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POKE writes a byte into a memory location.
 
POKE address,byte%
 
Usage Notes
    ■ If the argument is a single- or double-precision floating-point
      value or a long integer, it is converted to a 2-byte integer.
    ■ The POKE statement complements the PEEK function.
    ■ Before using POKE to directly manipulate data stored in far memory,
      use the DEF SEG statement and the SSEG function to set the current
      segment address. For example:
 
        ' Set the current segment address to the address of a$.
        DEF SEG = SSEG(a$)
        ' Determine the string's location within the segment.
        Offset1 = SADD(a$)
        ' Write the byte stored in
        POKE Offset1, PEEK(Offset2)
 
      ║ Note: BASIC moves string locations during run time. Therefore,
      ║       the DEF SEG statement must be executed immediately before
      ║       using the POKE statement.
 
Warning
    ■ Use POKE carefully. If used incorrectly, it can cause BASIC or the
      operating system to fail.
 
POKE and Expanded Memory Arrays
    ■ Do not use POKE to manipulate expanded memory arrays. If you start
      QBX with the /Ea switch, any of these arrays may be stored in
      expanded memory:
        -  Numeric arrays < 16K in size
        -  Fixed-length string arrays < 16K in size
        -  User-defined-type arrays < 16K in size
    ■ If you want to use POKE to manipulate an array, first start QBX
      without the /Ea switch. (Without the /Ea switch, no arrays are
      stored in expanded memory.)
    ■ For more information on using expanded memory, see
      ◄Using Expanded Memory►.
 
Programming With OS/2 Protected Mode
    ■ Any address referred to by POKE must be open for writing. If POKE
      refers to a memory address for which your process does not have write
      permission, the operating system may generate a protection
      exception, or BASIC may generate the error message, "Permission
      denied."