Computer Memory | Famous Books for UPSC Exam (Summary & Tests) PDF Download

Introduction

• Computer memory is a vital component within a computer system, serving to store both data and instructions crucial for processing and generating output.
• It accommodates storage needs ranging from immediate, short-term requirements to those necessary for extended durations.
• Memory encompasses various devices tasked with storing data, whether temporarily or permanently.
• Its function is indispensable in facilitating smooth data processing and retrieval, contributing significantly to overall system performance and functionality.

Memory Hierarchy

• The memory hierarchy is a structured arrangement of storage within contemporary computer architectures.
• It employs a hierarchical model designed to optimize both speed and capacity of memory resources.
• This hierarchy facilitates the utilization of memory components with the fastest access speeds and highest storage capacities.
• The organization of the memory hierarchy aims to strike a balance between speed and capacity requirements, ensuring efficient data processing and storage management.
• The hierarchy enables computers to access data swiftly while accommodating a range of storage needs.
  

Parameters of Memory 

• Storage Capacity: This parameter reflects the size of memory, typically measured in words or bytes. It encompasses both internal and main memory capacities.
• Access Modes: Memories consist of multiple locations, and information within these locations can be accessed in various ways, including randomly, sequentially, or directly.
• Access Time: Access time refers to the duration between initiating a read or write operation and the availability of data at the desired location.
• Physical Characteristics: Memory devices can be classified into electronic, magnetic, mechanical, and optical categories based on their physical properties.
• Permanence of Storage: Some materials, particularly magnetic ones, offer high permanence of storage, ensuring data retention for future use.

Types of Memory

In general, the memory is classified into two categories as follows
Memory is typically divided into two main categories:

• Primary memory, also known as main memory.
• Secondary memory, also referred to as auxiliary memory.

Primary Memory

• Main memory, also known as internal memory, directly interacts with the CPU, enabling the storage of data for immediate processing and tracking of ongoing operations.
• As it is volatile, primary memory loses its contents when power is switched off, making it temporary in nature.
• Primary memory can be categorized further into two types:
• Cache memory: High-speed memory that stores frequently accessed data for rapid retrieval by the CPU.
• RAM (Random Access Memory): Provides temporary storage for data and instructions actively used by the CPU during program execution.

Random Access Memory

• Also known as read/write memory, RAM (Random Access Memory) allows the CPU to both read from and write data and instructions to it.
• RAM serves as temporary storage for input data, output data, and interim results during program execution.
• RAM is classified into two categories:
  • Dynamic RAM (DRAM): Comprising memory cells with one capacitor and one transistor each, DRAM requires continuous refreshing to maintain stored information. It is slower, less costly, and occupies less space on the motherboard.
  • Static RAM (SRAM): Retains data as long as power is supplied to the memory chip, eliminating the need for periodic refreshing. SRAM employs multiple transistors per memory cell and does not use capacitors. Due to its high speed, SRAM is commonly utilized as cache memory, albeit at a higher cost compared to DRAM.

Cache Memory

• Cache memory acts as a storage buffer, holding frequently accessed data temporarily and facilitating rapid access for the CPU.
• Positioned between RAM and the CPU, cache memory operates at very high speeds, enhancing processing efficiency.
• Its primary function is to accelerate data retrieval, thereby boosting overall system performance.
• Due to its high cost, cache memory is typically smaller in size compared to RAM.
• Computers typically feature cache memory ranging from 256 KB to 2 MB in size.

Read Only Memory

• Also referred to as non-volatile memory or permanent storage, ROM (Read Only Memory) retains its content even when power is turned off.
• ROM possesses read-only capability, meaning data can be read from it but not written to it.
• Once programmed during manufacturing, ROM chips cannot be reprogrammed or rewritten.
• ROM is categorized into three types:
  • Programmable ROM (PROM): Once programmed, its contents remain fixed and cannot be altered. PROMs are typically programmed during manufacturing.
  • Erasable Programmable ROM (EPROM): Similar to PROM, EPROM can be erased by exposure to strong ultraviolet light and then rewritten, hence also known as Ultraviolet Erasable Programmable ROM (UVEPROM).
  • Electrically Erasable Programmable ROM (EEPROM): Similar to EPROM, EEPROM can be erased and rewritten electrically. It offers flexibility as the burning process is reversible through exposure to electric pulses. EEPROM is commonly used for holding BIOS and other firmware.

Tit - Bits

• Flash memory is a semiconductor-based non-volatile rewritable memory used in devices like digital cameras, mobile phones, and printers.
• Virtual memory is a technique enabling the execution of processes not entirely in main memory. A key benefit is accommodating programs larger than the available main memory.
• A buffer is a temporary physical storage utilized to hold data during the execution of processes from one location to another.

