Last Updated on October 18, 2023 by Ankit Kochar
Computer memory encompasses the designated storage capacity within a computer, serving as the repository for both transient and enduring data, programs, and directives. It stands as a fundamental element of any computing system, facilitating the swift retrieval and processing of information by the central processing unit (CPU). Within a computer, memory is categorized into two primary forms: primary memory, encompassing Random Access Memory (RAM) and Read-Only Memory (ROM), and secondary memory, which includes Hard Disk Drives (HDDs), Solid State Drives (SSDs), among others. Primary memory offers rapid data access, and it is tasked with retaining data actively used by the CPU. Conversely, secondary memory provides larger storage capacity at a comparatively slower data access rate, designed to store data that is not immediately required by the CPU. The quantity and type of memory a computer is equipped with wield substantial influence over its overall performance and operational speed.
What is Primary Memory?
Primary memory, often referred to as main memory or internal memory, represents a category of computer memory situated directly on the central processing unit (CPU). This memory module temporarily houses data and instructions during their processing. Notably, it operates as a swift and volatile form of memory, signifying that data is retained temporarily and is erased when the power supply is discontinued.
There are two types of primary memory:
Random Access Memory (RAM)
Random Access Memory (RAM) is a type of computer memory that is used to store data that is being actively used by the processor. RAM allows the processor to quickly read and write data, which is essential for the smooth operation of a computer. Unlike other forms of memory, such as hard drives and solid state drives, data stored in RAM is lost when the computer is powered off. There are two types of RAM:
Dynamic RAM (DRAM): Dynamic Random Access Memory (DRAM) is a type of random access memory (RAM) that stores each bit of data in a separate capacitor within a memory cell, with the level of charge in the capacitor representing a 0 or 1. The capacitors in DRAM cells slowly leak their charge over time, so the memory has to be constantly refreshed in order to maintain its data. This makes DRAM slower than other types of RAM, but it is also less expensive to produce, which has made it the most widely used type of memory in computers and other electronics.
Static RAM (SRAM): Static Random Access Memory (SRAM) is a type of random access memory (RAM) that uses bistable latches instead of capacitors to store each bit of data. Unlike DRAM, SRAM does not need to be constantly refreshed, which makes it faster and more reliable than DRAM. However, SRAM is also more expensive to produce, and it requires more transistors per bit of memory, which makes it less dense and more expensive to implement in large quantities. As a result, SRAM is typically used in applications where high-speed and low-latency access to data is critical, such as in cache memory, but it is not used as widely as DRAM in general-purpose computing applications.
Read-Only Memory (ROM)
Read-Only Memory (ROM) is a type of non-volatile memory that is used to store permanent data in a computer or other electronic device. Unlike RAM, data stored in ROM cannot be easily modified or deleted. Instead, it is meant to be read by the processor and used as a starting point for the device’s operation. There are several subtypes of ROM:
Programmable Read-Only Memory (PROM): It is a type of non-volatile memory that can be programmed by the user, but once programmed, the data cannot be modified or deleted. Unlike other types of ROM, such as EPROM and EEPROM, PROM can be programmed by the user to store specific data.
PROM chips were commonly used in early computer systems, as well as in other types of electronic devices, to store permanent data such as firmware and other system parameters. The user would program the PROM using a special device called a PROM programmer, which would write the desired data to the memory.
Once the data was written to the PROM, it could not be changed, which made the device useful for storing data that was intended to be permanent and unchanging. Over time, other types of non-volatile memory, such as EEPROM and flash memory, have become more popular, as they offer more flexibility and the ability to change the stored data without physical manipulation. However, PROM remains an important type of memory, especially in embedded systems and other applications where the data needs to be locked and unchangeable.
Erasable Programmable Read-Only Memory (EPROM): It is a type of non-volatile memory that can be programmed and reprogrammed multiple times. Unlike traditional Read-Only Memory (ROM), which is permanent and cannot be altered, EPROM can be erased using ultraviolet light and reprogrammed with new data. This makes it useful in various applications such as embedded systems, computer firmware, and other devices that require rewritable memory.
EPROMs use a floating gate transistor to store each bit of data. When the gate is charged, it traps electrons and creates a threshold voltage that represents a binary 1. When the gate is discharged, it represents a binary 0. To erase the EPROM, ultraviolet light is used to discharge the floating gate, effectively wiping the memory.
