Memory of Computer

Memory

Computer memory is the storage space in computer where data is to be processed and instructions required for processing are stored.

The memory is divided into large number of small parts called cells. Each location or cell has a unique address which varies from zero to memory size minus one.

Just like humans, computers rely a lot on memory. They need to process and store data, just like we do. However, computers store data in digital format, which means the information can always be called up exactly the way it was stored.

Also, unlike our memory, the computer's memory doesn't get worse over time.

Computers don't remember or forget things the way that human brains do. Computers work in binary. They either know something or they don't—and once they've learned, barring some sort of catastrophic failure, they generally don't forget.

Memory is primarily of three types

• Cache Memory
• Primary Memory/Main Memory
• Secondary Memory

Cache Memory

Cache memory is a very high speed semiconductor memory which can speed up CPU. It acts as a buffer between the CPU and main memory.

It is used to hold those parts of data and program which are most frequently used by CPU. The parts of data and programs are transferred from disk to cache memory by operating system, from where CPU can access them.

Primary Memory (Main Memory)

Primary memory holds only those data and instructions on which computer is currently working. It has limited capacity and data is lost when power is switched off.

It is generally made up of semiconductor device. The data and instruction required to be processed reside in main memory. It is divided into two subcategories RAM and ROM.

Characteristics:

• These are semiconductor memories
• It is known as main memory.
• Usually volatile memory.
• Data is lost in case power is switched off.
• It is working memory of the computer.
• Faster than secondary memories.
• A computer cannot run without primary memory.

It has two sub-categories:

1. RAM :

RAM (random access memory) is the place in a computer where the operating system, application programs, and data in current use are kept so that they can be quickly reached by the computer's processor.

RAM is much faster to read from and write to than the other kinds of storage in a computer, the hard disk, floppy disk, and CD-ROM.

However, the data in RAM stays there only as long as your computer is running. When you turn the computer off, RAM loses its data. That is why it is called volatile memory.

RAM can be compared to a person's short-term memory and the hard disk to the long-term memory. The short-term memory focuses on work at hand, but can only keep so many facts in view at one time.

Unlike the hard disk which can become completely full of data so that it won't accept any more data, RAM never runs out of memory. It keeps operating, but much more slowly than you may want it to.

It has two parts:

A. SRAM: Static Random Access Memory

B. DRAM: Dynamic Random Access Memory

2. ROM:

As the name suggests, read-only memory, or ROM, stores information that can only be read. Modifying it is either impossible or very difficult.

ROM is also a type of non-volatile storage, which means that the information is maintained even if the computer loses power.

This is typically referred to as the firmware of a computer. The firmware represents the basic code to get the computer started. Once the computer is up and running, the CPU takes over.

Firmware is also referred to as BIOS, or basic input/output system. On most modern computers, the read-only memory is located on a BIOS chip. The BIOS chip is normally plugged into the motherboard.

You have probably heard of the term CD-ROM, which stands for compact disc read-only memory. This is another type of ROM that is impossible or difficult to change.

• PROM - Programmable Read Only Memory.
• EPROM - Erasable Programmable Read Only Memory.
• EEPROM - Electrically Erasable Programmable Read Only Memory.

Secondary Memory

This type of memory is also known as external memory or non-volatile. It is slower than 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. Contents of secondary memories are first transferred to main memory, and then CPU can access it. For example: disk, CD-ROM, DVD etc.

Characteristic:

• These are magnetic and optical memories
• It is known as backup memory.
• It is 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 secondary memory.
• Slower than primary memories.

Some of the examples of Secondary memory are:

CD-ROM 

A CD-ROM is a pre-pressed optical compact disc which contains data. The name is an acronym which stands for "Compact Disc Read-Only Memory".

• Computers can read CD-ROMs, but cannot write to CD-ROMs which are not writable or erasable.
• It’s a non volatile memory.
• It can be read using Laser rays.

USB or Universal Serial Bus

USB, short for Universal Serial Bus, is an industry standard developed in the mid-1990s that defines the cables, connectors and communications protocols used in a bus for connection, communication, and power supply between computers and electronic devices

• USB was designed to standardize the connection of computer peripherals (including keyboards, pointing devices, digital cameras, printers, portable media players, disk drives and network adapters) to personal computers, both to communicate and to supply electric power.

CD-RW

CD-RW (Compact Disc-ReWritable) is a digital optical disc storage format. A CD-RW disc is a compact disc that can be written, read arbitrarily many times, erased, and written again.

The technology was introduced in 1997.

DVD

Short for Digital Versatile Disc or Digital Video Disc, a DVD or DVD-ROM is a disc capable of storing more amounts of data on one disc than a Compact Disc(CD).