Mean Time Between Failure. A statistical assessment of the average time taken for a something to fail, a measure of predicted reliability. The MTBF of a piece of equipment is dependent on the reliability of each of its components. Generally the more components the lower the MTBF, so packing more into one integrated circuit can reduce the component count and so increase the reliability. Modern digital components are highly reliable. Even complex electro-mechanical assemblies such as hard disk drives now offer MTBFs of up to a million hours; some 110 years! Note this does not mean a drive has been run for 110 years and failed just once, nor that it is expected to run for this period without failure, but it does indicate the average failure rate of many components of the same type.