Here's what I've done w/ my 3400c. I've used this
CF to IDE 2.5" adapter with a single 2 GB CF card. This works well, but I installed this over a year ago before I learned about
@Action Retro suggestion to use these
M.2 Sata SSD to 2.5' IDE adapters to
with low-cost M.2 Sata drives. I believe these have higher throughput and I'm testing them in Retro computers first, with the CF solution as a fall back if the drive is not recognized. Sorry I don't know if this newer, faster solution will work in a 3400.