Real-time clock

A real-time clock (RTC) is a computer clock (most often in the form of an integrated circuit) that keeps track of the current time.

Although the term often refers to the devices in personal computers, servers and embedded systems, RTCs are present in almost any electronic device which needs to keep accurate time.

Realtimeclock Motherboard Baby AT crop
Dallas Semiconductor (DS1387) real-time clock from an older PC. This version also contains a battery-backed SRAM.


The term real-time clock is used to avoid confusion with ordinary hardware clocks which are only signals that govern digital electronics, and do not count time in human units. RTC should not be confused with real-time computing, which shares its three-letter acronym but does not directly relate to time of day.


Although keeping time can be done without an RTC,[1] using one has benefits:

  • Low power consumption[2] (important when running from alternate power)
  • Frees the main system for time-critical tasks
  • Sometimes more accurate than other methods

A GPS receiver can shorten its startup time by comparing the current time, according to its RTC, with the time at which it last had a valid signal.[3] If it has been less than a few hours, then the previous ephemeris is still usable.

Power source

Inside the Real-time clock IC vnutri u nei neonka
Lithium battery inside the real-time clock IC

RTCs often have an alternate source of power, so they can continue to keep time while the primary source of power is off or unavailable. This alternate source of power is normally a lithium battery in older systems, but some newer systems use a supercapacitor,[4][5] because they are rechargeable and can be soldered. The alternate power source can also supply power to battery backed RAM.[6]


Most RTCs use a crystal oscillator,[7][8] but some have the option of using the power line frequency.[9] In many cases, the oscillator's frequency is 32.768 kHz.[7] This is the same frequency used in quartz clocks and watches. This frequency is exactly 215 cycles per second. It is a convenient rate to use with simple binary counter circuits. Also, it is too high for humans to hear. The quartz tuning fork of these crystals does not change size much from temperature, so temperature does not change its frequency much.

Some RTCs use a micromechanical resonator on the silicon chip of the RTC. This reduces the cost of an RTC by reducing its complexity and parts count. Micromechanical resonators are much more sensitive to temperature than quartz resonators. So, these compensate for temperature changes using an electronic thermometer and electronic logic.[10]

Many commercial RTC ICs are accurate to less than 5 parts per million.[11] In practical terms, this is good enough to perform celestial navigation, the classic task of a chronometer. In 2011, Chip-scale atomic clocks were invented. Although more expensive, they keep time within 50 picoseconds (5x10^-11).[12]


AT Motherboard RTC and BIOS
This chip, labeled ODIN, is a generic equivalent to a particular Dallas RTC.

Many integrated circuit manufacturers make RTCs, including Epson, Intersil, IDT, Maxim, NXP Semiconductors, Texas Instruments, STMicroelectronics and Ricoh. A common RTC used in single-board computers is the Maxim Integrated DS1307.

The RTC was introduced to PC compatibles by the IBM PC/AT in 1984, which used a Motorola MC146818 RTC. Later, Dallas Semiconductor made compatible RTCs, which were often used in older personal computers, and are easily found on motherboards because of their distinctive black battery cap and silkscreened logo.

In newer systems, the RTC is integrated into the southbridge chip.[13]

Some microcontrollers have a real-time clock built in, generally only the ones with many other features and peripherals.

Radio-based RTCs

Some modern computers receive clock information by digital radio and use it to promote time-standards. There are two common methods: Most cell phone protocols (e.g. LTE) directly provide the current local time. If an internet radio is available, a computer may use the network time protocol. Computers used as local time servers occasionally use GPS[14] or ultra-low frequency radio transmissions broadcast by a national standards organization (i.e. a radio clock[15]).

Historic RTCs

Some older computer designs such as Novas and PDP-8s[16] used a real-time clock that was notable for its high accuracy, simplicity, flexibility and low cost. The computer's power supply produces a pulse at logic voltages for either each half-wave or each zero crossing of AC mains. A wire carries the pulse to an interrupt. The interrupt handler software counts cycles, seconds, etc. In this way, it can provide an entire clock and calendar.

