Data Storage
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Notes
Primary Storage
- **Primary storage** is directly accessed by the CPU and holds data/instructions currently in use.
- It is **volatile** (except ROM) and has **small capacity** but **fast access times**.
- Examples: **RAM**, **ROM**, **cache**, and **registers**.
- Primary storage is more expensive per gigabyte than secondary storage.
RAM (Random Access Memory)
- **RAM** is volatile primary storage that holds data and instructions **currently in use**.
- Contents are lost when power is off; data must be copied from secondary storage for CPU access.
- RAM is **read/write** and has a **much larger capacity** than ROM.
- Used in devices like smart TVs to store current video stream or active game state.
ROM (Read Only Memory)
- **ROM** is non-volatile primary storage that holds the **bootstrap loader** and **BIOS**.
- It is **read-only** and has a **small capacity** (e.g., 512 KB).
- ROM is located on the motherboard and is faster than secondary storage but slower than RAM.
- Its purpose is to store start-up instructions to boot the computer.
Secondary Storage
- **Secondary storage** is non-volatile and used for **long-term storage** of programs and data.
- It has **large capacity** but **slower access** than primary storage.
- Three main types: **magnetic**, **solid-state (flash)**, and **optical**.
- Key characteristics: capacity, speed, cost, portability, durability, reliability.
Magnetic Storage
- Uses **magnetised particles** on spinning **platters** to store binary 0s and 1s.
- Data is organised into **tracks** and **sectors**; a read/write head accesses data via an actuator.
- Advantages: high capacity, low cost per GB, moderate speed.
- Disadvantages: moving parts prone to damage, noisy, less portable.
Solid-State (Flash) Storage
- Uses **electronic circuits** (NAND/NOR gates) with **floating-gate transistors** to store charge.
- Each cell holds one bit; a charge on the floating gate represents a 0 or 1.
- Advantages: very fast, durable (no moving parts), silent, portable.
- Disadvantages: higher cost per GB, limited read/write cycles.
Optical Storage
- Uses a **laser** to create **pits** and **lands** on a disc surface to represent binary data.
- Examples: CD, DVD, Blu-ray; CD-R is read-only, CD-RW is rewritable.
- Advantages: very low cost, portable, silent.
- Disadvantages: low capacity, slow speed, prone to scratches.
Virtual Memory
- **Virtual memory** is an extension of RAM located on **secondary storage**.
- Used when RAM is full: inactive pages are moved to virtual memory to free RAM.
- Virtual memory is **much slower** than RAM and negatively impacts performance.
- Increasing physical RAM reduces reliance on virtual memory and improves speed.
Cloud Storage
- **Cloud storage** stores data on remote servers accessed via the **Internet**.
- Advantages: accessibility from anywhere, scalability, automatic backups, collaboration.
- Disadvantages: requires internet connection, ongoing subscription cost, security concerns.
- Data is typically stored on magnetic or solid-state drives in data centres.
Comparison of primary and secondary storage characteristics.
Internal structure of a magnetic hard disk drive.
How virtual memory extends RAM by swapping pages to secondary storage.
Practice questions
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1.Which of the following is a characteristic of RAM?
Easy- AIt is non-volatile
- BIt is read-only
- CIt is volatile
- DIt holds the bootstrap instructions
2.What is the purpose of ROM in a computer?
Easy- ATo store data currently in use by the CPU
- BTo store the bootstrap instructions for starting the computer
- CTo provide large-capacity long-term storage
- DTo act as virtual memory when RAM is full
3.Which type of secondary storage uses a laser to read and write data by creating pits and lands?
Medium- AMagnetic storage
- BSolid-state storage
- COptical storage
- DCloud storage
4.Which of the following is an advantage of solid-state storage compared to magnetic storage?
Medium- ALower cost per gigabyte
- BHigher storage capacity
- CNo moving parts
- DLouder operation
5.A computer has 4 GB of RAM and frequently uses virtual memory. What is a consequence of relying heavily on virtual memory?
Hard- AThe computer's performance improves
- BThe computer's performance decreases
- CThe RAM size is effectively increased
- DData is lost when the power is turned off
6.Which of the following is a disadvantage of cloud storage?
Easy- AData can be accessed from anywhere
- BAutomatic backups are provided
- CAn internet connection is required
- DStorage capacity can be scaled easily
7.In a magnetic hard disk, data is stored on:
Medium- APits and lands
- BPlatters coated with magnetic material
- CNAND gates
- DFloating gates
8.Which of the following best describes why a computer needs both primary and secondary storage?
Hard- APrimary storage is non-volatile and secondary storage is volatile
- BPrimary storage provides fast access for current data, while secondary storage provides long-term non-volatile storage
- CPrimary storage has a larger capacity than secondary storage
- DSecondary storage is directly accessed by the CPU
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