Figure 2.7An operating system shares

Operating System Fundamentals
21
The Process Table
As previously discussed, processes need to share the CPU. Sometimes the CPU does not complete an entire process before the operating system tells it to start working on another one. This system of sharing is what makes multitasking possible. Keeping track of all of the processes is done with the
Process Table. The Process Table lists all of the processes that are currently being run, those that are waiting to be executed and those that have been temporarily suspended. It also keeps track of the current status, or state, of each process. This allows the CPU to restart those processes again when they are needed. Figure 2.8 (right) shows processes from the Windows XP process table, as displayed in the Task Manager. We will take a closer look at processes and process management in Unit 3.
Memory Management
Memory is used by a computer to temporarily hold data and instructions that are being used by applications, the operating system and hardware devices. Since atypical computer has between 1 and 4 GB of memory (RAM, and since modern operating systems can run many devices and applications at the same time, there is a lot of memory to keep track of. As we noted in the previous chapter, RAM is divided up into small spaces (usually 32 bits. Each space has its own address. An operating system must be able to keep track of all of those memory addresses and how they are currently being used. The operating system typically performs three major functions with respect to memory management
1. Gives memory to each application and device as needed
2. Protects applications (and their data) from each other
3. Protects the system from bad applications (that might try to use too much memory, or corrupt data from other applications We will take a more detailed look at how operating systems manage memory in Unit 4.

Download 2.34 Mb.

Share with your friends: