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Subject: Computer Organization and Architecture

Topic: Module 2

Difficulty: Low

• Computer data storage,often called storage or memory refers to computer components,devices,and recording media that retain digital data used for computing for some interval of time.
• Computer data storage provides one of the core functions of modern computer,ie,Information retention.
• So far,no practical universal storage medium exists,and all forms of storage have some drawbacks.
• Therefore a computer system usually contains several kind of storage each with individual purposes.

MEMORY CHARACTERISTICS

• The complex subject computer memory can be made manageable by classifying the memory systems according to their key characteristics.

The most important characteristics are:-

• Memory type
• Memory size
• Memory location
• Word length
• Addressable unit
• Unit of transfer
• Access method

THE MEMORY HIERARCHY

• The goal of any memory system is to provide adequate storage capacity with an acceptable level of performance and cost.
• One can achieve these goals by employing several memory types - with different cost/performance ratios-that are organized to provide a high average performance at a low average cost per bit.
• The objective of the organization is to achieve a good trade-off between cost,storage capacity and performance for the memory system as a whole.

As one goes down the hierarchy,the following occur

• Decreasing cost per bit
• Increasing capacity
• Increasing access time
• Decreasing frequency of access of the memory by the CPU

Thus smaller,more expensive memories are supplemented by larger,cheaper and slower memories.

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A memory is just like a human brain. It is used to store data and instructions. Computer memory is the storage space in the computer, where data is to be processed and instructions required for processing are stored. The memory is divided into large number of small parts called cells. Each location or cell has a unique address, which varies from zero to memory size minus one. For example, if the computer has 64k words, then this memory unit has 64 * 1024 = 65536 memory locations. The address of these locations varies from 0 to 65535.

Memory is primarily of three types −

Cache Memory

• Primary Memory/Main Memory

Secondary Memory

Cache memory is a very high speed semiconductor memory which can speed up the CPU. It acts as a buffer between the CPU and the main memory. It is used to hold those parts of data and program which are most frequently used by the CPU. The parts of data and programs are transferred from the disk to cache memory by the operating system, from where the CPU can access them.

The advantages of cache memory are as follows −

• Cache memory is faster than main memory.
• It consumes less access time as compared to main memory.
• It stores the program that can be executed within a short period of time.
• It stores data for temporary use.

Disadvantages

The disadvantages of cache memory are as follows −

• Cache memory has limited capacity.
• It is very expensive.

Primary Memory (Main Memory)

Primary memory holds only those data and instructions on which the computer is currently working. It has a limited capacity and data is lost when power is switched off. It is generally made up of semiconductor device. These memories are not as fast as registers. The data and instruction required to be processed resides in the main memory. It is divided into two subcategories RAM and ROM.

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.

This type of memory is also known as external memory or non-volatile. It is slower than the main memory. These are used for storing data/information permanently. CPU directly does not access these memories, instead they are accessed via input-output routines. The contents of secondary memories are first transferred to the main memory, and then the CPU can access it. For example, disk, CD-ROM, DVD, 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.

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A computer is an electronic device and that accepts data, processes on that data, and gives the desired output. It performs programmed computation with accuracy and speed. Or in other words, the computer takes data as input and stores the data/instructions in the memory (use them when required). After processes the data, it converts into information. Finally, gives the output.

Here, input refers to the raw data that we want the machine to process and return to us as a result, output refers to the response that the machine provides in response to the raw data entered and the processing of data may involve analyzing, searching, distributing, storing data, etc. Thus, we can also call a computer data processing system.

What is Computer Memory?

Computer memory is just like the human brain. It is used to store data /information and instructions . It is a data storage unit or a data storage device where data is to be processed and instructions required for processing are stored. It can store both the input and output can be stored here.

Characteristics of Computer Memory

• It is faster computer memory as compared to secondary memory.
• It is semiconductor memories.
• It is usually a volatile memory, and main memory of the computer.
• A computer system cannot run without primary memory.

How Does Computer Memory Work?

When you open a program, it is loaded from secondary memory into primary memory. Because there are various types of memory and storage, an example would be moving a program from a solid-state drive (SSD) to RAM. Because primary storage is accessed more quickly, the opened software can connect with the computer’s processor more quickly. The primary memory is readily accessible from temporary memory slots or other storage sites.

Memory is volatile, which means that data is only kept temporarily in memory. Data saved in volatile memory is automatically destroyed when a computing device is turned off. When you save a file, it is sent to secondary memory for storage.

