Know and understand internal memory including random access memory (RAM), read-only memory (ROM)

Topic: Types and Components of Computer Systems – Internal Memory (RAM & ROM)

1. Syllabus Map – What Is Covered Here?

2. Hardware vs. Software – A Quick Reminder

• Hardware – the physical components you can touch (CPU, RAM, ROM, monitor, keyboard, storage, etc.).
• Software – the programmes and data that tell the hardware what to do (operating system, applications, firmware).
• Internal memory (RAM & ROM) is pure hardware, but it stores software instructions (e.g., the BIOS/UEFI firmware).

3. Main Components of a Computer System

• CPU (Central Processing Unit) – executes instructions, performs arithmetic & logic, controls data flow.
• Internal Memory – RAM (working memory) and ROM (firmware). Directly addressable on the system bus, giving the CPU nanosecond‑level access.
• I/O Devices – keyboards, mouse, display, printers, network cards. Communicate with the CPU via dedicated controllers and the system bus.
• Backing (Secondary) Storage – HDD, SSD, USB flash, optical media. Provide permanent data storage but are accessed through I/O controllers, making them slower than internal memory.

4. Role of the Operating System (OS) in Memory Management

• Loads the kernel from secondary storage into RAM during boot.
• Manages RAM allocation to running programmes using virtual memory and paging techniques.
• Provides each programme with its own address space, protecting them from one another.
• Coordinates with the CPU’s cache hierarchy (L1, L2, L3) to keep the most frequently used data as close to the processor as possible.
• Uses the ROM‑stored firmware (BIOS/UEFI) only for low‑level tasks such as hardware initialisation and Secure Boot verification.

5. Types of Computers and Their Memory Needs

• Desktop PCs – typically 8 GB – 32 GB RAM, BIOS/UEFI stored in a 1‑4 MB flash ROM.
• Laptops & Tablets – similar RAM ranges but often use low‑power DDR4/DDR5 and soldered‑on flash ROM for faster boot.
• Servers – 64 GB – several TB RAM, ECC (error‑correcting code) memory, firmware stored in flash ROM with advanced security (TPM, Secure Boot).
• Embedded devices (e.g., calculators, digital watches) – a few kilobytes of ROM for firmware and a small amount of SRAM for temporary data.

6. Random‑Access Memory (RAM)

RAM is the computer’s short‑term, high‑speed working memory.

• Volatility: Volatile – data disappears when power is removed.
• Read/Write: Both operations are possible.
• Speed: Nanosecond‑scale access (typically 10‑30 ns for DDR4/DDR5).
• Capacity: Measured in megabytes (MB) or gigabytes (GB); modern PCs 4 GB – 64 GB or more.
• Major Types

  • Dynamic RAM (DRAM) – stores each bit as a charge in a capacitor; requires periodic refresh (≈ 64 ms).
  • Static RAM (SRAM) – uses flip‑flops; no refresh needed, faster, higher power consumption; used for CPU cache.
  • Synchronous DRAM (SDRAM) & DDR families

    • DDR, DDR2, DDR3, DDR4, DDR5 – successive generations with higher transfer rates, lower voltage, and tighter timing.

• Cache Hierarchy (CPU‑internal SRAM)

  • L1 cache – 16‑64 KB per core, fastest.
  • L2 cache – 256 KB‑2 MB, slightly slower.
  • L3 cache – 2‑32 MB shared among cores, still faster than main RAM.

• Virtual Memory & Paging

  • The OS treats RAM as a limited resource and swaps out inactive pages to secondary storage, creating the illusion of more memory.
  • When RAM is full, performance degrades because the system must read/write pages to the SSD/HDD.

• Typical Uses

  • Running the operating system, applications, and active data.
  • Temporary buffers for I/O operations (e.g., video playback, printing).

7. Read‑Only Memory (ROM)

ROM holds permanent instructions required for system start‑up and low‑level control.

