I have a late 2012 27-inch iMac Core i7 and when I insert a 4GB or 32GB SD card it does not read. Looking at System Report I only see the following
Built in SD Card Reader:
Vendor ID: 0x14e4
Device ID: 0x16bc
Subsystem Vendor ID: 0x106b
Subsystem ID: 0x0000
Revision: 0x0001
Link Width: x1
Link Speed: 2.5 GT/s
Now after blowing into the built-in SD card reader it works.
Built in SD Card Reader:
Vendor ID: 0x14e4
Device ID: 0x16bc
Subsystem Vendor ID: 0x106b
Subsystem ID: 0x0000
Revision: 0x0001
Link Width: x1
Link Speed: 2.5 GT/s
Now after blowing into the built-in SD card reader it works.