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Types of Computer Storage Devices

Alfred is a long-time teacher and computer enthusiast who works with and troubleshoots a wide range of computing devices.

A collection of computer storage devices such as disk drives, RAM, and flash memory

A collection of computer storage devices such as disk drives, RAM, and flash memory

The different types of computer storage devices refer to electronic components that store digital data within and outside the computer. This storage can be temporary or persistent. These devices can be grouped under primary memory and secondary memory hardware. While primary memory is both volatile and nonvolatile, secondary memory is only nonvolatile.

Data in volatile memory is only available when the computer is powered up, while data in a nonvolatile memory is retained even in the event of power outage. This means that volatile memory is temporary while nonvolatile memory is persistent.

Primary Memory

Primary memory is a type of storage used to mean random access memory (RAM) but actually, refers to any memory that works directly with the processor. It is either volatile or non-volatile.

The following are examples:

  • Dynamic Random Access Memory - DRAM (volatile)
  • Static Access Memory - SRAM (volatile)
  • Read-Only Memory - ROM (non-volatile)

1. Dynamic Random Access Memory (DRAM)

Dynamic random access memory(DRAM), usually called random access memory (RAM), is the main or working memory inside your computer. It is where the operating system, applications, and other computer data are loaded every time the computer is powered up.

DRAM chips is used personal computers such as the desktop and laptop computers

DRAM chips is used personal computers such as the desktop and laptop computers

DRAM hardware is made of integrated circuit chips whose data can be accessed randomly. This means that data can be moved around in any order with disregard to access location.

If the computer is powered down, data stored within DRAM is either returned to non-volatile secondary storage devices or is lost, thus its volatility.

This is why the user is asked to save files he/she is working on to secondary storage media. The Documents folder and drives preceded with letters C: and D: are examples of popular storage locations on a Windows computer.

A file that has not been saved to secondary memory may be lost once the power to the computer is lost. If the AutoSave feature is enabled in a compliant application, however, parts of the file may be recovered the next time the application is accessed.

The more RAM a computer has, the faster it seems to perform. This does not necessarily mean that DRAM speeds up a computer. Actually, it allows the operating system and installed applications to load and run in bigger virtual room, hence the concept of faster performance.

Less RAM usually provides limited space for operating system and applications to run all at the same time, thus the need to share the little that is available. In this state, the computer may appear to be sluggish and slow.

2. Static Random Access Memory (SRAM)

Static Random Access Memory is a type of memory which works directly with the microprocessor. This super-fast memory is the go-between the slow main memory and the super-fast microprocessor.

User input data is initially stored in main memory (DRAM) awaiting processor manipulation. Because the speed of DRAM is not at par with processor speed, the faster SRAM fetches and works with the processor in data manipulation.

Once the raw data has been processed, the resultant information is passed on to DRAM.

SRAM is usually processor cache and is much smaller in capacity compared to DRAM. However, it is capable of storing fetched data more efficiently because of its multiple transistors. DRAM uses only one transistor and will need to be refreshed continuously in order to retain data while the processor is working.

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3. Read-only Memory (ROM) Hardware

Read-only memory contains non-volatile software in computers and other electronic devices. The software is usually referred to as firmware. ROM is embedded in ROM semiconductor chips.

The ROM chip in an old desktop motherboard

The ROM chip in an old desktop motherboard

In a typical personal computer, the motherboard ROM contains Basic Input/Output System (BIOS) firmware about computer hardware components.

During POST (power on self-test) for example, the firmware runs a test to initialize all connected hardware parts and verify if they are in good shape. Once the hardware parts have been verified, the BIOS hands over boot instructions to the master boot record (MBR) sector of the disk drive, which initiates the loading of the operating system.

Firmware-embedded read-only memory hardware has also evolved into flash memory semiconductor chips which can be reprogrammed. This makes it easy to install updates in computers and embedded systems. Upgrading the firmware in devices leads to better component compatibility with new software and hardware.

To ensure maximum operation of the computer, the microprocessor is in close contact with data stored in motherboard ROM. Besides the typical motherboard ROM, other components like display, network and sound cards also contain in them BIOS data.

The ROM chip in a display adapter

The ROM chip in a display adapter

Types of ROM Chips:

EAROM for Electrical Alterable Read Only Memory can be erased, read and re-programmed without removing the chip from the computer.

  • PROM for Programmable Read Only Memory can be programmed by the user and the programmed data is held permanently once programmed.
  • EPROM for Erasable Programmable Read Only Memory is similar to PROM but has an advantage in that it can be erased and reprogrammed. But for one to erase it, the EPROM must be removed from the computer.

Secondary Memory

 A hard disk drive and 2.5' solid state disk drive

A hard disk drive and 2.5' solid state disk drive

Secondary memory is secondary because it allows retention of data even during power outage. It is a non-volatile memory. Unlike primary memory, data stored on secondary storage devices may not directly communicate with the microprocessor. Data is first transferred to the main and cache memory from where manipulation by the processor takes place.

Data retention in secondary memory devices can be internal and external:

Internal storage: Typically, the operating system and applications which make the computer usable, reside within internal storage devices.

Examples of internal storage devices:

  • Hard disk drives
  • Solid state disks

External storage: Data that is not retained inside the computer is stored in external storage devices. Such data can be moved from one computer to another.

