Cache memory

RAM is not fast enough to keep up with the CPU. Cache Memory is used in-between the CPU and the RAM and holds the most frequently used data or instructions to be processed. There are three different grades of Cache. Some systems will only have level 1 and level 2. More advanced systems will include the level 3.

Level 1 (L1) is the primary and is on or very close to the processor. Level 2 (L2) is second closest to the CPU and is more common to be on the motherboard. Level 3 (L3) is the most advanced cache and will speed up the memory even further. Cache memory is used for the most frequently used data and instructions.

Level one cache utilizes small amounts of memory in the CPU whereas level two hides out in a chip near the CPU. It actually connects to the CPU itself and helps to keep it from overclocking when accessing its own memory.

Hard drive

A Hard Drive is a form of computer memory that allows you to permanently store data. This is where all of your permanent files and programs are stored. On computers running with Microsoft windows the Hard Drive is often called C-Drive. The size of a Hard Drive is typically measured in gigabytes.

There is another division of the types of memory into primary and secondary. Primary memory is the memory that can be directly accessed by the CPU which constantly interacts with it, retrieves data stored therein, goes through instructions and execute them as per the requirement. All the information, data and application are loaded there in uniform manner.

Secondary memory is not directly accessible to the CPU. This memory does not lose the data when the system is powered off. The most familiar form of secondary memory that is widely used is external Hard Disk. Some examples of secondary memory are USB sticks, floppy drives and Zip drives.

Virtual memory

Virtual memory is a system where all physical memory is controlled by the operating system. When a program needs memory, it requests it from the operating system. The operating system then decides what physical location to place the memory in. Virtual memory typically comes into place when applications are too large for the RAM to handle. The operating system uses the hard drive to temporarily store information and take it back when needed. This is normally a lot slower than actual RAM and can possibly degrade performance if used to heavily.

This offers several advantages. Computer programmers no longer need to worry about where the memory is physically stored or whether the user's computer will have enough memory. It also allows multiple types of memory to be used. For example, some memory can be stored in physical RAM chips while other memory is stored on a hard drive. This drastically increases the amount of memory available to programs. The operating system will place actively used memory in physical RAM, which is much faster than hard disks. When the amount of RAM is not sufficient to run all the current programs, it can result in a situation where the computer spends more time moving memory from RAM to disk and back than it does accomplishing tasks; this is known as thrashing.

Systems that employ virtual memory:

• use hardware memory more efficiently than systems without virtual memory

• make the programming of applications easier by:

  • delegating to the kernel the burden of managing the memory hierarchy; there is no need for the program to handle overlays explicitly.

  • obviating the need to relocate program code or to access memory with relative addressing.

Memory virtualization is a generalization of the concept of virtual memory.

Virtual memory systems usually include protected memory, but this is not always the case.