There are various kinds of memory accessible. It’s operation will depend upon the type of primary memory used. but normally, semiconductor-based memory is more related with memory. Semiconductor memory made up of IC (integrated circuits) with silicon-based metal-oxide-semiconductor (MOS) transistors.

Types of Computer Memory

In general, computer memory is of three types:

• Primary memory
• Secondary memory
• Cache memory

Now we discuss each type of memory one by one in detail:

1. Primary Memory

It is also known as the main memory of the computer system. It is used to store data and programs or instructions during computer operations . It uses semiconductor technology and hence is commonly called semiconductor memory. Primary memory is of two types:

• S RAM (Static RAM): S RAM uses transistors and the circuits of this memory are capable of retaining their state as long as the power is applied. This memory consists of the number of flip flops with each flip flop storing 1 bit. It has less access time and hence, it is faster.
• D RAM (Dynamic RAM): D RAM uses capacitors and transistors and stores the data as a charge on the capacitors. They contain thousands of memory cells. It needs refreshing of charge on capacitor after a few milliseconds. This memory is slower than S RAM.
• MROM(Masked ROM): Hard-wired devices with a pre-programmed collection of data or instructions were the first ROMs. Masked ROMs are a type of low-cost ROM that works in this way.
• PROM (Programmable Read Only Memory): This read-only memory is modifiable once by the user. The user purchases a blank PROM and uses a PROM program to put the required contents into the PROM. Its content can’t be erased once written.
• EPROM (Erasable Programmable Read Only Memory): EPROM is an extension to PROM where you can erase the content of ROM by exposing it to Ultraviolet rays for nearly 40 minutes.
• EEPROM (Electrically Erasable Programmable Read Only Memory): Here the written contents can be erased electrically. You can delete and reprogramme EEPROM up to 10,000 times. Erasing and programming take very little time, i.e., nearly  4 -10 ms(milliseconds). Any area in an EEPROM can be wiped and programmed selectively.

2. Secondary Memory

It is also known as auxiliary memory and backup memory. It is a non-volatile memory and used to store a large amount of data or information . The data or information stored in secondary memory is permanent, and it is slower than primary memory. A CPU cannot access secondary memory directly. The data/information from the auxiliary memory is first transferred to the main memory, and then the CPU can access it.

Characteristics of Secondary Memory

• It is a slow memory but reusable.
• It is a reliable and non-volatile memory.
• It is cheaper than primary memory.
• The storage capacity of secondary memory is large.
• A computer system can run without secondary memory.
• In secondary memory, data is stored permanently even when the power is off.

Types of Secondary Memory

1. Magnetic Tapes: Magnetic tape is a long, narrow strip of plastic film with a thin, magnetic coating on it that is used for magnetic recording. Bits are recorded on tape as magnetic patches called RECORDS that run along many tracks. Typically, 7 or 9 bits are recorded concurrently. Each track has one read/write head, which allows data to be recorded and read as a sequence of characters. It can be stopped, started moving forward or backward, or rewound.

2. Magnetic Disks: A magnetic disk is a circular metal or a plastic plate and these plates are coated with magnetic material. The disc is used on both sides. Bits are stored in magnetized surfaces in locations called tracks that run in concentric rings. Sectors are typically used to break tracks into pieces.

Hard discs are discs that are permanently attached and cannot be removed by a single user.

3. Optical Disks: It’s a laser-based storage medium that can be written to and read. It is reasonably priced and has a long lifespan. The optical disc can be taken out of the computer by occasional users.

Types of Optical Disks

CD – ROM

• It’s called compact disk. Only read from memory.
• Information is written to the disc by using a controlled laser beam to burn pits on the disc surface.
• It has a highly reflecting surface, which is usually aluminium.
• The diameter of the disc is 5.25 inches.
• 16000 tracks per inch is the track density.
• The capacity of a CD-ROM is 600 MB, with each sector storing 2048 bytes of data.
• The data transfer rate is about 4800KB/sec. & the new access time is around 80 milliseconds.

WORM-(WRITE ONCE READ MANY)

• A user can only write data once.
• The information is written on the disc using a laser beam.
• It is possible to read the written data as many times as desired.
• They keep lasting records of information but access time is high.
• It is possible to rewrite updated or new data to another part of the disc.
• Data that has already been written cannot be changed.
• Usual size – 5.25 inch or 3.5 inch diameter.
• The usual capacity of 5.25 inch disk is 650 MB,5.2GB etc.
• DVDR (writable)
• DVDRW (Re-Writable)
• DVD-ROMS (Digital Versatile Discs) : These are read-only memory (ROM) discs that can be used in a variety of ways. When compared to CD-ROMs, they can store a lot more data. It has a thick polycarbonate plastic layer that serves as a foundation for the other layers. It’s an optical memory that can read and write data.
• DVD-R : DVD-R is a writable optical disc that can be used just once. It’s a DVD that can be recorded. It’s a lot like WORM. DVD-ROMs have capacities ranging from 4.7 to 17 GB. The capacity of 3.5 inch disk is 1.3 GB.

