The 8051 architecture supports a number of physically separate memory areas or memory spaces for program and data. Each memory area offers certain advantages and disadvantages. There are memory spaces that can be read from but not written to, memory spaces that can be read or written, and memory spaces that can be read or written more quickly than other memory spaces. This wide variety of memory space is quite different from most mainframe, minicomputer, and microcomputer architectures where the program, data, and constants are all loaded into the same physical memory space within the computer. Refer to the Intel 8-Bit Embedded Controllers handbook or other 8051 data books for more information about the 8051 memory architecture.