University Guide to Computer Storage Devices and Memory and Storage Devices

Comparison of Primary and Secondary Memory

• Primary memory and secondary storage are classified based on two main factors: volatility and purpose.

• Volatility:

  • RAM (Random Access Memory): This is volatile memory. It loses its contents when the power is turned off. It is used to store data currently in use to ensure fast communication with the CPU.

  • Secondary Storage: This is non-volatile or permanent storage. It holds data even when the power is off. When you "save" a file, it moves from the temporary version in RAM to a permanent version in storage.

• ROM (Read-Only Memory): Unlike RAM, ROM is permanent and holds computer startup instructions. It is accessed primarily at the beginning of the computer's operation and is generally not accessed frequently afterward.

• Purpose: The primary purpose of RAM is speed and facilitating CPU communication, whereas the purpose of secondary storage is the long-term retention of large amounts of data.

Classifying Storage: Internal vs. External

• Storage devices are categorized based on two criteria: Placement (where the device sits) and Connection/Interface (how it connects to the system).

• Internal Storage:

  • These devices sit inside the main computer case.

  • They are connected directly to the motherboard.

  • Examples include internal $HDD$ (Hard Disk Drive), internal $SSD$ (Solid State Drive), and $eMMC$ (embedded MultiMediaCard).

• External Storage:

  • These devices are connected from outside the computer case.

  • Connections are made through an interface like a $USB$ (Universal Serial Bus) port or a network.

  • Examples include $USB$ flash drives, external $HDD$/$SSD$ boxes, and optical drives.

• Interface Details: An interface is the connection used to link an external device to the computer. For instance, a $USB$ pen drive has a slot that connects to the laptop's port. Inside that slot, you can typically see four metallic components that facilitate the connection.

• Defining "Drive Bay": In the context of storage, a "drive bay" is often used as a fancy name for a port or a slot where a drive is inserted or housed.

Deep Dive into Specific Storage Technologies

• HDD (Hard Disk Drive):

  • A magnetic storage device with moving parts.

  • Because it has physical moving disks, it is more prone to wear and tear compared to solid-state technologies.

• SSD (Solid State Drive):

  • Contains no moving parts, making it more durable than an $HDD$.

  • It uses NAND technology (specifically Not-AND logic gates) and floating gates to store data.

  • Often preferred for storing operating systems because it is faster and less likely to lose data due to physical shock.

  • It can be classified as internal (if soldered to the motherboard) or external (if enclosed in a separate box and connected via cable).

• eMMC (embedded MultiMediaCard):

  • Used primarily for storing multimedia data.

  • For example, when you buffer a video, the data is often stored in the $eMMC$.

• Optical Drives:

  • Includes $CDs$, $DVDs$, and Blu-ray discs.

  • These are generally considered external storage devices as many modern systems require a separate external drive to read them.

• NAS (Network Attached Storage / Network Attached Service):

  • A device connected to a router/network rather than a single computer.

  • It acts like a "personal cloud" or a family backup system.

  • All users on a specific $WLAN$ (Wireless Local Area Network) at home can access and store files on it simultaneously.

  • Advantages over public cloud (e.g., Google Drive):

    • Offers more storage capacity.

    • Provides complete privacy and control over data (no third-party access).

    • Not dependent on third-party server uptime or the risk of global server hacks.

• LTO Tape Cartridge:

  • A magnetic tape technology involving a plastic tape coated with magnetic material.

  • Data is stored on the magnetic material.

  • Although largely considered an obsolete technology for daily use, it is an external device that requires a specialized tape drive to read.

Storage Device Classification Table

Questions & Discussion

• Student Question: What type of primary memory is volatile?

• Teacher Response: RAM is volatile. It loses its contents when power is lost. Permanent versions of what is in RAM live in storage, which is non-volatile.

• Student Question: Is a $CD$ an external or internal device?

• Teacher Response: $CDs$ are external storage because you generally do not have the drive inside the case anymore; you connect a separate drive.

• Student Question: Describe the characteristics of an $SSD$ and why it is preferred for operating systems.

• Teacher Response: It has no moving parts, making it more durable and resistant to wear and tear compared to an $HDD$. It is faster and more reliable for critical system files.

• Student Question: Why would you use a $NAS$ instead of Google Drive?

• Teacher Response: It is private. You are in charge of your data. You have your own passwords for family members, and you aren't reliant on Google's servers. It's often more cost-effective for very large amounts of data, like a $5\,\text{TB}$ family backup.

• Question regarding Smartphones: A smartphone has no "drive bay" but keeps photos through every restart. What storage does it use?

• Answer: It uses internal secondary storage, specifically $SSD$/Flash technology based on NAND gates. It is durable (critical because phones are often dropped), portable, and has no moving parts. Common capacities include $64\,\text{GB}$, $128\,\text{GB}$, $256\,\text{GB}$, and up to $1\,\text{TB}$.