**Characters : Characters and character strings must be enclosed in single or double quotes; For example, "A" or 'hello'. Characters are translates into their ASCII codes by the assembler, so there is no difference between using "A" and 4h (the ASCII  code for "A") in a program.

table 4.1   Data-Defining Pseudo-ops

Pseudo-op                              Stands for

DB                                           define byte

DW                                         define word

DD                                         define doubleword  (two consecutive words)

DQ                                         define quadword (four consecutive words) 

DT                                          define tenbytes (ten consecutive bytes)