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Background and Identification ¶ 

The ThinkPad T420 was introduced in 2011 as a mainatream business laptop. These machines are typically used in applications where a mobile workstation is not required and a standard laptop is sufficient.

Machine Identification ¶ 

You can identify your machine as a ThinkPad T420 or T420i by looking at the bottom right corner of the LCD bezel. The model of the machine is printed in this location.

Block Image

To identify the factory specifications, look for a 7 digit System Type. It will look something like this:

Block Image
  • Ready to ship: XXXX-XXX

To find the specs on a machine with a CTO SKU, you will need to look up the system serial number and see what Lenovo lists under Machine Info in Lenovo Support. For ready to ship models, it can generally be found with a Google search or through Lenovo Support.

To locate the serial number, look on the same sticker that has your system SKU number. It should read like this: S/N XX-XXXXX. To locate the factory specs on a CTO model, you will need this to determine the exact specifications of the system, but it can also be used to determine if a ready to ship model has been customized with extra hardware or ordered with extra accessories when purchased, like extra batteries. It is also required to check the warranty on the system, and will tell you when the system was purchased.

How the T420i varies from the T420 ¶ 

The T420i is similar in the sense it shares the same chassis, but the machine is just not as common. The differences between the standard T420 and T420i aren't substantial enough to affect the average person buying a secondhand one, but you should be aware of the limitations the T420i has the standard system does not.

  • Processor: The T420i ships with the Core i3 2310M processor, which makes it somewhat unique. This processor was never offered on the standard T420.
  • Intel AMT: Since these systems ship with the Core i3 2310M, the BIOS does not have the vPro Option ROM licensed.
  • Computrace: While Intel AMT is not available, the Comutrace Option ROM is included with these systems,
  • Graphics cards: The T420i can only be puchased with Intel HD Graphics. These systems never received the option of including dedicated graphics.
  • RAM: This machine only accepts 8GB per Lenovo. However, the Core i3 2310M supports 16GB per Intel's ARK documentation.
  • Ethernet: The T420i uses a Intel 82577LC Ethernet chipset, rather then the 82577LM chipset found in the standard T420.

The ONLY variation in parts between the T420 and T420i is the motherboard FRU used. This is because the T420i board lacks the AMT code, along with the option of getting dedicated graphics. Outside of this, all other FRU's are shared between systems and are serviced the same way.

In fact, the lack of AMT code on the T420i may be worth considering and in some cases, an advantage for security conscious users who don't want to have to remember to disable Intel AMT if they ever have to reset the BIOS to the defaults. It's also not likely Lenovo will patch it, so you will have to disable it with every BIOS reset or buy a T420i to get around the problem.

While the T420i is very similar, these differences MIGHT matter to some buyers and need to be considered when you are looking at the two machines. However, the variations are minor and rarely matter on the secondhand market due to the age of the system.

Specifications ¶ 

Processor ¶ 

Non vPro

  • Intel® Core™ i3 2310M (2.1GHz, 3MB L3, 1333MHz FSB) Note: T420i only.
  • Intel® Core™ i5-2410M (2.3GHz, 3MB L3, 1333MHz FSB)
  • Intel® Core™ i5-2450M (2.5GHz, 3MB L3, 1333MHz FSB)


  • Intel® Core™ i5-2520M (2.5GHz, 3MB L3, 1333MHz FSB)
  • Intel® Core™ i5-2540M (2.6GHz, 3MB L3, 1333MHz FSB)
  • Intel® Core™ i7-2620M (2.7GHz, 4MB L3, 1333MHz FSB)
  • Intel® Core™ i7-2640M (2.8GHz, 3MB L3, 1333MHz FSB)

Most machines use the Core i5 2520M. There are systems with i7 processors, but these are rare and are likely to be upgraded processors, unless you can verify the system shipped with it by looking for a sticker with a Lenovo FRU or checking online.

Note: Lenovo did not ship these systems with quad core processors. Systems with a QM part installed are user upgraded. Do this upgrade at your own risk.