EPROMs have been largely replaced by other forms of non-volatile memory, such as Electrically Erasable Programmable Read-Only Memory (EEPROM) which offer higher density, faster reprogramming speeds, and lower power consumption.
Electrically Erasable Programmable Read-Only Memory (EEPROM): It is a type of non-volatile memory that can be programmed and reprogrammed electrically, rather than using ultraviolet light as in the case of Erasable Programmable Read-Only Memory (EPROM). EEPROMs are often used in a wide range of applications, including embedded systems, computer firmware, automotive systems, and other devices that require rewritable memory.
EEPROMs store data in a similar way to EPROMs, by using a floating gate transistor to represent each bit of data. However, in EEPROMs, the gate can be charged or discharged using electrical signals, rather than ultraviolet light. This allows for faster and more convenient reprogramming of the memory.
One of the key advantages of EEPROM over other types of memory is its ability to retain data even when the power is turned off. This makes it ideal for applications where data must be preserved even if the device is not in use. In addition, EEPROMs can be reprogrammed many times over their lifespan, making them more flexible and cost-effective than other types of memory in certain applications.
There are several different types of EEPROMs available, including Serial EEPROMs, Parallel EEPROMs, and Serial Peripheral Interface (SPI) EEPROMs. Each type offers different advantages and trade-offs in terms of speed, density, and other characteristics.
What is Secondary Memory?
Secondary memory, also recognized as external memory or non-volatile memory, constitutes a category of computer memory designated for the extended storage and retrieval of data. In contrast to primary memory, which is volatile and positioned directly on the CPU, secondary memory is non-volatile, signifying that it preserves its data even when the power source is disconnected. Additionally, secondary memory operates at a more leisurely pace compared to primary memory but compensates for this by offering greater storage capacity at a lower cost.
There are several types of secondary memory:
Hard Disk Drive (HDD)
It is a type of storage device that uses rotating disks, or platters, to store and retrieve digital data. The data is stored on the magnetic surface of the platters using read/write heads that float on an air cushion above the platters. The platters are housed in a sealed unit and are rotated by a spindle motor at a constant speed.
HDDs are one of the most common forms of data storage and have been used in computers and other electronic devices for decades. They offer a large capacity for storing data, relatively low cost per unit of storage, and are relatively durable.
However, HDDs are also relatively slow compared to other forms of storage such as solid-state drives (SSDs). This is because the read/write heads must physically move to the location on the disk where the data is stored, and the platters must rotate to the correct position, which takes time. In addition, HDDs are prone to mechanical failure, which can result in data loss.
Solid State Drive (SSD)
It is a type of storage device that uses NAND-based flash memory to store and retrieve digital data. Unlike traditional Hard Disk Drives (HDDs), which use rotating disks to store data, SSDs have no moving parts, which makes them faster, more reliable, and more durable.
In an SSD, data is stored in a series of interconnected flash memory chips, which are organized into pages and blocks. Data is read from and written to the flash memory using a controller, which manages the movement of data between the flash memory and the computer.
One of the key advantages of SSDs over HDDs is their speed. Because there are no moving parts, data can be accessed much more quickly, leading to faster boot times, faster application launches, and overall improved system performance. Additionally, SSDs are less prone to mechanical failure and can withstand physical shocks and vibrations better than HDDs.
Another advantage of SSDs is their lower power consumption, which can result in longer battery life in laptops and other mobile devices. In addition, SSDs are generally quieter and generate less heat than HDDs, making them ideal for use in compact and silent systems.
Optical Disk Drive (ODD)
An Optical Disk Drive (ODD) is a type of storage device that uses laser technology to read and write data on optical disks, such as CDs, DVDs, and Blu-ray disks. The laser reads the data from the disk by reflecting off of the bumps and valleys in the disk’s surface, which represent binary data. The drive then converts the binary data into digital data that can be used by a computer.
ODDs are commonly used for a variety of applications, including data backup and storage, software installation, and multimedia playback. CDs and DVDs are particularly popular for data backup due to their low cost and ease of use, while Blu-ray disks are used for high-definition video playback.
