Specifications

©Copyright 2001-2013 SD Group (Panasonic, SanDisk, Toshiba) and SD Card Association
Physical Layer Simplified Specification Version 4.10
95
Application Notes:
Performance may increase when larger data is written by one multiple wr
ite command. Therefore,
the host may use larger RU sizes and transfer multiple RUs with one multiple-write command.
4.13.1.4 Read Performance
Two kinds of read performances are defined. It is possible to insert either type of read operation during
write operations. All read operations, regardless of read address shall meet this performance
specification.
(1) Read Performance of Stream Data
This is simply called Read Performance (Pr). Pr is defined as minimum average random RU read
performance. The average is measured over 256 random single RU read operations. Each RU is
read by a multiple-read command. Pr shall be greater than or equal to Pw.
(2) FAT and Directory Entry Read Time
T
FR
(4KB) is defined as the maximum time to read a 4KB FAT and Directory Entry. The FAT and
Directory Entry Read Time (S
FR
[KB]) is defined using the CEIL function:
FAT Read Time of S
FR
[KB]:
)4(
4
)( KBT
KB
S
ST
FR
FR
FRFR
⋅






=
...............................................(2)
(: CEIL function - Convert decimal fraction x to the smallest integer greater than or equal to x.)
Refer to Table 4-57 for the values defined for each Speed Class.
4.13.1.5 Performance Curve Definition
Figure 4-49 shows the write performance bar chart of P(Nu) of equitation (1). An AU consists of 16 RUs
in this example. Joining the points of each bar shows the performance curve, which can be determined
from the two parameters, Pw and Pm.
Figure 4-49: Card Performances between 16 RUs
0
16
1
16
2
16
3
16
4
16
5
16
6
16
7
16
8
16
9
16
10
16
11
16
12
16
13
16
14
16
15
16
Performance Curve
[MB/sec]
Ratio of Used RU
Full Performance
Better Performance
16
16