Here are notes I’ve put together on the T420, from my own experience with my own machines. Some of my notes will probably be useful to people that intend to mod and upgrade their machines, while other parts of it might just be useless babble. There’s your warning.

Most of this was originally put together in October of 2019, so keep that in mind in case I’m totally off about something in terms of pricing.

Specs

The T420 I got off of on letgo came with an i5-2540M, the NVS 4200M GPU, 4Gb RAM, 320Gb HDD, and a 1600x900 screen. (Future Will here: I no longer have this model–I now use one without a dGPU and with the 1366x768 panel. I gave the one I originally got to a friend.)

The 2540M mine came with is generally decent enough for web surfing, multitasking, office tasks, lighter virtual machines (small Linux & Android VMs for testing), very light gaming, and some emulation (it can handle most systems up to the N64 era, but the GC/PS1/Xbox era is basically unusable).

Upgrading to i7 and higher RAM improves on a lot of this. From just upgrading to 8Gb of RAM, I can run more resource-intensive VMs with little to no problem. I can also run more tabs in Firefox and Chrome without needing to worry (much) about my memory consumption.

Other configurations are on the ThinkWiki page; I can’t summarize it more efficiently than what’s already there.

Upgradeability and Expandability

You can upgrade nearly everything on this computer, which is great.

• You can upgrade to up to 16Gb RAM without issue.
• You can upgrade to an i7 CPU with proper electrical requirements, etc., covered below.
• HDD can easily be replaced with a SATA SSD.
• Ultrabay replacements exist that allow you to swap out your CD drive for a hard drive if you’re into that.
• ExpressCard extensions exist that allow you to use USB 3.0 on this machine, since it only has USB 2.0 ports. Unfortunately, a lot of the cheaper ones on the market don’t work very well. You can also use it for an eGPU.
• Empty mini-PCIe slot on the bottom of the machine. Can be used for an eGPU, a WWAN card (with whitelisted BIOS, for Hackintosh or just better WiFi, etc.), or an mSATA SSD (more expensive than SATA, but may be practical in some cases).

A few notes:

• Don’t tighten the screw that goes into the battery bay for the palmrest too much. It will bend the palmrest and it drives me nuts. 0/10, wouldn’t recommend.
• Messing around with the palmrest may eventually lead to the clasps not wanting to hold the display down. Can’t speak for anyone else’s experience, but in my case, I had removed the palmrest several times over the course of a couple months for CPU shenanigans and after a few times, the clasps move freely after opening and closing the lid anymore. Upon taking it apart again and attempting to reseat the wire(?) into its grooves, it still persists. This in combination with the problem above is going to force me to buy a new palmrest before giving it to someone else. Also a 0/10, wouldn’t recommend.
• Docks are pretty nice. You can make (basically) a full desktop setup if you want to, especially if it’s hooked up to one or more monitors, external keyboard and mouse, and/or external speakers. If you’re clever, you can also mount the dock to a wall and use it without even needing to open the laptop. 10/10, would recommend.

RAM

It’s recommended to use name-brand RAM, making sure it’s not “value-RAM” since it’s minimally tested and liable to eventually fail. Samsung, Crucial, etc.–if a lot of people know what it is, it’s probably a good bet.

I’ll throw in that some no-name brands will buy b-stock from name brands and do their own testing. These are generally fine, but you may want to proceed with caution. An example of this is A-Tech Components (not sure if they sell compatible RAM in this case, but they’ve been reliable for me).

Used RAM will usually work well enough if it’s tested and known to be working. I got a used 8Gb kit of Crucial DDR3 1333MHz SODIMMs on eBay for $27; not the best deal but cheaper than a lot of Crucial RAM on the market. They’ve worked for me for the last year or so without any issue.

CPU

In my opinion, the i5-2540M and 2450M are the most practical choices you have for this machine–they sit around the $20 range. However, they don’t provide the best performance out of the compatible processors.

You can upgrade to an i7-2620M if you really want to, since it has the same TDP as the 2540M. If you’re upgrading from an i3 or something lower than the i5-2540M, and you need to be able to use it without your laptop being hooked up to a charger, then it might be a worthy upgrade, but it costs anywhere between $40-$50.

At that price point, you’re a lot better off just buying a 2630QM (roughly $45), or a 2720QM (anywhere between $40-$50)–both of which have 4 cores/8 threads (vs. the 2520M/2540M/2620M’s 2c/4t). The 2630QM and 2720QM both have 45W TDPs vs. the 2540M’s 35W TDP. If you try stress-testing them without being plugged in, your T420 will shut down without warning. While I haven’t tested it while using a slice battery, I can’t imagine it ending much differently. Overall, I don’t really recommend these options, but they do provide better performance, so you should be the judge of the trade-offs.

Just don’t put it under heavy load when you can’t afford to let it shut down, ok? Either that or just constantly use it as a desktop (paired with a dock, peripherals, and additional monitors, this actually isn’t that bad of an option).

