.ds
.reserve

The .ds and .reserve statements are used to reserve a number of 8 bit bytes.
syntax:
        [<label>] .ds      <expr>
        [<label>] .reserve <expr>

e.g.
        fred    .db     1       ; reserve 1 byte and call it fred
        jack    .db     1*2     ; reserve 1 word and call it jack
        bert    .db     1*4     ; reserve 1 long word and call it bert
The .ds statement is also very useful for generating series of constants
e.g.

        .sect   some_unique_sect_name
        .data

monday          .ds     1
tuesday         .ds     1
wednesday       .ds     1
thursday        .ds     1
friday          .ds     1
saturday        .ds     1
sunday          .ds     1
this gives us an ordered list of numbers coressponding to the days of the week with monday as day 0 and sunday as day 6. If we needed to change this so that monday is day 1 and sunday is day 7 we would simply add an .org statement before monday like this:
        .sect   some_unique_sect_name
        .data

        .org    1

monday          .ds     1
tuesday         .ds     1
wednesday       .ds     1
thursday        .ds     1
friday          .ds     1
saturday        .ds     1
sunday          .ds     1
If we then needed to change the list such that sunday becomes the first day in the list and is day 1 and all the other days are relative to it we would simply exit the above to give the following:
        .sect   some_unique_sect_name
        .data

        .org    1

sunday          .ds     1
monday          .ds     1
tuesday         .ds     1
wednesday       .ds     1
thursday        .ds     1
friday          .ds     1
saturday        .ds     1
Compare this with the alternative below (which is much more difficult to maintain):
monday          .equ    0
tuesday         .equ    1
wednesday       .equ    2
thursday        .equ    3
friday          .equ    4
saturday        .equ    5
sunday          .equ    6
BEWARE: defining bytes in the code section of a CPU that has a program counter that counts in words may cause the location counter to be incremented to an odd address. Also note that the length of a block of data will be reported as half the expected size. This will not affect the space reserved, just the observed length.