从数据存储类型来说，8051系列有片内、片外程序存储器，片内、片外数据存储器，片内程序存储器还分直接寻址区和间接寻址类型，分别对应code、data、xdata、idata以及根据51系列特点而设定的pdata类型，使用不同的存储器，将使程序执行效率不同，在编写C51程序时，最好指定变量的存储类型，这样将有利于提高程序执行效率(此问题将在后面专门讲述)。与ANSI-C稍有不同，它只分SAMLL、COMPACT、LARGE模式，各种不同的模式对应不同的实际硬件系统，也将有不同的编译结果-From the data storage type, the 8051 series chip and off-chip program memory on-chip and off-chip data memory, on-chip program memory sub-direct addressing area and indirect addressing types, respectively, corresponding to the code, data, xdata types of idata pdata set according to the characteristics of the 51 series of, use different memory, different program execution efficiency will, in the preparation of the C51 program, it is best to specify variable storage type, so there will be help to improve the efficiency of the program (this issue will be devoted to later). Slightly different from the ANSI-C, only points SAMLL COMPACT, LARGE mode, various modes corresponding to the actual hardware system will also be different from the compiled results