ZIP Codes are a system of postal codes used by the United States Postal Service since 1963.
 The term "ZIP", an acronym for "Zone Improvement Plan", was chosen to suggest that the mail travels more efficiently, and therefore more quickly (zipping along), when senders use the code in the postal address.
 The basic format consists of five digits.
 An extended 'ZIP+4' code, introduced in 1983, includes the five digits of the ZIP Code, a hyphen, and four additional digits that determine a more specific location within a given ZIP Code.
In Algeria, the postal codes of province capitals are composed of the province code as in and three zeros, for example: 16000 for Algiers, while the postal codes of other cities, towns, and villages in the province are the provincial code followed by three numerals.
 See "list of postal codes of Algerian cities" for the postal codes of all of Algeria's 1,541 municipalities, and other places with their own postal code.
Russian Post has a system of postal codes (Russian: почтовый индекс , "pochtovyy indeks") based on the federal subject a place is located in.
 Each postal code consists of six digits with first three referring to the federal subject or the administrative division with special status.
 Some larger subjects begin with several three-digit codes.
 For instance, Moscow's postal codes fall in range from 101 to 129.
Postal codes in Brunei are alphanumeric, consisting of two letters followed by four digits in the format of YZ0000, where Y denotes the district code, Z denotes the mukim code, the first two digits denote the area or village code, and the last two digits denote the nearest post office code (e.g. the postal code for Pantai Mentiri Golf Club is BU2529).
Norwegian Postal Codes are 4-digit codes, known in Norwegian as "postnummer" (literally "post number").
 Posten, the Norwegian postal service, makes small modifications to the postal code system each year.
 In 1999 Posten made considerable changes to the postal codes in Norway.
Postal codes in Israel (Hebrew: מיקוד‎ ‎ , "Mikud") are numeric and consist of seven digits.
 They are assigned from north to south, thus, Metula in the north has 1029200 as its postal code, and Eilat in the south was assigned 88xxxxx.
 Jerusalem postal codes start with the digit 9, although this does not correspond with its geographical location.
 Each postal code corresponds to a mail carrier route or RR, thus, when the letters are sorted by the postal code, they are assigned to a specific carrier.
Postal codes in the Netherlands, known as "postcodes", are alphanumeric, consisting of four digits followed by two uppercase letters.
 The letters 'F', 'I', 'O', 'Q', 'U' and 'Y' were originally not used for technical reasons, but almost all existing combinations are now used as these letters were allowed for new locations starting 2005.
 The letter combinations 'SS', 'SD' and 'SA' are not used because of their associations with the Nazi occupation of the Netherlands.
A Canadian postal code is a six-character string that forms part of a postal address in Canada.
 Like British and Dutch postcodes, Canada's postal codes are alphanumeric.
 They are in the format "A1A 1A1", where "A" is a letter and "1" is a digit, with a space separating the third and fourth characters.
 As of September 2014, there were 855,815 postal codes using "Forward Sortation Areas" from A0A in Newfoundland to Y1A in the Yukon.
Postal codes in Argentina are called "códigos postales ".
 Until 1998 Argentina employed a four-digit postal code for each municipality, with the first digit representing a region in the country, except in the case of the city of Buenos Aires (which had different postal codes starting in 1000 and with the other numbers varying according to the zone).
 The unique codes became the base for the newer system, officially called CPA ("Código Postal Argentino ", Argentine Postal Code).
Postal codes used in the United Kingdom are known as postcodes (originally postal codes).
 They are alphanumeric and were adopted nationally between 11 October 1959 and 1974, having been devised by the GPO (Royal Mail).
 A full postcode is known as a "postcode unit" and designates an area with a number of addresses or a single major delivery point.

Question: A Canadian postal code is a six-character string that forms part of a postal address in Canada, like British and Dutch postcodes, Canada's postal codes are alphanumeric, Postal codes in the Netherlands, known as "postcodes", are alphanumeric, consisting of how many digits followed by two uppercase letters?
Answer: four