Computers as Components, 2nd Edition

60 CHAPTER 2 Instruction Sets

2.2.1 Processor and Memory Organization

Different ver sions of theARM architecture are identified by different numbers. ARM7

is a von Neumann architecture machine, while ARM9 uses a Harvard architecture.

However, this difference is invisible to the assembly language programmer, except

for possible performance differences.

The ARM architecture supports two basic types of data:

■ The standard ARM word is 32 bits long.

■ The word may be divided into four 8-bit bytes.

ARM7 allows addresses up to 32 bits long.An address refers to a byte,not a word.

Therefore, the word 0 in the ARM address space is at location 0, the word 1 is