TweakTown reports the SD memory card specification 4.0 is expected to be finalized by Spring 2010. The new standard enabled transfer speeds of up to 300MB/s, almost three times faster than the current specification. The new memory cards will be backwards compatible, but will be limited to a max of 104MB/s with current hardware.
The higher speed is accomplished by changing the data transfer scheme from parallel to serial using low-voltage differential signaling (LVDS). This also means the number of pins on the cards themselves and in the readers will increase from the current nine in order to get the speed increase. It's been said the new cards, despite having more pins, will be able to operate in current hardware, only the speeds will of course be limited to a max of 104MB/sec.