One of the key advantages of ODDs is their portability, as the disks can be easily transported and played on any compatible drive. Additionally, ODDs are relatively inexpensive and have a large storage capacity compared to other forms of storage, such as floppy disks or early forms of solid-state storage.
However, ODDs have some disadvantages compared to other forms of storage, such as solid-state drives (SSDs) or hard disk drives (HDDs). Optical disks are prone to scratches and other physical damage, which can result in data loss. In addition, ODDs are slower than other forms of storage, as the laser must physically scan the disk to read the data.
USB Flash Drive
A USB flash drive, also known as a thumb drive or flash drive, is a small, portable storage device that connects to a computer via a USB (Universal Serial Bus) port. The device uses NAND-based flash memory to store and retrieve data, which is accessed by the computer using a built-in controller.
One of the key advantages of USB flash drives is their portability and compact size, as they can be easily carried in a pocket or on a keychain. They are also relatively inexpensive and offer a convenient way to store and transfer data between computers.
Another advantage of USB flash drives is their speed, as they can transfer data much faster than traditional storage devices, such as floppy disks or CDs. Additionally, USB flash drives are durable and are not prone to physical damage like disks, which can be scratched or damaged.
One of the main disadvantages of USB flash drives is their relatively small storage capacity compared to other forms of storage, such as hard disk drives (HDDs) or solid-state drives (SSDs). Additionally, USB flash drives are prone to data loss if they are lost, stolen, or damaged.
In other words, secondary memory provides long-term storage for data and programs and is an essential part of a computer system. It is less expensive and provides larger storage capacity than primary memory but is also slower in access time.
Difference Between Primary Memory and Secondary Memory
Here is a comparison table between primary memory (also known as main memory or internal memory) and secondary memory (also known as external memory or non-volatile memory) in computer systems:
|Feature||Primary Memory||Secondary Memory|
|Definition||Volatile memory located on CPU||Non-volatile memory for long-term data storage|
|Volatility||volatile (data is lost when power is turned off)||Non-volatile(retains data even after power is turned off)|
|Purpose||Stores data and instructions temporarily for quick access by the CPU||Stores data and programs for long-term storage and retrieval|
|Examples||Dynamic RAM (DRAM), Static RAM (SRAM)||Hard Disk Drive (HDD), Solid State Drive (SSD), Optical Disk Drive (ODD), USB Flash Drive, Memory Card|
|Used as||Main memory||Backup and archival storage|
|Uses||Holds data and instructions temporarily while they are being processed||Stores data and programs for long-term use|
|Storage Technology||Dynamic capacitors, flip-flops||Magnetic disks, flash memory|
|Method of data transfer to CPU||Directly||Indirectly|
|Endurance||Limited by number of write cycles||Durable|
|Reliability||Less reliable due to volatility||More reliable due to non-volatility|
|Upgradability||Easy to upgrade||Hard to upgrade|
Understanding the concepts of primary and secondary memory is crucial for anyone interested in computer systems. Primary memory, including RAM and ROM, is the fast, volatile memory directly accessible by the CPU for temporary data storage. In contrast, secondary memory, such as HDDs and SSDs, provides non-volatile, long-term storage for data, albeit at a slower access speed. The combination and configuration of these memory types significantly impact a computer’s performance and capabilities.
FAQs on Primary Memory and Secondary Memory
Here are some frequently asked questions (FAQs) about primary memory and secondary memory in computer systems:
1. What are examples of primary memory?
Examples of primary memory include Random Access Memory (RAM) and Read-Only Memory (ROM). RAM is used for temporary data storage, while ROM contains firmware and is non-volatile.
2. What are examples of secondary memory?
Common examples of secondary memory include Hard Disk Drives (HDDs), Solid State Drives (SSDs), USB drives, and optical discs like CDs and DVDs.
3. Why is primary memory called volatile?
Primary memory is called volatile because it temporarily stores data, and this data is lost when the power supply to the computer is turned off. It does not retain information when the system is powered down.
4. What is the purpose of secondary memory?
Secondary memory serves as long-term storage for data and programs that need to be retained even when the computer is turned off. It provides a larger storage capacity compared to primary memory.
5. How does primary memory differ from secondary memory in terms of speed and size?
Primary memory is faster but smaller in size, while secondary memory is slower but offers a larger storage capacity. Primary memory is optimized for quick data access, while secondary memory is designed for long-term storage.