Computer memory is any physical device capable of storing information temporarily, like RAM (random access memory), or permanently, like ROM (read-only memory). Memory devices utilize integrated circuits and are used by operating systems, software, and hardware.

Memory is the electronic holding place for the instructions and data a computer needs to reach quickly. It's where information is stored for immediate use. Memory is one of the basic functions of a computer and is also used by a computer's operating system, hardware and software.

The term memory is often synonymous with the term primary storage or main memory.

There are technically two types of computer memory: primary and secondary. The term memory is used as a synonym for primary memory or as an abbreviation for a specific type of primary memory called random access memory (RAM). This type of memory is located on microchips that are physically close to a computer's microprocessor.

Computer memory operates at a high speed compared to storage that is slower but offers higher capacities. If needed, contents of the computer memory can be transferred to storage; a common way of doing this is through a memory management technique called virtual memory.

Memory can be either volatile and non-volatile memory. Volatile memory is memory that loses its contents when the computer or hardware device loses power. Computer RAM is an example of volatile memory. It is why if your computer freezes or reboots when working on a program, you lose anything that hasn't been saved. Non-volatile memory, sometimes abbreviated as NVRAM, is memory that keeps its contents even if the power is lost. ROM is an example of non-volatile memory.

It is very common for new computer users to be confused by what parts in the computer are memory. Although both the hard drive and RAM are memory, it's more appropriate to refer to RAM as "memory" or "primary memory" and a hard drive as "storage" or "secondary storage."

When someone asks how much memory is in your computer, it is often between 1 GB and 16 GB of RAM and several hundred gigabytes, or even a terabyte, of hard disk drive storage. In other words, you always have more hard drive space than RAM.

When a program, such as your Internet browser, is open, it is loaded from your hard drive and placed into RAM. This process allows that program to communicate with the processor at higher speeds. Anything you save to your computer, such as a picture or video, is sent to your hard drive for storage.

There are several types of memory for computers. They are listed below.

Memory is primarily of three types −

• Cache Memory

• Primary Memory/Main Memory

• Secondary Memory

Cache memory is a very high speed semiconductor memory which can speed up the CPU. It acts as a buffer between the CPU and the main memory. It is used to hold those parts of data and program which are most frequently used by the CPU. The parts of data and programs are transferred from the disk to cache memory by the operating system, from where the CPU can access them.

Advantages

The advantages of cache memory are as follows −

• Cache memory is faster than main memory.

• It consumes less access time as compared to main memory.

• It stores the program that can be executed within a short period of time.

• It stores data for temporary use.

Disadvantages

The disadvantages of cache memory are as follows −

• Cache memory has limited capacity.

• It is very expensive.

Primary memory holds only those data and instructions on which the computer is currently working. It has a limited capacity and data is lost when power is switched off. It is generally made up of semiconductor device. These memories are not as fast as registers. The data and instruction required to be processed resides in the main memory. It is divided into two subcategories RAM and ROM.

ROM

ROM stands for Read Only Memory. The memory from which we can only read but cannot write on it. This type of memory is non-volatile. The information is stored permanently in such memories during manufacture. A ROM stores such instructions that are required to start a computer. This operation is referred to as bootstrap. ROM chips are not only used in the computer but also in other electronic items like washing machine and microwave oven.

ROM is separated into three categories:

• PROM

• EPROM

• EEPROM

Advantages of ROM

The advantages of ROM are as follows −

• Non-volatile in nature

• Cannot be accidentally changed

• Cheaper than RAMs

• Easy to test

• More reliable than RAMs

• Static and do not require refreshing

• Contents are always known and can be verified

RAM

RAM (Random Access Memory) is the internal memory of the CPU for storing data, program, and program result. It is a read/write memory which stores data until the machine is working. As soon as the machine is switched off, data is erased.

There are six types of RAM:

• EDO RAM

• SDRAM

• DDR RAM

• DDR2 RAM

• DDR3 RAM

• DDR4 RAM

This type of memory is also known as external memory or non-volatile. It is slower than the main memory. These are used for storing data/information permanently. CPU directly does not access these memories, instead they are accessed via input-output routines. The contents of secondary memories are first transferred to the main memory, and then the CPU can access it. For example, disk, CD-ROM, DVD, etc.

Characteristics of Secondary Memory

• These are magnetic and optical memories.

• It is known as the backup memory.

• It is a non-volatile memory.

• Data is permanently stored even if power is switched off.

• It is used for storage of data in a computer.

• Computer may run without the secondary memory.

• Slower than primary memories.

The concept of memory and storage can be easily conflated as the same concept; however, there are some distinct and important differences. Put succinctly, memory is primary memory, while storage is secondary memory. Memory refers to the location of short-term data, while storage refers to the location of data stored on a long-term basis.

Memory is most often referred to as the primary storage on a computer, such as RAM. Memory is also where information is processed. It enables users to access data that is stored for a short time. The data is only stored for a short time because primary memory is volatile, meaning it isn't retained when the computer is turned off.

The term storage refers to secondary memory and is where data in a computer is kept. An example of storage is a hard drive or a hard disk drive (HDD). Storage is nonvolatile, meaning the information is still there after the computer is turned off and then back on. A running program may be in a computer's primary memory when in use -- for fast retrieval of information -- but when that program is closed, it resides in secondary memory or storage.

How much space is available in memory and storage differs as well. In general, a computer will have more storage space than memory. For example, a laptop may have 8 GB of RAM while having 250 GB of storage. The difference in space is there because a computer will not need fast access to all the information stored on it at once, so allocating approximately 8 GB of space to run programs will suffice.

The terms memory and storage can be confusing because their usage today is not always consistent. For example, RAM can be referred to as primary storage -- and types of secondary storage can include flash memory. To avoid confusion, it can be easier to talk about memory in terms of whether it is volatile or nonvolatile -- and storage in terms of whether it is primary or secondary.

Flash memory is a long-life and non-volatile storage chip that is widely used in embedded systems. It can keep stored data and information even when the power is off. It can be electrically erased and reprogrammed. Flash memory was developed from EEPROM (electronically erasable programmable read-only memory).

Flash memory is widely used with car radios, cell phones, digital cameras, PDAs, solid-state drives, tablets, and printers. The picture is an example of a MicroSD flash memory card. For additional information and examples, see our flash memory card page.

In fact, flash memory is known as a solid state storage device, meaning there are no moving parts -- everything is electronic instead of mechanical.

Flash has a limited lifespan so you should minimize writes and erasures.

When a computer receives data from an input device (e.g., keyboard), the data goes through an intermediate stage before it's sent to an output device (e.g., monitor). A processing device is any device inside a computer that interprets and manipulates incoming data during this stage. For example, in the diagram below, the CPU is the processing device.

Processing device examples

Some of the most common processing devices inside of a computer include the following:

• Central processing unit (CPU)

• Graphics processing unit (GPU)

• Motherboard

• Network card

• Sound card

• Video card