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Types of Computer Memory (Storage)
Computer memory hardware devices refer to electronic components whose major purpose is to store digital data within and out of the computer. Data and information can be stored on temporary or permanent basis.
Computer memory hardware can be grouped under primary and secondary media.
While primary memory is both volatile and nonvolatile, secondary memory is only nonvolatile, meaning that it is capable of storing data for latter use.
Primary memory is commonly used to mean random access memory (RAM) but actually refers to all memory that work in tandem with the processor. To put it differently, primary memory is working memory.
The central processing unit (CPU) or accelerated processing unit (APU) reads instructions stored in primary memory.
Therefore, primary memory is primary simply because data stored within primary memory devices can communicate directly with the microprocessor.
Primary memory can be volatile or nonvolatile meaning that data in volatile memory will get lost while data in nonvolatile memory will be retained in the event of power outage.
The following are examples of primary memory:
- Dynamic Random Access Memory - DRAM (volatile)
- Static Access Memory - SRAM (volatile)
- Read Only Memory - ROM (nonvolatile)
1. Dynamic Random Access Memory (DRAM)
Dynamic random access memory, usually called RAM is the main or working memory. DRAM hardware is made of integrated circuit chips whose data can be accessed in random manner. Random means that data can be moved around in any order with disregard to access location.
Actually, DRAM is where the operating system, applications and other computer data are loaded every time a computer is powered up.
If the computer is powered down though, data stored within DRAM is either returned to secondary storage devices (nonvolatile) or is completely lost, thus its volatility.
This is why the user is always asked to save files he/she is working on. Saving commits data to secondary storage media. A file that has not been saved to secondary memory is usually lost once the computer is lost.
The more RAM a computer has, the faster it seems to perform. This does not necessarily mean that DRAM speeds up a computer. Actually, RAM allows the operating system and installed applications to load and run in bigger space, hence the concept of faster performance.
2. Static Random Access Memory (SRAM)
Static Random Access Memory is special purpose memory working inside the microprocessor. This super-fast memory is the go-between the slow main memory and super-fast microprocessor.
When a computer user inputs data to be processed, this is initially stored in main memory (DRAM) awaiting the processor to work on it. Because the speed of DRAM is not equal to the processor speed, SRAM which is much faster memory is called upon to fetch and deliver the data to the processor.
The processor will attempt to solve the task at hand and thereafter pass a solution to SRAM which in turns will feed the main memory with relevant information.
SRAM which is usually processor cache is much smaller in capacity compared to DRAM but 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.
3. Read-only Memory (ROM)
Read-only memory is a type of non-volatile data storage in computers and other electronic devices embedded in ROM semiconductor chip.
In the typical personal computer, the motherboard ROM contains Basic Input/Output System (BIOS) information about computer hardware components.
During POST (power on self-test) for example, the firmware basically runs a test to identify 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 first boot disk drive as configured in BIOS setup.
Many types of ROM chips are not literally read only, as updates are possible. Upgrading the chip can improve motherboard, card or 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.
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 is secondary because data stored within secondary storage media (usually disks) cannot directly communicate with the microprocessor. Data stored in such media is first transferred to main memory (DRAM) from where manipulation by the processor can occur.
Secondary memory is nonvolatile and allows the computer retention devices to retain data on a permanent basis.
Data retention in secondary devices can be internal and external:
Secondary storage media that retain digital data inside the computer are classed under internal storage. Typically, the operating system and applications which make the computer usable, reside within internal storage devices.
Examples of internal storage hardware:
- Hard disk drive
- Solid state disk
Secondary storage forms that are not placed inside the confines of a computer, are classed under external storage devices. Such data include audio/visual files, documents, installation applications e.t.c. that have to be moved from one computer to another.
Example of internal storage device:
- External disk drive
- Optical disks
- Flash drive
- Memory card
- Floppy disk
- Zip disk
Secondary memory devices can be grouped under:
1 Magnetic memory
2 Optical memory
3 Flash memory
4 Paper memory
1. Magnetic Storage Devices
Magnetic storage simply refers to digital data that is stored onto magnetized storage devices. Usually, magnetic storage media are called disks and are placed inside drive mechanisms like 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 hard disk, floppy disk and magnetic tapes.
Hard Disk (Drive)
A hard disk drive (HDD), also hard drive or hard disk, is made up of circular platters which are made of magnetic surfaces, enabling them to store data electronically. The word drive actually imply 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, 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.
Connectivity between hard disk drive and computer motherboard can be achieved via IDE, SCSI and SATA connectors.
Floppy Disk (Drive)
Floppy disks became popular in 1970s when they were standard media for data transfer and storage. The first standard floppy disk size was 5¼ inch in 1970s 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 2000s when optical disks, memory card and USB sticks gained popularity.
Magnetic recording uses strips of magnetic plastic film to record data.
In its early stages, magnetic media was born out of 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.
2. Flash Memory Devices
Flash memory storage is nonvolatile memory which is increasingly taking over from the popular disk drive technology as media of data retention in computing devices.
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
Solid State Disk (SSD)
Solid state disk (SSD) unlike the traditional HDD uses 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
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.
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 Devices
CD, DVD, HDVD and Blu-ray are examples of optical media and are usually inserted into the computer via a drive tray at the front of the system unit, or 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 Hardware
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.