Memory ¶ 

Most T420 systems ship with ~4GB of RAM, unless it was upgraded by the previous owner or shipped with more memory then this from the factory. On a non CTO SKU, you can quickly figure this out by googling the system type. On a CTO SKU, run the serial number through Lenovo's support page. Look at the Machine Identification section to see how to identify if you have a CTO or Ready to Ship model, and find your system serial number.

Memory capacity and type (Official)

  • Memory type: DDR3 1.5V
  • Memory speed: 1333MHz (Recommended)

Maximum supported memory:

  • T420: 16GB
  • T420i: 8GB

Memory upgrades (unofficial)

Disclaimer: Since the machine this page was written around is the i5 2520M model, I am not able to test the stability with 32GB installed. Do this upgrade at your own risk.

  • Supported Memory types: Sandy Bridge is DDR3L-Aware. While Lenovo does not support this, you should not have any problems with DDR3L modules installed. However, this may not be the case 100% of the time.
  • Memory speeds: 1600MHz (will downclock to 1333MHz)

Maximum memory capacity:

  • T420 (With Core i7 upgrade): 32GB
  • T420i (Core i3 or or Core i5 upgrade): 16GB

General information on installing DDR3L compatibility:

  • While DDR3L is likely to be stable, it may downgrade to 1.5V in the event the 1.35V voltage level is not supported. Remember that Sandy Bridge is DDR3L aware, but is not officially supported at the 1.35V level.
  • To avoid any problems (if DDR3L is used), find modules that are advertised to downgrade to 1.5V to avoid having to buy memory a second time.
  • If dual voltage memory is installed and is accepted at the 1.35V voltage level, you will see a marginal improvement in battery runtime.
  • Do a 6-8 hour Memtest 86+ run and see if the system reports any problems running with DDR3L. If everything checks out, you are good to go.
  • 1.35V only modules are unlikely to work.

Hard Drive ¶ 

This machine can run with 2 drives installed. It can take an mSATA SSD and a 2.5" SATA hard drive.

Note: While the WWAN slot can accept an mSATA SSD, the drive will only run at SATA II speeds in this slot.

While the WWAN slot only runs at SATA II speeds, this is sufficient for a small boot SSD. It is recommended that this is supplemented by a spinning hard drive for mass storage.

Important: The SATA spec on this machine is unclear. According to Crucial, this machine is SATA III capable. However, it has only been validated with SATA II drives. Since this is poorly documented, a SATA III drive with SATA II compatibility is recommended.

Video cards ¶ 

This machine shipped with 2 configuration options

  • Intel HD Graphics 3000
  • Intel HD Graphics 3000/nVidia NVS 4200M (nVidia Optimus enabled)

Important: When you are buying the system, decide if you want a iGPU or Dual GPU system BEFORE you buy, if you care about this. If you get a Intel only one, you are stuck with Intel video and CAN NOT add a dGPU.

WiFi ¶ 

Warning: This machine has a WiFi whitelist. In order to install other cards that are not listed, a no WL BIOS is required. These systems will POST with an 1802 error without this modification.

Supported cards:

Supported, but not recommended:

  • ThinkPad BGN (RealTek - Stockton) 1x1 BGN
  • Intel Centrino Wireless-N 1000 (Condor Peak) 1x2 BGN

Supported Recommended cards

  • Intel Centrino Advanced-N 6205 (Taylor Peak) 2x2 AGN
  • Intel Centrino Ultimate-N 6300 (Puma Peak) 3x3 AGN

You must buy a card that has a Lenovo FRU on the label to ensure compatibility. Unless you are willing to flash a no WL BIOS or alter the card's PCI ID to get around the whitelist, you will need to make sure you have a Lenovo card. It helps to know the FRU of the card you want, to make it easier to find.

WWAN cards ¶ 

Note: All supported WWAN cards are obsolete. Use an external device or flash a no WL BIOS and install a modern card.

The vast majority of machines are billed as WWAN upgradeable. This means the machine has the antennas and SIM slot installed, but does not include the card. The WWAN card goes next to the bottom RAM slot.

