There are different speed grades for SD cards, which are measured with the same system as CD-ROMs, in multiples of 150 KB/s. Basic cards transfer data up to 6 times as fast (900 KB/s) as the standard CD-ROM speed. High-speed cards are made with higher data transfer rates like 66x (10 MB/s), and high-end cards have speeds of 150x or higher. Some digital cameras require high-speed cards to record video smoothly or capture multiple still photographs in rapid succession. Most devices today comply to the SD card specification 1.01, with maximum speed of 66x. Higher speeds of up to 133x are defined by specification 1.1.
Since the OCZ SD Duo as two interfaces, it was tested twice with each benchmark program (one using the SD interface, and another time using the USB interface). The SD interface was tested using an internal 8-in-1 card reader, with a direct connection to a USB 2.0 port. The OCZ SD Duo was tested on a PC with the specifications below.
- AMD 3800+ X2
- Asus A8N-SLI Deluxe motherboard
- 2GB Corsair DDR-400
- 8-in-1 flash card reader (USB 2.0)
SanDisk mini SD 1GB 
OCZ Duo (SD Interface) 
OCZ Duo (USB Interface) The card is able to reach its rated speed of 80x (12MB a second), but only through the direct USB interface. Real-world usage yields an average 40x speed (6MB a second).
SD memory is limited to 4-bit chunks, which is probably the limiting factor, and the cause of the lower bandwidth. In real world use, however, this is plenty fast for most digital cameras, unless you’re taking uncompressed photos 3 times a second (in which case you probably have a camera with a CompactFlash interface).
