Computer memory is an umbrella term for all types of data storage technology that’s built into or can be externally connected to a computer device or server. There are two memory types, primary and secondary, which are accessed depending on their use by the computer.
Some types of computer memory are designed to be fast, meaning the central processing unit (CPU) can access data stored there quickly. Other types are designed to be low cost, so large amounts of data can be stored economically.
This article will help you understand the various types of computer memories, their use cases, importance, and subcategories.
Table of Contents
- Primary memory is memory the CPU can access directly.
- Random-access memory (RAM) is short-term memory, where only the data currently in use by the CPU is kept.
- Read-only memory (ROM) is non-volatile memory that connects by electronically modified post manufacturing.
- Secondary memory is long-term and persistent data storage that’s not directly accessed by the CPU.
- A hard disk drive (HDD) is a non-volatile, electro-mechanical data storage hardware for persistent and long-term data storage.
- A solid-state drive (SSD) is a solid-state, non-volatile storage hardware that uses integrated circuit assemblies.
- An optical (CD or DVD) drive is persistent storage written and read with a specialized laser.
- A tape drive is persistent data storage hardware that uses magnetic tape.
- A storage array is a data storage system containing multiple disk drives.
- Network-attached storage (NAS) is a dedicated file storage that supports simultaneous multi-user access.
- Cloud storage is an off-site server where digital data can be stored in logical pools.
Primary Memory Types
|Stands for||Random-access memory||Read-only memory|
|Storage capacity||Up to 256GB per chip||up to 8MB per chip|
|Use||In standard computing operations||During the boot process|
|Types||DRAM, SRAM||PROM, EPROM, EEPROM|
Primary memory is the segment of computer memory the CPU is able to access directly. It’s usually placed in close physical proximity to the CPU in order to minimize communication times.
Both RAM and ROM are used to store data for direct access by the CPU. However, only RAM is volatile, meaning its data is deleted once the system has been powered down, whereas ROM is non-volatile, meaning it keeps its data after the system has been powered down.
Random Access Memory
Random-access memory gets its name from the way the CPU accesses it and scans its lines for the appropriate information randomly, not following strict directions. This is to equalize the time of access between all stored bits of data.
One of the defining features of RAM memory is that it’s incredibly fast, only marginally slower than the CPU itself. RAM is used to hold the data the CPU needs while it runs a program, which saves it time to reach the secondary storage every time it needs a piece of data or instruction.
However, RAM is also one of the most expensive components of a computer device, with its cost often measured per gigabyte. In fact, the high cost of RAM is the main reason why computers have to rely on both primary and secondary memory.
Types of RAM
Dynamic RAM (DRAM)
DRAM is the most common and beneficial variety of RAM used in computers, containing both a transistor and a capacitor in each of its cells. All computers must contain both RAM and DRAM to function and operate effectively.
Over the past few decades, there have been numerous versions of DRAM. The oldest is known as a single data rate (SDR) DRAM. However, newer devices use evolved versions such as DDR2, DDR3, and DDR4, as they tend to be more energy-efficient and more productive than their older counterparts. But since the different types aren’t compatible, a computer device only includes one type of DRAM throughout.
Static RAM (SRAM)
SRAM is faster than both the RAM and DRAM, but it’s considerably more expensive and bulky, including six transistors in each cell.
That’s why SRAMs are only used in small quantities in the computer. They’re almost always employed as cache memory, used to mediate the communication between the device’s main RAM and CPU to bridge the gap in clocking speeds.
The fastest and smallest implementation of an SRAM is as a cache memory inside the CPU’s core, working at the same speed to eliminate delays.
ROM gets its name because data stored on it is immutable and cannot be removed or changed using ordinary methods. It’s another incredibly fast type of computer memory that can be found in close proximity to the device’s CPU.
Unlike RAM, ROM is a non-volatile memory that doesn’t lose its data when it no longer receives power—like when the computer is turned off. In this aspect, it overlaps with secondary memory in which the storage of data on it is long-term.
Instructions on the ROM are the first thing the CPU begins to read and execute when a device is turned on. It usually contains “bootstrap code” which allows the computer to carry out the necessary steps for launching the operating system on the secondary memory.
You can find ROM in all types of electronic devices such as game consoles and car radio and navigation systems.
Types of Rom
Programmable ROM (PROM)
PROM is different from true ROM by being manufactured in its empty state instead of sold and distributed with the instructions already on it. PROMs can be programmed later using a PROM programmer or burner.
Erasable Programmable ROM (EPROM)
The information stored on an EPROM can be erased and then reprogrammed. This can only be done by taking it out of the device and exposing it to ultraviolet light. Then, new data is reburned on it.