The clock also usually formed the basis of computers' software timing chains; e.g. it was usually the timer used to switch tasks in an operating system. Counting timers used in modern computers provide similar features at lower precision, and may trace their requirements to this type of clock. (e.g. in the PDP-8, the mains-based clock, model DK8EA, came first, and was later followed by a crystal-based clock, DK8EC.)

A software-based clock must be set each time its computer is turned on. Originally this was done by computer operators. When the Internet became commonplace, network time protocols were used to automatically set clocks of this type.

In Europe, North America and some other grids, this RTC works because the frequency of the AC mains is adjusted to have a long-term frequency accuracy as good as the national standard clocks. That is, in those grids this RTC is superior to quartz clocks and less costly.

This design of RTC is not practical in portable computers or grids (e.g. in South Asia) that do not regulate the frequency of AC mains. Also it might be thought inconvenient without Internet access to set the clock.

Clockless CPUs

Some motherboards are made without real time clocks. The real time clock is omitted either out of the desire to save money (as in the Raspberry Pi system architecture) or because real time clocks may not be needed at all (as in the Arduino system architecture).

See also


  1. ^ Ala-Paavola, Jaakko (2000-01-16). "Software interrupt based real time clock source code project for PIC microcontroller". Archived from the original on 2007-07-17. Retrieved 2007-08-23.
  2. ^ Enabling Timekeeping Function and Prolonging Battery Life in Low Power Systems, NXP Semiconductors, 2011
  3. ^ ‹See Tfd›US 5893044 Real time clock apparatus for fast acquisition or GPS signals
  4. ^ New PCF2123 Real Time Clock Sets New Record in Power Efficiency, futurle
  5. ^ Application Note 3816, Maxim/Dallas Semiconductor, 2006
  6. ^ Torres, Gabriel (24 November 2004). "Introduction and Lithium Battery". Replacing the Motherboard Battery. Archived from the original on 24 December 2013. Retrieved June 20, 2013.
  7. ^ a b Application Note 10337, ST Microelectronics, 2004, p. 2
  8. ^ Application Note U-502, Texas Instruments, 2004, p. 13
  9. ^ Application Note 1994, Maxim/Dallas Semiconductor, 2003
  10. ^ "Maxim DS3231m" (PDF). Maxim ds3231m RTC. Maxim Inc. Retrieved 26 March 2019.
  11. ^ "Highly Accurate Real-Time Clocks". Maxim Semiconductors. Retrieved 20 October 2017.
  12. ^ "Chip Scale Atomic Clock". Microsemi. Retrieved 20 October 2017.
  13. ^ "ULi M1573 Southbridge Specifications". Retrieved 2007-08-23.
  14. ^ "GPS Clock Synchronization". Spectracom. Retrieved 20 October 2017.
  15. ^ "Product: USB Radio Clock". Meinburg. Retrieved 20 October 2017.
  16. ^ Digital Equipment Corp. "PDP-8/E Small Computer Handbook, 19" (PDF). Gibson Research. pp. 7–25, the DK8EA. Retrieved 12 November 2016.

External links


AES51 is a standard first published by the Audio Engineering Society in June 2006 that specifies a method of carrying ATM (Asynchronous Transfer Mode) cells over Ethernet physical structure intended in particular for use with AES47 to carry AES3 digital audio transport structure. The purpose of this is to provide an open standard, Ethernet based approach to the networking of linear (uncompressed) digital audio with extremely high quality-of-service alongside standard Internet Protocol connections.

This standard specifies a method, also known as "ATM-E", of carrying asynchronous transfer mode (ATM) cells over hardware specified for IEEE 802.3 (Ethernet). It is intended as a companion standard to AES47 (Transmission of digital audio over ATM networks), to provide a standard method of carrying ATM cells and real-time clock over hardware specified for Ethernet.

Busy waiting

In computer science and software engineering, busy-waiting, busy-looping or spinning is a technique in which a process repeatedly checks to see if a condition is true, such as whether keyboard input or a lock is available. Spinning can also be used to generate an arbitrary time delay, a technique that was necessary on systems that lacked a method of waiting a specific length of time. Processor speeds vary greatly from computer to computer, especially as some processors are designed to dynamically adjust speed based on external factors, such as the load on the operating system. As such, spinning as a time delay technique often produces unpredictable or even inconsistent results unless code is implemented to determine how quickly the processor can execute a "do nothing" loop, or the looping code explicitly checks a real-time clock.