3. Cache Memory

It is a type of high-speed semiconductor memory that can help the CPU run faster. Between the CPU and the main memory, it serves as a buffer. It is used to store the data and programs that the CPU uses the most frequently.

Advantages of Cache Memory

• It is faster than the main memory.
• When compared to the main memory, it takes less time to access it.
• It keeps the programs that can be run in a short amount of time.
• It stores data in temporary use.

Disadvantages of Cache Memory

• Because of the semiconductors used, it is very expensive.
• The size of the cache (amount of data it can store) is usually small.

FAQs on Computer Memory

Q.1: what is volatile and non volatile memory.

Volatile memory is used to store information based on power supply. If the power supply is off, all the data and information on this memory will be lost. For example, RAM (Random Access Memory). Whereas non-volatile memory is used to store information even when the power supply is off. For example, ROM (Read Only Memory). 

Q.2: How many 128 * 8 memory chips are required for a memory capacity of 4096*16?

Number of chips required = Required RAM size/ Available chip capacity  = (4096 * 16)/(128 * 8) = 64

Q.3: Explain any four differences between RAM and ROM?

RAM ROM It stands for Random access memory. It stands for read only memory. It is the fastest memory. It is slower memory as compare to RAM. It is volatile memory. It is non-volatile memory. In this memory, data will erase when the power is off In this memory, data will not erase even if the power is off

Q.4: How to erase data in EPROM?

In EPROM , using ultraviolet rays we can easily erase data.

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• Units Of Memory

Memory is basically a device that has the capacity to store information. A memory unit is the amount of data that the memory can hold. Besides, we measure this storage capacity in terms of bytes. Moreover, there are different units of memory as per the requirement. Before studying the units of memory let us know about the memory.

Parts of  Memory

Primary memory.

This is the internal memory that stores the data and instructions of the CPU. It is volatile in nature (data is lost when the power is disconnected).

The primary memory has two types:

RAM (Random Access Memory)

As per the name, data can be accessed randomly and quickly.

ROM (Read Only Memory)

As per the name, we can only read data and cannot write (store) to it.

Secondary Memory

As we know that the primary memory is volatile therefore, we need some devices to store the data permanently so we use some external storage devices for this purpose which we name as the secondary memory. Some examples: CD, DVD, etc.

Units of Memory

The storage capacity of the memory is expressed in various units of memory. These are as follows:

A microprocessor uses binary digits 0 and 1 to decide the OFF and ON state respectively, of various circuits. Furthermore, a bit is the smallest unit of representation in the binary language.

A nibble is a collection of 4 bits.

A byte is the representation of a group of 8 bits. Moreover, a byte is a unit that expresses any word, symbol, or character in the computer language. Besides, computer memory is always in terms of multiples of bytes.

A computer word is similar to a byte, as it is also a group of bits. Moreover, a computer word is fixed for each computer. At the same time it varies from computer to computer. Besides, the length of a computer word is the word-size or word length . Therefore, a computer stores information in the form of computer word.

• It is the most common unit of memory which is the smallest of all. But, it is greater than the byte.
• The abbreviation for kilobytes is ‘KB’.
• It contains 1000 bytes. Besides, it is synonyms to kibibytes which contain 1024 (2^10) bytes.
• Megabytes usually measures the size of text documents, graphics of websites, individual files, etc.
• The abbreviation for megabyte is ‘MB’.
• It contains 1000,000 bytes. Besides, it is synonyms to mebibytes which contains 1048576 (2^20) bytes.
• Kilobytes usually measure the size of large files. For example high-resolution images, songs, storage of compact disks, etc.
• The abbreviation for the gigabyte is ‘GB’ or ‘gigs’.
• It contains 1000,000,000 bytes. Besides, it is synonyms to gibibytes which contain 1073741824 (2^30) bytes.
• Kilobytes usually measure the capacity of storage devices.
• The abbreviation for terabytes is ‘TB’.
• It contains onetrillion bytes. Besides, it is synonyms to tebibytes which contains 2^40 bytes.
• Kilobytes usually measure the capacity of large storage devices, for example, HDDs (Hard Disk Drives).
• The abbreviation for petabyte is ‘PB’.
• It contains 10^15 bytes. Besides, it is synonyms to pebibytes which contains 2^50 bytes.
• Petabytes usually measure the total data storage in large networks or server farms. For example, the data in Google or Facebook data servers is around more than 10 PBs.
• The abbreviation for exabyte is ‘EB’.
• It contains 10^18 bytes. Besides, it is synonyms to exbibytes which contains 2^60 bytes.
• The exabyte unit is so large that it does not even measure the storage of large cloud servers. Rather, it can be used to measure the amount of data transfer over the internet for a certain time limit.
• The abbreviation for zettabyte is ‘ZB’.
• It contains 10^21 bytes. Besides, it is synonyms to zebibytes which contains 2^70 bytes.
• It can measure a huge amount of data. In fact, the whole data in the world is just a few zettabytes.
• The abbreviation for yottabyte is ‘YB’.
• It contains 10^24 zettabytes. Besides, it is synonyms to yobibytes which contains 2^80 bytes.
• It is a tremendously huge unit of measurement. Therefore, it has no practical use.