Secondary Memory

• Secondary memory stores large volumes of data and information for extended durations.
• Data in secondary memory cannot be directly processed by the CPU and must be copied into primary storage (RAM) first.
• It serves to store data and programs when they are not actively being processed, functioning as a non-volatile and permanent storage solution.

Secondary memory devices encompass various types:

Magnetic Storage:

• Hard Disk Drive
• Floppy Disk
• Magnetic Tape

Optical Storage:

• CD
• DVD
• Blu-ray Disk

Solid State Storage:

• Pen/Flash Drive
• Memory card

Hard Disk Drive (HDD)

• A hard disk drive (HDD) is a non-volatile, random-access digital data storage device commonly used for storing and retrieving digital information.
• HDDs utilize rotating disks, known as platters, coated with magnetic material to store data.
• Programs installed on a computer are typically stored on the hard disk.
• The hard disk consists of a spindle that holds multiple platters, each requiring two read/write heads for accessing data.
• All read/write heads are connected to a single access arm to ensure synchronized movement.
• Information is organized into bands called tracks, with each platter having the same number of tracks. A track location cutting across all platters is termed a cylinder.
• Tracks are further divided into pie-shaped sections known as sectors.

Floppy Disk (Diskette)

• Floppy disks are utilized for data storage, albeit with limited capacity and slower access speeds compared to hard disks.
• They are typically round in shape and consist of a thin plastic disk coated with iron oxide.
• Data is recorded or retrieved from the disk's surface through a slot on the envelope.
• Floppy disks are removable from the drive, allowing for easy transportation of data.
• They are available in three sizes: 8-inch, 5¼-inch, and 3½-inch.

Magnetic Tape

• Magnetic tapes are constructed from a plastic film material coated with magnetic substances, providing a permanent storage solution for data.
• Capable of both reading and recording data, magnetic tapes facilitate sequential data storage.
• Typically, magnetic tapes are 12.5 mm to 25 mm wide and range from 500 m to 1200 m in length.
• Data stored on magnetic tapes comprises tiny segments of magnetized and demagnetized areas on the material's surface.
• Magnetic tapes offer durability and the ability to be written, erased, and rewritten as needed.
• They boast high data storage capacity, with access to data typically occurring in a sequential manner.

Compact Disk

• CDs, or Compact Disks, represent the most prevalent and cost-effective form of optical disk storage.
• They serve as data storage devices and are commonly used for storing digital audio as well.
• Files on CDs are stored in contiguous sectors.

CDs are classified into three primary types:

• CD-ROM (Compact Disk-Read Only Memory)
• CD-R (Compact Disk-Recordable)
• CD-RW (Compact Disk-Rewritable)

Digital Video Disk

• DVD, also known as Super Density Disk (SDD) or Digital Versatile Disk, is an optical disk storage medium introduced by Philips, Sony, Toshiba, and Panasonic in 1995.
• Offering higher storage capacity than compact disks, DVDs maintain the same physical dimensions.
• Depending on the disk type, DVDs can store several gigabytes of data, ranging from 4.7 GB to 17.08 GB.
• DVDs are commonly used for storing music or movies and can be played back on televisions or computers.
• They are non-rewritable media, meaning once data is recorded, it cannot be erased or rewritten.

DVDs are available in three main varieties:

• DVD-ROM (Digital Video Disk-Read Only Memory)
• DVD-R (DVD-Recordable)
• DVD-RW (DVD-Rewritable)

Tit-Bits

• Data transfer rate indicates the speed at which data is written to or read from a disk.
• The root directory serves as the primary folder on a disk, holding information about all other folders present on the disk.

Hard disk

• A hard disk is considered a fixed disk, meaning it cannot be removed from the drive once installed.

Blu-ray Disk

• Blu-ray disks (BD) are optical disk storage media designed to store data, typically in DVD format.
• Each layer of a Blu-ray disk can hold approximately 25 GB (23.31 GB) of data.
• The name "Blu-ray" refers to the blue laser used to read the disk, enabling higher data density compared to the red laser used in DVDs.
• Blu-ray disks can store almost five times more data than single-layer DVDs.

Variations in Blu-ray formats include:

• BD-ROM (Read-only)
• BD-R (Recordable)
• BD-RW (Rewritable)
• BD-RE (Rewritable)

Pen/Thumb Drive

• A pen drive, also known as a flash drive, is a portable data storage device comprising flash memory with a USB interface.
• These drives are characterized by their small size, portability, and rewritable nature.
• USB flash drives are considerably smaller than floppy disks and are typically removable.
• They come in various storage capacities ranging from 256MB to 64GB and are commonly used for transferring and storing information between computers.

Memory Cards

• These clip-shaped data storage devices are commonly utilized in a variety of electronic devices such as digital cameras, mobile phones, and laptops.
• They are characterized by their small size, re-recordable capability, easy portability, and lightweight design.

Secondary Memory Device and their Storage Method and Capacity

Basic Units of Memory Measurements