and k is lower case.......
To technical people there is a difference: k (lower case) is the SI prefix for 1000 while K (upper case) is the computer geeks abbreviation for 1024.
BUT since the eighties it has gradually leaked from technical jargon to a more widespread use by normal people, so that today you see job ads mentioning a salary of "50K". Non technical people informally use K (upper case) to mean 1000.