Frequently Asked Questions (FAQs)

Q1. What is memory and units of memory?

A1. Memory is basically a device that has the capacity to store information. A memory unit is the amount of data that the memory can hold.

Q2. List various units of memory.

A2. various units of memory are as follows:

Memory Concepts

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Advantages of RAM

• It is a faster type of memory in a computer.
• It requires less power to operate.
• Program loads much faster
• More RAM increases the performance of a system and can multitask.
• Perform read and write operations.
• The processor can read information faster than a hard disc, floppy, USB, etc.

Disadvantages of RAM

• Less RAM reduces the speed and performance of a computer.
• Due to volatile, it requires electricity to preserve the data.
• It is expensive than ROM
• It is unreliable as compared to ROM
• The Size of RAM is limited.

Read-Only Memory (ROM)

ROM is a memory device or storage medium that is used to permanently store information inside a chip. It is a read-only memory that can only read stored information, data or programs, but we cannot write or modify anything. A ROM contains some important instructions or program data that are required to start or boot a computer. It is a non-volatile memory; it means that the stored information cannot be lost even when the power is turned off or the system is shut down.

Types of ROM

There are five types of Read Only Memory:

• MROM (Masked Read Only Memory): MROM is the oldest type of read-only memory whose program or data is pre-configured by the integrated circuit manufacture at the time of manufacturing. Therefore, a program or instruction stored within the MROM chip cannot be changed by the user.
• PROM (Programmable Read Only Memory): It is a type of digital read-only memory, in which the user can write any type of information or program only once. It means it is the empty PROM chip in which the user can write the desired content or program only once using the special PROM programmer or PROM burner device; after that, the data or instruction cannot be changed or erased.
• EPROM (Erasable and Programmable Read Only Memory): It is the type of read only memory in which stored data can be erased and re-programmed only once in the EPROM memory. It is a non-volatile memory chip that holds data when there is no power supply and can also store data for a minimum of 10 to 20 years. In EPROM, if we want to erase any stored data and re-programmed it, first, we need to pass the ultraviolet light for 40 minutes to erase the data; after that, the data is re-created in EPROM.
• EEPROM (Electrically Erasable and Programmable Read Only Memory): The EEROM is an electrically erasable and programmable read only memory used to erase stored data using a high voltage electrical charge and re-programmed it. It is also a non-volatile memory whose data cannot be erased or lost; even the power is turned off. In EEPROM, the stored data can be erased and reprogrammed up to 10 thousand times, and the data erase one byte at a time.
• Flash ROM: Flash memory is a non-volatile storage memory chip that can be written or programmed in small units called Block or Sector. Flash Memory is an EEPROM form of computer memory, and the contents or data cannot be lost when the power source is turned off. It is also used to transfer data between the computer and digital devices.

Advantages of ROM

• It is a non-volatile memory in which stored information can be lost even power is turned off.
• It is static, so it does not require refreshing the content every time.
• Data can be stored permanently.
• It is easy to test and store large data as compared to RAM.
• These cannot be changed accidently
• It is cheaper than RAM.
• It is simple and reliable as compared to RAM.
• It helps to start the computer and loads the OS.

Disadvantages of ROM

• Store data cannot be updated or modify except to read the existing data.
• It is a slower memory than RAM to access the stored data.
• It takes around 40 minutes to destroy the existing data using the high charge of ultraviolet light.

RAM Vs. ROM

Secondary memory.