A couple of notes on upgrading the CPU:

• Having the dual heat pipe won’t help with thermals if you actually have the dGPU. Some people recommend it if you’re upgrading the CPU. That’s not really necessary for the most part, unless you decide to go with a 45W option.
• Attempting to stress test a 2720QM isn’t an optimal experience. The laptop will get warm and you’ll see CPU temps rise to 100C fairly quickly. Unplugging your T420 during this time will cause it to nearly immediately shut down.
• One of the i5’s is your best option if you need a laptop that works well as a laptop, though you can still upgrade if you would like. Most of the i5’s are on par with the i5 5500U from 3 years later. They’re very usable chips, even today.
• You can flash the laptop with Coreboot to get it to work with 3rd gen Intel chips. I didn’t mess with this, so I can’t advise. Logically it’d be a good investment if you want maximum bang for your buck, and you’re willing to put in the work.

HDD/SSD

Take the HDD case cover off, remove the hard drive with the plastic flap attached to the caddy, take the internal cover off of the HDD and caddy, take screws out from the caddy, replace the drive with your drive of choice, then reassemble.

This is simple enough not to really need pictures to do it. I’ve done this several times with different HDDs, the first time around I never opened this laptop before. If you don’t know what’s what, just make sure your laptop is off (battery disconnected), then look for the cover with a screw in it on the end of the laptop opposite of the CD drive.

Here’s a good, decently-priced configuration: +$10 ultrabay-to-HDD adapter, +~$20 500Gb 2.5" 7200RPM hard drive, +$28 240GB 2.5" SSD. Good performance and a good amount of space for about $60.

Need to go cheaper than that? Try getting a cheap 240GB mSATA SSD on Amazon. Some go for around $40, which gives you a decent amount of space if the laptop already comes with a hard drive.

If you need to go even cheaper than that, forget any secondary storage and just get a decent SSD. They’re cheap enough now that 240GB drives go for less than $30. If you really need more storage than that, just get a 1TB HDD (~$40 new, ~$30 used).

ExpressCard Slot

Some people recommend using a USB 3.0 adapter for the ExpressCard slot. I’m iffy on this one.

One of the cheapo ones I bought was based on NEC so it worked… Sometimes. If you unplugged it or jostled it a little by accident while the laptop was on, it stopped working until you restarted. If you unplugged something, it wouldn’t register that until you restarted. You get the picture. Not an ideal experience.

I also tried updating drivers as much as possible in Windows and found other drivers (eXtensible something something), but nothing fixed these problems. Apparently there are issues with power management for the NEC/Renesas based cards which may or may not be fixed in Linux. See this thread for more info.

If you look through some of the recommended adapters, you’ll notice that some of them apparently don’t have the same issues. If you find any that work well, great. I only tried one brand and then lost interest. Apparently Gmyle brand cards work well enough.

Screen

You can upgrade the screen to a 1080p panel if you really want to do that. I don’t think I’d recommend it since it seems expensive for me–it’s $40 to $50 just for the converter board with the cable you need for the panel, then still need to shell out another $50+ for the panel itself. On top of that, it’ll also drain the battery faster than the 900p option. Overall, it’s not terribly prohibitive, but it seems like too much for me.

You can also upgrade to the 1600x900 panel, which only requires the screen and a cable. You can see someone else’s Youtube video showing how they upgraded their machine here.

The 768p panel is noticeably worse than the 900p panel, but it’s still not as bad as a 15" 768p panel. I don’t like it very much, but I don’t have too many complaints about it.

Cost

All prices listed here are rough guidelines of cost after shipping is considered. Not everything here is likely to be correct–especially now–so do your own research.

The cost is roughly $50-$100 if you’re buying used instead of “refurbished” on eBay as of Oct. 2019. “Refurbished” are anywhere between $105-$200. (There’s one outlier at above $220, but let’s ignore that.)

Higher resolution and tested-to-POST used models are around $100, the higher end of the spectrum for the used category. Models that are tested that come without charger AND hard drive/caddy/etc. sit around $50-$80. That’s life, unfortunately.

Note: I really wouldn’t recommend paying much more than $50 for a T420 if it comes without a charger and a hard drive–you’re gonna have to do work after buying it, so is it really worth it to pay more than $70 after shipping when you’ll end up spending over $100 once you get a hard drive, hard drive caddy, and the charger? I’d say no–you’ll barely pay more for a tested-and-working model with the hard drive and caddy, even if you have to buy the charger afterward (~$10). ~$60 or under might be worth it if you’re willing to do a little work to save a little money and already have a hard drive on hand.

Aside from that gripe, these seem like okay enough prices–not great but not terrible. If there’s some stupid hike on prices, I’d recommend waiting it out. (Prices are higher as of Sept. 2020; just wait them out.)

You can find deals on them here and there when you find guys that are trying to sell for some quick cash. I got my original model for $60 because the guy needed $60 immediately more than $100 if he waited another week or two. It worked out, because I was too broke to afford $100, but $60 was within the ballpark. The one I recently got off of Reddit only cost me the price of shipping.

Conclusion

This is my favorite laptop that I’ve ever had, as well as had the opportunity to work inside of.

It’s portable enough for my needs (~5 pounds); it’s physically solid; the keyboard is nice; the screen isn’t great but it’s better than a 15" 1366x768 screen (manufacturers: why do you make these?).

And, on top of that, it’s decently mod-able (as you can see above). I love this stupid laptop, but I realize there are far better machines out there.