Technical Overview SD Specification Overview SD Speed Classes and Implementation Introducing New Features on SD Card Issues on Using SD Card in the Market
AU Size and RU Size User Area is divided by AU (Allocation Unit) – AU Size indicates physical boundary of SD memory card – A set of AU Sizes is defined by specification – Write order of AU may be random AU is divided by SU (Sub Unit) (including AU=SU) – Card Performance is the min. average sequential write time to each SU • e.g, C4 = 4MB/sec, C10, U1 = 10MB/sec
– SU is written by multiple of write commands sequentially SU is divided by RU (Recording Unit) – A write command writes multiple of RU data at a time (at least one RU) AU (Allocation Unit)
Example of SU (AU) Performance Speed Class defines Minimum Average Performance – Write Performance of each SU (AU) may differ – Average Write Performance to each SU is more than Speed Class value
There is No Standard to Define Maximum Speed – Usually Max. Speed is limited by either bus performance or memory performance • In 4‐bit mode, 1 byte is transferred every 2 clocks • Bus Clock frequency determines bus performance Write Performance (MB/s)
Example Card Configuration of Memory Units • AU Size can be divided by both Memory Block Size and Sub Unit Size • This architecture enables SD Memory Card to use Memory Block which is not match to Sub Unit • AU Size is limited by the minimum number of AUs Memory Blocks
AU Size
6MB
Sequential Write
Sub Units 8MB SU
6MB 24MB AU
8MB SU
6MB
Sequential Write
8MB SU
6MB
24MB AU
• One AU may consist of multiple of memory blocks • Memory block is allowed to configure Sub Unit boundary mismatch
• Host can manage user area regardless of considering Memory Block Size • Host writes SU sequentially • Host should prepare SU buffer