Secondary memory is a permanent storage space to hold a large amount of data. Secondary memory is also known as external memory that representing the various storage media (hard drives, USB, CDs, flash drives and DVDs) on which the computer data and program can be saved on a long term basis. However, it is cheaper and slower than the main memory. Unlike primary memory, secondary memory cannot be accessed directly by the CPU. Instead of that, secondary memory data is first loaded into the RAM (Random Access Memory) and then sent to the processor to read and update the data. Secondary memory devices also include magnetic disks like hard disk and floppy disks, an optical disk such as CDs and CDROMs, and magnetic tapes.

Features of Secondary Memory

• Its speed is slower than the primary/ main memory.
• Store data cannot be lost due to non-volatile nature.
• It can store large collections of different types, such as audio, video, pictures, text, software, etc.
• All the stored data in a secondary memory cannot be lost because it is a permanent storage area; even the power is turned off.
• It has various optical and magnetic memories to store data.

Types of Secondary Memory

The following are the types of secondary memory devices:

A hard disk is a computer's permanent storage device. It is a non-volatile disk that permanently stores data, programs, and files, and cannot lose store data when the computer's power source is switched off. Typically, it is located internally on computer's motherboard that stores and retrieves data using one or more rigid fast rotating disk platters inside an air-sealed casing. It is a large storage device, found on every computer or laptop for permanently storing installed software, music, text documentation, videos, operating system, and data until the user did not delete.

Floppy Disk

A floppy disk is a secondary storage system that consisting of thin, flexible magnetic coating disks for holding electronic data such as computer files. It is also known as Floppy Diskette that comes in three sizes like 8 inches, 5.5 inches and 3.5 inches. The stored data of a floppy disk can be accessed through the floppy disk drive. Furthermore, it is the only way through a new program installed on a computer or backup of the information. However, it is the oldest type of portable storage device, which can store data up to 1.44 MB. Since most programs were larger, that required multiple floppy diskettes to store large amounts of data. Therefore, it is not used due to very low memory storage.

CD (Compact Disc)

A CD is an optical disk storage device, stands for Compact Disc. It is a storage device used to store various data types like audio, videos, files, OS, Back-Up file, and any other information useful to a computer. The CD has a width of 1.2 mm and 12 cm in height, which can store approximately 783 MB of data size. It uses laser light to read and write data from the CDs.

Types of CDs

• CD-ROM (Compact Disc Read Only Memory): It is mainly used for bulk size mass like audio CDs, software and computer games at the time of manufacture. Users can only read data, text, music, videos from the disc, but they cannot modify or burnt it.
• CD-R (Compact Disc Recordable): The type of Compact Disc used to write once by the user; after that, it cannot be modified or erased.
• CD-RW (Compact Disc Rewritable): It is a rewritable CD disc, often used to write or delete the stored data.

DVD Drive/Disc

DVD is an optical disc storage device, stands for Digital Video Display or Digital Versatile Disc . It has the same size as a CD but can store a larger amount of data than a compact disc. It was developed in 1995 by Sony, Panasonic, Toshiba and Philips four electronics companies. DVD drives are divided into three types, such as DVD ROM (Read Only Memory), DVD R (Recordable) and DVD RW (Rewritable or Erasable). It can store multiple data formats like audio, videos, images, software, operating system, etc. The storing capacity of data in DVD is 4.7 GB to 17 GB.

Blu Ray Disc (BD)

Blu Ray is an Optical disc storage device used to store a large amount of data or high definition of video recording and playing other media files. It uses laser technology to read the stored data of the Blu-ray Disk. It can store more data at a greater density as compared to CD/ DVD. For example, compact discs allow us to store 700 MB of data, and in DVDs, it provides up to 8 GB of storage capacity, while Blu-ray Discs provide 28 GB of space to store data.

A pen drive is a portable device used to permanently store data and is also known as a USB flash drive. It is commonly used to store and transfer the data connected to a computer using a USB port. It does not have any moveable part to store the data; it uses an integrated circuit chip that stores the data. It allows the users to store and transfer data like audio, videos, images, etc. from one computer to any USB pen drive. The storing capacity of pen drives from 64 MB to 128 GB or more.

Cache Memory

It is a small-sized chip-based computer memory that lies between the CPU and the main memory. It is a faster, high performance and temporary memory to enhance the performance of the CPU. It stores all the data and instructions that are often used by computer CPUs. It also reduces the access time of data from the main memory. It is faster than the main memory, and sometimes, it is also called CPU memory because it is very close to the CPU chip. The following are the levels of cache memory.

