Abstract: Magnetic disks comprising a substrate and glass materials which are used in the manufacture of hard disc substrates. The glasses can have the following compositions (in per cent by weight on an oxide basis): SiO2 10-30, Al2O3 0-5, B2O3 0-8, Li2O 0-8, Na2O 1-10, with Li2O+Na2O 5-10, K2O 0-3, MgO 5-16, CaO 0-15, with MgO+CaO>15-25, SrO+BaO 0-8, ZrO2 0-8, TiO2 7-25, La2O3 0-10, Nb2O5 5-20, V2O5 0-10, CeO2 0-1, As2O3+Sb2O3+F 0.1-1. These glasses can have high dimensional stability as a result of their high specific modulus of elasticity, to be especially suited for hard disk substrates.