PAL vs. NTSC
DVDs are also formatted for use on two conflicting regional television systems: 480i/60 Hz and 576i/50 Hz, which in analog contexts are often referred to as 525/60 (NTSC) and 625/50 (PAL/SECAM) respectively. Strictly speaking, NTSC, PAL and SECAM are all analog chroma-encoding formats which have no relevance in the digital domain (as evident in the conflation of PAL and SECAM, which are actually two distinct analog color systems). However, these terms continue to be used (improperly) as a method of identifying refresh rates and vertical resolution.
NTSC is the analog color TV format historically associated with the United States, Canada, Japan, Mexico, Philippines, Taiwan, and other countries. PAL is the analog color TV format historically associated with most of Europe, most of Africa, China, India, Australia, New Zealand, Israel, North Korea, and other countries (and Brazil, but using the refresh rate and resolution commonly associated with NTSC). Some DVD players only play discs identified as NTSC or PAL, while others can play both standards.
In general, it is easier for consumers in PAL countries to view NTSC DVDs than vice versa. Almost all DVD players sold in PAL countries are capable of playing both kinds of discs, and most modern PAL TVs can handle the converted signal.† However, most NTSC players cannot play PAL discs, and most NTSC TVs do not accept 576i video signals. Those in NTSC countries, such as in North America, generally require both a region-free, multi-standard player and a multi-standard television to view PAL discs, or a converter box, whereas those in PAL countries generally require only a region-free player. There are also differences in pixel aspect ratio (720 × 480 vs. 720 × 576) and display frame rate (29.97 vs. 25). Again, NTSC discs can be played on most DVD systems worldwide, while PAL discs play on very few players outside of PAL/SECAM countries. However, as of 2009, around 80% of NTSC TVs and DVD players are capable of playing PAL DVDs, due to them being upgraded with converter systems.