Computer Sub Systems

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Notes

What is a Sub-System?

A **sub-system** is a smaller part of a computer system that works together with other sub-systems to create a fully functional system.
Example: a car's sub-systems include the engine, brakes, and wheels; each can be broken down further (e.g., engine → spark plugs, sensors, pistons).
In computers, the five main sub-systems are: **CPU**, **memory**, **storage**, **input devices**, and **output devices**.
CPU sub-systems include the **control unit**, **registers**, and **arithmetic logic unit (ALU)**.
Sub-systems help **troubleshoot** problems by isolating each part for separate examination.
They give developers a clear picture of how complex systems are built.

The Five Main Computer Sub-Systems

**Central Processing Unit (CPU)** – executes instructions.
**Memory** – stores data and instructions temporarily for the CPU (e.g., RAM).
**Storage** – stores data and software permanently (e.g., HDD, SSD).
**Input devices** – allow a user to enter information (e.g., keyboard, mouse).
**Output devices** – display information or create physical output (e.g., monitor, printer).

Problem Decomposition

**Decomposition** is the process of breaking down a large problem into a set of smaller problems.
Smaller problems are **easier to solve** and can be solved **independently**.
Each smaller problem can be **tested independently** and then combined to produce the full solution.
Example: creating a computer game can be decomposed into levels, characters, and landscape – each handled by separate teams.
Decomposition requires thinking about four component parts: **inputs**, **processes**, **outputs**, and **storage**.

Inputs, Processes, Outputs, and Storage (IPOS)

**Inputs** – data entered into the system (e.g., width and height of a rectangle).
**Processes** – subroutines and algorithms that turn inputs and stored data into outputs (e.g., width × height).
**Outputs** – data produced by the system (e.g., calculated area displayed on screen).
**Storage** – data stored on a physical device or in memory while the program runs (e.g., width, height, area stored temporarily in RAM).

Benefits of Decomposition

Smaller problems are **easier to solve** than one large problem.
Each smaller problem can be solved **independently** of the others.
Smaller problems can be **tested independently**.
Smaller problems can be **combined** to produce a solution to the full problem.

A simple series circuit illustrating how sub-systems (power, switch, output, measurement) connect in a computer system analogy.

Practice questions

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1.What is a sub-system in a computer system?
Easy
- AA smaller part of a computer system that works together with other sub-systems to create a fully functional computer system
- BA program that manages hardware resources
- CA type of storage device
- DA network of computers
2.Which of the following is NOT one of the five main sub-systems of a computer?
Easy
- ACentral Processing Unit (CPU)
- BMemory
- COperating system
- DInput devices
3.Which sub-system is responsible for executing instructions?
Medium
- AMemory
- BStorage
- CCentral Processing Unit (CPU)
- DOutput devices
4.What is the main function of the memory sub-system?
Medium
- ATo store data and software permanently
- BTo execute instructions
- CTo store data and instructions temporarily for the CPU
- DTo allow a user to enter information
5.Which of the following is an example of how computer sub-systems can be further broken down?
Hard
- ACPU - control unit, registers & arithmetic logic unit (ALU)
- BMemory - ROM and RAM
- CStorage - HDD and SSD
- DInput devices - keyboard and mouse
6.What is an advantage of using sub-systems in a computer system?
Medium
- AThey make the system more complex and harder to understand
- BThey allow developers to isolate and troubleshoot problems more easily
- CThey increase the cost of the system
- DThey reduce the need for software
7.What is decomposition in problem solving?
Easy
- ABreaking down a large problem into a set of smaller problems
- BCombining multiple problems into one large problem
- CIgnoring the details of a problem
- DSolving a problem without any planning
8.Which of the following is a benefit of decomposition?
Medium
- ASmaller problems are harder to solve
- BEach smaller problem can be solved independently of the others
- CSmaller problems cannot be tested independently
- DSmaller problems cannot be combined to produce a solution