Electronically Erased Programmable ROM (EEPROM)
EEPROM differs from both PROM and EPROM by not needing to be taken out to erase and reprogram. While the reformatting process can be slow, it’s not done often and usually only to update critical code such as firmware or BIOS.
Secondary Memory Types
Secondary memory is a segment of computer memory defined by being persistent, non-volatile, and not directly accessed by the device’s CPU.
It tends to be more affordable than primary memories and is available with much greater capacities. These enable users to store personal data and information along with software, applications, and services that can be accessed indirectly by the computer’s CPU through its RAM.
Hard Disk Drives
Hard disk drives, also referred to as hard disks or hard drives, are electro-mechanical data storage devices that are capable of keeping and restoring data over a long period of time.
They’re built from a stack of rotating disks held in place by spindles. While the plates themselves aren’t magnetic, they’re coated with a magnetic material that stores the data.
The part that reads and writes the data is called the head. It’s capable of moving over the platter and inscribing it with 1s and 0s to write and read data. The platter spins fast, enabling the head to read the data stored on it with great efficiency.
HDDs are the cheapest option per gigabyte when compared to other long-term secondary storage. However, it’s not the go-to solution for many tech enthusiasts, as it’s less durable. If the platter’s surface is scratched, information can be lost.
Not to mention, HDDs have many moving parts, all of which have their own possible points of error. As for convenience, they are noisy, consume a lot of power, and can be slower to access and write compared to the speed of the average RAM.
That said, HDDs are great for long-term storage and archiving. They’re often found in older and more budget-friendly desktop computers and laptops.
Read more about hard disk drives, their types, and how they work.
Solid State Drives
Solid-state drives are a type of semiconductor, long-term, non-volatile storage. They use NAND flash memory in persistent data storage and are typically used as secondary storage in a computer to hold personal files.
An SSD unit consists of a controller, NAND flash for memory storage, and a DRAM. The three components work together to create a miniature ecosystem for persistent data storage for a device.
SSDs work by using flash memory that keeps data inside an integrated circuit. Each flash memory chip within an SSD is made up of an array of blocks lined in a grid. Within individual blocks are memory cells, called sectors, where the data is kept.
This delicate architecture means data on an SSD can be written, read, duplicated, and transferred electronically without making noise or requiring movement. Without the mechanical parts found in their HDD counterparts, SSDs are capable of operating silently and efficiently with minimal chances of physical damage.
While SSDs aren’t as durable, they can last up to five years, and some units can be guaranteed by their manufacturer for up to 10 years. This means they aren’t as effective for archival and long-term storage.
The same goes for cost. They’re faster and more compact, but SSDs are considerably more expensive. They also tend to be smaller in capacity, but you can still find units going up to 30TB for a premium.
Read more about solid-state drives in an enterprise setting, their performance, and pricing.
Optical (CD or DVD) Drives
Optical storage is an umbrella term used to define data storage methods where a laser is used to store and retrieve data on optical storage media. The most common variety of optical storage are CDs, DVDs, and Blu-ray discs.
Most optical storage discs available nowadays are read/write, allowing you to repeatedly erase and reburn new information onto their surface.
CDs, DVDs, and Blu-ray discs don’t work independently. They require a specialized drive for reading and writing called an optical drive. Those can either be built into the laptop or desktop computer, or they can be connected externally using a data-transfer cable.
An optical drive works by shooting a low-energy laser beam to scan the surface of the spinning optical storage media. How fast the writing and reading process depends on the spinning speed of the disc.
On a micro level, optical discs have grooves and protrusions the optical drive can detect by analyzing how the laser reflects off of its surface.
They are incredibly cheap and easy to carry, making them ideal for offline data exchange and transfers between individuals. However, their storage capacity is minuscule in comparison to other secondary memory solutions. While the average CD is 640MB, DVDs can range between 4.7GB and 18GB, while quad-layer Blu-ray discs can reach 128GB.
Tape drives are long-term, persistent, and non-volatile data storage devices that use magnetic tapes to store, read, and write bits of data. They consist of an outer covering that protects a loop of flexible material that carries the data.
Similarly to optical storage, tape storage cannot be accessed without specialized equipment. A tape drive is the device where a tape is inserted to be read. It uses linear tape technology or a helical scan to read the magnetic markings on the tape.
Tape drives are ideal for long-term and archival storage, as the average unit can last for up to 30 years. They’re also cost-efficient and easy to maintain, making them suitable for keeping large volumes of data.
That said, they’re rarely used in computer desktops and laptops because they’re bulky and incredibly slow. That’s because the tape drive would have to rewind and go through the length of the entire tape to reach a specific point and pull data from it, unlike HDDs and SSDs that can be accessed more efficiently.
Read more about tape storage and its latest trends in the storage industry.
