The live version of this guide is available on the LinusTechTips forum here. This page was only created for code testing and is no longer used, so the information here has not been updated in several years.

Please use the up-to-date version on the forum: https://linustechtips.com/topic/729232-guide-to-display-cables-adapters-v2/

How to use:
  • Use the output (left) dropdown only, for general information about an interface (DVI, HDMI, etc.)
  • Use the input (right) dropdown only, to see all options for connecting to a specific port on a display
  • Use both dropdowns for information about a specific adapter combination — make sure they are in the right order!
  Output
(Computer / Source) 		  Input
(Monitor / TV / Display) 		 
   
(Note: Order matters! Make sure that the Output / Input are in the correct order and not reversed.)
 
Click to Expand:

› Maximum Refresh Frequency and Resolution of Everything [Link]
Close


› Which Cable Type Should I Use? (DisplayPort vs. HDMI vs. DVI vs. VGA) [Link]
Close


› Connecting to a 120+ Hz Display [Link]
Close


› Active vs. Passive Adapters [Link]
Index:
What's the Difference? (Preface)
Passive Adapters
Passive adapter compatibility has nothing to do with analog and digital
Passive adapter compatibility has nothing to do with bandwidth
Passive adapters are not necessarily limited to the lowest common denominator
Do passive adapters add any latency?
Do passive adapters reduce image quality?
Active Adapters
Do active adapters add any latency?
Do active adapters reduce image quality?
How can I tell if an adapter is passive or active?
Which type should I use?


What's the difference between a passive adapter and an active adapter? (Preface)

There are a lot of myths and confusion surrounding passive and active adapters, and there seems to be very little understanding of exactly what they are, how they both work, and how to identify them. Hopefully this article will help clear things up.

First, to make some general points clear since there is a lot of misinformation spread around:

Passive Adapters:
  • Compatibility is completely arbitrary and is based on how each interface (DVI, HDMI, etc.) is designed. It has absolutely nothing to do with whether signals are digital or analog.
  • Passive adapters are not necessarily limited to the lowest common denominator in terms of bandwidth / feature support, etc.; this depends on the specific interfaces involved.
  • Passive adapters may or may not work in both directions; this depends on the specific interfaces involved (DVI, HDMI, etc.), it does not depend on the adapter itself.
Active Adapters:
  • Active adapters may or may not require additional power connectors; some do and some don't.
  • Active adapters may or may not be expensive or bulky; some are and some aren't, usually it depends on the specific interfaces being converted, as some conversions are more complex than others.
  • Any two interfaces can (in theory) be connected with an active adapter, although in practice not every conceivable combination of interfaces has an adapter manufactured for it.
  • Capabilities (maximum bandwidth, feature support such as audio, etc.) are limited to the lowest common denominator; if one of the interfaces doesn't support something, it won't carry through an active adapter.
  • Active adapters may or may not work in both directions; it depends on the specific adapter. The vast majority of active adapters only work in one direction, but it is not impossible for an active adapter to be bi-directional.

From a technical standpoint, the difference between an active adapter and a passive adapter is in the basic principle of operation. Being able to tell the difference between a passive and active adapter isn't as simple as looking for external features like power cables, bulkiness, or cost. Some active adapters require power cables, but less complex ones can get enough power directly from the port. Some active adapters, like DisplayPort to VGA, can be very inexpensive, compact, reliable, and require no power cables, and for this reason they are often mistaken or mislabeled as "passive adapters". However, these external features are not the criteria which actually define whether an adapter is passive or active.

So what is the difference exactly? Well...

There are many different signaling formats, or methods of representing and transmitting the information that makes up a video signal. Each different interface (VGA, HDMI, DisplayPort, etc.) uses a different format; they represent the information in different ways. If you (as a system designer) want your device to be able to communicate information to another device which uses a different format, there are two ways for this to happen. You can design your device to be able to communicate using the other device's format (make it "multi-lingual" in a sense), or you can insert a third-party device between them to convert the information from one format to the other en route (a "translator" if you will). A passive adapter works via the first approach, and an active adapters works via the second approach.

Passive Adapters

A passive adapter works via the first approach described in the preface. As it turns out, the ports on your graphics card or laptop or other source device can output signals in multiple different formats. For example, DisplayPort ports are not just limited to sending DisplayPort signals; they can send signals in the HDMI or DVI formats if required. Of course, the only problem is that the DisplayPort port cannot physically morph itself into an HDMI port to allow you to plug in HDMI cables, so this is why the "passive adapter" is needed; the adapter does not do anything at all to the format of the electrical signal, it is just there to change the shape of the port to allow you to plug the correct cable in. When you use a DisplayPort to HDMI passive adapter, the adapter is not "converting" DisplayPort signals into HDMI signals. The electrical signals coming from the DP port are already in the HDMI format, the adapter is just changing the physical shape of the port.

