c sizeof的有关问题

c sizeof的问题
typedef struct 
{
unsigned name:8; //名称
unsigned type:8; //数据类型
unsigned data:8; //数据
}DataModeA;

typedef struct 
{
unsigned name:8;
unsigned type:8;
unsigned data:16;
}DataModeB;

typedef struct
{
unsigned name:8;
unsigned type:8;
unsigned data:32;
}DataModeC;

sizeof计算结果
sizeof(DataModeA) = 4;
sizeof(DataModeB) = 4;
sizeof(DataModeC) = 8;

什么问题啊？

------解决方案--------------------------------------------------------
lz的疑惑在哪？
这是内存对齐，google之。