Topic 2: Computer Organization

Question 1

Identify the main components of the central processing unit (CPU) and draw a diagram showing their relationship.

Answer 1

arithmetic logic unit (ALU), control unit (CU), memory address register (MAR), memory data register (MDR)

Question 2

Outline the function of the arithmetic logic unit (ALU).

Answer 2

Performs all the basic arithmetic, logical or input/output operations.

Question 3

Outline the function of the control unit (CU).

Answer 3

Controls the retrieval of instructions from the primary memory unit, and the sequence of their execution. Provides the ALU with the data that needs to be processed as well as the instructions to be executed.

Question 4

Outline the purpose of the the memory address register (MAR).

Answer 4

Holds the memory address of the data to be used by the ALU, so that the ALU can fetch the corresponding content from the memory and process it accordingly. Connected to primary memory via the Memory (Address) Bus.

Question 5

Outline the purpose of the memory data register (MDR).

Answer 5

Holds the data that is to be used by the ALU and saved to the RAM. Loads the data at the address location the MAR is holding. Connected to primary memory via the Data Bus.

Question 6

Describe the role of primary memory.

Answer 6

The only storage directly accessible by the CPU. Holds data and instructions that are currently running on the computer system. Composed of many memory locations that are indexed by a memory address (a unique number corresponding to a memory location).

Question 7

Distinguish between Random Access Memory (RAM) and Read-only Memory (ROM).

Answer 7

ROM cannot be written to, but RAM can.
RAM is volatile (when power is lost, data its data is wiped), but ROM is non-volatile.
ROM is typically much smaller in capacity than RAM.

Question 8

Explain the use of cache memory.

Answer 8

Cache is smaller and faster memory that is located closer to the CPU. Cache holds information from RAM that is frequently accessed or that the computer system predicts it will need to access soon.
When the processor needs to to read from the main memory, it first checks if a copy of the data exists in cache. If not, it copies data from the main memory to the cache.
Cache memory is segmented in a hierarchy such as L1 cache, L2 cache, and so on. Level one cache has the smallest capacity but is the fastest (located directly on the microprocessor). Higher levels get larger but slower.

Question 9

State some differences between cache memory and RAM.

Answer 9

Cache memory is closer to the CPU than RAM.
Cache memory is much faster than RAM.
Cache memory is much more expensive than RAM so is much smaller.
Cache memory is separated into a hierarchy wtih L1, L2, and so on.

Question 10

Define the machine instruction cycle.

Answer 10

The basic operation cycle of a computer to execute a program by which an instruction is fetched from memory, and executed. It consists of four stages: fetch, decode, execute, and store.

Question 11

Describe the machine instructions cycle.

Answer 11

1. The CPU fetches instructions from the primary memory unit to the control unit by sending the appropriate address throught the memory (address) bus. The data is copied into the data bus and sent to the CU.
2. Instructions are decoded in the control unit.
3. The CPU executes the instructions.
4. The result of the execution is stored and the cycle is repeated. If it is stored in primary memory, the memory address is specified via the memory (address) bus and the data is sent through the data bus.

Question 12

Describe secondary memory.

Answer 12

Relatively slow memory that may be written to, but is non-volatile; its ontents will not be wiped if power is lost. Has a higher capacity to hold data compared to the primary memory. Also known as persistent storage. Examples: Hard disk drives (HDD), solid state drives (SSD), USB flash drives, DVD drives.

Question 13

Identify the need for secondary memory.

Answer 13

Since RAM is volatile, when a computer starts up, the RAM is empty. Instructions need to be copied into RAM from a persistent memory source. Without secondary memory, a computer would not be able to store instructions and data persistently. Any user data would have to be reinputted every time the user wished to use them.

Question 14

State some differences between primary and secondary memory.

Answer 14

Most computers have a smaller amount of primary memory and a larger amount of secondary memory.
Primary memory is volatile; it does not retain data when the power is turned off.
Primary memory is more expensive compared to secondary memory.
Primary memory is much faster compared to secondary memory.
Primary memory is directly accessed by the CPU whereas secondary memory is not.

