VHS
The Video Home System,[1] better known by its abbreviation VHS, is[2] a recording and playing standard developed by Victor Company of Japan, Limited (JVC) and launched in Europe and Asia in September 1975, and the United States in June 1976. By the 1990s, VHS became a standard format for consumer recording and viewing, after competing in a fierce format war with Sony's Betamax and, to much lesser extents, Philips' Video 2000, MCA's Laserdisc and RCA's Capacitance Electronic Disc.
VHS initially offered a longer playing time than the Betamax system, and it also had the advantage of a far less complex tape transport mechanism. Although VHS and Betamax were competing formats, several of VHS's critical technologies are licensed from Sony. Early VHS machines could rewind and fast forward the tape considerably faster than a Betamax VCR because they unthreaded the tape from the playback heads before commencing any high-speed winding. Most newer VHS machines do not perform this unthreading step, as head-tape contact is no longer an impediment to fast winding, owing to improved engineering.
DVD rentals surpassed VHS rentals in the US in 2003, surprising some industry officials.[3] By 2006, most major film studios stopped releasing new movie titles in VHS format, opting for DVD-only releases. Many leading retailers have stopped selling pre-recorded movies on VHS, although VHS pre-recorded cassettes are still popular with many collectors, mainly because there are thousands of titles that are still unavailable on DVD or other newer formats. In developing countries, the VHS is still a major medium to distribute home video. On December 23, 2008, the last major supplier of pre-recorded VHS tapes, Distribution Video Audio Inc. of Palm Harbor, Florida, shipped its final truckload.Technical details
The VHS cassette is a 7⅜" wide, 4" deep, 1" thick (187 mm × 103 mm × 25 mm) plastic clamshell held together with 5 Philips head screws. The flip-up cover that protects the tape has a built-in latch with a push-in toggle on the right side, as seen in the Bottom View. The VHS cassette also includes an anti-despooling mechanism as seen in the Top View, several plastic parts near front label end of the cassette between the two spools. The spool brakes are released by a push-in lever within a 1/4" hole accessed from the bottom of the cassette, about 3/4" in from the edge label. There is a clear tape leader at both ends of the tape to provide an optical auto-stop for the VCR transport mechanism.
The recording medium is a ½ inch (12.7 mm) wide magnetic tape wound between two spools, allowing it to be slowly passed over the various playback and recording heads of the video cassette recorder. The tape speed is 3.335 cm/s for NTSC, 2.339 cm/s for PAL. A cassette holds a maximum of about 430 m of tape at the lowest acceptable tape thickness, giving a maximum playing time of about 3.5 hours for NTSC and 5 hours for PAL at "standard" (SP) quality. Other speeds include LP and EP/SLP which double and triple the recording time, for NTSC regions. These speed reductions cause a slight reduction in video quality (from 250 lines to 230 lines horizontal); also, tapes recorded at the lower speed often exhibit poor playback performance on recorders other than the one they were produced on. Because of this, commercial prerecorded tapes were almost always recorded in SP mode.
As with almost all cassette-based videotape systems, VHS machines pull the tape from the cassette shell and wrap it around the head drum. VHS machines, in contrast to Betamax and Beta's predecessor U-matic, use an M-loading system, also known as M-lacing, where the tape is drawn out by two threading posts and wrapped around the head drum (and other tape transport components) in a shape roughly approximating the letter M.
VHS tapes have approximately 3 MHz of video bandwidth, which is achieved at a relatively low tape speed by the use of helical scan recording of a frequency modulated luminance (black and white) signal, with a down-converted "color under" chroma (color) signal recorded directly at the baseband. Because VHS is an analog system, VHS tapes represent video as a continuous stream of waves, in a manner similar to analog TV broadcasts. The waveform per scan-line can reach about 160 waves at max, and contains 525 scan-lines in NTSC (486 visible), or 625 lines in PAL (576 visible). In modern-day digital terminology, VHS is roughly equivalent to 320 pixels of horizontal resolution with a signal-to-noise ratio of the image at 43 dB.
JVC would counter 1985's SuperBeta with VHS HQ, or High Quality. The frequency modulation of the VHS luminance signal is limited to 3.1 megahertz which makes higher resolutions impossible, but an HQ branded deck includes luminance noise reduction, chroma noise reduction, white clip extension, and improved sharpness circuitry. The effect was to increase the apparent horizontal resolution of a VHS recording from 240 to 250 lines. The major VHS OEMs resisted HQ due to cost concerns, eventually resulting in JVC reducing the requirements for the HQ brand to white clip extension plus one other improvement.
In 1987 JVC introduced the new format called Super VHS which extended the bandwidth to over 5 megahertz, yielding 420 lines horizontal (equivalent to 560x486 in digital terminology). For comparison DVD is 540 lines (720 pixels) horizonal. The chroma resolution remained the same at approximately 0.6 megahertz bandwidth or 30 lines horizontal, as was common across analog tape standards from Umatic to VHS to ED Betamax. Even a live NTSC broadcast is limited to 120 chroma lines maximum. (For comparison DVD is 240 chroma horizontal.)