You can use the Date, Time, and Measurement Utilities to manipulate the date-time information and geographic location data used by a Macintosh computer. You can use the routines provided by the Date, Time, and Measurement Utilities to manipulate this information. This date-time information is expressed, using 4 bytes, as the number of seconds elapsed since midnight, January 1, 1904. At system startup the date-time information is copied into low memory and is accessible through the system global variable Time .
System software updates the value of the global variable Time each second.
Doing this is faster than manipulating the clock chip directly. The Date, Time, and Measurement Utilities provide four data structures that you can use to access date-time information. The month field contains the month of the year, where a value of 1 equals January and 12 equals December. The day field contains the number of the day, ranging from day 1 to day 31. The minute field contains the number of minutes, ranging from 0 to 59 minutes.