What is DisplayPort Multi-Stream Transport (MST) and Does Your Desktop KVM Switch Need It?
DisplayPort MST can be found on some of the latest desktop KVM switches, and while it is firmly established that multiple-monitor setups at desktop workstations can increase productivity and provide a better user experience, what exactly is DisplayPort MST, and does your desktop KVM switch really need it?
Desktop KVM switches provide both ergonomic style and advanced functionalities for the SOHO desktop environment. A key advantage of many desktop KVM models is the option to have multiple desktop displays. A much-quoted report by John Peddie Research from 2017 noted that multiple displays on a desktop can increase productivity by 42%, and the use of two or more monitors has grown from less than 30 percent of those surveyed in 2002 to as many as 90 percent in 2017. Application scenarios for extended desktops with multiple displays include the following:
- CAD design / Video post production
In tandem with this growth, just as the demand for higher resolutions and increased productivity is being met both commercially and in the home by DisplayPort 1.2, the format’s Multi-Stream Transport (MST) technology is also being touted as the future-proof solution for extended desktops everywhere, and DisplayPort MST can be found on some of the latest desktop KVM switches.
But while it has now been established that multiple-monitor setups at desktop workstations can increase productivity and provide a better user experience, what exactly is DisplayPort MST, and does your desktop KVM switch need it?
What is DisplayPort Multi-Stream Transport?
Multi-Stream Transport (MST) has been a feature of the DisplayPort standard since version 1.2 was released in 2010. The key factor of the technology’s usefulness for desktop users is that it allows multiple independent displays to be driven from a single DisplayPort output source device. These displays can connect to the source device via an MST hub or to each other in a daisy-chain configuration using just one DisplayPort cable to link them.
This setup allows for an extended desktop across all of the displays and therefore provides great benefits in a variety of applications. There are a few restrictions to MST functionality that should certainly be considered, but nothing that would be discouraging for most mid-level or even power desktop users.
So, if you are looking for an extended desktop and are wondering about a DisplayPort MST solution, the main things to consider are:
- MST Hubs and Daisy-Chaining
- Sharing Bandwidth between Displays
- Operating System Compatibility
MST Hubs and Daisy-Chaining Considerations
First, in order to take full advantage of MST, your monitors must be capable of daisy-chaining. That is, they need to have both a DisplayPort input and a dedicated DisplayPort output port. Once your first monitor is connected to the DisplayPort source, such as your desktop PC (or laptop), additional monitors can be daisy-chained from the first one using only a DisplayPort cable.
The latest DisplayPort 1.2-compatible monitors will support daisy-chaining, but if you have an older model, it can still be incorporated downstream, though you will need an extra DisplayPort hub instead of just a cable. Also, the last monitor in the chain does not need to support daisy-chaining; it only needs a DisplayPort input, so a DisplayPort 1.1 monitor, for example, would be fine.
These are the two most popular ways to use MST for a triple-display workstation.
On the left in the diagram above, monitor A connects to the laptop or PC that is the DisplayPort 1.2 source, while the three monitors are connected to each other using only a DisplayPort cable. On the right, the three monitors connect to an MST hub that connects to the laptop or PC that is the DisplayPort 1.2 source.
In both cases, the source device sees the three separate displays as an extended desktop, so you can choose to expand a single image across three displays (as shown below), which is perfect for immersive, high-resolution gaming or, for the efficiency and productivity of multi-tasking; simply dedicate each display to a separate application and work between them simultaneously.
Extended desktops are perfect for immersive gaming and productive multitasking.
Sharing Bandwidth between Displays
Second, there are, of course, limits to how many monitors you can downstream in your DisplayPort MST daisy-chain. According to the original VESA specification in 2010, up to 63 monitors can be supported by MST in theory, but this has no practical value due to the fact that the combined data requirements of all the displays in the daisy-chain cannot exceed the limits of the single DisplayPort port that the video source originates from, nor exceed the capabilities of your graphics cards. And for a DisplayPort 1.2 port, for example, that limit is 17.28 Gbit/s.
So in terms of real-life applications, you are probably looking at 3 or 4 monitors if you want to maintain reasonable resolutions for each of the displays. But this is still absolutely acceptable for most desktop applications. For example, splitting the total bandwidth coming from a DisplayPort 1.2 output allows desktop users to connect up to four independent 1920 x 1080 monitors or two high-resolution 2560 x 1600 monitors, which will certainly allow for easy multitasking while reducing bulky cable connections.
The table below shows the theoretical maximum number of monitors and the resolutions you can expect in a DisplayPort 1.2 MST setup for most practical purposes.
|Display Resolution||Theoretical Max. No. of Monitors Based on DisplayPort 1.2 Bandwidth|
|@ 60 Hz Refresh Rate||@ 30 Hz Refresh Rate|
|1920 x 1080 (1080p) / 1920 x 1200||4||8|
|2560 x 1600 (WQXGA)||2||4|
|4K UHD / 4K DCI||1||2|
Operating System Compatibility
Third, in addition to requiring a compatible graphics card, DisplayPort 1.2 MST-capable monitors, and the latest GPU drivers, it is important to also consider that only certain versions of Microsoft Windows fully support MST.
At the time of writing (March 2019), devices running Apple’s Mac OS X operating systems do not support DisplayPort daisy-chaining or MST hubs. So your Mac will, unfortunately, not be able to join the party.
[If you are a Mac user and are looking for a similar solution, check out the following:https://www.aten.com/eu/en/products/usb-&-thunderbolt/peripheral-switches/us7220/ ]
The Main Benefits of MST KVM versus Dual Display KVM Explained
When it comes to multi-display setups, there are a wide variety of KVM switches that support various ways to achieve extended desktops. However, you might not be sure about the difference between MST and dual-display models. If so, read on.
- Uncluttered Simplicity
- Cost-effective Multi-display Setup
- Desktop Flexibility
The main benefit of multi-display setups via MST is simplicity – one video output, one cable/hub. This makes it a more cost-effective solution for mid-to-high quality visuals while also providing a less-cluttered workspace. Plus, you are not limited to two displays – you can have as many as your GPU can drive – but this has implications, depending on your application. As we have discussed, while all the displays do not need to have the same resolution, the total pixel count will be split across them, so image quality can vary and will be less than in a dedicated dual-display setup. However, the advantage of this is that you can use a variety of different models of displays and various resolutions. For example, one 2560 x 1600 monitor could be used with two 1920 x 1080 monitors. And while all monitors in the middle of the daisy chain need to be DisplayPort 1.2 daisy-chainable (since they need the DisplayPort output), the last monitor can be an older DP 1.1 monitor (which only has a DisplayPort input). Furthermore, MST models feature a variety of display modes, so your desktop has more flexibility.
Dual-display KVM switch models, on the other hand, are generally going to be more expensive, and you will also need a suitable graphics card that supports dual/multiple displays, as opposed to MST-based setups where you only need a single output source. But, seeing as you won’t be needing to share bandwidth between your displays, if your application truly requires the absolute highest quality visuals, you are probably going to find MST somewhat lacking.
In conclusion, we can see that for a more budget-conscious user looking for a dual- or multi-display setup, KVM switches that support MST offer extra convenience, extra flexibility, and extra features.