The Oil Pump is a critical part of an automobile engine. Its function is to supply oil under pressure to the vital componets of the engine, such as the crankshaft, connecting rods and associated bearings, pistons, camshafts and its associated valve componets.

Types of Pumps:
There are two types of oil pumps. To the best of my knowledge; The low volume, high pressure pump is most common* and used in most automobiles today. The other type, being the high volume, low pressure pump which is used in diesel engines.

LV,HP Pumps:
Low Volume Pumps are designed to flow oil at a high pressure, dependant on engine speed, to ensure all of the critical components are well lubricated under their extreme operating conditions. Low Volume pumps typically have a small oil reserve in the oil sump.

HV,LP Pumps:
High Volume Pumps are designed to flow oil at a low pressure, but with a lot more oil. These types of pumps are generally designed around engines that do not have to spin very fast, such as that of the diesel engine. High Volume pumps typically have a very large sump that may hold upwards of 8 to 12 gallons of oil. Where as a normal car engine holds between 4 and 6 quarts.

Typical oil system componets:
Your typical oil system in a car usually consists of an oil pump pre-filter, pickup tube or hose, pump, and its driving mechanism (usually a series of gears connected to the crankshaft). After the pump: Typically your oil filter, followed by oil squirters, and feed lines to the camshaft or other critical componets, depending on engine design.

* Unable to find accurate information. Personal experience was the only item used in coming to this conclusion. If you have better information, I'd be glad to recieve it and make necessary corrections.