Can I use an 128GB SD card instead of an external hard drive on mac osx

I would view this as a short term solution for a number of reasons:

a) Internally, the SDXC reader in your laptop connects via USB, and SDXC cards are rarely as fast as internal SSD storage. So it will be slower that your internal storage, and a little slower than many external USB 3 hard drives. Chances are it will be fast enough to keep you happy though!

b) Leaving the SDXC card in the laptop#s slot all the time will leave a card poking out of the slot a little. Every time you bump the card you wear out the card and the slot a little bit.

c) SDXC cards are not designed to be written over and over and over again like a hard drive. They are by no means fragile these days but I would always expect the hard drive to last longer, even if the warranty on the two storage devices was identical.

d) A 128GB SDXC card is not cheap.. if you check out the used Mac market you may find it is cheaper to sell your current beast get a beefed up machine? Maybe! Could you tell me which machine you have?

e) It sounds like you should be managing your file sizes better. How long before you start shopping for a 256GB SDXC card? :(