• L1 Cache: The L1 cache is also known as the onboard, internal, or primary cache. It is built with the help of the CPU. Its speed is very high, and the size of the L1 cache varies from 8 KB to 128 KB.
• L2 Cache: It is also known as external or secondary cache, which requires fast access time to store temporary data. It is built into a separate chip in a motherboard, not built into the CPU like the L1 level. The size of the L2 cache may be 128 KB to 1 MB.
• L3 Cache: L3 cache levels are generally used with high performance and capacity of the computer. It is built into a motherboard. Its speed is very slow, and the maximum size up to 8 MB.

Advantages of Cache Memory

• Cache memory is the faster memory as compared to the main memory.
• It stores all data and instructions that are repeatedly used by the CPU for improving the performance of a computer.
• The access time of data is less than the main memory.

Disadvantage of Cache Memory

• It is very costly as compared to the Main memory and the Secondary memory.
• It has limited storage capacity.

Register Memory

The register memory is a temporary storage area for storing and transferring the data and the instructions to a computer. It is the smallest and fastest memory of a computer. It is a part of computer memory located in the CPU as the form of registers. The register memory is 16, 32 and 64 bits in size. It temporarily stores data instructions and the address of the memory that is repeatedly used to provide faster response to the CPU.

Primary Vs. Secondary Memory

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What Is RAM and Why Does Random Access Memory Matter?

Without your computer being able to store and access data quickly, none of your apps or other processes would work. That’s where your RAM comes in. But what is RAM exactly and how does it work? Keep reading to learn what RAM means, why it’s so important for smooth, fast processing, and how to optimize your computer’s RAM with specialized performance software.

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What is RAM on a computer?

RAM (random access memory) is a computer's short-term memory, where the data that the processor is currently using is stored. Your computer can access RAM memory much faster than data on a hard disk, SSD , or other long-term storage device, which is why RAM capacity is critical for system performance.

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What does RAM stand for?

RAM stands for random access memory , and it’s one of the most fundamental elements of computing. RAM is a temporary memory bank where your computer stores data it needs to retrieve quickly. RAM keeps data easily accessible so your processor can quickly find it without having to go into long-term storage to complete immediate processing tasks.

Every computing device has RAM, whether it’s a desktop computer (running Windows, MacOS, or Linux), a tablet or smartphone (running Android or iOS), or even an IoT computing device (like a smart TV). Nearly all computers have a way of storing information for longer-term access, too. But the memory needed to run the process you’re currently working on is stored and accessed in your computer’s RAM.

What does computer memory (RAM) do?

RAM is a form of temporary storage that gets wiped when you turn your computer off. RAM offers lightning-fast data access, which makes it ideal for the processes, apps, and programs your computer is actively working on, such as the data needed to surf the internet through your web browser .

To understand RAM, let’s use the analogy of a physical desk. Your working space is the top of the desk. That’s where you keep everything you frequently use within arm’s reach, so you won’t waste time searching through your drawers. By contrast, anything you don’t use that much or that you want to save for later goes into a desk drawer.

On your computer, your RAM is like the top of your desk, where you keep everything you need quick access to. And the data that you don’t use much or want to save for later is stored on a hard disk, either locally in your device or in the cloud.

What is RAM used for?

RAM is used for immediate data storage and retrieval. Your RAM can process information significantly faster than data on a hard disk — twenty to a hundred times faster, depending on the specific hardware and task.

To accomplish a specific task, computer operating systems load data from the hard disk into RAM to process it. When it’s finished actively working with that data, the computer converts it back into long-term storage.

When you open a program such as Microsoft Word, your computer loads the application into its RAM. If you open a document you already have saved on your computer, your operating system locates the file in long-term storage and copies the information onto its RAM. Once the data is in your RAM, you get near-instantaneous performance because RAM is lightning fast.

When you save a document, or any other type of file, the data gets copied to the hard disk or other long-term storage. And when you close an application, the computer operating system takes it out of its RAM, which frees up space in your computer’s short-term memory so you can work on your next project. If you forget to save a document to your hard drive and the power fails, all that work is gone, because the purpose of RAM is temporary storage.

RAM is used for immediate data storage and retrieval — any task that requires quick access to computing resources.

Another use for RAM is to help your computer load previously-accessed information more quickly. When you first turn on your computer and launch any application, such as PowerPoint or Spotify, it takes a while to load. But if you close a program and then relaunch it, the software opens almost instantly (especially if your PC is optimized for performance ). That’s because the data needed to load the app is stored in the significantly faster RAM rather than the hard disk.