Since passive adapters don't actually do anything themselves, they will only work for some very specific combinations of ports which have been pre-designed with the ability to communicate in other formats. The table below shows which connections are possible using passive adapters:

Every Possible Passive Adapter Combination
Output Port
(Computer / Source) 		Possible
Output Signals 		Comments
DisplayPort → DisplayPort
HDMI HDMI version/bandwidth dependent on source device and adapter
Single-Link DVI Can be connected to Dual-Link DVI ports, but will still be limited to Single-Link speed
HDMI → HDMI
Single-Link DVI Can be connected to Dual-Link DVI ports, but will still be limited to Single-Link speed
Dual-Link DVI-D → HDMI HDMI version/bandwidth dependent on source device and adapter
Single-Link DVI
Dual-Link DVI
Dual-Link DVI-I → HDMI HDMI version/bandwidth dependent on source device and adapter
Single-Link DVI
Dual-Link DVI
VGA
VGA → VGA Can be received by either a VGA input port or a DVI-I input port (DVI-I inputs are very rare, most displays have DVI-D inputs, not DVI-I)

This table is an exhaustive list of all possible connections that can be made using passive adapters between DP, HDMI, DVI, and VGA. If it is not listed above, it is not possible with a passive adapter.

While output ports can send multiple types of signals, most input ports will only accept signals in their native format. For example, if your display has a DVI-D input, it will only accept DVI signals. This means that you can connect to it from a DisplayPort, HDMI, or DVI output port, because all three of those ports know how to send the DVI signals that the input port requires.

On the other hand, if your monitor has a DisplayPort input, you can only connect to it from a DisplayPort source. Neither DVI nor HDMI output ports know how to send DisplayPort signals, so they cannot communicate with just a passive adapter. In this case, an active adapter would be required to convert one of the other signals into the DisplayPort format, since DVI and HDMI ports cannot output DisplayPort signals themselves.

The only type of input port that will accept more than one format is DVI-I, which can accept both DVI and VGA signals. However, it is very rare for a display to have a DVI-I input. Almost all DVI ports found on displays are DVI-D.

Passive adapter compatibility has nothing to do with analog and digital

Something important to notice about the table above is that the compatibility between formats has no relation to whether each format is analog or digital.

DisplayPort outputs are capable of sending DVI and HDMI signals, so a passive adapter can be used to connect a DisplayPort output to a DVI or HDMI input. However, DVI and HDMI outputs are not capable of sending DisplayPort signals, so a passive adapter cannot be used to connect a DVI or HDMI output to a DisplayPort input. Just because "they're both digital" doesn't mean passive adapters can be used.

DVI-I outputs are capable of sending VGA signals, so a passive adapter can be used to connect a DVI-I output to a VGA input. Just because "one's a digital standard and one's an analog standard" doesn't mean passive adapters can't be used. If your digital standard includes the ability to send analog signals when requested, then it's possible to use passive adapters to an analog standard, and that's all there is to it.

People imagine that when one signal is digital and the other is analog, this makes it impossible change one to the other without some processing involved, making passive conversion impossible. Meanwhile if they are both digital, they are more closely related and this makes conversion very simple (insert hand-waving here).

This talk about how easy or difficult it is to convert one signal to another is irrelevant here. Converting one signal to another is what an active adapter does. Passive adapters do not convert any signals. Yes, it is impossible to convert an analog format into a digital format without any processing. That's because it's impossible to convert ANY format to ANY OTHER format without processing. There is no such thing as "passively converting" a signal. It doesn't matter whether it is analog to digital or digital to digital; ANY kind of signal conversion is impossible without an active adapter, period.

Passive adapters work because source ports can output video in multiple different formats, so no conversion is necessary. These formats do not have to be related in any way. If you want to know whether or not you can use a passive adapter for a certain format, the answer has nothing to do with the port's other formats.

For example, if you want to know whether or not DVI ports can support passive adapters to VGA, DVI being a digital format doesn't have anything to do with VGA adapter support, because the DVI format isn't being used when you're using a passive adapter. The correct question is, "are DVI ports capable of sending VGA signals instead of DVI signals?", and the answer is "yes, if it's a DVI-I port". Thus, passive DVI to VGA adapters are possible, despite the DVI format itself being digital.

