ThinkPad T450s boots slowly after RAM upgrade

After I installed an 8 GB RAM stick in the single DIMM slot in a ThinkPad T450s, the system didn’t seem to be powering on successfully. The usual ThinkPad logo didn’t appear within a few seconds. Instead, the screen remained black for quite a long time. I powered off the system and tried reseating the DIMM, but the problem remained.

It turns out that I wasn’t patient enough. According to a Lenovo forum post, it may take a couple of minutes for the system to boot the first time after a RAM upgrade, as it “checks timings and configures the slots.” Subsequent boots go quickly, as expected.