Abstract: A combination of software and hardware in a computer system prevents a hard disk from starting if an environmental parameter (i.e. temperature) is outside operational limits. An extension to the basic input/output software normally used with IBM-PC architecture processes signals indicative of the ambient environmental parameter. The extension to the basic input/output software is added to silicon memory in the computer instead of being stored on the hard drive. Upon initial application of electrical power to the computer the hard drive is disabled while the extension determines whether the environmental parameter is within an acceptable limit. The extension enables the hard drive and allows the boot process to proceed only if the environmental parameter is within the limiting value.