What specification hardware do I need to run SQL Server for good performance?

A. (1) How long is a piece of string? (2) It depends.

These are the two most accurate answers that can be given, as completeinformation is needed on size of database, complexity, triggers, indices, DRI,number of users, transactions per minute, update ratio, row length, key sizesetc. before even a rough estimate can be provided. Plus hardware performance interms of cpu power and disk performance is always increasing at phenomenalrates.

However, as some general pointers :-

Memory is the most important resource until you get to 95% cache-hit ratio.It then doesn't matter too much how much extra memory you add. Start with 128Mbram (because ram is cheap), but make sure you have spare simm/dimm slots forexpansion.

Next come disks and the disk subsystem - especially for updates.Battery-backed write-back cache is good - the more the better. The more raidcontrollers you have the better - not because they are generally a bottleneck,but because you can then have multiple sets of read and write-back cacheassigned. Dedicating a controller just to the transaction log is good becausethis then gets some dedicated write-back cache.

Processors usually come last - SQL rarely gets processor bound except on thebiggest systems, but if you have the money then get 2 or more. The most benefitcomes from the 2nd with the law of diminishing returns kicks in after that. SQLscales well to 4 processors, and scales reasonably well to 8 (depending on thehardware implementation), but after that......... Remember that with 6.5 andbelow a single query will only ever use a single processor, whereas in SQL 7 itwill parellise queries if it thinks that will make it run faster.

Don't forget network cards and network design. You won't get 500 concurrentusers through a single 10Mbit Ethernet ISA card. If you have a significantworkload in terms of users or large result sets then make sure you havemultiple network cards - PCI bus master variety. Have the cards on differentrings/segments if your users are devolved that way - otherwise attach thecard(s) direct to a switch for full-duplex throughput and consider the use ofeither software or hardware card aggregation (like Raid for disks, but forcards). Some cards have this facility built-in to the hardware, but there are3rd party software drivers that will make it work for any card.