Spinning can be a valid strategy in certain circumstances, most notably in the implementation of spinlocks within operating systems designed to run on SMP systems. In general, however, spinning is considered an anti-pattern and should be avoided, as processor time that could be used to execute a different task is instead wasted on useless activity.

Clock port

The clock port is a commonly used term for the real-time clock interface of the Amiga 1200 computer. The port is a remnant of an abandoned design feature for addition of internal RAM and a clock for time keeping. However, it was later widely used as a general purpose expansion port by third-party developers for devices, such as, I/O cards, sound cards and even a USB controller. Although a real-time clock can be connected to the port, the clock was typically added by other means (usually integrated on CPU or RAM expansions) which leave the clock port free.The A1200 was the only Amiga model to have this unique 22-pin connector (some revisions of the A1200 motherboard have additional non-functional pins). However, as the address and data signals used by the interface are available through the internal expansion connectors of other Amiga models, clock port adaptors were later created by third-party developers for these systems. This enables owners of other popular models, such as the Amiga 500 or Amiga 600, to use the hardware created for this interface. Due to the popularity of clock port devices, developers even included one or more compatible clock port interfaces on Amiga Zorro boards to allow hosting such devices on these systems.Essentially, the connector provides an 8-bit data interface with limited addressing.

Freescale DragonBall

Motorola/Freescale Semiconductor's DragonBall, or MC68328, is a microcontroller design based on the famous 68000 core, but implemented as an all-in-one low-power system for handheld computer use. It is supported by μClinux. It was designed by Motorola in Hong Kong and released in 1995.The DragonBall's major design win was in earlier versions of the Palm Computing platform; however, from Palm OS 5 onwards it has been superseded by ARM-based processors from Texas Instruments and Intel. The processor is also used in some of the AlphaSmart line of portable word processors. Examples include the Dana and Dana Wireless.

The processor is capable of speeds of up to 16.58 MHz and can run up to 2.7 MIPS (million instructions per second), for the base 68328 and DragonBall EZ (MC68EZ328) model. It was extended to 33 MHz, 5.4 MIPS for the DragonBall VZ (MC68VZ328) model, and 66 MHz, 10.8 MIPS for the DragonBall Super VZ (MC68SZ328).

It is a 32-bit processor with 32-bit internal and external address bus (24-bit external address bus for EZ and VZ variants) and 32-bit data bus. It has many built-in functions, like a color and grayscale display controller, PC speaker sound, serial port with UART and IRDA support, UART bootstrap, real time clock, is able to directly access DRAM, Flash ROM, mask ROM, and has built-in support for touch screens.

It is an all-in-one computer on a chip; before the DragonBall EZ, Palm handhelds had twice as many ICs.

The more recent DragonBall MX series microcontrollers, later renamed the Freescale i.MX (MC9328MX/MCIMX) series, are intended for similar application to the earlier DragonBall devices but are based on an ARM processor core instead of a 68000 core.


The HP-27S was a pocket calculator produced by Hewlett-Packard, introduced in 1988, and discontinued between 1990 and 1993 (sources vary). It was the first HP scientific calculator to use algebraic entry instead of RPN, and though it was labelled scientific, it also included features associated with specialised business calculators.

The device featured standard scientific functions, including statistics and probability. Equations could be stored in memory, and solved and integrated for specified variables. Binary, octal, and hexadecimal number bases could be used. Business features included a real-time clock and calendar, as well as functions such as time value of money calculations.The calculator had 7k bytes of usable memory, shared among variables and formulas.

Its hardware features included a dot-matrix display of two rows of 22 characters. Depending on context, either the top row was used to display the current expression or a message, or the bottom row was used to show menu options, which could be selected with the corresponding keys. An infra-red transmitter was also included, allowing the machine to be used with a compatible printer, such as the HP 82240B. A beeper could be used to sound date/time alarms.

The 27S was not programmable in the conventional way, but it included an advanced formula-storage system with programming features. Within stored formulas, sub-formulas could be defined and later referred to by name. Loops and conditional execution could also be embedded within formulas.

