Rationale for aligning data on even bytes in a Unix shell file?

In a "C" file (of the Kornshell software) I stumbled across this
comment: "Each command in the history file starts on an even byte
and is null-terminated."

I wonder what's the reason behind that even-byte-alignment, on "C"
level or on Unix/files level. Any ideas?

Janis

Note: Since it's not a shell question but more of a programming or
platform related question I try to get the answer here (and not in
comp.unix.shell); just saying to prevent distracting calls to order.
Thanks.