If you enjoy reading about the history of airlines, I highly recommend Thomas Petzinger's "Hard Landing"...a good chunk of the book is devoted to the airlines' brutal fight over computer systems...reading it is a great look into how something so seemingly mundane as arranging ticket reservations was so revolutionary in changing the business...and how so fundamentally even primitive computers impact our lives:

https://books.google.com/books?id=GF5GZaTd8qsC&lpg=PA62&ots=...

Here's an excerpt regarding the state of the industry before computers:

> An airline seat is like fresh food—a grapefruit, say—in that it spoils after so much time on the shelf. Every empty seat taking off on every flight is a spoiled grapefruit and exactly as valueless. Both required time, effort, and money to create, and both came to a wasteful, meaningless end. And on an exceedingly large number of flights, the sale of one last seat, according to the First Rule of Airline Economics, could easily decide whether the plane flew the entire distance in the red or the black. As the builder of American Airlines, C. R. Smith had agonized continually over the problem of matching passengers with seats before the latter perished upon departure. The trick was to balance reservations against inventory, a far greater task than it might seem. At first, in the early 1930s, a single ledger had passed from hand to hand as agents in a central office recorded reservations and erased those that were canceled.

> With the advent of the DC-3, as the fleets and schedules of the airlines swelled and as the seating capacity of each plane increased, a single book became impractical, so multiple books were maintained. These had to be reconciled frequently—a massively time-consuming process—and even so, each book was inherently out-of-date at all times. Books gave way to chalk and slate boards and eventually to electric light boards. More and more agents were crammed into the reservations offices, with the line of sight to the blackboard limited by the space between structural support columns—22 feet in most buildings of the time. Some agents peered through opera glasses. Teletypes clattered. Clerks known as “card boys” scurried from desk to desk, eventually to be replaced by mechanical conveyors. One blackboard gave rise to multiple blackboards, which quickly encountered the same problems that multiple ledgers had caused.

> A science called “reservations theory” was born to cope with the exponentially worsening challenge, but to little avail; as with so much else in the airline business, there was no economy of scale in handling reservations. The more the airlines grew, the less efficient they became. The need to coordinate reservations among multiple cities—indeed, among multiple airlines—added still another dimension of complexity. For most of their history the airlines had been scheduled like railroads: numerous stops along a single line, with passengers boarding and disembarking at each stop, sometimes to board a second flight on a different airline flying in a roughly perpendicular direction. Confirming the itinerary for a single passenger traveling on two connecting airlines required no fewer than 20 separate communications, making the airlines, even in the 1940s, among the world’s biggest users of leased telephone lines. But what if the entire process could be automated?

Petzinger Jr., Thomas (2010-12-01). Hard Landing: The Epic Contest for Power and Profits That Plunged the Airlines into Chaos (Kindle Locations 1270-1275). Crown Publishing Group. Kindle Edition.