In 1979 Atari’s manual for programmers of its Video Computer System gave a short, blunt warning about the European version of the console: “PAL operates at 50 Hz compared to NTSC 60 Hz, a 17% reduction. If game play speed is based on frames per second, it will slow down by 17%. This can be disastrous for most skill/action carts.” For the next twenty years, players in Britain, most of Europe and Australia met that problem again and again. Games designed in Japan and America for 60 pictures a second arrived running at 50, with black bands across the top and bottom of the screen and music a little flat, unless the publisher had paid someone to convert them properly. The fix was known from the start, and the manual described it in the next sentence. Whether it was applied depended on the game, the publisher and the machine.
Fast facts
- NTSC: North America and Japan; 525-line pictures at about 60 fields a second
- PAL: Britain, most of Western Europe and Australia; 625 lines at 50 fields a second. A third standard, SECAM, also ran at 50, and Atari’s SECAM consoles used PAL software
- The 17 per cent: 50 is five-sixths of 60, so a game that moves its objects once a frame runs at five-sixths of its speed, 16.7 per cent slower
- Borders: PAL has more lines a frame, so a picture designed for NTSC leaves empty lines above and below it
- Pitch: most PAL machines ran their processors and sound chips from slightly slower clocks, so the same note values sound lower
- The cure: speed tables and timings written for 50 Hz, a taller picture, and retuned music; later, a 60 Hz mode on PAL consoles
Two television standards
A television picture is drawn line by line, top to bottom. NTSC, the American standard also used in Japan, has 525 lines in a full picture; PAL has 625. Both send a picture as two interlaced halves, called fields, and a games machine usually draws one field again and again without interlacing. The Amiga Hardware Reference Manual gives the figures for its own machine: “about 262 video lines from top to bottom, of which 200 normally are visible on the screen with an NTSC system. With a PAL system, the beam produces 312 lines, of which 256 are normally visible.” A field takes “approximately 1/60th of a second for an NTSC system and approximately 1/50th of a second for PAL.”
Every machine sold in both markets therefore came in two versions, with different crystals, different clock speeds and a different number of lines:
| Machine | NTSC | PAL |
|---|---|---|
| Atari VCS | 262 lines a frame, 192 of them picture | 312 lines, up to 228 of picture |
| NES | 6502 core at 1.789773 MHz; 262 lines, 20 of vertical blank | 1.662607 MHz; 312 lines, 70 of vertical blank |
| Commodore 64 | 1.02273 MHz; 263 lines of 65 cycles (early machines 262 of 64) | 0.98525 MHz; 312 lines of 63 cycles |
| Amiga | 68000 at 7.15909 MHz; 262 lines, 200 normally visible | 7.09379 MHz; 312 lines, 256 visible |
| Mega Drive | 68000 at 7.67 MHz; 262 lines, 224 of picture | 7.60 MHz; 312 lines, 224 or 240 of picture |
Some British machines were designed around 50 Hz television from the start. The ZX Spectrum’s video chip interrupts its processor once a frame, 50 times a second, and Spectrum programmers counted their timings from that.
Why games slowed down
Most action games of the period run their main loop once a frame, synchronised to the vertical blank. If a character moves two pixels a frame, it moves 120 pixels a second at 60 Hz and 100 at 50 Hz. Timers, animations and enemy waves all stretch the same way. That is the 17 per cent (strictly 16.7).
Atari’s guide described the way round it in 1979. A game that moved its objects with fractional speeds held in tables, “2 byte fractional addition techniques (or anything not based on frames per second)”, could be converted by “changing the fraction tables, avoiding major surgery on the program”. A converted game moves its objects a little further each frame to cover the same distance per second. That took time, and the extra lines of a PAL frame could cost more. Edge explained in 1994 that “programmers can often turn up the game speed in their code”, but that the taller PAL picture meant “a greater drain on the processor, making a full speed conversion hard to achieve”. Its example was the Jaguar’s Cybermorph, which ran “about 3-4% slower on a PAL Jaguar than on an NTSC model”, not 17 per cent, because its updates were not tied to the frame.
A slower game was also an easier one. Edge noted that American and Japanese games on an imported machine ran “at the speed they were actually designed to, making them faster and tougher in the process”.
Why music went flat
Sound suffered in two ways. A music routine called once a frame, from the vertical blank interrupt, plays its tune at five-sixths of the tempo on a PAL machine. And because sound chips were clocked from the same crystals as everything else, the same note values gave lower notes. Atari’s guide warned that “sounds will drop a little in pitch (frequency) because of a slower crystal clock”. Commodore’s Commodore 64 Programmer’s Reference Guide printed two tables of note values for its SID chip, one for a “φ2 clock of 1.02 MHz (shown as NTSC)” and one for “0.985 MHz (shown as PAL)”. A tune written with the NTSC values plays about 4 per cent flat on a PAL machine, about two-thirds of a semitone. On the NES, whose PAL processor runs about 7 per cent slower, the same tune comes out more than a semitone low unless it is retuned.
The borders
A PAL frame has 50 more lines than an NTSC one. A game drawn for NTSC’s 224 or 240 lines fills less of a PAL screen, and the spare lines show as black bands above and below the picture. Sega’s own manual for the Mega Drive shows the choice: the console’s video chip can draw 28 rows of characters, 224 lines, on either standard, or 30 rows, 240 lines, but only in PAL mode. A game that used the taller mode filled more of a European screen; one that did not left wide bands.
