Express Card slot and SD card slot difference?

CF card readers designed for use in ExpressCard slots are larger and much more fragile than USB CF card readers. If you use CF cards, get a USB reader, regardless of which MBP model you buy.

The SD card slot in the 13" or 15" MBP will be of no use at all to you if you don't use SD cards, unless you create a bootable SD card as an emergency startup "disk" in case your hard drive fails or needs fixing when you're far from home and office.

The _SD card slot_ is exactly what its name implies - it's a slot you can insert an SD memory card into. Most people use this to copy photos from SD memory cards they use in their cameras. It will only fit SD memory cards. Of course, you can also use SD memory cards for other purposes, such as file storage.

_The ExpressCard/34 slot is totally different._ ExpressCards provide additional interfaces for external devices. This is a newer version of what used to be known as PCMCIA, PCCard or CardBus. Very often people use ExpressCard/34 cards for additional FireWire or USB ports; or to add an eSATA port; or modem or wireless networking, etc.

A USB card reader will be just as fast as an ExpressCard CF reader with most cards.

MartinR:

Can I insert an SD card and use it to, say, store edited photos that I want to take to Walgreen's and print?

No difference to Apple. ExpressCard slot repair cases are internally marked as SD Card slot ones. Oh boy...

Yes, you can.