A modular computer system comprising: a rack mountable shelf having a housing, at least one information processing module removably receivable at a first face of said housing, wherein the first face is a front face of the housing and each said information processing module is configured as a server blade having an enclosure, at least one computer support module removably receivable at a second face of said housing, wherein the second face is a rear face of the housing, at least one power supply module removably receivable at said second face of said housing, a connections member forming a midplane within said housing, said connections member including: a circuit board mounted substantially vertically within said housing between said first and second faces of said housing; a plurality of first connectors arranged in a row along a first face of said connections member, each first connector being configured to connect to a connector of a said information processing module; a plurality of apertures in said circuit board which cooperate with openings in the enclosures of said information processing modules to allow a flow of cooling air therethrough; at least one second connector at a second face of said connections member configured to connect to a connector of said at least one computer support module; respective connection paths between said first and second connectors for at least information signals and management signals; at least one third connector at said second face of said connections member configured to connect to a connector of said at least one power supply module; and at least power connection paths from said third to said first and second connectors. a rack mountable shelf having a housing, at least one information processing module removably receivable at a first face of said housing, wherein the first face is a front face of the housing and each said information processing module is configured as a server blade having an enclosure, at least one computer support module removably receivable at a second face of said housing, wherein the second face is a rear face of the housing, at least one power supply module removably receivable at said second face of said housing, a connections member forming a midplane within said housing, said connections member including: a circuit board mounted substantially vertically within said housing between said first and second faces of said housing; a plurality of first connectors arranged in a row along a first face of said connections member, each first connector being configured to connect to a connector of a said information processing module; a plurality of apertures in said circuit board which cooperate with openings in the enclosures of said information processing modules to allow a flow of cooling air therethrough; at least one second connector at a second face of said connections member configured to connect to a connector of said at least one computer support module; respective connection paths between said first and second connectors for at least information signals and management signals; at least one third connector at said second face of said connections member configured to connect to a connector of said at least one power supply module; and at least power connection paths from said third to said first and second connectors. a circuit board mounted substantially vertically within said housing between said first and second faces of said housing; a plurality of first connectors arranged in a row along a first face of said connections member, each first connector being configured to connect to a connector of a said information processing module; a plurality of apertures in said circuit board which cooperate with openings in the enclosures of said information processing modules to allow a flow of cooling air therethrough; at least one second connector at a second face of said connections member configured to connect to a connector of said at least one computer support module; respective connection paths between said first and second connectors for at least information signals and management signals; at least one third connector at said second face of said connections member configured to connect to a connector of said at least one power supply module; and at least power connection paths from said third to said first and second connectors.