problem while installing ARM IDE in windows 8
Just a correction here. Keil MDK is updated as regularly as DS-5 and is supported through ARM's technical support channels just like DS-5. It is not legacy software.
Whether you use Keil MDK or DS-5 is dependent on what kind of device you are working on. In general, MDK is aimed at commercially available, off-the-shelf microcontrollers. DS-5 is aimed at ARM application processors and custom SoC designs. There's a more detailed explanation here: Embedded Microcontroller Tools for ARM | ARM DS-5 Development Studio and a table on keil.com: ARM Tools Comparison
Thanks, Joe, for the clarification. I know Keil is officially supported, and I used "legacy" with a different connotation Never liked the cluttered and overpriced Keil... And, ARM application processors are where my exclusive interest is these days, so I have to admit I am oblivious to everything else out there