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What is Computer Memory?

Computer memory, also known as RAM (Random Access Memory), is one of the critical parts required for the operation of your PC. Without it, your PC would not be able to load any applications (ie. Internet Browser) or even the operating system (ie. Windows). Second only to the processor, computer memory is the most important component for your PC's performance.

The Basics of RAM

When you open an application or file on your PC, it is loaded onto the RAM to allow the Processor to access the information generated by the application. If your PC's Processor only accessed information from the hard disk drive (HDD) it would make your computer very slow. The Processor has access to a total of three levels of computer memory on your PC including cache, RAM and virtual memory.

Information is accessed fastest from the cache, then the RAM and finally the virtual memory. The cache memory is fastest because it is actually located on the Processor itself, however it can only hold a few megabytes at best which makes the computer memory cost quite expensive.

RAM is the next best thing to the cache in terms of the computer memory performance and can easily be expanded (on most PC's) to reduce the computers dependency on the virtual memory.

The virtual memory (or paging file) is the cheapest form of computer memory, however it is also the slowest as it is actually stored on the HDD. It acts as a buffer for any information that cannot be stored on the RAM.

Types of Computer Memory

As soon as you switch on your PC, it is constantly using the RAM available. Here is an example of how the RAM on your PC is used:
  • When switching on the PC, it performs a power-on-self-test (POST) to ensure all components of your computer are functioning correctly. Part of this test requires the memory controller to perform a quick check of the RAM to ensure no errors are returned.
  • The PC will now load the basic input/output system (BIOS) onto the computer memory. This provides basic information on all the storage and plug and play devices installed, as well as the computer startup sequence and security options.
  • The operating system (OS) installed on your PC will now be loaded from the HDD onto the RAM. Only the critical information will stored on the computer memory to allow the Processor to have immediate access the OS, this improves the performance and functionality of the PC.
  • Once you have opened an application, it will be loaded onto the RAM. Your PC will not load the complete application onto the RAM to conserve usage of the computer memory. As you use more features and open files with the application, more information will then be loaded onto the RAM.
  • When saving a file or closing an application, the information stored on the RAM is removed and saved onto the HDD.
From the examples above, every time an application or file is opened, it is loaded onto the RAM. This allows the Processor to access the information easily. The Processor requests information from the RAM, performs the required task using the information and writes back the processed information back onto the RAM continuously. This cycle occurs millions of times every second on modern PC's. Once an application is closed or a file is saved to the HDD, it is removed from the RAM to allow new information to be stored. If the changes stored on the RAM are not saved to the HDD before being removed, they will be lost.

How much memory does my PC need?

The answer will depend on how you use your computer. A simple analogy is to picture the computer memory as your desk. Every application you are running is an object placed on your desk, and the more memory your application requires, the more space it occupies of your desk. As you open more applications, you will find there is little space left to place your objects on the desk.

As a backup in case you use up all the computer memory installed on your computer, your OS has a paging file (also known as Virtual Memory) that is stored on the hard disk drive. The OS will start moving information from the computer memory to the paging file as you use your computer. This paging file would be like moving an object from your desk to a shelf on the other side of the room. If you want to begin using that object again, you will need collect it from the shelf and place it back on the desk so you can begin using it again. Of course, if your desk is full of objects, you will need to move an object from the desk to the shelf to make space for the object you wish to use.

Computer Memory Usage Example

This is why you will find your PC's performance start to slow, as it will continue to swap objects from the desk (Computer Memory) to the shelf across the room (Paging File). To stop this from happening continually, you can either close applications that you are not using or upgrade to a bigger desk (Add more Memory).

What is ECC and Registered memory?

ECC (Error Correction Codes) is an additional chip on the memory module which detects and repair data errors produced during the read and write processes on the computer memory from the memory controller. The ECC can decrease the performance of the memory, however you will guarantee that no corrupt data will be sent to the CPU for processing. ECC memory is primarly used in servers rather then in desktop and notebook computers.

Registered memory (also known as buffered memory) will have an additional chip which acts a data register between the computer memory and the memory controller. This ensures that when the data currently stored on the computer memory is refreshed to the correct bit address location. This improves the stability of servers with larger amounts of RAM installed as the Memory Controller does not refresh the data stored on the computer memory as often.

Further Reading:
How Computer Memory Works - HowStuffWorks.com
Virtual Memory - Wikipedia