Nothing has a greater impact on application performance than application design. A poorly designed application will perform badly on the best hardware, and throwing more hardware at a bad design will often result in little application performance improvement.
Spend your up-front resources on sound application design principles and an exhaustive and representative QA process. For instance, during the design and development phases, developers should keep a close eye on the bottlenecks and address the most significant problem areas. During QA, the application should be load-tested using products like Segue Software Inc.'s SilkCentral, Mercury Interactive Corp.'s LoadRunner or even Microsoft Visual Studio's Application Center Test to see how the application performs under representative load and stress.
Spec your SQL Server hardware needs Home: Introduction Step 1: Invest in good application design Step 2: Understand your workload Step 3: Know your memory support limitations Step 4: Choose a reliable hardware brand Step 5: Take advantage of 64-bit Step 6: Take advantage of storage area networks Step 7: Properly configure your RAID arrays Step 8: Use separate disk controllers Step 9: Choose and optimize your disks wisely Step 10: Optimize CPU activity and speed