Apple II system clocks, also known as real-time clocks, were devices in the early years of microcomputing. A clock/calendar did not become standard in the Apple II line of computers until 1986 with the introduction of the Apple IIGS. Although many productivity programs as well as the ProDOS operating system implemented time and date functions, users would have to manually enter this information every time they turned the computer on. Power users often had their Apple II's peripheral slots completely filled with expansion cards, so third party vendors came up with alternative approaches with products like the Serial Pro and No-Slot Clock. No-Slot Clock (Dallas Semiconductor) The No-Slot Clock, also known as the Dallas Smartwatch (DS1216E), was a 28-pin chip-like device that could be used directly in any Apple II or Apple II compatible with a 28-pin ROM. Dallas Semiconductor produced the device as an easy implementation for a real-time clock for a variety of applications. The clock was powered by an embedded lithium battery, electrically disconnected until power was first applied to retain freshness. The non-replaceable battery had a life expectancy of 10 years. In an Apple II, the No-Slot Clock resided under any 28-pin ROM chip, including one on a peripheral card. A user had to remove the ROM from its socket, insert the No-Slot Clock, and then reinsert the ROM chip into the top of the No-Slot Clock. The No-Slot Clock was both ProDOS and Dos 3.3 compatible, however a software driver had to be patched into ProDOS or integrated into the applicable DOS 3.3 program. Once the driver was installed it emulated the Thunderclock. The No-Slot Clock was usually installed in the following locations on the motherboard in the following computers: Apple IIe: under the CD ROM (or CF ROM in later models) Apple IIc: under the Monitor ROM Apple IIc+: under the Monitor ROM Laser 128: under the ROM behind the metal cover on the bottom Serial Pro (Applied Engineering) The Serial Pro was a multifunction serial interface and clock/calendar card from Applied Engineering. By combining the functions of two cards into one, the Serial Pro freed up an extra slot for those with highly populated machines. This card was unique in the sense that it did not use "Phantom Slots" to achieve this functionality. Previous multifunction cards required that a secondary function be "mapped" to a different slot in the computer's memory, rendering that