You can refer to the above post and one of the major difference is ARM 9 has a memory management unit so that any OS like Linux etc can be ported to it.ARM can also support RTOS like uclinux .Major differences comes in execution ,pipelining ,some processors like OMAP and Davinci are dual core they have both ARM A8 core and DSP core .Clocking is also one of the major difference , ARM 7 runs at 80 Mhz or so and ARM 9 ,ARM A8 runs at 600 MHZ - 1.2 ,1.4 Ghz etc.Some ARM cores like DM3730 (OMAP 3) has a graphic accelerator and a dedicated video processing unit buit in the SOP these are mostly POP (Package over package ) packages.