Hardware

According to the manual the second USB connector provides additional power for the
CD/DVD Writer. Please make sure to connect both USB connectors to your computer???s USB ports.

Mine works just fine with the longer cable only plugged in. A second (extra power) cable might be necessary with a 3.5 inch HDD, whose motor requires more current.

Hi
when running/powering (with out an external ac adapter) the CD drive (or any device) from the usb (usually 1.1 will need the second usb connection)
the usb will provide power. The usb y cable is to use one port for a data/power connection and one port solely for power with a bus powered USB drive. Many laptop USB ports are not "powered", they may provide insufficient voltage for the USB bus powered drive. This allows you to draw power from two ports and generally this will be enough for both.

when reading a disc the power draw isn't that much and it may function just fine on the single plug,

but if you go ahead and try to write a full CD or DVD
you'll find that the extra power connector is required
writing requires anywhere from 1/3 to 2x more power than reading does
and the burn will likely fail to complete if the secondary power plug is not used

.

It's all 5Volts,just double the current. The standard limit is 500 mA per USB port, while some old hard drives need more juice than that.

Note that hardware damage can result if you plug a high-current device into a standard port. While USB is supposed to detect over-current, and not supply power, I've seen some USB adapters make an acrid burning smell followed by them no longer working.

In my opinion, more people need to understand the basics of electricity, such that connecting two 5V 500 mA USB connectors in parallel does not give you 10 volts, it gives you 5 volts at 1 Amp (5 watts).

In theory a 12 volt power supply could supply the same amount of power (5Watts), but the higher voltage would most likely burn out the interface and destroy any attached peripheral.

The second USB Plug is often only a Power Plug it has no Data Connections inside it.

if you look at the actual Cable you'll see that the Second USB Plug has a thiner cable it only has the leads for the extra Power.

So if you where to plug in that plug the drive would spin up but not actually appear on the Monitor.

Also if you look at the specs of your computer you may very well find that it doesn't actually provide 500 Milliamperes at the USB Sockets. Modern NB's have reduced the Available Current at the USB Ports to prolong Battery Life. So while it may not apply to your current computer it could very well apply to any other computer that you plug the drive into. Of course if you where to use a Powered USB Hub things would be different but even then I wouldn't be trusting what should be happening as what actually happens is quite often different.

Col

http://en.wikipedia.org/wiki/USB#Power

Many responses have partial right answers. One thing to keep in mind about USB power, is that there is a process between the requesting (device) and supply (host) side of things. Therefore and high current device will not draw more than can be supplied and conversly the device will know if not enough power can be supplied. That is supposed to keep both devices safe.

Now for that second connector, and other devices that may cause problems:
http://en.wikipedia.org/wiki/USB#Non-standard_devices

If you want something more confusing, check out Power Over Ethernet.