A rack mountable shelf is configured to support a plurality of field replaceable units in the form of server cartridges that each include at least one server processor. The rack mountable shelf is configured to provide communal services for said server cartridges, including at least one of supplying DC operating power to the server cartridges, distributing information signals between the server cartridges and processing system management signals for the server cartridges. Each of the server cartridges can be slideably received in a respective one of a series of server cartridge receiving locations arrayed side by side along the front of the shelf. The server cartridges can be configured as thin blades to provide a high server density. For example, 16 server cartridge receiving locations can be provided across the front of the shelf. The supply of DC operating power to the server cartridges can be provided by one or more field replaceable power supply units (e.g. two redundantly configured power supply units) mounted in the shelf. The distribution of information signals between the server cartridges can be provided by one or more switch units (e.g. two redundantly configured switch units) mounted in shelf. The processing of system management signals for the information processing modules is provided by one or more field replaceable service processor units (e.g. one service processor unit) mounted in the shelf. Each of the power supply, switch and service processor units can be slideably received in a respective receiving location at the rear of the shelf. A midplane including connectors with conductive paths therebetween can provide power, information signal and system mangagement signal connections between received field replaceable units. A multiple computer server can be formed from at least one rack mountable shelf as set out above.