Iriver H100 series

The iriver H100 series (originally iHP-100 series) is a series of discontinued portable digital audio players (DAP) made by iriver and originally released in October 2003. The models in the H100 series differ mainly in hard drive storage capacity. The players were succeeded by the iriver H300 series.


A Monolog is a Single Telephone Line Call Logging Device manufactured by British Telecom in the UK. The reason for connecting Monolog to a telephone line is to collect independent call and charging data to help resolve customer queries or complaints.

Monolog is usually connected to a customer's line at the telephone exchange although it is possible to monitor the line at the customer's premises.

Monolog is based on the Mitsubishi M50734SP-10 8-bit processor that uses an enhanced 6502 instruction set. The unit comprises two boards: a digital board that contains EPROM and RAM for storage of call records and an analogue board that provides the necessary interface components to the monitored telephone line.

Monolog is powered via four AA rechargeable batteries which are trickle charged at approximately 2 mA from a control line. This control line is also used for remote connection to the unit for the purposes of data retrieval.

NT (cassette)

NT is a digital memo recording system introduced by Sony in 1992, sometimes marketed under the name Scoopman. The system stored memos using helical scanning on special microcassettes, which were 30 × 21.5 × 5 mm with a tape width of 2.5 mm, with a recording capacity of up to 120 minutes. The Scoopmen cassettes are offered in three versions: The Sony NTC-60, -90, and -120, each describing the length of time (in minutes) the cassette can record.

NT stands for Non-Tracking, meaning the head does not precisely follow the tracks on the tape. Instead, the head moves over the tape at approximately the correct angle and speed, but performs more than one pass over each track. The data in each track is stored on the tape in blocks with addressing information that enables reconstruction in memory from several passes. This considerably reduced the required mechanical precision, reducing the complexity, size, and cost of the recorder.

Another feature of NT cassettes is Non-Loading, which means instead of having a mechanism to pull the tape out of the cassette and wrap it around the drum, the drum is pushed inside the cassette to achieve the same effect. This also significantly reduces the complexity, size, and cost of the mechanism.

Audio sampling is in stereo at 32 kHz with 12 bit nonlinear quantization, corresponding to 17 bit linear quantization. Data written to the tape is packed into data blocks and encoded with LDM-2 low deviation modulation.The Sony NT-2 Digital Micro Recorder, introduced in 1996 and shown here, features a real-time clock that records a time signal on the digital track along with the sound data, making it useful for journalism, police and legal work. Due to the machine's buffer memory, it is capable of automatically reversing the tape direction at the end of the reel without an interruption in the sound. The recorder uses a single "AA"-size cell for primary power, plus a separate CR-1220 lithium cell to provide continuous power to the real-time clock. The Sony NT-2, an improved successor to the Sony NT-1 Digital Micro Recorder, introduced in 1992, was the final machine in the series. The NT cassette systems cost more than a DAT recorder in their day, are fragile and relatively unreliable compared to other emerging recording technologies, and being unable to compete soon disappeared from the market. The devices are considered curiosities for collectors.

Nonvolatile BIOS memory

Nonvolatile BIOS memory refers to a small memory on PC motherboards that is used to store BIOS settings. It is traditionally called CMOS RAM because it uses a volatile, low-power complementary metal-oxide-semiconductor (CMOS) SRAM (such as the Motorola MC146818 or similar) powered by a small "CMOS" battery when system and standby power is off. The typical NVRAM capacity is 256 bytes.The CMOS RAM and the real-time clock have been integrated as a part of the southbridge chipset and it may not be a standalone chip on modern motherboards.


The PocketStation is a Memory Card peripheral by Sony Computer Entertainment for the PlayStation home video game console. Categorized by Sony as a combination of a Memory Card and a miniature personal digital assistant, the device features a monochrome liquid crystal display (LCD), infrared communication capability, a real-time clock, built-in flash memory, and sound capability. To use the device's memory card functionality, it must be connected to a PlayStation through a memory card slot. It was released exclusively in Japan on January 23, 1999.Software for the PocketStation was typically distributed as extras for PlayStation games, included in the CD-ROM, enhancing the games with added features. Stand-alone software could also be downloaded through the PlayStation console. The software is then transferred to the PocketStation for use. A built-in infrared data interface allows direct transfer of data such as game saves between PocketStation units, as well as multiplayer gaming.

