Types of Computer Memory –
There are many types of memory in a computer; the most basic is primary memory, also called system memory, and the secondary memory, commonly called storage.
Details about these memories are given ahead:
Primary memory is the main memory of a computer system. It stores the data temporarily. It holds only those data on which computer is currently working. Primary memory is directly accessed by the CPU. It has limited storage capacity and data is lost when power is switched off. Primary memory is a semiconductor memory because it is manufactured using semiconductor devices. The capacity of primary memory is very limited and is always less than that of secondary memory. It is more expensive than secondary memory.
Characteristics of Main Memory:
- These are semiconductor memories.
- It is known as the main memory.
- Usually volatile memory.
- Data is lost in case power is switched off.
- It is the working memory of the computer.
- Faster than secondary memories.
- A computer cannot run without the primary memory.
Types of Primary Memory:
There are two types of primary memory:
1. RAM (Random Access Memory)
2. ROM (Read Only Memory)
RAM stands for Random Access Memory. This is a volatile memory. This means it stores data or instructions temporarily. It is located on the motherboard. When you start the computer, Data and instructions from the hard disk are stored in RAM. The CPU uses this data to perform the required functions. RAM loses all data as soon as you shut down the computer.
The most important thing to understand about RAM is that RAM memory is very fast, it is a read/write memory. It is much more expensive than secondary memory.
Due to the high cost of RAM, most computer systems use both primary and secondary memory, RAM is further divided into two types :
(a) SRAM (Static Random Access Memory):
This stores a bit of data using the state of a six transistor memory cell.
(b) DRAM (Dynamic Random Access Memory):
This stores a bit data using a pair of transistor and capacitor which constitute a DRAM memory cell.
- Transistors are used to store information in SRAM.
- Capacitors are used to store data in DRAM.
- SRAM is faster as compared to DRAM.
- DRAM provides slow access speeds.
- These are expensive.
- These are cheaper.
- SRAMs are low density devices.
- DRAMs are high density devices.
- These are used in cache memories.
- These are used in main memories.
This means read only memory. It is a non-volatile memory. It stores the data permanently. These are the IC (integrated circuits) inside the PC that makes up the ROM. ROM stores a startup program called ‘Bootstrap Loader’. When the computer’s power is turned on “Bootstrap Loader” checks and starts the device connected to the PC. ROM can only be read by CPU but cannot be changed.
Types of Read Only Memory (ROM) :
(a) PROM (Programmable Read Only Memory):
PROM is read only memory that can be modified only one time by a user.. Once programmed, the data and instructions contained in it cannot be changed.
(b) EPROM (Erasable Programmable Read Only Memory):
It can be reprogrammed. To delete data from it, place it in front of an ultra violet light. To re-program it, delete all previous data
(c) EEPROM (Electrically Erasable Programmable Read Only Memory):
Data stored in EEPROM can be deleted and modified as many times as user wants. Implementing electric field can erase data, no need for ultra-violet light. We can only delete parts of the chip.
Secondary memory is permanent memory. It is not directly accessible by CPU. It communicates with the CPU through the main memory. Secondary memory stores data and holds it even when power is off. It is used to store large amount of data or programs. It is less expensive than the primary memory.
Secondary memory refers to the various storage media on which a computer can store data and programs. Floppy disks, Hard Disks, magnetic disks, magnetic tapes are the examples of secondary memory.
The Secondary storage media are of two types :
- Fixed: Fixed Storage media is an internal storage medium like hard disk that is fixed inside the computer.
- Removable: Storage medium that are portable and can be taken outside the computer are termed as removable storage media like CD, DVD, Pen drive 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.
(i) Magnetic Tapes:
Magnetic discs are made of hard metal or synthetic plastic material. Magnetic material is coated on both sides of the disc platter and both sides can be used for storage. The magnetic disk provides direct access to both small and large computer systems. Magnetic audio tapes are used to record sound and music. Magnetic video tapes are used to record analog voice and video signals. These are low cost tapes. Hard disks and floppy disks are examples of magnetic tapes.
(ii) Floppy Disk:
Also known as floppy diskette, it is a removable, portable secondary storage device. This was created in 1964 by IBM. It is a small plastic disc about 3.5 inches in size. These disks have very low storage capacity and can store approximately 1.4 MB of data. It can be read or written by a floppy disk drive.
(iii) Hard Disk:
Hard disks are the secondary storage devices used to store data permanently. It is directly connected to the disk controller on the motherboard. Hard disks are flat, circular plates made of aluminum or glass and coated with a magnetic material. Hard disk platters
typically spin very fast at 5400 to 7200 cycles/minute.
It has unlimited storage space and its storage capacity ranges from 20 GB to 500 GB. It used to install a new program or application on the device. Software programs, images, videos, etc. all can be saved to the hard drive.
There are two types of hard disks.
1. Internal Hard Disk:
Internal hard drives are located inside your computer. Most computers come with a single internal hard drive, which includes the operating system and pre-installed applications.
2. External Hard Drive:
An external hard drive, also called a portable hard drive. It is a device connected to the outside of a computer via a USB connection. It is often used to back up a computer or portable storage.
(iv) Optical Drives:
Optical drives are a storage medium from which data is read and written by a laser. Optical disks can store up to 6GB of data. Optical storage devices are the most widely used and reliable storage devices.
The most commonly used types of optical storage devices are:
A compact disc is a flat, round, optical storage medium invented by James Russell. It is a portable storage medium that was used to digitally store and play the audio, video and other data. Compact discs have greater storage capacity than floppy disks. These disks can store 650-700 MB of data. This is a very reliable storage media.