Brief review of analogue television standards
(Presented in order of historical appearance,
sources: Sony & Wikipedia articles about NTSC, PAL & SECAM)
Broadcast television systems (or terrestrial television systems outside the US and Canada) are the encoding or formatting systems for the transmission and reception of terrestrial television signals. NTSC, PAL and SECAM are all colour standards for analog television broadcast.
NTSC
The first American standard for analog television broadcast was developed by National Television System Committee (NTSC) in 1941.
In 1953, a second NTSC standard was adopted, which allowed for colour television broadcast compatible with the existing stock of black and white TV sets.
The NTSC standard was used in most of the Americas (except Argentina, Brazil, Paraguay, and Uruguay), Myanmar, South Korea, Taiwan, Philippines, Japan, and some Pacific Islands nations and territories.
An NTSC picture is made up of 525 interlaced lines and is displayed at a rate of 29.97 frames per second.
PAL
Phase Alternating Line (PAL) is a colour encoding system for analogue television. The PAL format was patented by Telefunken, Hanover, (then West-)Germany in December 1962.
PAL was adopted by most European countries, by all African countries that had never been a Belgian or French colony, by Argentina, Brazil, Paraguay, Uruguay, and by most of Asia (including the Middle East) and the Pacific.
Countries in those regions that did not adopt PAL were France, most ex-Soviet states, Japan, South Korea, Liberia, Myanmar, the Philippines, and Taiwan.
A PAL picture is made up of 625 interlaced lines and is displayed at a rate of 25 frames per second.
SECAM
SECAM ("Séquentiel de couleur à mémoire", French for "Colour sequential with memory"), is an analog colour television system that was used in France, some parts of Europe and Africa, and most ex-Soviet states.
Development of SECAM predates PAL, and began in 1956 by a team led by Henri de France working at Compagnie Française de Télévision (later bought by Thomson, now Technicolour).
Like PAL, a SECAM picture is also made up of 625 interlaced lines and is displayed at a rate of 25 frames per second.
The black & white television signals of the various European countries were so similar before the creation of the PAL and SECAM colour systems, that PAL and SECAM are in fact based on the same common foundations... except for the way in which PAL and SECAM each process colour information in a different way.
So, in practice, a PAL TV set can display a SECAM picture, but that picture will be black & white. Similarly, a SECAM TV set can also display a PAL picture, but that picture will also be black & white.
NTSC was considered undesirable in Europe because of its tint problem, requiring an additional control, which SECAM (and PAL) solved.
Black and White to colour transition
NTSC, PAL and SECAM are standards that permited existing black and white TV sets predating their introduction to continue to be operated as black and white TV sets. Because of this compatibility requirement, colour standards added a second signal to the basic monochrome signal, which carries the colour information.
Comparison table
| NTSC | PAL | SECAM | |
|---|---|---|---|
| Developed In | USA | (then West-)Germany | France |
| Number of lines used | 525 | 625 | 625 |
| Number of frames per second (fps) | 29.97 fps | 25 fps | 25 fps |
| Frequency (in Hertz) of the electric current | 60 Hz | 50 Hz | 50 Hz |
| Variants | 4.43, J, and M | B, D, G, H, I, N, M{1}, and NC | B, G, D, K, K1, and L |
{1} PAL M is an exception with 525 lines at 29.97 fps.
Disambiguation: PERITEL
Unlike NTSC/PAL/SECAM, PERITEL is absolutely not a colour standard for analog television broadcast but simply a norm for a connector that carries the various audio and video signals and their control.
Its full name is "Péritélévision". Péritel or PERITEL or SCART{2}{3} is the name of a 21-pin plug or socket.
Male (plug) on cables, female (socket) on TV sets and other devices that generate or process video (input or output).
PERITEL sockets are originally a French invention. Their use on all TV sets sold in France became legally mandatory at the end of 1979 — an obligation that ended in July 2015. Largely inspired by German DIN connectors, the idea was to carry all the signals needed to connect a TV set to its peripherals in a single cable: external subtitles or teletext decoder, VCR, game console, computer, Canal+ decoder, etc.
PERITEL transports different types of video signals (either in RGB or CVBS mode) with stereo sound, both in input{4} and output.
PERITEL sockets are compatible with 4:3 ratio (later extended to 16:9 ratio), 50 Hz or 60 Hz, 525-line and 625-line analogue video standards as well as PAL, SECAM or NTSC colour standards.
More information about PERITEL on Wikipedia (EN, FR).
{2} "Syndicat des Constructeurs d'Appareils Radiorécepteurs et Téléviseurs"
{3} PERITEL is also known internationally as EuroSCART, Euroconector and EuroAV or EXT, or EIA Multiport in the US. There is also a Japanese version of this connector, called JP21, which carries the same signals but in a different layout. Therefore, an adapter is needed between PERITEL and JP21 devices.
{4} RGB is limited on the TV set to input only: signal from "video source" to "TV set". RGB entering the TV set, yes. RGB exiting the TV set, no.
In 1982, as the development of a specific SECAM version of the computers (including FGTIA) could not be done overnight, Atari France modified PAL versions of the Atari 400 & 800 models, marketed under the names PERITEL Atari 400 and the PERITEL Atari 800.
This modification consists of an added video circuit which produces an additional RGB signal — very clear but limited to 8 colours — physically conveyed in a PERITEL{5} plug. Note that the original PAL video signal remains available on the TV antenna plug, as well as on the 5-pin 180° DIN monitor socket of the Atari 800.
Equipped with this PERITEL plug (in RGB mode of course), the natively-PAL computers could display a colour image on a SECAM TV set sold in France.
{5} Either a PERITEL cable directly attached to the computer, or a detachable cable that plugs into a dedicated 8-pin 270° DIN socket on the computer and provides a PERITEL plug at the other end.
Much later, Atari offered computers{6} in the SECAM colour standard for analog television broadcast, which physically connected to the TV set with a PERITEL plug, but this time in CVBS mode — hence the loss of picture clarity compared to RGB. For example, a SECAM Atari 800XL connected to the TV set of the time also with a PERITEL plug...
{6} See the table below
So, the names PERITEL Atari 400 & 800 are a bit inappropriate. A more accurate name would have been PAL + RGB Atari 400 & 800.
But, well, I can understand the marketing logic. By promoting models with this name "PERITEL", buyers who were not audio/video experts were reassured:
"Oui! I have a PERITEL socket on my TV set, sacrebleu!"
Which version exists for each computer?
| NTSC | PAL | SECAM | PERITEL | |
|---|---|---|---|---|
| Atari 400 | Yes | Yes | Yes | |
| Atari 800 | Yes | Yes | Yes | |
| Atari 1200XL | Yes | |||
| Atari 600XL | Yes | Yes | ||
| Atari 800XL | Yes | Yes | Yes | |
| Atari 65XE | Yes | Yes | ||
| Atari 130XE | Yes | Yes | Yes | |
| Atari XEgs | Yes | Yes | Yes | |
| Atari 800XE | Yes |
How do I determine if my computer is NTSC, PAL or SECAM?
For the Atari 1200XL and Atari 800XE, it is very simple, there is only one version.
The distinction between NTSC and PAL (or SECAM) is also quite easy to make, with a simple PEEK instruction in BASIC: PRINT PEEK(53268)
- If you get 15, your computer is NTSC
- If you get 1, your computer is PAL or SECAM
The difficulty comes with PAL or SECAM computers, because you have to look at the video sockets (monitor) on the back of the computer. Which one do you see?
- 5-pin 180° DIN? Then your Atari 800XL, 130XE or XEgs is PAL
- 6-pin 240° DIN? Then your Atari 800XL, 130XE or XEgs is SECAM
Are these NTSC, PAL and SECAM versions really different?
Fundamentally, they are exactly the same computers. I'd call them "variations", or "local adaptations". There are, however, some notable differences.
[1] Colour palettes
The colour palettes in NTSC on one side and PAL/SECAM on the other are equivalent but not strictly identical.
Please read the "256 Colours" article in the knowledge base for all the details.
[2] Speed
The speed is not exactly the same. The NTSC version operates at 1.79 MHz, while the PAL/SECAM version operates at 1.77 Mhz. Programs therefore run slightly more slowly in PAL/SECAM than in NTSC. The difference is around ±1%.
The FAQ reads:
This effect, while small, can be significant in applications that are computation- or timing-sensitive, such as music players, or in any programs designed to simulate real time.
I honestly think that games are easier to play in PAL/SECAM than in NTSC, because of the reduced speed.
Watch the demo that was presented at the 1985 Consumer Electronics Show (CES):
- For the reason given in [1], the robot is not the same colour in NTSC and PAL/SECAM
- For the reason given in [2], the robot moves more energetically and the music plays significantly faster in NTSC than in PAL/SECAM. And we're not talking 1% difference this time... The music in the robot sequence lasts 54.44 seconds in NTSC compared with 64.23 seconds in PAL/SECAM. So the PAL/SECAM version runs 20% slower...
Atari 8-bit computers 1985 CES demo (GTIA mode 9), NTSC version
For the video: Altirra emulator, Atari 800XL, NTSC, 1983 OS rev. 2.
Atari 8-bit computers 1985 CES demo (GTIA mode 9), PAL version
For the video: Altirra emulator, Atari 800XL, PAL, 1983 OS rev. 2.
[3] Other considerations
A PAL/SECAM program is more likely to run on an NTSC computer than the other way around.
The reason for this is historical. It has to do with CRT screens, with their beam of electrons bombarding the screen to draw an image, line by line.
During the "Vertical Blank Interrupt - VBI" period — when the image is completely drawn on the screen, and the electron beam in the bottom right-hand corner is cut off to go back to the top left-hand corner to draw the next image — the computer has precious time to do "something else".
In NTSC, the program has 2,508 machine cycles (on the 6502 CPU/microprocessor) at its disposal during the VBI.
In PAL/SECAM, the program has 8,208 machine cycles (on the 6502 CPU/microprocessor) at its disposal during the VBI.
If a program developed on a PAL/SECAM computer runs on an NTSC machine, then it is possible for the program to crash if it requires more machine cycles during the VBI than an NTSC computer can offer.
See the FAQ (section "How may a program behave on NTSC/PAL/SECAM computer versions?") for all the details.
Special thanks to Jerome Delsarte for all his expertise on video signals.
Knowledge base article: kb-hardware-0003-atari-8bit-ntsc-pal-secam-peritel
REV. 011.
