SD Ver 1.1 : The faster SD

Whereas the SD 1.01 standard specifies a maximum clock rate of 25 MHz, the newer SD 1.1 version doubles the clock rate to 50 MHz. Using 4-bit mode data transfer, this increases the theoretical data transfer rate of the newer SDs to 25MBps or 166X.

There are sites which state that the SD 1.1 standard allows for an optional 8-bit data bus width. If this is so, this can only be possible by adding more pin connectors like what was done with the 13-pin MMCplus (original MMC had only 7). The current 9-pin SD bus currently uses 4 pins for data, 3 for power/ground and a line each for clock and command/response signals.

As of this writing, the fastest SD card available is 133X~150X and comes in a 9-pin package.