Multitasking

• One specific role of the operating system is to manage different programs that are running at the same time. Not all operating systems can do this, but most modern ones can. The disk operating system that provides command-line capabilities in Windows is not capable of running more than one program at a time. In computer lingo, this means that DOS is not capable of multitasking.
  
  

Time Slices

• Operating systems allow different programs to run by assigning each one requesting execution its own slice of time. If you picture a pie divided into wedges, this concept may be easier to grasp. The whole pie represents a chunk of time, such as 1 second. The pie's slices are the time segments of each program, which added up sum to 1 second. You can label each slice with the name of a program -- Windows Explorer, Notepad and Firefox, for example -- to complete the illustration of this function of the operating system.
  
  

Memory

• The operating system also manages access to memory, another resource of your PC. Think of the operating system as a gatekeeper or guard whom you've entrusted with apportioning slices of random access memory to the programs that request it. When a program needs a block of memory to store a text document, for example, it doesn't scoop out that block at random from the list of memory addresses in your computer. If it did, it would likely take memory used by another program, and digital oblivion would result within microseconds. Instead, the program asks the operating system for the memory block. The operating system maintains a list of which program is using which blocks of memory as well as a list of free blocks. The operating system assigns a new free block to the requesting program based on these lists.
  
  

Device Drivers

• The operating system starts, stops and directs device drivers, which are programs that communicate with your hard drive, flash drive, keyboard, and also your software-based devices, such as virtual drives. For example, when you request a word-processing document on your C: drive, the operating system forwards that request to the device driver for that hard drive. The device driver scans its internal lists that track which files are stored on which sectors of the disk, then retrieves the file you requested to the operating system. The operating system then provides you with the file.