• Volatility: Non‑volatile – retains data without power.
• Read/Write Capability: Primarily read‑only; some types can be re‑programmed (EPROM, EEPROM, flash).
• Speed: Microsecond‑to‑millisecond access – slower than RAM but fast enough for boot tasks.
• Typical Capacity: A few kilobytes (KB) to several megabytes (MB).
• Types of ROM

  • Masked ROM (MROM) – programmed during chip fabrication; cannot be altered.
  • Programmable ROM (PROM) – can be written once after manufacture using a special programmer.
  • Erasable PROM (EPROM) – UV‑light erases the chip; can be re‑programmed many times.
  • Electrically Erasable PROM (EEPROM) / Flash – erased and re‑programmed electrically; used for BIOS/UEFI chips, micro‑controller firmware, SSD/NVMe storage.

• Typical Uses

  • Firmware (BIOS or UEFI) that performs the Power‑On Self‑Test (POST) and initiates the boot process.
  • Embedded system firmware (calculators, digital watches, automotive ECUs).
  • Secure storage of cryptographic keys in some specialised devices.

8. Comparison of RAM and ROM

9. How RAM and ROM Work Together – Detailed Boot Process

1. Power‑on → the CPU receives a reset signal.
2. Firmware fetch – the CPU reads the BIOS/UEFI code stored in ROM (or flash ROM).
3. POST (Power‑On Self‑Test) – hardware checks (memory, keyboard, storage, etc.).
4. Secure Boot verification (optional) – the firmware’s digital signature is checked against a trusted key stored in the TPM; if the signature fails, the boot is halted.
5. Boot device selection – firmware locates the operating system loader on secondary storage (HDD/SSD, USB, network).
6. Kernel loading – essential kernel files are copied from secondary storage into RAM.
7. Control handed to OS – from this point the CPU executes instructions from RAM; ROM remains unchanged, acting as a stable reference for low‑level routines.
8. Runtime interaction – the OS continues to use RAM for applications, while firmware in ROM may be called on for hardware‑specific tasks (e.g., entering sleep mode).

10. Emerging Memory Technologies (Brief Overview)

• Non‑Volatile RAM (NVRAM) – combines RAM speed with ROM‑type persistence (e.g., MRAM, FeRAM). Used in some high‑reliability systems and emerging IoT devices.
• 3D‑XPoint / Intel Optane – a fast, byte‑addressable memory that sits between traditional RAM and SSDs, offering lower latency than NAND flash.
• Hybrid Memory Cube (HMC) & Wide I/O – stacked‑die DRAM with very high bandwidth, primarily in servers and high‑performance computing.

11. Safety, Security and e‑Safety of Internal Memory

• Memory encryption – modern CPUs (e.g., Intel SGX, AMD SEV) can encrypt data stored in RAM to defend against cold‑boot attacks.
• Firmware security – BIOS/UEFI can be protected with digital signatures and Secure Boot; trusted platform modules (TPM) store the keys.
• Data protection on shutdown – although RAM clears on power‑off, residual data may linger; encryption of the OS and full‑disk encryption mitigate risks.
• e‑Safety considerations – always obtain firmware updates from the manufacturer’s official website; verify signatures before installation to avoid malware that could compromise the entire system.

12. Communicating Memory Concepts to Different Audiences

Activity: Prepare a 3‑minute presentation for a group of younger students (Year 7) explaining why a computer needs both RAM and ROM. Use everyday analogies such as:

• RAM = a desk – you spread out the papers you are working on; when you leave the room (power off) the desk is cleared.
• ROM = a locked cupboard – it holds the instruction manual (firmware) that tells you how to set up the desk each time you start work.

13. Quick Revision Questions

1. What is the main difference between volatile and non‑volatile memory?
2. Explain why RAM is called “random‑access”.
3. List two types of ROM and describe how each can be re‑programmed.
4. Why is it important for the BIOS/UEFI to be stored in ROM rather than RAM?
5. Match each capacity with the correct memory type:

   • 4 GB – _
   • 256 KB – _
   • 8 GB – _
   • 64 KB – _

14. Further Reading / Cross‑Reference Table