Maximum Memory Density in Bits per Kilogram Under Bekenstein and Limit Bounds

This paper examines what memory density, in bits per kilogram, the Bekenstein bound actually permits once region size is treated honestly. The calculation is performed in a frame with a finite maximum density, the neutron-branch value rho_A = 9.718e+57 kg per cubic metre, with the electron branch at 2.874e+51 kg per cubic metre for comparison. Headline results include a bounce temperature of 3.278e+22 K, a Landauer cost at that temperature of 3.137e-01 J per bit against 2.871e-21 J per bit at 300 K, a Bekenstein allowance of 1.049e+94 bits for the stated centimetre reference region, and a Margolus-Levitin rate of 2.209e+103 per second for the same region. Bits per kilogram fall as the region grows at fixed density, so the most favourable figure belongs to the smallest stated region, not to bulk matter. All numbers are computed from the stated assumptions in the accompanying script; the study is simulated and computed, not measured.