Notes on Computer System Fundamentals

THE COMPUTER SYSTEM

A computer system is composed of several fundamental components that work together to perform processing tasks. The core parts include the central processing unit (CPU), primary storage, secondary storage, input devices, output devices, and communications devices. These components are illustrated in Figure 0.1, which shows how the CPU interacts with memory, storage, and I/O devices to execute programs and handle data. The system is designed so that data and instructions flow from input devices into memory, are processed by the CPU, stored temporarily or permanently, and finally presented to users through output devices or transmitted via communications devices.

THE SYSTEM UNIT

Inside the system unit lie essential elements that enable the computer to function. Memory provides fast, temporary storage for data and instructions during processing, while adapter cards such as sound cards and video cards expand the system’s capabilities. The system unit also houses ports for external connections, drive bays for storage devices, and the power supply that distributes electrical power to all components. These components are arranged to allow efficient data flow between processing, storage, and I/O operations, with the processor serving as the central engine.

THE SYSTEM UNIT – THE MOTHERBOARD

The motherboard is the main circuit board in the system unit. It contains the processor, memory chips, and adapter cards, and it provides the electrical connections and pathways (buses) that allow data to move between components. This board coordinates the activities of the computer by linking the CPU, memory, storage controllers, and I/O interfaces.

WHAT IS THE OTHER NAME OF MOTHERBOARD?

A common riddle in the slides asks for the other name of the motherboard. The question presents the letters “S T E A M B R O D S Y” as a clue. The answer is shown as SYSTEM BOARD, which is another widely used term for the motherboard.

THE CPU

The CPU manipulates raw data into a more useful form and controls the other parts of the computer system. It works with primary storage to hold data and program instructions temporarily during processing, while secondary storage retains data and programs when they are not actively being processed. The CPU is the component that interprets instructions, performs calculations, and coordinates the activities of memory, storage, and I/O devices to complete tasks.

INPUT, OUTPUT, AND COMMUNICATION DEVICES

Input devices convert data and instructions into electronic form suitable for input into the computer. Output devices convert electronic data produced by the computer into a form people can understand, such as text, images, or sound. Communication devices provide connections between the computer and networks, enabling data transmission to other computers or devices.

HOW COMPUTERS REPRESENT DATA

All symbols, pictures, and words must be reduced to a string of binary digits for computer processing. A binary digit, or bit, represents either 0 or 1. These are the only digits used in the binary (base-2) number system employed by computers. A string of eight bits that stores a single number or character in a computer system is called a byte, which serves as the basic unit of storage. As an example, the capital letter A is represented in binary as 01000001, and ASCII representations map such binary patterns to characters.

ASCII AND EBCDIC CODING

Two common coding systems map characters to 8-bit binary patterns: Extended Binary Coded Decimal Interchange Code (EBCDIC) and American Standard Code for Information Interchange (ASCII). EBCDIC represents every number, letter, or special character with eight bits and was used primarily on IBM and other mainframes. ASCII was originally designed as a seven-bit code, but most modern computers use eight-bit versions. In ASCII, the binary value 01000001 represents the letter A, and other characters follow similar mappings.

DATA REPRESENTATION – STEP-BY-STEP

Converting a letter to binary and back involves several steps. When a user presses the capital letter D (Shift+D), an electronic signal representing D is sent to the system unit. This signal is converted into the ASCII binary code for D (for example, 01000100) and stored in memory for processing. After processing, the binary code is converted back into an image and displayed on the output device. This sequence illustrates how the computer encodes, stores, processes, and renders data.

THE CPU AND PRIMARY STORAGE

The CPU is the part of the computer where the manipulation of symbols, numbers, and letters occurs, and it controls the other parts of the system. Primary storage temporarily stores data and program instructions during processing and holds data being used by the program. In contrast, secondary storage keeps data and programs when they are not actively being used by the CPU, allowing long-term retention beyond the immediate processing cycle.

PROCESSOR AND ITS COMPONENTS

A processor, synonymous with the CPU in many contexts, includes two main parts: the Control Unit and the Arithmetic Logic Unit (ALU). The processor interprets and carries out basic instructions that operate a computer. The Control Unit directs and coordinates operations, while the ALU performs arithmetic, comparison, and logical operations. The processor is sometimes referred to simply as the processor or CPU.

MACHINE CYCLE

A machine cycle comprises four operations of the CPU. Step 1 is Fetch, where a program instruction or data item is retrieved from memory. Step 2 is Decode, where the instruction is translated into the commands needed to perform the task. Step 4 is Store, where the result is written back to memory. Step 3 is Execute, where the actual command is carried out. Note that some diagrams list steps in a different order, but the standard sequence is Fetch → Decode → Execute → Store. This cycle repeats for successive instructions as programs run.

ALU AND CONTROL UNIT – FURTHER DETAILS

The ALU, together with the Control Unit, forms the core of all central processing units. The ALU handles the principal logical and arithmetic operations, including addition, subtraction, multiplication, division, and determining the sign or zero-status of numbers. The Control Unit coordinates the other parts of the system, reading a stored program one instruction at a time and directing the components to perform the required tasks.

WHAT IS A MACHINE CYCLE—REVISITED

A machine cycle is the fundamental operation that enables a CPU to process instructions. It encompasses fetching the instruction from memory, decoding it into actionable commands, executing the instruction, and finally storing the result back in memory. This sequence ensures that software instructions are translated into hardware actions in a controlled and repeatable manner.

PROCESSOR SELECTION AND CLOCK SPEED

Selecting a processor involves trade-offs between speed and cost. In general, a faster processor costs more. Typical processor families include Celeron, Itanium or Xeon, and the Pentium family, with clock speeds ranging from around 1.3 GHz to 3.0 GHz and higher. The chart indicates varied options in terms of clock speed and processor line, illustrating that higher performance often correlates with higher price and capability.

PRIMARY STORAGE – FUNCTIONS

Primary storage is a category of computer storage with three main functions: (1) stores all or part of the program that is currently being executed, (2) stores the operating system programs that manage the computer’s operation, and (3) holds data that the program is using. Data and programs reside in primary storage before processing, during processing between steps, and after processing finishes, prior to being returned to secondary storage or produced as output.

MAIN MEMORY (ALIAS FOR PRIMARY STORAGE)

The other name for primary storage is Main Memory. This memory is fast and directly accessible by the CPU for the duration of program execution, enabling quick read and write operations essential for processing tasks.

MEMORY MEASUREMENT

Memory is described in units such as kilobytes (KB), megabytes (MB), gigabytes (GB), and terabytes (TB). The abbreviations and approximate sizes are: $$ ext{KB} = 10^3 ext{ bytes},\