Purpose of various SIB are given below:

MIB - Main index for system information. Contains scheduling information on SIBs and up to two scheduling blocks

SIB1 - Contains NAS information as well as information on timers for use in idle or connected mode

SIB2 - Contains information on the URAs that are available. There can be up to 8 URAs in a cell

SIB3 - Contains information on the cell selection and reselection parameters that the UE should use whilst in idle mode

SIB4 - Similar to SIB3 contents for connected mode. if no SIB4 then UE should use SIB3

SIB5 - Contains information on the common physical channels in the cell (PICH, AICH, P-CCPCH, PRACH, SCCPCH) for a UE in idle mode

SIB6 - Same like SIB5 to use in connected mode

SIB7 - Contains information on fast changing cell parameters such as the upliink interference levels (used for open loop power control for the PRACH) and the dynamic persistence value (also used for PRACH)

SIB8 - for FDD mode only. Contains static information for CPCH

SIB9 - for FDD mode only. Contains dynamic information for CPCH

SIB10 - For FDD mode only. Sent via FACH, contains informatino relevant to the DRAC procedure

SIB11 - Contains measurement control information for a UE in idle mode

SIB12 - Contains measurement control information for a UE in connected mode

SIB16 - Contains information on channel configuration (physical, transport and RB) to be stored in the UE for use during handover to UTRAN

SIB18 - Contains PLMN identities for neighbouring cells to be considered for use by a UE that is in either idle or connected mode