Example of internal storage devices:

  • External disk drives
  • Optical disks
  • Flash drives
  • Memory cards
  • Floppy disks
  • Zip disks

Secondary memory devices can be grouped under:

  • Magnetic memory
  • Optical memory
  • Flash memory
  • Paper memory

1. Magnetic Storage

Magnetic storage simply refers to digital data that is stored onto magnetized memory devices. Usually, magnetic storage media are called disks and are placed inside drive mechanisms like the disk drive or optical disk drive.

Data stored in magnetic media is read using read/write drive heads and can be stored for days and years.

Popular magnetic media include the hard disk, floppy disk and magnetic tapes.

Hard Disk (Drive): A hard disk drive is made up of circular platters which are made of magnetic surfaces, enabling them to store data electronically. The word drive actually implies a mechanism that makes it possible for data to be read or written on the hard disk.

Hard disk drive form factors are 3.5 and 2.5 inches for desktops and laptops respectively.

The first known hard disk drive shipped in 1956 with IBM’s RAMAC 305 system. This gigantic drive was equivalent to two refrigerators, had fifty 24 inch disk platters, and stored less than 4 megabytes of data.

Subsequent drives and disks became smaller over time, making hard disk drive the most commonly used internal storage media in desktop and laptop computers. From just under 4MBs, the storage capacity of hard disk drives has exploded to 8 terabytes and more.

Despite everything good about hard disk drives, they have remained mechanical in design and therefore, prone to failure in the event of shock and power related mishaps. These and other reasons explain the recent massive adoption of flash memory as defacto media of storage in mobiles.

The platters inside a hard disk drive

The platters inside a hard disk drive

Connectivity between hard disk drive and computer motherboard can be achieved via IDE, SCSI and SATA connectors.

PATA and SATA connectivity

PATA and SATA connectivity

Floppy Disk (Drive): Floppy disks became popular in the 1970s when they were standard media for data transfer and storage. The first standard floppy disk size was 5¼ inch but soon evolved to 3½ inch towards the end of 1980s.

Floppy disks stored data on thin, magnetic flexible vinyl material which actually felt floppy.

Both floppy disk sizes became obsolete in the 2000s when optical disks, memory card and USB sticks gained popularity.

Floppy disk drive

Floppy disk drive

Magnetic Tape: Magnetic recording uses strips of magnetic plastic film to record data.

In its early stages, magnetic media was born out of the desire to record sound, before crossing over to data and video recording. Such media is referred to as magnetic tape when used to store data for computing purposes.

Much as tape media are still being manufactured for audio-visual recording purposes, the technology is being replaced fast by flash and other media.

Magnetic tape

Magnetic tape

2. Flash Memory

Flash memory storage is nonvolatile memory which is increasingly taking over from the mechanical hard disk drive as media of data retention.

Unlike magnetic and mechanical hard disks which are prone to failure because of power and shock related issues, flash memory operates by electrical charge and can withstand sizeable shock, pressure and temperature.

Flash memory is much faster than hard disks and comparable to computer main memory (RAM).

NAND and NOR are two popular flash memory technologies and have become the standard media for internal and external storage of mainly mobile devices.

Examples of flash memory media include:

  • Solid State Disks
  • Cell phone memory
  • Flash disks
  • Memory cards
A NAND flash memory card

A NAND flash memory card

Solid State Disk (SSD): Unlike the traditional HDD, SSDs use semiconductor chips much like RAM chip hardware. Semiconductor chips for SSDs are not mechanical like HDDs and are non-volatile, unlike the volatile RAM chips.

SSDs have quickly become the replacement option for those that are tired of low-speed HDD. Though priced far above its counterpart, the benefit derived from this tradeoff can guarantee immediate satisfaction because of speed and peace of mind.

SSDs come in three popular form factors:

  • 2.5 inch SSD fits in the old HDD bay in laptops
  • mSATA for WLAN like connector in tablets and ultrabooks
  • M.2 socket in tablets and ultrabooks
An mSata SSD in Samsung ultrabook

An mSata SSD in Samsung ultrabook

Memory Card: The memory card is a family of flash memory devices used to store digital data like images and video files inside digital cameras and other mobile devices.

For example, the SD (secure digital) card can be connected to the laptop computer or using USB SD card reader.

Memory card reader and SD card attached

Memory card reader and SD card attached

USB Flash Disk Drive: A USB disk is a small thumb size device used to store and transfer all kinds of computer data. Flash disks normally connect to the computer via USB ports and is a popular means of storing and transferring files between computers.

3. Optical Storage

CD, DVD, HDVD and Blu-ray are examples of optical storage. They are usually inserted into the computer via drive bays at the front of the system unit, on the side, or front of a laptop computer. These drives are designed to read and/or write data.

Newer and ultra-thin laptops ship without optical drive units. The assumption is that most users are increasingly retaining data and installing computer applications using the cloud.

4. Paper Storage

Paper and book forms account for large chunks of data storage around the world.

Most paper storage is achieved through printing and storage in cabinet files for future reference. Of course paperwork can be cumbersome but is still a simpler way to interact with long documents, and most formal documents are still printed for filing.

Left is mSata SSD and right is M.2 SDD computer storage devices

Left is mSata SSD and right is M.2 SDD computer storage devices

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

© 2014 Alfred Amuno


Alfred Amuno (author) from Kampala on June 25, 2014:

Thanks Dataload. Hope it serves those who need it most.

DATALOAD from Michigan on June 25, 2014:

There's a lot of information packed in this article. Great overview of the subject.

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