Finally added mSATA SSD to my T420 and now have 3 drives booting multiple operating systems, what a joy 😁 : r/thinkpad
45N8081 Lenovo 128GB MLC SATA 3Gbps 2.5-inch Internal Solid State Drive (SSD) for ThinkPad T420
Lenovo ThinkPad T420 Laptop- 128GB SSD, 4GB RAM, Intel i7 CPU, Windows – Buffalo Computer Parts
Fortysomething Geek: Thinkpad T420 triple drives with MSATA and Ultrabay
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Lenovo ThinkPad T420 14.0" Black USED Laptop - Intel Core i5 2540M 2nd Gen 2.6 GHz 8GB SODIMM DDR3 SATA 2.5" 256GB SSD DVD-RW Windows 10 Pro 64-Bit - Walmart.com
For Lenovo Thinkpad T420 T430 T510 T530 W700 Optibay Aluminum 2.5" Ssd Case Hdd Enclosure 2nd Hdd Caddy 12.7mm Sata 3.0 - Hdd & Ssd Enclosure - AliExpress