Why is the hard drive made of aluminum? Why is steel not used, despite being cheaper?The actual disks are made from an aluminum substrate. Aluminum is the best choice for minimizing the inertia of the disk pack, which reduces the energy required to spin it. A steel pack would use much more energy. Many other materials, magnets, copper, gold, oxides, diamond like coatings, insulators are inside disk drivesfirst I am guessing weight as there are 6 discs in there and just whipping them up to speed of 16000RPM takes some power. And the magnetic factor would play a roll at that speed and you would lose data.. It is not aluminum...it is aluminum alloy. Steel is not cheaper. And as temperatures change the steel would expand more than the aluminum alloy and you would lose your data as it has moved. Just a guess.Hard disk (hard drive) construction. Hard disks are rigid platters, composed of a substrate and a magnetic medium. The substrate – the platter\'s base material – must be non-magnetic and capable of being machined to a smooth finish. It is made either of aluminum alloy or a mixture of glass and ceramic.Computer hard drives are made of aluminum platters coated with a layer of magnetic material. Each tiny magnetic domain represents one bit of information. A typical drive has a round platter of 9.5 cm in diameter with a hole of 2.5 cm diameter at the center.Aluminum does not rust or corrode under normal circumstances and if anodized it is already oxidized and covered with the second hardest naturally occurring material on earth alumina , in its gem form it is known as ruby or sapphire.Other related question