I received an email message from an IIS Administrator UPDATE reader who wanted to know more about Web server hardware. I'm happy to oblige.

The server market has changed lately, and some of these changes are noteworthy. The market suggests that thin is in again. No product has been spared: thin clients, thin disks, and thin servers. Over the past few months, all three major server manufacturers—Compaq, Dell, and IBM—have introduced a thin server, so thin, in fact, that you might mistake it for another rack component. The servers might be small, but their performance isn't puny.

The new servers take up only 1U (1U=1.75") of rack space. Yes, you read that right—a server less than 2 inches tall. For those of you keeping score at home, that's more than 40 servers in a full-size rack. Imagine the cable plant necessary to support more than 40 servers. Figure a power cable, networking cable, and video, keyboard, and mouse cables: That's a minimum of 5 cables times 42 servers (in a 42U rack), giving you more than 200 cables that have to run somewhere.

I think these servers will lend themselves to the booming Web server industry as an easy way to run a lights-out shop. Manufacturers are marketing the small, 1U units as rip-and-replace servers because they have few serviceable internal parts. If a server fails, you merely replace the entire thing and return the original for repair.

The first generation of 1U servers that came to market had almost no hot-swappable or removable parts for an administrator to service. Now, we're seeing two 1" hot-swappable drives as standard fare. Dual processors and dual NICs are also options. Memory sizes, however, are often limited to 4GB, and because of the nature of the designs, you still can't get redundant power supplies.

These servers won't be the perfect fit for every use. When you compare features against price, you might find that the larger 2U and 3U servers are cheaper than the compact servers. But when space and support are scarce, the 1U server might well fit your need.