Our PTO is still divided into sick, personal, holiday, and vacation days. Personal and vacation days can be taken as half days.
Vacation requests for the following year are due by early December. First choice within each department goes by seniority with the company, not necessarily by seniority with the department. But if you miss the deadline, you get what's leftover. The request forms (used to be on paper, now on the computer) want you to list specific weeks within a month, but in reality you can easily change those weeks within the month at a later time, or pick five scattered days within the month, etc.
My department has various amounts of vacation days available each month. (Rather, each period. January, April, July, and October are 5 week periods.) The five week periods have more vacation time available, but the other months vary widely. There's hardly any time in December. Other departments have different availability each period depending on their needs.
New hires are usually stuck with one week of January vacation for several years. Not really enough time to plan anything since the vacation schedule comes out in late December. We try to give everyone in the department a week during June, July, or August if they want one, but it's not always possible. The waiting list for a December vacation might be 15 years or more.
But vacation time is inviolable. No one is ever asked to postpone or give up their vacation time. It's already planned and budgeted for. If someone suddenly goes out on disability or maternity leave, etc., we work around it and make do the best we can.
I can't be on vacation the same time as my supervisor, and there are a couple of other similar restrictions based on position.