Programming bugs are generally mistakes in computer instructions that cause erroneous results.
When computer systems were programmed in the 1960's and 70's, only two digits were alotted for the year. This saved considerable computer resources because memory costs were high and there was limited space for program code. Data processing managers knew that the programs would not function in the year 2000, but at the time, they thought the systems would not be in use that long. However, PC's and Mac's are not immune to date changes. Electronic equipment and appliances like VCR's and coffee makers also contain embedded systems, so these are potentially at risk.