflections can pile up and blow the driver. This does not mean the
line voltage has fully settled by the end of the bit; with worst-case
undertermination. However, there's been enough damping by the end of the bit
that the reflection amplitude has been reduced to manageable levels. The low
speed cable length was limited to 18ns to keep transmission line effects from
impacting low speed signals.

From:  http://en.wikipedia.org/wiki/Universal_Serial_Bus

USB 1.1 maximum cable length is 3 metres (9.8 ft) and USB 2.0 maximum cable
length is 5 metres (16 ft).[27] Maximum permitted hubs connected in series is 5.
Although a single cable is limited to 5 metres, the USB 2.0 specification
permits up to five USB hubs in a long chain of cables and hubs. This allows for
a maximum distance of 30 metres (98 ft) between host and device, using six
cables 5 metres (16 ft) long and five hubs. In actual use, since some USB
devices have built-in cables for connecting to the hub, the maximum achievable
distance is 25 metres (82 ft) + the length of the device's cable. For longer
lengths, USB extenders that use CAT5 cable can increase the distance between USB
devices up to 50 metres (160 ft).


I'll let you research the video signal quality problems of long VGA DB15 or DVI
cable runs on your own.  I will say now that the electrical signal drive
circuitry on almost all VGA cards is not designed to drive into a load over 50+
ft cables.  Sure, ultra expensive cables can maybe get you to 100 ft without
significant image quality loss (but again the cables cost as much as a PC), but
to go beyond 100 ft you really need a balun, especially if you're trying to run
high resolutions and refresh rates.

Apparently you've only looked at my email display name up to this point, not the
domain I'm sending from.  ;)

You've not actually tried to do what you talk about here or you'd have already
run into the 100 problems you'll have making this work, just on the hardware
side of it alone.  I've been there and done that WRT to console extension.  It's
a niche market and the products that actually make it work worth a damn are
*not* cheap.  On some installations I've done, the hardware, cabling, and labor
cost was 10x what a PC and CAT5 would have cost, but the customer had to have it
that way for security reasons.

I'm telling you from experience, doing remote consoles *correctly* is expensive,
and you're talking about far more capability than we were doing with adding USB
and sound capability.

-- 
Stan