Likewise, if you want to know whether DisplayPort to VGA passive adapters exist or not, asking "is the DisplayPort format digital or analog" is completely irrelevant, because there aren't any DisplayPort signals involved when a passive adapter is used. The question is "are DisplayPort ports capable of sending VGA signals instead of DisplayPort signals?", and the answer is "no", so DisplayPort to VGA signals are therefore not possible. It has nothing to do with the DisplayPort format being digital, DisplayPort simply wasn't designed with the ability to alternatively send VGA signals, while DVI was.

There are no rules of thumb, like "digital to digital is possible passively, analog to digital isn't". The compatibility of passive adapters is completely arbitrary and just comes down to what capabilities each video standard was designed with.

Passive adapter compatibility has nothing to do with bandwidth

Another surprise to most people is that DisplayPort 1.2 doesn't support passive adapters to HDMI 2.0, or that DisplayPort and HDMI don't support passive adapters to Dual-Link DVI, only to Single-Link DVI. Upon being informed of this, the response is usually something along the lines of "well that doesn't make any sense; they're both digital, and the bandwidth of DisplayPort is greater than Dual-Link DVI / HDMI 2.0, etc. so a passive adapter should work!" But again, this is based on a misunderstanding of how passive adapters work.

People imagine that a passive DP to DVI adapter is "converting" DisplayPort signals into DVI signals, as if the image is originally sent as a DisplayPort signal and an adapter transforms it into an equivalent Dual-Link DVI signal, which should work because any Dual-Link DVI data stream will "fit" inside a DisplayPort signal since the bandwidth of DisplayPort is greater than that of DL-DVI. This is all very sensible sounding, and is a wonderful description of how an active adapter works, not a passive adapter.

A passive adapter does not "convert" a signal from format to another. The original signal is sent in the desired format to begin with, and the adapter is just changing the physical shape of the port so that the correct cables can be plugged in. In a DisplayPort to DVI (or HDMI to DVI) passive adapter, the DisplayPort output port is essentially used as a DVI port; all of the pins are used to send the same electrical signals that a DVI port's pins would (more or less). Of course, the DisplayPort port is still shaped like a DisplayPort port and so DVI cables will not fit—that's what the passive adapter is needed for—but electrically it is acting as a DVI port. But a DisplayPort port also only has 20 pins (compared to 19 pins on SL-DVI-D and 25 pins on DL-DVI-D), so it can only send signals that a Single-Link DVI port would send; it is physically impossible for it to send Dual-Link DVI signals in this manner, because it simply doesn't have enough pins to send the same signals that a DL-DVI port would. HDMI ports (which have 19 pins) are also subject to the same restriction; they can only send Single-Link DVI signals, not Dual-Link.

And again a similar concept applies to DisplayPort to HDMI adapters; many people are perplexed when they discover that DisplayPort 1.2 only supports adapters up to HDMI 1.4. "But DP 1.2 has more bandwidth than HDMI 2.0!" Yes it does—but since adapters don't work by "converting" DisplayPort signals into equivalent HDMI signals, it doesn't matter if HDMI 2.0 signals "fit" inside a DisplayPort 1.2 signal. The bandwidth of DisplayPort is irrelevant, because there are no DisplayPort signals involved at all. DisplayPort 1.2 only supports adapters to HDMI 1.4 because the DisplayPort control chips are not designed to send HDMI signals greater than that (mostly because DisplayPort 1.2 was published in 2009 and HDMI 2.0 didn't exist until around 2013 or so). DisplayPort 1.3 (2014) does support passive adapters to HDMI 2.0.

Passive adapters are not necessarily limited to the lowest common denominator

Another bit of seemingly sensible wisdom which turns out to be not always true is that when using a passive adapter, you'll be limited to lowest capabilities of the two interfaces involved. For example, if using a DVI to HDMI adapter, many people will tell you that audio won't work. After all, DVI signals contain no audio, and converting an audio-free signal to the HDMI format won't make audio magically appear. But again, this is based on the idea that an adapter "converts" DVI signals into HDMI signals, so this is information that applies to active adapters, not passive adapters. When using a passive adapter from a DVI source to an HDMI display, the output device detects an HDMI display and sends HDMI signals to it, including audio. Whether DVI signals contain audio or not is irrelevant, because there are no DVI signals involved. The adapter isn't "converting" DVI signals into HDMI signals, the signals are sent in the HDMI format to begin with.

While it is sometimes true that you'll be limited to the lowest capabilities between the two interfaces, it isn't always true. Check the specific adapter combination you are wondering about using the dropdown interface at the top of this guide.

