You (all of you swearing it is DOS) are all betraying utter ignorance. (Fact, not attack).
A character-based "green screen" (or amber, or grey, or blue) does not imply "DOS" certainly not in what you are obviously referring to mean as MS-DOS/PC-DOS. You do your reputations online no good by perpetuating that lie.

For the record, it could be UNIX. It could be a very modern Linux. It could be Windows 7 (or Windows 8) in a command line mode using Windows PowerShell. It could be any number of character-based User Interfaces. None of which are "DOS". Which say nothing about what the underlying operating system is nor the power of that system, nor the application software running on it.

Now it so happens that it is not UNIX nor Linux nor Windows PowerShell. As a knowledgeable poster mentioned, it is an IBM mainframe cluster running a very old Operating System still marketed by IBM for gargantuanally ginormous simultaneous transaction processing, TPF. Which is not the more commonly known, also natively character-mode (hell, natively Punch-Card mode but that is long supplanted by JCL 'cards') mainframe OS Z/OS aka OS/390 aka OS/370 aka OS/360 aka its best-known moniker over its evolution, MVS. Which contrary to rumor, never really stood for Man Versus System. Though if you've ever watched a SYSLOG fly by, you might think so.

Meanwhile, you know what is running on those "terminals" that you are calling DOS? Almost certainly, Microsoft Windows. Probably running an IBM 3270-family Terminal Emulator Program like Attachmate, Rumba or others, because nobody makes real 3270 terminals anymore for decades. Actually those terminals could be PCs running Linux with a 3270 emulator too. Talking TCP/IP most likely wrapped a half-century around SNA.

Still not DOS. And not DOS/VSE either, which was a simplified operating system for mainframes.

Your statements that it is "DOS" as in PC-DOS are akin to your saying "I had a model airplane that flies because I wound up a rubber band. It looked a lot like that 737 outside the window. Therefore that must be powered by a rubber band."


Please don't spew ignorance. There may well be a point to be made about the benefits of a WIMP (windows icon mouse pointer) interface with powerful nested command macros simplifying the underlying airline system, as being better than a command line interface (CLI). But there is also a lot of evidence that for experienced users on a properly designed and written CLI, transactions can be faster than on a graphic interface. Also less repetitive stress injury because no constant moving hand from keyboard to mouse, moving mouse in a restricted physical space.

Or as EAASY SABRE on CompuServe used to go:
AIR,23MAY,EWR,PBI,CO
was a much quicker way to book my 1980s/1990s flights on Continental to Florida online compared to when American pulled EAASY SABRE replacing it with Travelocity.