A special breed of redundancy is proliferating in our modern world as we increasingly rely on abbreviations and acronyms in the busyness of our technology. Some people insist it is redundant to say "ATM machine" because ATM means Automated Teller Machine. They add that it is redundant to say "HIV virus" because HIV means Human Immunodeficiency Virus, "AIDS syndrome" because AIDS means Acquired ImmunoDeficiency Syndrome, "CPU unit" because CPU means Central Processing Unit. It sounds particularly silly when we come up with a plural such as "CPU units" — Central Processing Unit units. It is perhaps too easy to get caught up in this, however. "CD disk" can be redundant, but nowadays the abbreviation CD can refer to a number of things, including the machine itself. Occasionally, an abbreviation — like CD, ATM — becomes more of an idea unto itself than a shortened version for a set of words, and the abbreviation ought to be allowed to act as modifier.