Mac Forum / General / Hardware / January 2007

DVI is just digital video, nothing else.  You can use this directly with
almost any digital lcd monitor, a few previous-generation Apple monitors
excepted, and via a DVI->VGA adapter with any modern analog monitor.  If
you have a really old analog Apple monitor you'll need a second adapter,
since these monitors aren't VGA.

The Apple digital monitors mentioned above that don't use DVI use ADC.
ADC includes the same digital video signal as well as power and usb.
These Apple monitors _require_ ADC, since they don't have their own
power supply.  They support usb as well, since they include a built-in
hub.  Afaik no one other than Apple ever made monitors that accept ADC.

There are DVI+power&usb -> ADC and ADC-power&usb -> DVI adapters
available as well.

I assume you are talking about the 15-pin connector with angled sides
and two rows of pins. The connector type is officially known as a
"DA-15". I don't know if it has an official name in its role as a Mac
monitor connector. It is used to connect an analog RGB monitor, and
adapters can be used to convert the connector to VGA (15 pins in three
rows), which works with a lot more monitors.

Probably a QuickSilver (or an earlier model).

ADC ("Apple Display Connector") is a superset of DVI ("Digital Video
Interface"), in that it contains all of the same signals, plus it
supplies USB and power (and Firewire?) to the monitor. ADC has round
sides, DVI has roughly square sides. As far as I know, only Apple made
monitors which used the ADC connector.

You can get adapters to convert between ADC and DVI. The one for
connecting a DVI monitor to an ADC connector is simple, but the one for
connecting an ADC monitor to a DVI computer requires connections to a
power supply, DVI port and USB port.

The ADC or DVI connector is usually used with a digital RGB monitor,
typically LCD. The connector on the computer also usually has analog
signals, so can be used with a VGA (or higher resolution) analog RGB
monitor via an adapter, and with some older Mac monitors via a pair of
adapters (DVI/ADC to VGA, then VGA to Mac monitor connector).

There are several standards for the DVI connector: DVI-D is digital
only, and DVI-I contains both digital and analog signals. The one on
video cards supplied by Apple has always been DVI-I. As far as I know,
ADC always has the analog signals on the computer. A monitor with a DVI
connector is more likely to omit support for analog, so you usually
can't connect one to a VGA port on a computer.

This would be the DB-15.

This signals coming off of this are VGA-compatible, but many Macs
require certain "sense pins" to be wired in the connector in order to
tell the computer what resolutions the monitor supports.

You can get adapters to convert this to a VGA connector.  The good
adapters have switches you can set (according to the instructions) for
setting the sense pins correctly.

An ADC port contains wiring for DVI, VGA, power, and USB.  You can get
an adapter to use it with a DVI or VGA monitor if you can't find an ADC
monitor.

Apple's DVI ports are usually DVI-I, which has VGA-compatible analog
video in addition to digital.  You can get an adapter to use this with
VGA monitors.

ADC was yet another attempt by Apple to clean up cable clutter by
putting everything in one cable.  As I mentioned above, it contains
analog video (VGA-compatible), digital video (DVI-compatible), power
(eliminating the need for a separate monitor power cord) and USB (to
allow for a hub in the display, and to allow software to configure the
display.)

ADC was eventually abandoned because it requires special video cards.
In order to put ADC on an otherwise-normal video card, Apple needed to
add a proprietary extension to the slot, to provide the power and USB.

It also forces users to get an expensive ($100) adapter if they want to
use an ADC monitor with a non-ADC computer, since the adapter needs to
incorporate a power supply.

This may help:
http://docs.info.apple.com/article.html?artnum=58692

-- David