Hardware Revision Notes

What is an Embedded System?

An embedded system is a specialised computer system integrated into another device, performing a dedicated function. It is not a general-purpose computer.

Characteristics of Embedded Systems

They are typically designed for specific tasks, often with real-time constraints. They usually have limited resources, are power-efficient, and are robust for their intended environment. They combine hardware and software components.

Common Uses of Embedded Systems

Embedded systems are found in a vast array of devices: washing machines, microwaves, cars (ECUs), smartwatches, medical instruments, industrial machinery, and consumer electronics like digital cameras or remote controls. Their presence is often transparent to the user, as they facilitate core device functionality.

Components of an Embedded System

Typically includes a microcontroller or microprocessor, memory (RAM, ROM, Flash), input/output peripherals, and purpose-built software (firmware) that controls its operation.

Role of Secondary Storage

Secondary storage provides non-volatile data storage, meaning data is retained even when power is removed. It is used for long-term storage of operating systems, software, and user files. It offers larger capacities and lower cost per unit of storage compared to primary storage (RAM), though it is slower to access.

Types of Secondary Storage

1. Magnetic Storage: Data is stored by magnetising tiny sectors on a spinning disk. Examples include Hard Disk Drives (HDDs). Known for high capacity and low cost.
2. Optical Storage: Data is stored and read using lasers. Indentations (pits) and flat areas (lands) on a disc surface represent binary data. Examples include CDs, DVDs, and Blu-ray discs.
3. Solid State Storage: Data is stored electronically in non-volatile flash memory chips. Examples include Solid State Drives (SSDs) and USB flash drives. Offers faster access speeds, greater durability, and lower power consumption compared to magnetic drives, but generally higher cost per gigabyte.

Von Neumann Architecture Essentials

The von Neumann architecture is a computer design where program instructions and data share a single memory space. This avoids bottlenecks associated with separate storages and allows for flexible data and instruction handling by the CPU. Key components like the CPU, main memory (RAM), and input/output devices are interconnected via buses ensuring efficient data flow and processing capabilities.

CPU Components and Roles

The CPU consists of the Control Unit (CU), which interprets instructions and manages operations; the Arithmetic Logic Unit (ALU), responsible for calculations, comparisons, and logic; and registers, which are small, fast storage areas within the CPU for immediate data. The clock generates timing signals, synchronising all CPU operations and the fetch-decode-execute cycle, ensuring each step occurs at the correct time.

The Fetch-Decode-Execute Cycle

This is the fundamental operation cycle of a CPU. First, 'Fetch' retrieves an instruction from memory using the address bus to specify location and the data bus to bring the instruction to the CPU. Second, 'Decode' interprets the instruction, determining what operation needs to be performed. Third, 'Execute' performs the operation, potentially using the ALU and registers. The control bus coordinates these steps.

Role of Buses in Data Transfer

Buses are groups of wires that facilitate communication within the computer system. The 'Address Bus' carries memory addresses from the CPU to RAM, specifying the location of data or instructions. The 'Data Bus' transports actual data or instructions between the CPU, RAM, and I/O devices. The 'Control Bus' carries control signals, directing and coordinating activities throughout the system, ensuring proper data flow and operation sequencing.