Data Center Knowledge and The Register report on Dell joining the Container list of suppliers, Rackable, Sun, and Verari.

Dell Inc. (DELL) is building a data center in a shipping container for a customer, and will follow with a container product line. "We have (a container system) in the works for a customer," a Dell insider told The Register. "We are looking at that space very, very closely." The Register's Ashlee Vance said it appears Dell has "geared up a container for Microsoft's late April RFP."
The "data center in a box" concept has been embraced by Microsoft, which plans to pack between 150 and 220 40-foot containers into the first floor of its new Chicago data center. Microsoft executives say the new facility will house up to 300,000 servers.
Dell joins a growing herd of hardware vendors offering container solutions, including Sun Microsystems (JAVA), Rackable (RACK) and Verari Systems all report strong interest in their container products. Last month IBM said its new iDataPlex series of cloud computing servers is being offered in a 40-foot trailer, marking IBM's first foray into container-based systems.
Dell squeezes cloud into a shipping container
By Ashlee Vance in Santa Clara → More by this author
9 May 2008 19:22

Exclusive Sun Microsystems endured a lot of ribbing when it first popped out a data center in a shipping container. Now, however, it looks like all the majors are heading in that direction, including Dell, which The Register has learned has a containerized data center in development.
"We have (a container system) in the works for a customer," said a Dell insider. "We are looking at that space very, very closely."

All of the focus on containers is highlighting an interesting change Microsoft has made on the Data Center hardware industry. In the past, Microsoft has written hardware specification documents like this one.

This publication is the first in the Hardware Support and Directions for Windows Server series, which shares the Microsoft intention and investment direction for support of specific hardware technologies in current and future releases of the Windows Server operating system. This series focuses on Windows Server features that are relevant to the hardware capabilities of a server.

This is soft pitch to server OEMs and other hardware vendors to build good Windows Server boxes. This document will not drive big changes.

Given the purchasing by Microsoft's data center properties (search, hotmail, maps,etc.) are now driving Server OEMs with custom RFPs like the CBlox RFP, OEMs are building exactly what Microsoft wants to run a more efficient data center. And, versus Google's model of requiring exclusive designs no one else in the industry can purchase, the Microsoft skus spill into the rest of the market.

To confirm the idea, here is speculation on ask.com's sku being marketed by Dell.

One system, however, really caught our attention and is worth some ink now. It's the XS23, which regular folk cannot buy.
Dell refuses to comment on the server publicly, although we managed to work some information about the hardware out of source.
The XS23 squeezes 4 two-socket servers (in a 2X2 stack) in a 2U chassis along with twelve 3.5 inch SAS/SATA drives across the front of the system. It was designed for a search company, which we believe was Ask.com.
As we understand it, the disk to DIMM count was very important for this search customer, who wanted three drives for every server. This design was enough for the unnamed customer to buy tens of thousands of systems, according to our source.
The Dell system consumes 25 per cent less space than your general purpose blades, which do about 16 two-socket servers in 10U. Dell, of course, stripped out the redundant power supplies and fans to get that density, but these cloud folks have software that can deal with failures just fine.
We even managed to obtain a couple photos of the XS23. The big daddy shots are here and here.

One of the most valuable lists would be Microsoft's data center equipment RFPs and the equipment they chose, but don't hold your breath waiting for Microsoft to make this publicly available. It would be a PR disaster with almost every Server OEM screaming.