Specifications

©Copyright 2001-2013 SD Group (Panasonic, SanDisk, Toshiba) and SD Card Association
Physical Layer Simplified Specification Version 4.10
101
Figure 4-52 : Measurement of Pw (AU size is larger than 4MB)
4.13.2.2.2 Performance Move
In contrast with Speed Class for SDSC and SDHC, Pm is not supported in SDXC. This means that
Speed Class host shall write data to the entire free AUs so that SDXC card can provide Class
performance. Pm shall be set to 0 in SD Status of SDXC card.
Application Note:
The amount of unwr
itten memory and the amount of Speed Class recordable memory may be
different. Speed
Class hosts can maximize the amount of recordable memory by defragmenting
and freeing AUs for use when Speed Class performance is required.
4.13.2.3 Read Performance
The read performance of an SDXC card has the same definition as that for SDSC and SDHC. Pr is
defined as the minimum average random RU read performance over 256 RUs. Pr shall be greater than
or equal to Pw.
T
FR
(4KB) is defined as the maximum time to read 4KB data.
4.13.2.4 FAT Update
The SDXC FAT update cycle has almost the same definition as in SDSC and SDHC. The only
difference is the data type and its location. In the case of SDXC, the FAT update cycle consists of three
write operations, FAT, Bitmap and directory entry. The FAT is written starting at any 512-byte boundary
address and with any size up to 16Kbytes. Bitmap is written starting at any 512-byte boundary address
and with any size from 512-byte to 16Kbytes.
A directory entry should be created before starting recording and the same block should be written by
512-byte single block write (either CMD24 or CMD25).
Average and Maximum FAT Write Time ( T
FW
(ave.) and T
FW
(max.) ) are the same as defined for SDSC
and SDHC. Average FAT Write time is defined as the maximum sliding average of 8 FAT update cycles.
Note that a Speed Class host can insert FAT update at any RU boundary. Insertion of FAT update never
affects Pw.
4.13.2.5 CI (Continuous Information) Update
CI (Continuous Information) is a new structure used to manage exFAT file fragments. It is newly defined
in the Part2 File System Specification Version 3.00. CI may be updated during Speed Class recording.
Creating CI is optional for the host. The specific feature of CI update is described below.
• CI can be inserted at any RU boundary. The frequency of CI update depends on the host
implementation.
RU
...
AU
(Multiple of 4MB)
4MB
Memory area
in the card
4MB
4MB
Speed Class host writes sequentially in an AU in unit of RU
Performance is measured over each 4MB boundary.
Performance of the AU = min (Pw
1
, Pw
2
, …
Pw
N
)
=> Pw is defined as minimum performance of all
AUs in memory area
Pw
1
Pw
2
Pw
3
Pw
N
...
...