This is a common question that students ask. The answer is actually really simple, but it's not always what a student wants to hear.
If you're talking about Pell Grants, then your FA is based on Payment Period (or Period of Enrollment), such as a semester, quarter, trimester, etc. If you have two semesters in the Period of Enrollment, then your Pell will be split in half, with each disbursement coming once per semester. If you're in a quarter system, then (for a very confusing reason that will be discussed in another posting) the Pell is split into three disbursements. And so on. You only receive Pell for the amount of Payment Periods you actually attend, so if you attend one quarter in the award year, then you only receive one quarter's amount of Pell.
If you're talking about loans, typically your loans have to have a minimum of two disbursements, although some schools are actually allowed to have one disbursement. There are many schools who could have one disbursement, but choose not to use it. Your loan is based on the amount of time in your loan period, which could be an academic year or a single Payment Period (depending on your situation). At a semester-based school, if your loan is for the academic year, then it would last for two semesters which means two disbursements. At a quarter-based school, typically your loan is for three quarters (one academic year), so the loan is split into thirds, one for each quarter.
The good thing about Pell not coming at once is if you drop before the year is over, you still have Pell left to use at another school (if you switch) or at your current school (if you stay). The good thing about loans not coming at once is (once again) if you drop, you don't owe back the entire loan, just the part that came in and the school was entitled to keep. If you attend one semester and then drop, then you only owe back $4750 (combined Sub and Unsub for a first year Independent student), but if your entire loans had come in, then you'd owe $9500 (combined Sub and Unsub for a first year Independent student). That's a big difference. Just remember, your FA is based on the amount of time and number of credits you are attending from Payment Period to Payment Period.