The original Japanese ship date for the PocketStation was set for December 23, 1998, but it was delayed a full month. Sony only shipped an initial 60,000 units of the peripheral when it was released on January 23, 1999. It was initially available in two case colors: white and clear. It proved extremely popular, selling out all over the region. Sony planned to release the PocketStation outside Japan, engaging in promotional activity in Europe and North America, but the release did not occur. SCEA cited an inability meeting Japanese demand as the reason for the PocketStation's absence. Despite this, a few games, such as Final Fantasy VIII and SaGa Frontier 2, retained PocketStation functionality in their localized versions.The PocketStation's most popular game was Dokodemo Issho, which sold over 1.5 million copies in Japan and is the first game to star Sony's mascot Toro. The PocketStation was discontinued in July 2002 after having shipped nearly five million units.On November 5, 2013, it was announced that the PocketStation would be revived as an application for the PlayStation Vita, allowing users to play PocketStation format minigames for any classic PlayStation games that they own. Originally it was only available to PlayStation Plus members, it was later released to the general public. It remains an exclusive to the Japanese PlayStation Vitas.

The PocketStation also shares similarities with Sega's VMU for the Dreamcast.

Pokémon Mini

The Pokémon Mini (Japanese: ポケモンミニ, Hepburn: Pokemon Mini, officially stylized as Pokémon mini) is a handheld game console that was designed and manufactured by Nintendo and themed around the Pokémon media franchise. It is the smallest game system with interchangeable cartridges ever produced by Nintendo, weighing just under two and a half ounces (71 grams). It was first released in North America on November 16, 2001, then in Japan on December 14, 2001, and in Europe on March 15, 2002. The systems were released in three colors: Wooper Blue, Chikorita Green, and Smoochum Purple.Features of the Pokémon mini include an internal real-time clock, an infrared port used to facilitate multiplayer gaming, a reed switch for detecting shakes, and a motor used to implement force feedback. The Nintendo GameCube game Pokémon Channel features playable demo versions of several Pokémon mini games via console emulation. Also included in the game is Snorlax's Lunch Time, a Pokémon Channel exclusive. Some games were only released in Japan, such as Togepi's Adventure.

Various hackers have reverse engineered the Pokémon mini (with the aid of the aforementioned emulator in Pokémon Channel) in order to enable the creation of homebrew games, and to allow official games to be played on other platforms (such as a PC, Dreamcast and various others).

Power Management Unit

The Power Management Unit (PMU) is a microcontroller that governs power functions of digital platforms. This microchip has many similar components to the average computer, including firmware and software, memory, a CPU, input/output functions, timers to measure intervals of time, and analog to digital converters to measure the voltages of the main battery or power source of the computer. The PMU is one of the few items to remain active even when the computer is completely shut down, powered by the backup battery.

For portable computers, the PMU is responsible for coordinating many functions, including:

Monitoring power connections and battery charges

Charging batteries when necessary

Controlling power to other integrated circuits

Shutting down unnecessary system components when they are left idle

Controlling sleep and power functions (on and off)

Managing the interface for built in keypad and trackpads on portable computers

Regulating the real-time clock (RTC)The PMU controls almost every power-consuming function in an Apple computer. It is constantly running diagnostics on the various power-related operations and checking them against the current Energy-Saver settings, allowing the PMU to actively manage power consumption for optimum user performance.

The PMUs functions may become corrupt over time. If this happens, it may become unresponsive and stop performing tasks. The user may not notice the PMUs malfunctions so much as the side effects of the corruption, including:

Failure to turn on

Failure to restore from sleep mode

Failure to recognize connected devices (FireWire, USB, etc.)Resetting the PMU in these circumstances can be a relatively quick and easy fix to some of these issues. There is a keyboard shortcut on newer Apple laptops with an internal battery, nicknamed "SCOP". This stands for Shift Control Option Power. This "reboots" the PMU software in order to get it working as it should. For Apple laptops with a removable battery, resetting the PMU involves unplugging the power adapter, disconnecting the battery, then holding down the power button for five seconds. Another PMU-related fix would be to reset the logic board, where one removes the backup battery on the board for a few minutes, then reinstalls it, causing the PMU to reset itself with clean, fresh parameters (that need to be corrected, if desired, to its previous state) during the next Mac OS boot (for typical PC users, this is similar to "resetting the CMOS").

