In this video from ITFreeTraining, I will look at the DVI and VGA connectors. These
connectors are legacy connectors and generally not used any more, but you will find them
on old computers and other devices like projectors.
The Digital Visual Interface or DVI interface was first released in 1999. It was designed
to replace the VGA connector which I will cover later in the video. The DVI connector
comes in many different connector types.
DVI supports both analog and digital signals. VGA was an analog signal and thus DVI supports
analog to allow it to be backwards compatible with VGA. Lastly, DVI supports both single
link and dual link.
Single link means there is only the one signal in the cable. Dual link means there are two
signals. Having two signals essentially means that you can double the amount of data that
is sent through the cable. This is essential when you start using DVI for higher resolutions.
The DVI connectors can be divided into three different types. DVI is old technology so
for the exam you will not be required to know too much about it. It is useful to be aware
there are different types of connectors for troubleshooting purposes.
The first connector is DVI-A. The A stands for Analog. So essentially this DVI connector
only supports an analog signal. The analog signal is there for VGA compatibility. You
will generally see this connector on an adapter like the one shown. The adapter converts a
VGA signal to a DVI signal. Since the input is VGA, only an analog signal needs to be
outputted.
The next connector type is DVI-D. The D stands for digital. The digital connector comes in
single link and dual link. You can see the dual link has additional pins to carry the
second signal.
The last connector is the DVI-I connector. The I stands for integrated. The connector
essentially supports both analog and digital signals. The connector also comes in single
link and dual link. If you purchase a DVI cable it will most likely be a DVI-I connector.
Also, if you were to purchase a device in the current market, considering DVI is a legacy
connector, if the device has a DVI connector it is most likely to be a DVI-I connector.
A DVI-I cable will plug into a DVI-A or DVI-D connector. For this reason, you would always
buy a DVI-I connector, but nowadays it would be difficult to find a cable that is not a
DVI-I cable. However, not all DVI-I cables are created equal.
Today, if you purchased a DVI cable, it will most likely have a DVI-I connector. Shown
here is a single link cable. If I compare this with a dual link cable that I purchased,
you will notice that the same connector is used on both. If I were to take a guess, I
would say that the manufacturer finds it cheaper to manufacturer the one type of plug rather
than different plugs. This may make it cheaper to make, but means you can’t tell if the
cable is single or dual link by looking at the plug. Some single link cables will have
a single link plug while others will have the dual link plug.
When you purchase a DVI cable, have a look at the packaging and see if it says dual link.
If it does not say dual link, don’t assume it is, most likely it is not. A lot of cables
will have writing on the cable to help identify what kind of cable it is and what it is capable
of. In the case of dual link, notice that dual link is printed on the cable.
Different cables are also made of different quality. A poor quality DVI cable will have
signal problems and may not be able to display higher resolutions. This becomes more problematic
when the cable is longer in length. When purchasing a DVI cable, make sure you check what the
specification of the cable is before you buy it, otherwise the cable may not be able to
do what you want.
The DVI specification supports a lot of different resolutions and timings. What resolutions
are supported will be determined by your video card and your monitor. The maximum resolution
supported by DVI single-mode is 2560 by 1600 at 30 hertz or 1920 by 1200 at 60 hertz.
If you are using dual mode, this essentially doubles the amount of data that can be transmitted
through the video cable. This increases the maximum resolution to 3840 by 2400 at 30 hertz
and 2560 by 1600 at 60 hertz.
This essentially means that DVI supports 4k resolution, but you will only be able to get
30 hertz. For this reason, if you are using 4k resolution you most likely will be using
HDMI or DisplayPort rather than DVI.
DVI and HDMI uses the same signaling, but use different voltages and features. Since
they are similar it is possible to convert between the two using an adapter or a cable
with different connectors on each end.
HDMI is a new standard so has newer features. Thus, when you convert between the two, you
will be losing some features. The only advantage DVI has over HDMI is that it supports VGA.
So, you won’t be able to get a HDMI to VGA adapter, however you will be able to get a
HDMI to VGA converter. Although they size of the converter may differ, converters will
have some additional electronics in order to convert the signal and thus they will be
a larger and a bit bulky. Usually the electronics is in incase in a square or rectangle plastic
housing. VGA is very old technology, so using adapters generally does not cause problems.