Supported cards:

  • Ericsson F5521gw (3G/HSPA+/GSM capable)
  • Sierra Wireless Gobi™ 3000 (HSPA/CDMA EV-DO)


Dual network cards (GSM and CDMA):

These cards must be released from the previous account, if the system was previously used on a CDMA provider. If the card was used on a CDMA network and was not released, the card is useless. This is because CDMA relies on an embedded SIM card, and the account data will be stored on this embedded SIM card. Even if you tore into the card and cleared the chip out without killing the card, it is still registered with the previous carrier and they will reject it.

There is a potential exception here: If the card was on a GSM network, you MAY be able to use it anyway. Do not count on this, but it's something that may end up working. This may work, since the embedded SIM is not being used; rather, an external SIM card under the RAM door is used. BE WARNED the card may be blocked, if the seller retained the IMEI number. If the seller or previous owner did not do this, you should be in the clear if the card has been released from the previous account and the seller did not retain the information from the card.

GSM only: These cards are relatively safe, compared to dual network cards. These do not require account removal like CDMA cards do, but failing to do this may end up "bricking" the card, should the IMEI ever get blocked. I recommend getting the seller to tell you it is clear, or have them do it before you buy the card, if this is at all possible. If you can't do this, you are buying the card with the risk it will be blocked at any time, without warning. The service is tied to the SIM card on these cards, but the IMEI can be blacklisted, which will kill the card.

To recap:

  • Dual network cards with a residual CDMA account are useless. Check for a residual account on machines that mention mobile broadband from Verizon or Sprint, or if the card came out of one of these systems, verify it is clear to use before buying it.
  • CDMA cards must be clear to use them, especially if the previous account is with Verizon or Sprint.
  • GSM only is safer, and can likely be on multiple accounts.
  • GSM can still be blocked via the IMEI.

Known issues with used systems ¶ 

Computrace Persistence Module (plus a way to check if it is still active) ¶ 

These machines support the Computrace Persistence Module. This can be a problem if the subscription was left on the machine itself before sale. It is important to check this before buying the machine. To do this, do the following:

  • Boot up the machine, and get to the BIOS. You can do this in a few ways, but the easiest way to do it is to press F12 and load the BIOS from this menu. This is also a good time to check for a SVP, POP or HDP.
  • If the machine warns you that Computrace is active and it cannot be disabled, the subscription is active. DO NOT use the machine in this state.

If you see this upon loading the BIOS, this also indicated an active Computrace subscription:

Block Image

To remove this, you will need to contact Absolute Software and request the subscription be removed. If everything is good, they will remove it.

Note: If you use a non Microsoft OS (Ex: Linux), you will need to install Windows temporarily to unlock Computrace.

Once you do this, disable Computrace. This shouldn't be disabled permanently, so a soft disable is recommended. It may also be a good idea to save the receipt or get a notarized transfer papers in case proof is needed.

BIOS Passwords ¶ 

There are 3 BIOS password levels that apply to this system. Some are worse then others, but here is the list:


Lenovo systems do not have a backdoor password to fall back on. If this password is lost, you will need to replace the motherboard. While these methods will not be discussed on this device page, it can be removed without replacing the motherboard.

Hard Disk password

Note: This is not an issue if you know the master password for the system. The master password can be used to unlock the hard drive.

These passwords cannot be removed without replacing system hardware, generally speaking. Some systems back this up to the ATMEL chip, so this password may be copied to your replacement hard drive. This will render the hard drive useless.

If you are not sure if this will happen, install a hard drive you do not mind losing for verification. If it doesn't copy over, it is safe to install the new hard drive. If it does, you will need to reset the motherboard before replacing the hard drive.

Power on Password

Note: Before resetting this, check for a SVP. Doing this to a system with a POP and SVP will cause the system to default to the SVP and render the system useless!

Unlike other passwords, this is easy to reset. To remove a POP from the system, remove the CMOS battery and hold the power button for 30 seconds to ensure the CMOS RAM has no reserve power. Upon rebooting, you will run into a checksum error where the machine will use the factory default BIOS settings.

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