In short, RAM is used for any task that requires quick access to computing resources. A Windows feature called SuperFetch helps make this access even faster and more seamless, by recording your usage patterns and automatically pre-loading applications and files into RAM based on your behavior.

CPU vs RAM: which is more important?

The central processing unit (CPU) is your computer’s nerve center, where all the calculations necessary to run software applications are carried out. But, in order to function quickly and smoothly, CPUs rely on RAM to provide high-speed access to the data they need — it’s a team effort.

So, while both are vital components, when it comes to optimizing PC performance, if your processor’s maxed-out , upgrading or overclocking your CPU will provide more raw processing power, enabling you to run more resource intensive programs and take on bigger multitasking loads. On the other hand, increasing RAM capacity will mainly enable faster and more complex processes.

How much memory do I need?

The more RAM your computer has, the faster it runs. If your device is old, you might need to upgrade the RAM or other hardware. Every open application (including browser tabs) consumes RAM. When you run out of RAM, your computer has to move things around to free up space on the hard disk , which slows down your computer.

Note that RAM is different from storage: If you turn off your PC, the information in your RAM is gone, but the data saved in your long-term storage ( SSD or HDD ) is saved.

The amount of RAM you need depends on the apps and programs you use, how many of them you have open at the same time, and how impatient you are. We always want our devices to respond instantly to our commands, so if you notice sluggish performance, check your RAM and other PC specs and make sure that you’re not overtaxing your computer.

Usually, you need far less RAM than you do hard disk space. Again, think of that physical desk at home. The more space you have on the desktop, the more pieces of paper you can spread around. But you may still need a big filing cabinet to store all the files you’ve collected over time.

Back in the days when hardware was based on Pentium CPUs, you rarely needed more than 8MB of RAM — perhaps 32 MB if you were a serious tech geek. 

That was plenty to run Windows 95, the first versions of Microsoft Word, and early PC games like Doom. Today, a web browser with a bunch of open tabs can easily consume over 2.2GB of RAM.

When you buy a computer, you have several options of RAM capacity: 4GB, 8GB, 16GB, or even more memory (32GB, 64GB) if you use high-end editing software or are an enthusiastic gamer.

Lower-end or legacy devices usually come with 4GB of RAM, while higher-end (and more expensive) machines have 8GB or 16GB of RAM. And you can find professional-level computers with even more RAM.

But how much RAM do you really need and for what? Here are our recommendations, which apply to any operating system or personal computer hardware:

4 GB of RAM: If you use your computer to browse the web, work with standard Office applications, and do light photo editing, you’ll be fine with 4GB of RAM.

8 GB of RAM: Heavy multitaskers or light gamers should choose a computer with 8GB of RAM.

16+ GB of RAM: Some tasks are computing intensive, such as serious gaming, video editing, programming, or having to run multiple intensive tasks simultaneously. Those who demand professional-level performance with no slowdowns will need 16+GB of RAM.

What happens when you don’t have enough RAM? How do you know?

When the computing tasks exceed the current amount of memory on your computer, the operating system has to choose an application and move it to the hard drive. When you switch back to that application, it needs to retrieve that information before you can work with it. This is called paging or swapping , and it’s time-consuming. The process causes delays and performance drops.

You can make your computer run faster and better by regularly clearing wasteful clutter out of your RAM. You can do this manually, but it’s easier to do with a specialized software tool. If you notice your computer’s performance dropping, install optimization software like Avast Cleanup , which will disable wasteful background services and processes and give you back the RAM lost to unnecessary programs.

Are there different types of RAM?

Yes, there are multiple types of RAM. As with other forms of computer hardware, scientists are always trying to decrease energy consumption while increasing speed and capacity. RAM has been around since the first days of computing, and in early microcomputing eras it required enthusiasts to plug in chips one at a time. Things have come a long way since then.

By the late 1990s and early 2000s, the main types of RAM were SRAM (static RAM), DRAM (Dynamic RAM), and SDRAM (Synchronous Dynamic RAM).

Today, the most common type of RAM is DDR-SDRAM , or Double Data Rate Synchronous Dynamic Random-Access Memory. And there are various iterations, including DDR2, DDR3, DDR4, and even DDR5.

DDR (double-data rate) allows simultaneous multiple file transfers. The latest version of DDR5-RAM can achieve data rates of up to 51.2 gigabytes per second. But supply-chain shortages make DDR5 difficult to get — and very expensive.

The most commonly used RAM is still DDR4 memory, which also comes in multiple types and speeds. Generally, these memory sticks run at or above speeds of 2,400MHz. If you want to squeeze maximum performance out of your memory, you can get higher clocked RAM ranging from 3,200MHz all the way up to 5,000MHz (which is important for gamers and GPU overclockers ). The more MHz your RAM has, the faster it runs.