Storage arrays, also known as disk arrays, are storage systems that consist of a collection of fast-spinning HDDs, SSDs, or a hybrid of both storage types. This is mostly used for storing data as object-based, file-based, or block-based.
As secondary storage on a large scale, storage arrays include more than the storage devices themselves. Physical components of an array include storage drives, power canisters, controller fans, humidity fans, disk shelves, and storage controllers.
They’re the most common alternative to server storage, as arrays combine multiple drives into a single, large-scale data storage system with centralized management.
This system is capable of storing and reliably maintaining petabytes of data at a time. Data in storage arrays is accessible by local client nodes as well as remote computers through an application programming interface (API) or a dedicated graphical user interface (GUI) control panel.
The limitation of a storage array is the high possibility of wasted memory space. This is because individual arrays must be homogeneous, containing only a single type of value and being categorized as such, like an integer array or a float array.
Storage arrays are employed by organizations, businesses, and enterprises with a large volume of data that needs to be managed centrally but accessed remotely by multiple users. This type isn’t suitable for individual users, as the upkeep and maintenance surpass the capabilities of a single person.
Read more about storage arrays and SSDs.
Network-attached storage is a file-based storage that’s connected to a wider computer network. This enables multiple groups of users and heterogeneous devices to access the storage and retrieve data as needed for processing.
A NAS comprises a NAS unit, a NAS box, and a NAS head or server, where the data is stored on discs, drives, or a combination of the two. The system part includes its own CPUs and RAM to facilitate the communication between clients and the storage. The term NAS refers to both the software and hardware components used in this storage type.
NAS combines both software and hardware and a collection of communication and file-sharing protocols over a network. Those protocols, also called rules, control how authorized computers and user accounts can access the data remotely but feel like the data is stored locally on their device.
Generally, they tend to be limited in scalability and only perform as well as the protocols used to govern them. Also, relying on NAS for storage can direct a lot of traffic toward your local area network (LAN) line and reduce availability.
While NAS is mostly used by large corporations and enterprises, it can be adapted to suit the needs of a small team of professionals. It’s ideal for situations where more than one device needs to access the same data simultaneously. It’s also great for collaborative work, as it only offers the latest version of a file.
Read more about network-attached storage, how it works, and how it’s used in real-life situations.
Cloud storage is a type of persistent and non-volatile data storage where data is kept off-premises in logic pools. The term “cloud” refers to physical storage devices that span multiple servers.
The ownership along with the upkeep and maintenance of those remote servers is more often the responsibility of the host company. However, some companies, especially larger ones, sometimes prefer to own their cloud operations even when off-premises.
The components of a cloud storage solution include software, hardware, and services. This includes storage servers, client infrastructure, cloud infrastructure, access applications, security software, and an internet connection.
Cloud storage, however, isn’t recommended for companies handling sensitive information such as financial information and customer data, as it poses a security risk compared to other varieties of data storage. Also, it shouldn’t be used to store operation-critical data, as any downtime or loss in connection could remove access to the entirety of the cloud.
In cloud storage, the data is kept remotely on servers but can be accessed through an internet connection from anywhere and using any device. It’s widely used by both businesses and individuals to store data and files they need to access regularly, without having to carry them around locally or on external storage.
Read more about cloud storage, how it works, and the different types of cloud architectures.
What Is the Difference Between Primary and Secondary Memory?
While there are many ways data storage devices can be categorized, one is by how they’re used by a computer.
If the computer’s CPU directly communicates with a type of data storage, it’s considered primary storage, meaning it’s essential to the functioning and operation of the device. Secondary memory, on the other hand, encompasses a variety of storage device types that aren’t accessed directly by the CPU but through the primary storage.
Volatility is another difference between primary and secondary storage. RAM and its types are considered volatile storage, where all data stored is erased if the hardware was powered down. Secondary memory, alternatively, is capable of keeping its data even after it loses power.
When it comes to speed, primary storage needs to be fast in order to keep up with the rate of the CPU core. Secondary memory is relatively slower and isn’t suitable for direct CPU access.
Another element is the cost per gigabyte. Because primary memory storage is designed to be incredibly fast, it’s also expensive and sold with smaller storage capacities. A single secondary storage device can reach terabytes in size and still be reasonably priced.
Understanding the Types of Computer Memory
Computer memory is a term used to refer to any device capable of storing data. It’s divided into two categories depending on its relationship to the computer’s CPU and storage volatility.
Primary storage is accessed directly by the CPU and works at high speeds, but it’s volatile and loses data when disconnected from power. This includes RAM in all types and ROM in all types.
Secondary storage is rarely accessed directly by the CPU and therefore can be made to run slower to save on costs. It’s non-volatile and capable of keeping data long-term for anywhere from a few years to over three decades. Examples include HDD, SDD, tape, NAS, and optical drives.