Learning Objectives

  • State the role of the CPU and the memory unit.
  • Explain why units of a computer must be interconnected.
  • Preview the memory hierarchy and the motherboard.

Detail: cabinet and motherboard, memory hierarchy, how the CPU uses memory.

Central Processing Unit

The CPU (processor) fetches instructions from memory, decodes them, and executes them (the fetch–decode–execute cycle). It contains an ALU (arithmetic and logic), control unit, and registers (tiny, fastest storage). Clock speed and core count affect how many operations it can complete per second, but real speed also depends on memory and storage.

Memory unit

Primary memory (RAM) holds the operating system, programs, and data currently in use. It is volatile: contents vanish when power is off. Secondary storage (HDD, SSD) is non-volatile and slower. Registers and cache sit between the ALU and RAM so the CPU is not waiting on every byte.

Interconnecting the units

The motherboard is the printed circuit board that holds the CPU socket, RAM slots, chipset, and expansion slots. Buses (address, data, control) carry signals among CPU, memory, and I/O. Without a shared interconnection, the CPU could not read a keystroke or write a file.

Nepal / lab example

When a lab PC “feels slow,” the cause is often too little RAM (memory unit) or a failing HDD, not a “weak CPU” alone. Matching hardware to the job is a management decision as well as a technical one.

Key Takeaways

  • CPU executes; memory holds working data; buses and the motherboard connect them.
  • Faster storage closer to the CPU costs more per byte.
  • Hardware topics in this unit all sit on that three-part model.

Discussion Questions

  1. Why can a fast CPU still stall?
  2. What is the difference between RAM and an SSD in one sentence each?
  3. What does a bus carry that a cable to a printer also needs, conceptually?