The PMU is very sensitive and a reset may be necessary if a backup battery dies. Even plugging in one's laptop in the wrong order can cause issues (power into the outlet first, THEN power to the computer). Never turn off an attached UPS without first unplugging the AC adapter.

Real-time clock alarm

A real time clock alarm is a feature that can be used to allow a computer to 'wake up' after shut down to execute tasks every day or on a certain day. It can sometimes be found in the 'Power Management' section of a motherboard's BIOS setup. However, newer BIOS setups do not include an RTC alarm option, although it can still be set from within user applications. Wake On LAN, Wake on ring, and IPMI functions could also be used to start a computer after it is turned off.

In Linux, the real time clock alarm can be set or retrieved using /proc/acpi/alarm or /sys/class/rtc/rtc0/wakealarm. Alternatively the rtcwake utility may be used which prevents problems when using local time instead of UTC by automatically processing the /etc/adjtime file. systemd can be used to wake a system and run a task at a specific time.In Microsoft Windows there are different programs which could be used to 'wake up' a computer from standby or hibernation. Task Scheduler settings for power management can be used to 'Wake the computer to run this task'.

Super I/O

Super I/O is a class of I/O controller integrated circuits that began to be used on personal computer motherboards in the late 1980s, originally as add-in cards, later embedded on the motherboards. A super I/O chip combines interfaces for a variety of low-bandwidth devices. The functions below are usually provided by the super I/O if they are on the motherboard:

A full set of IBM PC/AT-compatible peripherals, excepting the interrupt and DMA controllers:

A floppy-disk controller

An IEEE 1284-compatible parallel port (commonly used for printers)

One or more 16C550-compatible serial port UARTs

An embedded controller and/or keyboard controller that is sometimes connected to a PS/2 keyboard and/or mouse interface.

An Intel 8254-compatible programmable interval timer

A battery-backed real-time clock and nonvolatile BIOS memoryMost chips include some additional low-speed devices, such as:

Temperature, voltage, and fan speed sensors

Chassis intrusion detection

Pulse-width modulation fan speed control

A serial BIOS ROM interface (if the ROM is not directly on the LPC bus itself)

An infrared port controller

A game port (not provided by modern super I/O chips anymore because Windows XP is the last Windows OS to support a game port)

A watchdog timer

A consumer IR receiver

a MIDI port

Some general-purpose input/output pins

Legacy Plug and Play support for the included devicesBy combining many functions in a single chip, the number of parts needed on a motherboard is reduced, thus reducing the cost of production.

The original super I/O chips communicated with the central processing unit via the Industry Standard Architecture (ISA) bus. With the evolution away from ISA towards use of the Peripheral Component Interconnect (PCI) bus, the Super I/O chip was often the biggest remaining reason for continuing inclusion of ISA on the motherboard.

Modern super I/O chips use the Low Pin Count (LPC) bus instead of ISA for communication with the Central processing unit. This normally occurs through an LPC interface on the southbridge chip of the motherboard.

Companies that make super I/O controllers include Nuvoton (formerly Winbond), ITE, Fintek, and Microchip Technology. National Semiconductor used to make super I/O controllers but sold that business to Winbond, which already had a competing super I/O controller business. In 2005, Winbond then spun off its logic businesses to a wholly owned subsidiary, Nuvoton. SMSC made super I/O chips and then got acquired by Microchip Technology.

Toshiba T1000

The Toshiba T1000 was a laptop computer manufactured by the Toshiba Corporation in 1987. It had a similar specification to the IBM PC Convertible, with a 4.77 MHz 80C88 processor, 512 kB of RAM, and a monochrome CGA-compatible LCD. Unlike the Convertible, it includes a standard serial port and parallel port, connectors for an external monitor, and a real-time clock.

