Memory management in operating systems




Facts |

The operating system has to keep up to monitor everything happening on your computer, which it manages. She is one, and the tasks it has to solve a great many. The processor is not the only device, which looks after the operating system. Another of her mission is to manage the memory. She needs to make sure that all the processes were run smoothly. Why are we talking about processes and not about the applications? The answer to this question of our readers have found in the article on the principles of the distribution of the operating system most precious resource, the CPU time.

Control to the operating system your computer’s memory consists of two main tasks:

Each process should be enough memory to run it. It occupies the space of the memory should not be available to another process, and he himself should not be wedged in the space allotted to another process
In the system there are different types of memory. They should be used so that each process work with maximum efficiency

The first task is to install the operating system limitations for certain types of software, and individual applications.

As an example, imagine an incredibly weak computer with RAM to 1 megabyte, which we take for 1000 kilobytes to avoid complicated calculations that does not help us to understand the essence of the issue. During the boot process, the operating system of the computer’s imaginary “bites” as much memory as you need it. The operating system has priority over other programs. Imagine that the operating system to boot, you need only 300 kilobytes of memory.

Imagine memory as a bath, which sank to the bottom of the operating system and start to load different drivers needed to control the computer’s hardware. Drivers should be considered a computer, you need 200 kilobytes of memory. Once everything is loaded, without which your computer will not work correctly, application processes still had 500 kilobytes of RAM.

When loaded into memory starting applications, each of which takes a certain amount of memory blocks whose size is set by the operating system. If the block size of 2 KB each process takes a chunk of memory, the size of which is a multiple of two kilobytes. That is, certain number of times to 2 kilobytes. Applications are loaded into the blocks of fixed size. Each block begins and ends short-stopper, of 4 to 8 bytes. Blocks and constraints preclude a situation where one application might overlap in memory to another. After all, in order to see happen is an Overlay sometimes enough to make a mistake with one or two bits. But what do you do when the allotted under the 500-kilobyte application memory space is filled?

Most computers today are designed so that you can build up their memory by putting into the slot of the motherboard additional bracket. For example, if the computer memory, one gigabyte, it can be increased to two. This is the best, but quite expensive and are not always supported by the configuration of the computer solution. Computer experts know that most of the application information stored in the RAM is not being used at any given point in time.

The processor has access to only one memory location at a time. Thus, much of the amount of available RAM is used. Hard disk space is much cheaper than RAM, so the movement of information from RAM to disk can significantly (and most importantly – free of charge) to “extend” the RAM. This solution is called virtual memory technology, and of him we already wrote .

The hard drive is one of the many types of memory managed by the operating system. Its space is inexpensive, it is possible to store large amounts of information. But the hard disk is the slowest repository of information, taking a very low level in the hierarchy of computer memory .

The operating system maintains a balance between the needs of the many processes. For this it uses different types of memory, data traveling between them in the manner required by the current situation. These blocks are moved (which is also called pages).

To be continued …

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