Super Play set out the difference for buyers in its first issue, in November 1992. The official British Super Nintendo was a PAL machine, while imported machines “run approximately 17% faster and with a full screen picture”, without the bands at the top and bottom, and “British Mega Drives suffer from exactly the same problem”. By 1994 Edge was calling the “full-screen 60Hz display” of an imported console “vastly superior to the 50Hz letter-boxed display common to UK PAL systems”, and said the difference had “fuelled imports of American SNES systems” (see Import Gaming).
The reverse direction
On home computers the traffic often ran the other way. The European scenes wrote for PAL machines, and their work could fail on American ones. An NTSC Commodore 64 has fewer lines and fewer cycles in each frame, so a demo that uses every cycle of a PAL frame, or changes colours on a line that an NTSC chip does not draw, cannot run unchanged (see Raster Effects). The American magazine Commodore World told its readers in 1996 that a PAL demo would sometimes show “flicker and distortion” on an NTSC machine, and that “other times, a PAL demo just plain won’t load”. American users relied on “NTSC-fixed” versions, adapted by other groups. That year, the magazine counted about 20 new NTSC or NTSC-fixed demos and “probably (at the very least) four times as many PAL demos”.
Full screen, full speed
By the mid-1990s a proper conversion had become a selling point. After its PAL version of Daytona USA was criticised, Sega Europe told Sega Saturn Magazine at the end of 1995 that it would release no more PAL versions until they were as close to the Japanese originals as possible: “full screen, full speed games GUARANTEED!” N64 Magazine expected good conversions from Rare, which, being “based here in Britain”, understood “the concerns of UK Nintendo fans”, and had “made an excellent full-speed, full-screen job of Killer Instinct Gold”. Not every game managed it: reviewers had warned that the British Super Nintendo version of the original Killer Instinct ran a little slower than the American one.
The next answer was to stop converting. Most televisions sold in Britain by the late 1990s could show a 60 Hz picture, and the Dreamcast could send one. The Official Dreamcast Magazine explained in 1999 that a British Dreamcast could output “a PAL-encoded signal at 50Hz (with borders) or at a non-standard 60Hz (without borders)”. Sonic Adventure offered the choice, and the magazine reckoned that “around 80% of UK TVs can display a 60Hz signal”. By 2002 Australia’s Official PlayStation 2 Magazine listed “60Hz mode”, yes or no, in its review panels, next to widescreen support.
Sources
- Steve Wright, Stella Programmer’s Guide (Atari, 1979), “PAL/SECAM conversions”: line counts and frame times for NTSC and PAL, the 17 per cent, fractional speed tables, the drop in pitch, and SECAM.
- Amiga Hardware Reference Manual, 3rd edition (Commodore-Amiga, Addison-Wesley, 1991): chapter 1, the 68000 at 7.15909 MHz (NTSC) and 7.09379 MHz (PAL); chapter 2, fields of 262 and 263 lines (NTSC) and 312 and 313 (PAL); chapter 3, visible lines and field times.
- Sega Genesis Software Manual (Sega, 1990, revised 1992): lines per screen in NTSC and PAL, the 240-line V30 mode in PAL only, and the version register at
$A10001(7.67 MHz NTSC, 7.60 MHz PAL). - Commodore 64 Programmer’s Reference Guide (Commodore Business Machines): system frequency of 1.02273 MHz (NTSC) and 0.98525 MHz (PAL), and appendix E, the two tables of music note values.
- Christian Bauer, The MOS 6567/6569 video controller (VIC-II) and its application in the Commodore 64 (1996), section 3.4: lines and cycles per line for the 6569, 6567R8 and 6567R56A.
- NESdev Wiki, “Cycle reference chart” (community reference, web, secondary): master and CPU clocks, lines, vertical blank and frame rates for the NTSC and PAL NES. https://www.nesdev.org/wiki/Cycle_reference_chart
- Edge issue 10, July 1994, p. 58: feature on television standards (the 17 per cent; turning up the game speed; the extra lines; Cybermorph 3–4 per cent slower; imports “faster and tougher”; American SNES imports). Edge issue 6, March 1994, letters: the UK Jaguar and Cybermorph.
- Adrian Dickens, Spectrum Hardware Manual, 2nd edition (Melbourne House), chapters 7 and 8: the ULA’s interrupt 50 times a second, at the end of each video frame.
- Super Play issue 1, November 1992: buyer’s guide to UK, American and Japanese machines (the 17 per cent, the full-screen picture, British Mega Drives).
- Commodore World issue 15, May–July 1996, Sherry Freedline, “Delightful Demos”: PAL demos on NTSC machines, NTSC-fixed demos and the year’s numbers.
- Sega Saturn Magazine issue 2, December 1995, news: Sega Europe’s promise of full-screen, full-speed PAL conversions after Daytona USA.
- N64 Magazine issue 5, August 1997, Blast Corps review: Rare and Killer Instinct Gold.
- Total! issue 46, October 1995, p. 28, and Computer and Video Games issue 168, November 1995, p. 80: the slower PAL Super Nintendo Killer Instinct.
- Official Dreamcast Magazine (UK), special issue, October 1999, p. 72: 50 Hz and 60 Hz output, Sonic Adventure, and the 80 per cent estimate.
- Official PlayStation 2 Magazine (Australia, Derwent Howard) issues 2 and 3, May and June 2002, and issue 10, January 2003: review panels listing “60Hz mode”.