What is the difference between 128 MB sd card and a 2gb sd card?

Their storage capacity. 2gb SD Card can store more data than 128mb SD Card.

Unit

Equivalent

1 kilobyte (KB)

1,024 bytes

1 megabyte (MB)

1,048,576 bytes

1 gigabyte (GB)

1,073,741,824 bytes

1 terabyte (TB)

1,099,511,627,776 bytes

1 petabyte (PB)

1,125,899,906,842,624 bytes