Multisync monitor
A monitor that synchronizes with multiple scan rates for flexible display use.
A multisync monitor—also called a multiscan or multimode monitor—is a type of raster-scan analog video display that can lock onto a range of different horizontal and vertical scan rates. This is unlike fixed-frequency monitors, which are limited to one specific set of scan rates. While the term is most often used for CRT displays, the underlying idea applies to other screen technologies as well. These monitors are typically used with computers, though they sometimes serve as television displays.
The first multiscan computer monitors appeared in the mid-1980s, providing flexibility as computer video hardware moved from a single fixed scan rate to multiple possible rates. "MultiSync" was a trademark belonging to one of NEC's early multiple-sync monitors.
Early home computers sent video to ordinary televisions or composite monitors that used fixed-rate standards like NTSC, PAL, or SECAM. These standards embedded sync pulses in the video signal but did not use them to set the actual scan rates. Dedicated computer monitors also initially relied on fixed scan rates. For example, IBM's 1981 PC offered two video cards (MDA and CGA), each intended for a custom IBM monitor with a fixed rate. CGA timings matched NTSC television, while MDA used a different timing for higher-resolution text. Early Macintosh monitors likewise used fixed rates.
In 1984, IBM's EGA added a second resolution, requiring a monitor that could handle two scan rates: the original CGA rate and a new one for the enhanced modes. Such displays, which could be manually switched between two sync rates, were called dual-scan monitors. The NEC Multisync, released in 1985 for the IBM PC, supported a broad range of sync frequencies, including those for CGA, EGA, PGC, various third-party extended standards, and future standards.
IBM's 1987 VGA standard expanded to three fixed scan rates.
- First release
- 1985
- Notable trademark
- MultiSync (NEC)
- Early horizontal range example
- 15 to 31 kHz (NEC Multisync)
- Typical minimum horizontal scan
- 31 kHz (modern multiscan monitors)
- Typical lcd vertical scan range
- 60 Hz to 75 Hz
- Vga horizontal scan
- 31.5 kHz
Lore & Background
Multiscan computer monitors appeared during the mid 1980s, offering flexibility as computer video hardware shifted from producing a single fixed scan rate to multiple possible scan rates. Early dedicated computer monitors often relied on fixed scan rates; for example, IBM's original 1981 PC was sold with a choice of two video cards (MDA and CGA) intended for use with custom IBM monitors that still used fixed scan rates. In 1984, IBM's EGA added a second resolution, necessitating a monitor supporting two scan rates, known as dual-scan displays. The NEC Multisync was released in 1985 for use with the IBM PC, supporting a wide range of sync frequencies including those for CGA, EGA, PGC, various extended forms, and standards yet to be released.
By the late 1980s, PC and Mac owners with multiple graphics cards required unique monitors for each. After 1987's VGA, the IBM market developed Super VGA cards using many different scan rates, culminating in the VBE and eventually the Generalized Timing Formula, which permitted graphics cards to output arbitrary resolutions. By the late 1990s, graphics cards offered resolutions from 1024x768 at 60 Hz to at least 1600x1200 at 85 Hz, and during system boot the display would operate at standard low resolution, requiring a monitor capable of horizontal scanning from at least 31 to 68 kHz. VESA established standardized lists and timings, later superseded by the Generalized Timing Formula and Coordinated Video Timings.
Reader's Guide
The multisync monitor's significance lies in its ability to adapt to the rapidly evolving landscape of computer video standards, eliminating the need for a separate monitor for each graphics card or resolution. Early implementations supported limited fixed frequencies signaled through sync pulse polarities, while later designs like the NEC Multisync supported a continuous range of scan rates derived from sync signal timing. This flexibility allowed a single monitor to work across multiple platforms and video cards, as long as frequencies were within range. In modern monitors, microprocessor control typically prevents synchronization to unsupported scan rates, protecting components from damage. For LCD monitors, the multisync concept is implemented differently: because they are fixed-pixel displays, they must scale the image or display it centered with black borders when the input resolution does not match the panel's native pixel count. While most LCDs accept a wide range of horizontal scan rates, they generally accept only 60 Hz to 75 Hz vertical scan rates, though gaming monitors with 120 Hz and above have appeared.
Did You Know?
- The term 'MultiSync' was specifically a trademark of one of NEC's first multiple-sync monitors.
- Early dual-scan displays could be manually switched between two sync rates, such as those for CGA and EGA.
- Most modern multiscan computer monitors have a minimum horizontal scan frequency of 31 kHz.
- LCD monitors typically accept only 60 Hz to 75 Hz vertical scan rates, though gaming models offer 120 Hz and up.
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