Do passive adapters add any latency?

No.

Do passive adapters reduce image quality?

No.

Active Adapters

Active adapters (or "signal converters") use the second approach described in the preface; both the source device and the display send/receive signals in their native formats, but there is a device in the middle (the adapter) which converts the information from one format to the other. Active adapters are required for any combination of ports that isn't possible with passive adapters (as listed above). Active adapters have also been used in some situations historically to circumenvent limitations of passive adapters; for example, some older AMD graphics cards could support up to 6 monitors, but only maximum of two could be using DVI/HDMI signals (including sending DVI/HDMI signals through a DisplayPort port via a passive adapter); the rest had to use native DisplayPort output. DisplayPort to DVI/HDMI active adapters were useful in this case to allow additional DVI/HDMI connections, since the graphics card would send native DisplayPort signals, which were then intercepted by the adapter and converted to the DVI/HDMI format en route.

Active adapters have a processor which converts between the two formats, so they are more expensive than passive adapters and may require a power cable, depending on the complexity of the conversion. Since active adapters convert information from one format into its equivalent in a different format, they are limited only to the features and capabilities supported by both formats. This means active adapters won't support anything that isn't supported by both sides of the connection, including limitations on maximum bandwidth, audio support, and any other features such as G-Sync or daisy-chaining. In addition, certain active adapters may have their own limitations depending on what the signal processor can handle. For example, many (but not all) HDMI to DisplayPort active adapters are limited to 1920×1200 at 60 Hz. Even though both connections can go beyond that, the processor used inside those adapters can’t process data quickly enough to do more than that. For 1440p or 4K resolutions, even more expensive adapters with more powerful processors must be used.

Active adapters usually only work in one direction. An active adapter that receives a VGA signal and converts it into HDMI usually isn’t equipped to receive HDMI signals and turn them into VGA instead. When purchasing an active adapter, read the product description carefully.

In theory, any signal can be converted to any other signal with an active adapter, although in practice there is not an adapter manufactured for every conceivable combination of ports.

Do active adapters add any latency?

Depends on the adapter, but usually they do not add any meaningful amount of latency.

Do active adapters reduce image quality?

No. But when converting between two different formats the image quality will only be as good as the worse format.

How can I tell if an adapter is passive or active?

Some people think that "active adapter" means it has an additional plug for power, but this is not the case. If an adapter needs a power cable, it is definitely an active adapter, but if it doesn't need a power cable, it could still be either an active or a passive adapter. It is not possible to tell the difference between them by looking at them, because "active" and "passive" aren't defined by any external feature, as explained above. Some active adapters may have conversion circuitry so small that it can be powered from the port and embedded in the cable termination, so that it appears just like any normal passive adapter cable.

Sometimes it isn't possible to tell whether an adapter is active or passive, but there are some steps you can take to rule out one or the other. Only specific combinations of ports are possible with passive adapters, listed in the table a few paragraphs above. If the adapter you are looking at isn't a type listed on that table, it must be an active adapter (or fake). If it is a combination listed on that table, then it could be either passive or active. Usually the product description will tell you, but if it doesn't, you should generally assume it is passive, because companies don't normally make active adapters for port combinations that can already be done using passive adapters.

However, there are some exceptions to this. Even though DisplayPort supports passive adapters to HDMI and Single-Link DVI, there are many active adapters also available for these combinations due to restrictions on multi-monitor configurations on some older AMD graphics cards (see here). So DisplayPort to DVI adapters or DisplayPort to HDMI adapters may either be passive or active; reading the product description will usually tell you.

In addition sometimes active adapters may be required between DisplayPort and HDMI depending on which versions you want; for example, DisplayPort 1.2 does support passive adapters to HDMI, but only up to HDMI 1.4; to get a full HDMI 2.0 connection from DisplayPort 1.2, you need an active adapter.

More specific information on what combinations are supported with passive adapters can be found by entering a specific combination of ports in the dropdown menus at the top of this guide.

Which type should I use?

If a passive adapter is possible for the configuration you want (check using the utility at the top of this guide), then usually you should use the passive adapter. Active adapters tend to be more expensive and less reliable, and only exist for situations where passive adapters won't work.

Close


› Active Adapter Requirements for Multi-Monitor Configurations [Link]
Close


› Do HDMI Cables Have Versions? [Link]
Close


› Is HDMI Limited to 60 Hz? [Link]
Close



› Bandwidth / Maximum Refresh Frequency Calculator [Link]
Close