Con­sider this lit­tle com­par­i­son: if the read/​write head were a Boe­ing 747, and the hard-​​disk plat­ter were the sur­face of the Earth:

• The head would fly at Mach 800
• At less than one cen­time­ter from the ground
• And count every blade of grass
• Mak­ing fewer than 10 unre­cov­er­able count­ing errors in an area equiv­a­lent to all of Ireland

~ Where Do Hard Drive Heads Come From?.