• Computer Memory: A memory is just like a human brain. It is used to store data and instructions. Computer memory is the storage space in computer where data is to be processed and instructions required for processing are stored.
  • Memory is primarily of three types:
    1. Cache Memory: Cache memory is a very high speed semiconductor memory which can speed up CPU. It acts as a buffer between the CPU and main memory.
    2. Primary Memory or Main Memory: Primary memory is also known as main memory. It only holds those data and instructions on which computer is currently working. It has limited capacity and data is lost when power is switched off. Primary memory can be divided into:
      1. RAM (Random Access Memory): It is Volatile or temporary memory. Faster memory, Data gets erased when power supply goes off. RAM is of two types -
        • Static RAM (SRAM) : The word static indicates that the memory retains its contents as long as power is being supplied. However, data is lost when the power gets down due to volatile nature.
        • Dynamic RAM (DRAM) : DRAM, unlike SRAM, must be continually refreshed in order to maintain the data. This is done by placing the memory on a refresh circuit that rewrites the data several hundred times per second.
      2. ROM (Read Only Memory): It is Non Volatile or permanent memory. Slow memory,Data stored permanently. Various types of ROM:
        • MROM (Masked ROM): The very first ROMs were hard-wired devices that contained a pre-programmed set of data or instructions. These kind of ROMs are known as masked ROMs, which are inexpensive.
        • PROM (Programmable Read Only Memory): PROM is read-only memory that can be modified only once by a user. The user buys a blank PROM and enters the desired contents using a PROM program
        • EPROM (Erasable and Programmable Read Only Memory): EPROM can be erased by exposing it to ultra-violet light for a duration of up to 40 minutes. Usually, an EPROM eraser achieves this function. During programming, an electrical charge is trapped in an insulated gate region.
        • EEPROM (Electrically Erasable and Programmable Read Only Memory): EEPROM is programmed and erased electrically. It can be erased and reprogrammed about ten thousand times. Both erasing and programming take about 4 to 10 ms (millisecond). In EEPROM, any location can be selectively erased and programmed.
    3. Secondary Memory: It is also known as auxiliary memory or non-volatile memory. It is slower than main memory. These are used for storing data or information permanently. For example: hard disk, CD-ROM, DVD etc
      1. Hard disk drive (sometimes abbreviated as Hard drive, HD, or HDD) is a non-volatile memory hardware device that permanently stores and retrieves data on a computer. A hard drive is a secondary storage device that consists of one or more platters to which data is written using a magnetic head, all inside of an air-sealed casing. Internal hard disks reside in a drive bay, connect to the motherboard using an ATA, SCSI, or SATA cable, and are powered by a connection to the PSU (power supply unit).
        Hard drive consists of the following components: the head actuator, read/write actuator arm, read/write head, spindle, and platter.
      2. Short for Solid-State Drive (or Solid-State Disk, although it doesn't use a disk mechanism), an SSD is a storage medium that uses non-volatile memory as a means of holding and accessing data. Unlike a hard drive, an SSD has no moving parts which gives it advantages such as faster access time, noiseless operation, higher reliability, and lower power consumption.
        SSDs primarily use the SATA connection which has a theoretical maximum transfer rate of 750 MB per second. However, a newer generation of SSDs is emerging that utilize a PCIe connection, offering speeds of up to 1.5 GB per second.
      3. USB flash drive, data stick, pen drive, memory unit, key chain drive and thumb drive, a jump drive is a portable storage device. It is often the size of a human thumb (hence the name), and it connects to a computer via a USB port. Flash drives are an easy way to store and transfer information.
        Unlike a standard hard drive, the flash drive has no movable parts; it contains only an integrated circuit memory chip that is used to store data.
      4. SD Card(Short for Secure Digital Card): the SD Card is one of the more common types of memory cards used with electronics.
        Types of SD cards: The three versions of the SD card, along with their physical dimensions, are shown below.
        • SD - 32mm x 24mm x 2.1mm.
        • miniSD - 21.5mm x 20mm x 1.4mm.
        • microSD - 15mm x 11mm x 1.0mm.

  • Memory storage Units:
    Units Description
    Bit A binary digit is logical 0 and 1 representing a passive or an active state of a component in an electric circuit.
    Nibble A group of 4 bits is called nibble.
    Byte A group of 8 bits is called byte. A byte is the smallest unit, which can represent a data item or a character.
    Word A computer word, like a byte, is a group of fixed number of bits processed as a unit, which varies from computer to computer but is fixed for each computer. The length of a computer word is called word-size or word length. It may be as small as 8 bits or may be as long as 96 bits. A computer stores the information in the form of computer words.
  • Higher storage Units:
    1. Kilobyte (KB): 1 KB = 1024 Bytes

    2. Megabyte (MB): 1 MB = 1024 KB

    3. GigaByte (GB): 1 GB = 1024 MB

    4. TeraByte (TB): 1 TB = 1024 GB

    5. PetaByte (PB): 1 PB = 1024 TB

  • Cloud storage is a model of data storage in which the digital data is stored in logical pools, the physical storage spans multiple servers (and often locations), and the physical environment is typically owned and managed by a hosting company. These cloud storage providers are responsible for keeping the data available and accessible, and the physical environment protected and running. People and organizations buy or lease storage capacity from the providers to store user, organization, or application data.
    The most commonlly used cloud storages are: Amazon Cloud Drive, Apple iCloud, Box, Carbonite, Dropbox, Google Drive, Microsoft OneDrive, Mozy,and many more
  • SATA, in full serial advanced technology attachment, also called serial ATA, an interface for transferring data between a computer�s central circuit board and storage devices. SATA was designed to replace the long-standing PATA (parallel ATA) interface.
  • BIOS (basic input/output system) is the program a personal computer's microprocessor uses to get the computer system started after you turn it on. It also manages data flow between the computer's operating system and attached devices such as the hard disk, video adapter, keyboard, mouse and printer. BIOS software is stored on a non-volatile ROM chip.
  • CMOS is short for Complementary Metal-Oxide Semiconductor. CMOS is an on-board, battery powered semiconductor chip inside computers that stores information.
  • The motherboard serves as a single platform to connect all of the parts of a computer together. It connects the CPU, memory, hard drives, optical drives, video card, sound card, and other ports and expansion cards directly or via cables. It can be considered as the backbone of a computer.

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