The time and date get passed on to the software in the system. It could also be the operating system, which handles most all the other operations that other programs rely on. It could also be the application programs themselves, your spreadsheet, word processing, graphics, or database software. And most software tells time by checking the operating system. See the following figure.
Different computers handle time and date information in different ways.
But it depends on the software. Problems with the BIOS Older BIOS store the date in 6 digits. For much the same reasons as with the RTC, the BIOS may store the date in a format where the year 2000 seems to be 99 years earlier than the year 1999. Problems with BIOS can vary in degree. Some BIOS cannot handle the century digits at all.