Bill Cunningham wrote:
I have two cord with an external DVD/RW I bought some time back. There's
two cords the one I use with USB 2 on my tower to the DVD/RW and looks like
data but it's power too.

This second one IDK what it's for. I goes to the "power" interface on
the DVD/RW. I guess I don't need it. But idk what would. Is it to get your
DVD/RW to move faster or something?

Bill



Is it like this ?

A USB cable with two headers ?

VCC ---------+
X----- |
X----- |
GND ---+ |
__________| |
| |
| VCC ---------+---------- 5V 1A max
| D+ -------------------- USB2 data
| D- --------------------
| GND ---+---------------- GND
} |
+----------+

It's a way to extract more current flow
for the +5V VCC supply to the drive.

In that diagram, two 5V 500mA connectors work
together, to make a 5V 1000mA powering source. The
connectors should not go into the same USB stack,
and should be staggered on different stacks (to
avoid the Polyfuse opening).

*******

Some drives have a barrel connector for
powering with an external adapter. Which
is another way to do it. The external adapter
then provides the 5V the "slim" drive is using.

On full sized 5.25" drives, the adapter is 12V
or 12V/5V with four pins. And the adapter has
no trouble running those (only a BluRay might
be a bit much for your average hard drive adapter).
I don't think you're referring to one of those
older full height motorized tray ones.

*******

If the drive was "USB3", then the higher current
rating of the USB3 plug may mean just one
connector is needed.

The DVD drive spins at a controlled speed, so no,
it doesn't go faster if the voltage is increased
or anything. It's strictly regulated with a
three phase motor (with low torque ripple) and
the laser actually tracks a spiral path, like the
DVD was a long play vinyl recording.

The drive has three spinning states it can be in:

1) No data errors. The rotational speed cannot speed
up indefinitely. Presumably the media tag is used
to decide what a good max speed is. DVDs rotate slower
than CDs, in practical usage. Since good media is hard
to find, you might get up to around 7MB/sec or so.

2) Seeing too many errors. In this state, the motor may
be set to a lower rotational speed, in the belief that
this will give a better opportunity for data recovery.
Note that even without this, the three dimensional Reed
Soloman error recovery is very good, and uncorrected errors
hardly get through.

3) When the DVD really screws up, is when the laser cannot
track the groove. DVD+ and DVD- use a different encoding
for the groove. The laser uses that modulation (whatever it
is), to keep the laser head (which doesn't touch the disc),
right over top of the spiral path it has to follow. it
is the "loss of laser lock" which actually causes unreadable
media, and the motor running in fits and jerks. If the
laser could maintain lock as in (2), then Reed Solomon
does the rest.

HTH,
Paul