Hi asp,
I have a T420 that is quite happily running Win 7 on a normal hard drive & I have a T410 that runs Win 7 on an SSD. Not used an mSATA SSD but so long as the BIOS picks it up then you should be fine. UEFI on Win 7 won't make a great deal of difference but you may as well use it if you have the option. You will know if you can as when installing Windows 7 you should see UEFI at the beginning of one of the disks, just pick that to install to.
UEFI is better on 8 as you have the fast boot & secure boot up options. I use Win 8 off an SSD dual booted with Ubuntu on my desktop & that starts really quickly. The way UEFI has been written allows for much faster loading than standard BIOS. I won't get bogged down in the difference here as it could go on for pages! Best just Google it if you want to know
Trim support should be automatically enabled on an SSD that supports it. It is important to note that the BIOS must be set to AHCI to allow for trim support under Windows 7, but this should be so anyway even from any standard SATA drive. Some SSD's come with or have downloadable software that will give you the info about TRIM but you can check if it's on or off from CMD. Open an elevated CMD prompt & type: fsutil behavior query disabledeletenotify
Results explained below:
DisableDeleteNotify = 1 (Windows TRIM commands are disabled)
DisableDeleteNotify = 0 (Windows TRIM commands are enabled)
Note that this will only tell you if it's enabled or not & not if your drive supports it or not. You would need a utility from the drive manufacturer for that.
So in short, make sure BIOS is set to AHCI, install Win 7 or 8 & install to the option which has UEFI listed in front of the drive & away you go! I would be very surprised if the hardware for a T420 were not fully supported under Windows 8 so unless time is a problem, try it & see!!