There’s also VRAM (Video Random Access Memory), which is used in graphics cards to process graphical data during gaming, photo editing, or other graphics-heavy activities. Video RAM is even faster than normal memory, and it usually comes in the form of GDDR (Graphics Double Data Rate), which is a specific type of memory optimized for graphics rendering. The latest generation — GDDR6 — can achieve an overall data rate of up to 72 Gbps.

Some top-end graphics cards use another type of VRAM known as High Bandwidth Memory (HBM) - hard to find and certainly not cheap.

DRAM vs SRAM

SRAM (static RAM) and DRAM (dynamic RAM) are common types of RAM that each use different technology to store data. Whereas SRAM uses transistors that preserve memory as long as they receive a steady trickle of power, DRAM uses capacitors that need to be periodically “refreshed” by comparatively large bursts of energy every few milliseconds.

The main difference between SRAM vs DRAM based on dynamic capacitors is that while SRAM technology is smaller, faster, and more energy efficient, it’s also much more expensive. For this reason, SRAM is typically used for cache memory, while DRAM is usually used in a computer’s main memory.

Most modern computers now use an upgraded form of DRAM known as synchronous DRAM, or SDRAM . Although SDRAM is much faster than legacy DRAM, it’s still slower than SRAM and consumes a lot of power.

What is ROM?

ROM , or read-only memory, is a form of memory that a computer can read but not write onto. ROM is often used to store and play back music (CDs) or movies (DVDs). Unlike RAM, a computer can’t write new data onto ROM, it can only read it, or play it back.

How do I get more RAM without upgrading?

If you’re struggling with low PC performance, or if your computer has only 4GB of RAM or less, the best way to improve computing speed without buying a new machine is to free up your available RAM. There are two ways to get more RAM without upgrading your RAM cartridges:

Close active programs. Any browser tabs you have open (especially in Chrome) or applications you’re running consume RAM. So if you don’t need a tab open or aren’t actively using an app, close it. Only launch what you actually use.

Use Sleep Mode: Our own Avast Cleanup includes a feature that frees up memory by hibernating applications you don’t use. Get Avast Cleanup to free up RAM.

What should I look out for when buying RAM?

The latest generations of DDR4 RAM clock in at around 2,400MHz. Gamers will want DDR4 memory that operates at speeds of around 3,200MHz for Intel chips and 3,600MHz for AMD chips. Other users (such as professional programmers, multimedia editors, and hardcore gamers) may look for higher clocked memory with speeds up to 4,800MHz from specialist manufacturers like G.Skill or Corsair.

Clock speeds are one thing, but another important factor to consider when buying RAM is latency — the time delay between when a command in memory is entered and when it’s executed. The lower the latency, the higher the performance.

For high-level performance, you’ll need memory above 4,000MHz with a latency of around CAS (Column Address Strobe or Signal) 15-18 or less. When buying RAM, you might see this listed as CL 16 (Column Latency 16), for example. For regular users, this is unlikely to make a meaningful impact, but gamers should take note.

And if you want to upgrade RAM on your Mac , ensure it's possible to add RAM to your model before you start shopping. 

Keep in mind the 32-bit Windows versions

Finally, you can’t just install infinite amounts of RAM in your PC and expect it to work. In order to use more than 4GB of RAM, you need to run a 64-bit version of Windows — 32-bit versions are limited to 3.5GB of memory only. If you’re still using the 32-bit edition of Windows 7, you’ll need to upgrade to 64-bit Windows to use 4GB of RAM or more.

But, note that installing a 64-bit version of Windows on an old machine with less memory may have a negative impact. Addresses in Windows are now 64 bits long, rather than just 32 bits. This means a larger memory footprint for each application. Depending on which applications you use, Windows 64-bit might use 20–50% more of your memory. So running a 64-bit version makes sense only if you have larger system memory.

On today’s PCs, Windows 10 64-bit (and now Windows 11) is installed by default and will work very fast on PCs with 4GB of RAM or more.

Optimize your PC to get more RAM

Manually cleaning or upgrading your RAM can be a hassle. At Avast, we developed a patented technology called Sleep Mode, which detects and disables resource-draining programs when they’re not being actively used. And we built that feature directly into our performance optimization software.

Download a free trial of Avast Cleanup , go into the Speed Up section, and look for Background and Startup Programs. With the apps you don’t actively need put to sleep, you’ll notice performance improvements immediately.

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