More questions

9.In the context of decomposition, what are the four component parts developers need to think about?
Hard
- AInputs, processes, outputs, and storage
- BHardware, software, data, and users
- CPlanning, coding, testing, and deployment
- DCPU, memory, storage, and input/output
10.For a program that calculates the area of a rectangle, what is the 'process' component?
Medium
- AWidth of the rectangle
- BHeight of the rectangle
- CWidth x height
- DCalculated area of the rectangle
11.Which of the following best describes the relationship between sub-systems and the overall computer system?
Hard
- ASub-systems operate independently and do not affect each other
- BSub-systems work together to create a fully functional computer system
- CSub-systems are only found in software
- DSub-systems are optional and not necessary for the computer to function
12.Which of the following is an example of an output device?
Easy
- AKeyboard
- BMouse
- CMonitor
- DHard drive
13.A student is designing a program to calculate the average temperature for a week. She enters seven temperature values. Which of the following correctly identifies the inputs, processes, outputs and storage for this program?
Medium
- AInputs: seven temperatures; Processes: sum divided by 7; Outputs: average temperature; Storage: temperatures and average stored in memory
- BInputs: seven temperatures; Processes: sum divided by 7; Outputs: average temperature; Storage: average stored on hard drive permanently
- CInputs: average temperature; Processes: sum divided by 7; Outputs: seven temperatures; Storage: temperatures stored in memory
- DInputs: seven temperatures; Processes: sum of temperatures; Outputs: average temperature; Storage: no storage needed
14.A computer systems developer is troubleshooting a fault. Which of the following best describes how using sub-systems helps in this process?
Medium
- AEach sub-system can be examined separately to isolate the fault
- BSub-systems make the computer run faster
- CSub-systems allow all parts to be tested at the same time
- DSub-systems eliminate the need for troubleshooting
15.A team of developers is creating a new video game. They decompose the project into levels, characters, and landscape. Which of the following is a benefit of this decomposition?
Hard
- AEach smaller problem can be solved independently and then combined
- BThe game will have better graphics
- CDecomposition reduces the total amount of code needed
- DDecomposition ensures the game will have no bugs
16.Which computer sub-system is responsible for storing data and instructions temporarily for the CPU?
Easy
- AMemory
- BStorage
- CInput devices
- DOutput devices
17.A program needs to calculate the total cost of items in a shopping cart. The user enters the price and quantity for each item. Which of the following correctly identifies the 'processes' component when decomposing this problem?
Medium
- AMultiply price by quantity for each item and sum the results
- BThe price and quantity entered by the user
- CThe total cost displayed on the screen
- DThe items stored in a database
18.A school library system is being designed. The system must allow students to borrow books, return books, and search for books. Which of the following is the most appropriate decomposition of this system?
Hard
- AInputs: student ID, book ID; Processes: check availability, update records; Outputs: confirmation message; Storage: database of books and loans
- BInputs: book title; Processes: display book details; Outputs: search results; Storage: none
- CInputs: student name; Processes: print receipt; Outputs: book; Storage: list of students
- DInputs: book ID; Processes: delete record; Outputs: error message; Storage: none
19.A company is developing a new smartphone app. They decide to decompose the problem into user interface, data storage, and network communication. Which of the following is an advantage of this approach?
Hard
- AEach part can be developed and tested independently
- BThe app will require less memory
- CThe app will be more secure
- DThe development time will be shorter
20.Which of the following best describes the role of the CPU sub-system in a computer?
Medium
- AIt executes instructions
- BIt stores data permanently
- CIt allows the user to enter information
- DIt displays information on the screen
21.A programmer is writing a program that reads a list of numbers from a file, sorts them, and writes the sorted list to a new file. Which of the following correctly identifies the storage component?
Medium
- AThe numbers are stored in memory while the program runs and on the hard drive as files
- BOnly the sorted list is stored on the hard drive
- COnly the original file is stored in memory
- DNo storage is needed because the numbers are processed immediately
22.A team is developing a weather monitoring system. They decompose the problem into data collection, data analysis, and data presentation. Which of the following is NOT a benefit of this decomposition?
Hard
- AThe system will be more complex to design
- BEach part can be tested independently
- CDifferent teams can work on different parts simultaneously
- DSmaller problems are easier to solve
23.A technician is troubleshooting a computer that fails to boot. By isolating the memory sub-system and testing it with known working RAM, the technician identifies faulty RAM. Which advantage of using sub-systems does this demonstrate?
Medium
- ASmaller problems can be solved independently
- BSub-systems can be further broken down
- CThe ability to isolate a sub-system makes it easier to identify and fix issues
- DDeveloping software relies on sub-systems
24.Which of the following is an example of an input sub-system in a computer?
