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Spare memory is exactly what it sounds like: extra RAM to which the system can copy if it detects too many correctable errors or an uncorrectable error in the current memory bank. The system administrator can swap the memory out during scheduled downtime or nonpeak times. Memory mirroring is a technique in which the system makes a copy of every piece of data in identical banks. If the primary bank fails, the system makes a fast, seamless transition to the mirrored bank. The only problem with this technique is the doubling of memory costs and the halving of the total amount of memory you can put in the system. DDR RAM is about twice the price of standard SDRAM--about $250 to $400 per gigabyte if you buy it online--so costs can add up quickly (see "Server Chips Ahoy!").

All three servers also have USB ports, which are standard on desktop PCs. Although these ports can be very useful for attaching things such as USB KVM (keyboard, video, mouse) equipment, they also raise security concerns. Anyone can pick up an 80-GB USB hard drive for about $200, attach one to a server and help himself or herself to a chunk of company data. Obviously, physical security is critical.

We found as many differences as similarities in the units we tested. The IBM and Dell servers came with three 36-GB, 15,000-RPM SCSI hard disks; the HP unit had half that storage: three 18-GB 15,000-RPM SCSI hard disks. HP said it couldn't provide us with the 36-GB drives we requested. The ProLiant's hard disk subsystem problems, however, stemmed from cache algorithms, not size. The IBM unit was considerably larger than the other two units--7U rather than 4U--but the extra space was put to good use.

The Dell PowerEdge 6650 won our Editor's Choice award. This solid machine produced good performance numbers across the board and offers better usability and maintenance features than the competition. Best of all, its $31,885 list price, which includes the OS, is $5,200 less than IBM's, and $5,800 less than HP's price. IBM's server is solid, but it lacks some of Dell's rackmount serviceability features. The HP ProLiant DL580 G2's disk-performance issues keep us from recommending the machine.