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关于Block(块)和sector(扇区)

2015-04-17 16:41阅读：

http://blog.sina.cn/dpool/blog/u/5330372181

关于Block(块)和sector(扇区):(在针对于SD卡和文件系统)
1. 在SD卡上:
block : A number of bytes, basic data transfer unit (SD中最小的读写单位)。
block length 可以被 SET_BLOCKLEN (CMD16)设置 。
SDHC and SDXC block length 是固定的512Bytes。
协议原文：
7.2.3 Data Read
The SPI mode supports single block read and Multiple Block read operations (CMD17 or CMD18 in the
SD Memory Card protocol). Upon reception of a valid read command the card will respond with a
response token followed by a data token (refer to Figure 7-3). In case of Standard Capacity Card, the
size in the data token is determined by the block length set by SET_BLOCKLEN (CMD16). In case of
SDHC and SDXC Cards, block length is fixed to 512 Bytes regardless of the block length set by
CMD16.
ont >sector: A number of blocks, basic erase unit (SD擦除单位)
可以设置为N*block
协议原文：
SECTOR_SIZE
The size of an erasable sector. The content of this register is a 7-bit binary coded value, defining the
number of write blocks (see WRITE_BL_LEN). The actual size is computed by increasing this number
by one. A value of zero means one write block, 127 means 128 write blocks.


2. 在文件系统上
(1):
Block是文件系统上的概念，一般文件系统block大小为4K。
Sector是磁介质硬盘最小单元，一般为512字节。
Block值一般与sector值是不相等的。
(2):
扇区（block）是驱动可以操作的最小单位，是磁盘级别的。
一个磁盘扇区（sector)512个字节（现在有4K的了）,扇区（sector)是磁盘的最小存储单位,
块(block)是文件系统层的，mkfs时可以设置块的大小.
磁盘块(block)应该是类似FAT的簇大小的概念，是操作系统中分配磁盘容量的最小单位.
块(block)是数据存储的最小单位！

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