操作系统物理地址空间与逻辑地址空间

物理地址空间

系统中的物理地址空间可以定义为主内存的大小。比较进程大小与物理地址空间非常重要。进程大小必须小于物理地址空间。

Physical Address Space = Size of the Main Memory 
If, physical address space = 64 KB = 2 ^ 6 KB = 2 ^ 6 X 2 ^ 10 Bytes = 2 ^ 16 bytes 
Let us consider, word size = 8 Bytes = 2 ^ 3 Bytes 
Hence, Physical address space (in words) = (2 ^ 16) / (2 ^ 3) = 2 ^ 13 Words 
Therefore, Physical Address = 13 bits
In General, 
If, Physical Address Space = N Words 
then, Physical Address = log2 N

逻辑地址空间

逻辑地址空间可以定义为进程的大小。进程的大小应该足够小，以便可以在主内存中存放。

假设，

Logical Address Space = 128 MB = (2 ^ 7 X 2 ^ 20) Bytes = 2 ^ 27 Bytes 
Word size = 4 Bytes = 2 ^ 2 Bytes 
Logical Address Space (in words) = (2 ^ 27) / (2 ^ 2) = 2 ^ 25 Words 
Logical Address = 25 Bits 
In general, 
If, logical address space = L words 
Then, Logical Address = Log2L bits