Easy
- AMonitor
- BKeyboard
- CHard disk drive
- DCPU
25.A team of developers is creating a weather app. They decompose the problem into data collection, data analysis, and data presentation. Which component part of decomposition does 'data analysis' represent?
Hard
- AInput
- BProcess
- COutput
- DStorage
26.A program calculates the total cost of items in a shopping cart. The user enters the price and quantity for each item. Which of the following correctly identifies the input and output?
Medium
- AInput: price and quantity; Output: total cost
- BInput: total cost; Output: price and quantity
- CInput: price; Output: quantity and total cost
- DInput: total cost and quantity; Output: price
27.A developer is designing a system that reads sensor data, processes it to detect motion, and sounds an alarm if motion is detected. Which of the following correctly identifies the four component parts of decomposition for this system?
Hard
- AInput: sensor data; Process: detect motion; Output: alarm sound; Storage: sensor data log
- BInput: alarm sound; Process: sensor data; Output: motion detection; Storage: none
- CInput: motion detection; Process: alarm sound; Output: sensor data; Storage: alarm log
- DInput: sensor data; Process: alarm sound; Output: motion detection; Storage: sensor data
28.A school library system is being designed. The system must allow students to borrow books, return books, and search for books. Which of the following is the most appropriate decomposition of this problem?
Medium
- AInput: student ID and book ID; Process: borrow, return, search; Output: confirmation or search results; Storage: book and member records
- BInput: book title; Process: borrow; Output: receipt; Storage: none
- CInput: student name; Process: search; Output: book list; Storage: only book records
- DInput: book ID; Process: return; Output: fine; Storage: only member records
29.A developer is decomposing a problem and identifies the following: 'The system will store user profiles on a hard drive.' Which component part does this correspond to?
Hard
- AInput
- BProcess
- COutput
- DStorage
30.A student is designing a program to calculate the average temperature for a week. She enters seven temperature values. Which of the following correctly identifies the four component parts?
Hard
- AInput: seven temperatures; Process: sum and divide by 7; Output: average temperature; Storage: temperatures and average stored in memory
- BInput: average temperature; Process: enter temperatures; Output: sum; Storage: none
- CInput: sum of temperatures; Process: divide by 7; Output: seven temperatures; Storage: average stored on hard drive
- DInput: seven temperatures; Process: sort temperatures; Output: sorted list; Storage: sorted list stored in memory
31.Which of the following is NOT one of the five main sub-systems of a computer system?
Easy
- ACentral Processing Unit (CPU)
- BMemory
- COperating System
- DOutput devices
32.What is the main function of the memory sub-system in a computer?
Easy
- AStores data and instructions permanently
- BStores data and instructions temporarily for the CPU
- CExecutes instructions
- DAllows a user to enter information
33.Which of the following is an example of an input device?
Medium
- AMonitor
- BPrinter
- CKeyboard
- DHard disk drive
34.What is the process of breaking down a large problem into a set of smaller problems called?
Medium
- AAbstraction
- BDecomposition
- CAlgorithm design
- DPattern recognition
35.A program calculates the total cost of items in a shopping cart. The user enters the price and quantity for each item. Which of the following correctly identifies the input and process?
Hard
- AInput: price and quantity; Process: calculate total cost
- BInput: total cost; Process: price and quantity
- CInput: price and quantity; Process: display total cost
- DInput: display total cost; Process: calculate total cost
36.A school library system is being designed. The system must allow students to borrow books, return books, and search for books. Which of the following is the most appropriate way to decompose this problem?
Hard
- ADecompose into: book database, user interface, and network
- BDecompose into: input, process, output, and storage
- CDecompose into: borrow, return, and search functions
- DDecompose into: hardware, software, and data
37.A smart greenhouse system monitors temperature and humidity using sensors, adjusts heating and watering accordingly, and logs data to a cloud server for later analysis. Which of the following correctly identifies the output sub-system in this scenario?
Medium
- AHeater and water valve actuators
- BTemperature and humidity sensors
- CCloud server storage
- DLogging software
38.A program is decomposed into the following components: read sensor data, convert to digital, calculate average, display result on screen, and save to file. Which component represents the 'process' part of the input-process-output-storage model?
Hard
- ACalculate average
- BRead sensor data
- CDisplay result on screen
- DSave to file
39.A technician is troubleshooting a computer that fails to display anything on the monitor. They swap the monitor with a known working one but the issue persists. Which sub-system should the technician isolate next?
Medium
- AOutput sub-system (graphics card or display cable)
- BInput sub-system (keyboard or mouse)
- CStorage sub-system (hard drive)
- DMemory sub-system (RAM)
40.Which of the following is the main function of the storage sub-system in a computer?
Easy
- ATo store data and software permanently
- BTo store data and instructions temporarily for the CPU
- CTo execute instructions
- DTo allow a user to enter information

