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The pressure–volume equations of state of iron–nickel–silicon alloy Fe_0.83Ni_0.09Si_0.08 (Fe-9.8wt.% Ni-4.0wt.% Si) and iron–silicon alloy Fe_0.93Si_0.07 (Fe-3.4wt.% Si) have been investigated up to 374GPa and 252GPa, respectively. The present compression data covered pressures of the Earth's core. We confirmed that both Fe_0.83Ni_0.09Si_0.08 and Fe_0.93Si_0.07 alloys remain in the hexagonal close packed structure at all pressures studied. We obtained the density of these alloys at the pressure of the inner core boundary (ICB), 330GPa at 300K by fitting the compression data to the third order Birch–Murnaghan equation of state. Using these density values combined with the previous data for hcp-Fe, hcp-Fe_0.8Ni_0.2, and hcp-Fe_0.84Si_0.16 alloys and comparing with the density of the PREM inner core, we estimated the Ni and Si contents of the inner core. The Si content of the inner core estimated here is slightly …