If you have kept your classic keyboard ThinkPad until now (like me) and haven’t kept up with technological advancements — what for when you can’t buy a laptop?? — then when your ThinkPad 25 shows up, you will find yourself trying to understand what you can connect to it — and quite probably you will feel very confused because the powers that be decided technology needs to be insanely confusing and inscrutable.

Let’s start with opening the T25 by removing the screws on the bottom and the entire bottom plate. No more service hatch. You will find two RAM slots inside but your old memory modules are no good, these are DDR4 slots and you need to buy DDR4 SO-DIMMs. If you want to buy a second 16GB module, just buy any 16GB Single DDR4 SO-DIMM, speed and such doesn’t really matter but Lenovo suggests 2400 MHz modules and the price difference is very small.

You will also find a number of M.2 slots. M.2 is an all encompassing standard for mobile expansion cards from storage devices through wifi to video capture and more. These cards are just a hair below one inch wide (22mm) and can be various lengths, the most common are 30mm (wifi cards), 44mm (WWAN and very few slower SSDs), 80mm (most fast SSDs). The cards have an edge connector with one or two cuts in them. These are matched by a plastic key on the slot. While the multitude of M.2 slots are slightly intimidating, at least you have the solace that if it fits in, then it will work. The various keys are marked with a letter. Different letters mean different capabilities. For example, the key M slot sitting in your 2.5" drive bay, holding the 512GB SSD is capable of hosting the speediest SSDs. You can buy bigger ones but they cost an arm and a leg — like 1300 USD for a 2TB one. If you need lots of storage, you need to buy a 00UR495 so you can host a 2.5" SATA disk here as the T470 does — but then you need to say your super speedy Samsung SM961 good bye.

The other m.2 slot is a key “B”. This holds the WWAN card (or not — information is conflicting whether it’s included or not) and it can replaced with an SSD. But the physical space is short, so unlike the common 2280 format, only 2242 SATA SSDs can go there. If you want a 128GB or a 256GB SSD, there are multiple choices, but for 512GB the only disk with actual availability is the Transcend MTS 400 series. Read this comment, however.

Just for completeness, the wifi card is a 2230 physical format, keyed for A and E slots and can’t host an SSD so just leave it alone.

And that’s it, there are no other things on the inside that you could easily exchange. (No, a reflow oven is not “easily exchange”!)

Outside, the only port that really needs to be talked about is the USB C connector. The physical connector provides four high speed lanes. There are various “cars” that can travel on these lanes, in practice you will use three: very fast USB (so called USB 3.1 Gen 2, 10 Gbps), DisplayPort (theoretically DisplayPort 1.3 but the T25 only supports DisplayPort 1.2). The third is a bus, not a “car”, called Thunderbolt 3. Thunderbolt 3 is a bus which carries — in the case of the T25 at least — one DisplayPort signal or two PCI Express lanes. The latter allows you to connect external graphics cards, ten gigabit ethernet adapters and such.

Gigantic confusion arises when you want to drive multiple monitors. DisplayPort 1.2 is capable of driving multiple monitors from a single connector, this is called Multi-stream Transport (MST). But this doesn’t raise the available video bandwidth from that connector. For example, the Ultra dock contains an MST hub and because of that, if you check the relevant Lenovo display support matrix you will see it can drive either a single 4K monitor at 60Hz or two at 30Hz. When you daisy chain two DisplayPort monitors, they are using this same capability. You can run four full HD monitors, three 1920x1200 monitors, two 1440p monitors, one 4K monitor, all at 60Hz. Do note MST support is way, way better in Windows than in Linux.

You can’t drive even one 5K monitor at 60Hz (or two 4K @ 60Hz). This would require the bandwidth of two DisplayPort 1.2 connectors. A full implementation of the Thunderbolt 3 standard does include two DP 1.2 signals but the T25 doesn’t have a full implementation, only a half. This also means that daisy chaining Thunderbolt docks or monitors containing such will not work — at least for the purpose of driving multiple monitors. A TB dock disembarks one DisplayPort passenger, drives a monitor with it and then provides a passthrough for the bus to continue. The next dock / monitor will also disembark a DP passenger and drive a monitor with it. Except the Alpine Ridge LP chip in the T25 only put one passenger on the bus, there’s no signal left.

Likely there’s a way: while it is not known whether DisplayPort on the Pro Dock and the DisplayPort hiding in the USB C connector are mutually exclusive or not it is very likely they can be used at the same time. If that’s indeed possible and you have an 5K monitor with dual DisplayPort inputs like the Dell UP2715K (but not the LG Ultrafine) then you just might get a lot of glorious pixels (although you’ll need bother with plugging a cable in addition to docking). The latest machine I was able to find information on is a T560 owner reporting being able to use the DisplayPort on the machine while using the DP on the dock, so it’d be quite shocking if the next generation regressed in this. I suspect the T25 (unlike the T470 it is a variant of) can actually drive four displays: DisplayPort via USB C, HDMI on the laptop, DisplayPort on the dock, internal display. This might even be the reason why a 940MX GPU was added to the T470: it is quad capable while the integrated graphics chip (the only thing the T470 has) is only capable of driving three independent displays (plus MST).

Now, ordinary DisplayPort can operate in such a way that it carries DVI / HDMI signals, this is still possible with USB C (theoretically at least, relevant docs warn you to not connect to a DP-to-HDMI or DP-DVI adapter but whether that’s just unsupported or downright not working, hell knows, make sure you have a good return policy if you try). To make things confusing, and man, is USB C good at it, there’s an alternate mode where HDMI cars travel on the four USB C lanes. In this mode HDMI CEC is supported for example, while HDMI-over-DP-over-USBC doesn’t support CEC. It’s very near impossible to tell whether a USB C to HDMI adapter uses DP or HDMI alt mode. And I myself have no idea whether the T25 supports HDMI alt mode either but I strongly support it doesn’t because this mode is just too new. At least the laptop has a HDMI port and the DP on the dock is certainly dual mode capable (ie. a passive, cheap DP-HDMI adapter is enough) so if you need HDMI I would very strongly recommend not messing with USB C.

Finally, USB C can receive and provide power. The so called Power Delivery mode, it can receive or provide as much as 100W in theory using 20V @ 5A, in practice the highest adapter on the market is only 90W. Also, I do not think the USB C port on the T25 is able to provide power delivery. So you can charge the laptop but you can’t charge another laptop off it. As it’s USB it must provide some power at 5V but the maximum amperage is yet unknown. I believe the standard prescribes at least 1.5A which is not a lot to charge a phone.

Questions?