1990s and 1900’s means the same thing, it means the period of time from 1900-1999. However, the 19th century would mean the 1800s :) 加油！

1900s is from 1900-1999, the century. The first half is 1900-1950. The 1990s is the decade of 1990-1999 The 1840s is the decade of 1840-1849 The 1700s is the century of 1700-1799 etc :)

Note that in modern style (the last 30 years or so), the apostrophe should only be used if we want the possessive form. Prior to that, the apostrophe was always used in such expressions, even when not possessive.

What does it mean by 1900’s? I don't know. 'By the 1900s' means 'before 1910'. (before the decade 1900-1910). Does the first half of 1900s mean 1900-1905 (Yes, usually!) or 1900-1950? (People sometimes, confusingly, use it with this meaning...) Thank you very much! - You're welcome. 🙂

"The 1900's", read aloud as "the nineteen hundreds," means every year that begins with 19-. It can be written with or without an apostrophe: "the 1900's" or "the 1900s." "The 1900's" means these exact years: 1900, 1901, 1902, 1903, 1904, 1905, 1906, 1907, 1908, 1909 1910, 1911, 1912, 1913, 1914, 1915, 1916, 1917, 1918, 1919 1920, 1921, 1922, 1923, 1924, 1925, 1926, 1927, 1928, 1929 1930, 1931, 1932, 1933, 1934, 1935, 1936, 1937, 1938, 1939 1940, 1941, 1942, 1943, 1944, 1945, 1946, 1947, 1948, 1949 1950, 1951, 1952, 1953, 1954, 1955, 1956, 1957, 1958, 1959 1960, 1961, 1962, 1963, 1964, 1965, 1966, 1967, 1968, 1969 1970, 1971, 1972, 1973, 1974, 1975, 1976, 1977, 1978, 1979 1980, 1981, 1982, 1983, 1984, 1985, 1986, 1987, 1988, 1989 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999 Thus, "the 1900's" refers to a century. "The first half of the 1900's" means 1900 through 1949, a total of fifty years. (You could argue about which half 1950 is in. But it doesn't matter. You would never use a vague phrase like "the first half of the 1900's" if you were trying to be precise.) I don't know a good way to refer to the decade 1900-1909. Sometimes it's called "the oughts" because the British sometimes call zero "ought," and read 1901 as "nineteen ought one." An INDEFINITE period of "1900 and a few years after" can be called "the turn of the century." "The 1900's" can also be called "the twentieth century" (the 20th century). Yes, this is VERY confusing. Think of it this way: A woman who is 19½ years old is "19," because she has COMPLETED 19 full years. However, she is in the middle of her _twentieth_ year. Here's a silly technical detail. ALMOST ALWAYS, the "twentieth century" means "the 1900's." But since was no "year 0." So sometimes people say that the first century was the years 1 through 100, and therefore the twentieth century was not 1900 through 1999, but 1901 through 2000.