Slides

What is a Sub-System?

A sub-system is a smaller part of a computer system that works with other sub-systems to create a fully functional system.
For example, a car has sub-systems: engine, brakes, wheels.
Sub-systems can be broken down further (e.g., engine → spark plugs, sensors, pistons).

Five Main Computer Sub-Systems

Central Processing Unit (CPU) – executes instructions.
Memory – stores data and instructions temporarily for the CPU (RAM).
Storage – stores data and software permanently (HDD, SSD).
Input devices – allow a user to enter information (keyboard, mouse).
Output devices – display information or create physical output (monitor, printer).

Which of the following is NOT one of the five main computer sub-systems?

CPU
Memory
Operating System
Storage

Advantages of Sub-Systems

Helps troubleshoot problems – isolating a sub-system makes it easier to identify and fix issues.
Developers can design and test each sub-system separately.
Gives a clear picture of how complex systems are built.

Which of these are advantages of using sub-systems?

They make it easier to troubleshoot problems.
They allow each part to be developed independently.
They increase the complexity of the overall system.

Problem Decomposition

Decomposition is breaking down a large problem into smaller, manageable problems.
Benefits: smaller problems are easier to solve, can be solved independently, tested independently, and combined to solve the full problem.
Example: a computer game can be decomposed into levels, characters, and landscape.

Decomposition is the process of breaking down a large problem into a set of ____ problems.

Inputs, Processes, Outputs, Storage

When decomposing a problem, consider four component parts:
Inputs: data entered into the system.
Processes: subroutines and algorithms that turn inputs and stored data into outputs.
Outputs: data produced by the system.
Storage: data stored on a physical device or in memory.

In the area of a rectangle program, what is the process?

Width of the rectangle
Width × Height
Calculated area
Storing width in memory

Example: Area of a Rectangle

Inputs: width of the rectangle, height of the rectangle.
Process: width × height.
Output: calculated area of the rectangle.
Storage: memory stores width, height, and area temporarily.

In the area of a rectangle program, the output is the calculated ____ of the rectangle.

Further Breakdown of Sub-Systems

Computer sub-systems can be broken down into smaller sub-systems.
Example: CPU can be broken down into control unit, registers, and Arithmetic Logic Unit (ALU).

Which of these are components of the CPU sub-system?

Control Unit
Registers
Hard Drive

What is the main function of the Memory sub-system?

Execute instructions
Store data and instructions temporarily for the CPU
Store data permanently
Allow user input

Summary

A computer system is made of sub-systems: CPU, Memory, Storage, Input, Output.
Decomposition breaks problems into smaller parts (inputs, processes, outputs, storage).
Sub-systems help with troubleshooting and development.

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