Unusually for an IBM compatible PC, the T1000 contained a 256 kB ROM with a copy of MS-DOS 2.11. This acted as a small, read-only hard drive. Alternative operating systems could still be loaded from the floppy drive, or (if present) the ramdisk.

Along with the earlier T1100 and T1200 systems, the Toshiba T1000 was one of the early computers to feature a "laptop" form factor and battery-powered operation.


The Visual Memory Unit (VMU), also referred to as the Visual Memory System (ビジュアルメモリ, Bijuaru Memori) (VMS) in Japan and Europe, is the primary memory card produced by Sega for the Dreamcast home video game console. The device features a monochrome liquid crystal display (LCD), multiplayer gaming capability (via connectors at the top), second screen functionality, a real-time clock, file manager, built-in flash memory, and sound capability. Prior to the launch of the Dreamcast, a special Godzilla edition VMU, preloaded with a virtual pet game, was released on July 30, 1998 in Japan.While its most basic function is as a removable storage device, the VMU may also serve as an auxiliary display during normal gameplay and, through the use of additional software (distributed as extras on Dreamcast GD-ROMs), acts as a handheld game console. Console-like features of the VMU include a screen, speaker, proper directional pad, four action buttons, the ability to connect and interact with other VMUs, and the ability to download additional games. While the standard VMU is white, colors were expanded to include many variations. Japan even saw the release of branded VMUs, such as those by Sonic Team, Capcom and Hello Kitty.

Volume serial number

A volume serial number is a serial number assigned to a disk volume or tape volume. It originated in 1950s in mainframe computer operating systems. In OS/360 line it is human-configurable, has a maximum length of six characters, is in uppercase, must start with a letter, and identifies a volume to the system in unique manner. For example, "SYSRES" is often used for a system residence volume.

In FAT and NTFS file systems, a volume serial number is a feature used to determine if a disk is present in a drive or not, and to detect if it was exchanged with another one. This identification system was created

by Microsoft and IBM during their development of OS/2. It was introduced in MS-DOS 4.01 in 1988.

The volume serial number is a 32-bit number determined by the date and time on the real-time clock on the current computer at the time of a disk's formatting. Previously, the method used to discern whether a disk was swapped was identified by reading the drive's volume label (much similar in concept to OS/360). However, even at that time the volume label was not required to be unique and was optional. Therefore, many users had not given disks any meaningful name and the old method failed.

WDC 65C134

The Western Design Center (WDC) W65C134S microcomputer is a complete fully static 8-bit computer fabricated on a single chip using a low power CMOS process. The W65C134S complements an established and growing line of 65xx products and has a wide range of microcomputer applications. The W65C134S has been developed for Hi-Rel applications, and where minimum power is required.

The W65C134S consists of a W65C02S (Static) Central Processing Unit (CPU), 4096 bytes of Read Only Memory (ROM), 192 bytes of Random Access Memory (RAM), two 16 bit timers, a low power Serial Interface Bus (SIB) configured as a token passing Local Area Network, Universal Asynchronous Receiver and Transmitter (UART) with baud rate timer, one 16-bit "Monitor Watch-Dog Timer" with "restart" interrupt, twenty-two priority encoded interrupts, ICE Interface, Real-Time clock features including Time of Day (ToD) clock, Bus Control Register (BCR) for external memory bus control, interface circuitry for peripheral devices, and many low power features.

The innovative architecture and the demonstrated high performance of the W65C02S CPU, as well as instruction simplicity, result in system cost-effectiveness and a wide range of computational power. These features make the W65C134S a leading candidate for Hi-Rel and other microcomputer applications.

This product description assumes that the reader is familiar with the W65C02S CPU hardware and programming capabilities. Refer to the W65C02S Data Sheet for additional information.


The ZX8302 was a ULA integrated circuit designed for the Sinclair QL microcomputer. Also known as the QL's "Peripheral Chip", it interfaced the CPU to the Microdrives, QLAN local area network interface and RS-232 ports (transmit only) and also provided a real-time clock. The ZX8302 was IC23 on the QL motherboard.

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