INT 7A - IBM 3270 Workstation Program API - SESSION SERVICES
        AH = 09h
        BX = 8020h (synchronous request)
        CX = 0000h
        DX = ID of session manager (SESSMGR)
        AL = service
            01h get session ID
            02h get session info
            04h dettach from session
            05h attach to session
            06h get list of windows available
            07h get environment of window
            08h get 'PIF' (program information file) info
            0Ah get base window ID
            0Bh get cursor info
        ES:DI -> control block
Return: ???