DVI in comparison to HDMI has a limited color model. HDMI supports more color spaces than
DVI. When sending video data over a cable, the color can be encoded using differences
in color and luma known as chroma subsampling. Essentially, more data is used for differences
in the intensity in the brightness and less is used for the color. It is done this way
because our eyes are more sensitive to changes in brightness than changes in color.
Support for 4 4 4 essentially means luma and color use the same amount of data to encode.
Four is the maximum so in other words, no subsampling has occurred. So essentially,
what you start with is what you get out the other side.
In contrast lower values like 4 2 2 essentially means that less data is used to encode. Luma
is first followed by color so more data is used to encode luma or light intensity compared
with color. It is a compromise, but our eyes are more sensitive to luma than color, so
this gives us a better result. If you want the best results, you will be better off using
HDMI rather than DVI when you have the choice.
The next difference is that HDMI supports audio. If your monitor has inbuilt speakers,
a HDMI cable will be able to transmit audio to the monitor while the DVI cable is not
able to.
In order to promote interoperability between HDMI and DVI, HDMI supports some DVI digital
signals directly. Essentially some of the lower resolutions of DVI and HDMI have the
same signaling specification. So, a HDMI device will always display, at least, some of the
lower DVI resolutions.
DVI does not support HDCP or High-bandwidth Digital Content Protection. This is a system
developed by Intel to prevent copying. Essentially when a signal travels over a cable it can
be copied. The easiest way would be to split the cable into two using a splitter. HDCP
attempts to prevent this from happening by encrypting the data as it travels over the
cable. If you are attempting to connect a device that requires HDCP in order to work,
you won’t be able to use a DVI cable.
There have been a lot of problems with HDCP, including loss of the master keys allowing
it to be hacked; you most likely won’t see too much of it unless you are using 4k resolution.
This is because a lot of problems with HDCP were not fixed until 4k resolution came out.
In a lot of cases, if HDCP is causing problems the device will allow you to switch it off.
For example, if you have a PlayStation 4 and you want to live stream your gameplay you
will need to switch it off. Switching off HDCP won’t cause any problems unless you
attempt to use a service like Netflix which uses HDCP for 4k videos.
Since HDCP mostly gets used with 4k and DVI only supports 4k at 30hetz, you are most likely
to be using HDMI with 4k. For this reason, HDCP is unlikely to cause you too many issues
if you convert from HDMI to DVI, since you won’t be using the higher resolutions.
To finish this video, I will have a look at the Video Graphics Array or VGA. VGA was released
in 1987 and uses a 15-pin connector. For a long time, it was the standard for video on
the PC.
VGA uses an analog signal rather than a digital signal found in newer devices. The advantage
of an analog signal is that, as the distance gets longer, the signal gets weaker but you
still get a signal. With digital, once you start losing the signal it becomes unusable.
Digital gets around this by using quality materials and techniques like twisting to
reduce interference. This increases the distance digital can be used for. However, digital
can send a lot more data than analog and this is one of the main reasons that analog is
no longer used.
VGA has a max resolution of 2048 by 1536 at 85 hertz. If you consider that the 4k standard
did not get released until 2005 and took a while before it took off, this is a fairly
decent maximum resolution. For this reason, even after the DVI standard was released,
VGA was still used on devices like laptops. Most likely this was because the VGA plug
was quite small compared with the DVI plug. If you required DVI, an adapter could be used
to convert the plug from VGA to DVI.
Nowadays, you don’t tend to see VGA plugs on laptops as they tend to use HDMI or DisplayPort
to connect an external monitor. DVI is not used so much, which is most likely due to
how old the technology is and how big the plug is.
Lastly, VGA does not support audio. VGA was quite a good standard for computing for a
long time, but nowadays it has really shown its age. You won’t see it used on new computers,
but you may still see it used on devices like projectors for backwards compatibility.
This concludes this video on DVI and VGA. I hope you found this video useful and informative.
Until the next video from us, I would like to thank you for watching.