Question 15

Define operating system.

Answer 15

An operating system (OS) is a set of software that controls the computer’s hardware resources and provides services for computer programs. It acts as an intermediate between software applications and the computer hardware.

Question 16

Explain the main functions of an operating system.

Answer 16

Peripheral communication: peripheral devices are external hardware devices (keyboards, monitors, mice, monitors, etc); the operating system communicates directly with hardware and provides and interface between hardware devices and applications.
Memory management: the OS manages how memory is used by applications and ensures that appplication’s memory use do not interfere with one another.
Resource monitoring and multitasking: the OS is responsible for efficient application of computer resources (the amount of memory the application is occupying, how much processor time it needs to function properly) and enabling multiple applications to run at once.
Networking: acts as an intermediary between applications and networks.
Disk access and data management: accesses data stored in memory and disks, manages file system structure.
Security: the OS is responsible for the overall security of the computer system including authentication and creating log files that keeps track of activities on the computer.

Question 17

Outline the use of a range of application software.

Answer 17

Word processors: used for production of any sort of document. (e.g. Microsoft Word, Google Docs)

Spreadsheets: a software application that is used for the organization and analysis of data by storing data in cells organized in rows and columns. (e.g. Microsoft Excel, Google Sheets)

Database management system (DBMS): manages databases and provides an interface between users and an interface. (e.g. Microsoft Access)

Web browsers: used to access, retrieve, and present content on the World Wide Web (e.g. Google Chrome, Firefox)

Email: allows for the exchange of digital messages.

Computer Aided Design (CAD): assits engineers in creating, modifying, analyzing, and optimizing a design. (e.g. autodesk)

Graphic processing software: allows a user to manipulate images (e.g. Adobe Photoshop)

Question 18

Identify common features of applications.

Answer 18

Many applications provide a graphical user interface (GUI) including elements like toolbars, menu lists, and dialogue boxes. Common GUI elements like these are often provided by the operating system, so application programmers do not need to recreate them each time.

Question 19

Define bit

Answer 19

A basic unit of information in computer systems, can have only two values: either 1 or 0.

Question 20

Define byte

Answer 20

A sequence of 8 bits.

Question 21

Define binary and know how to convert between binary and decimal.

Answer 21

A number system using two digits (0 and 1) where each digit represents a power of two. (e.g. 1101 = 8 + 4 + 1 = 13)

Question 22

Define decimal.

Answer 22

The standard base 10 number system using ten digits (0, 1, 2, …, 9). Each digit represents a multiple of a power of ten (e.g. 354 = 3100 + 510 + 4*1)

Question 23

Define hexadecimal and know how to convert between hexadecimal, binary, and decimal.

Answer 23

The base 16 number system which uses 16 digits: 0, 1, 2, 3, …, 9, A, B, C, D, E, F. A=10, B=11, C=12, and so on. Each digit represents a power of 16.

e.g. B6 = 1116 + 61 = 182 (decimal)

To convert from hex to binary, convert each individual digit to binary.
B6 = 1011 0110 (binary)

Question 24

How many different sequences can be constructed from n bits?

Answer 24

Each bit can be either 0 or 1 so there are 2^n different sequences.

Question 25

How are integers represented in a computer?

Answer 25

As binary numbers.

Question 26

How are characters represented in a computer (ASCII, Unicode)?

Answer 26

A character is assigned to a sequence of bits.

ASCII is a character encoding based on the English alphabet that uses 7 bits to achieve 128 different characters.

Unicode is a more complex character encoding that allows for additional characters including non-English characters and other symbols.

Question 27

Why is the Unicode character encoding needed?

Answer 27

The ASCII character-encoding can only represent 128 different characters. This is enough to represent the latin alphabet, punctuation marks, but not enough to represent characters used in other languages that do not use the Latin alphabet. The Unicode character-encoding uses more bits to represent more characters.

Question 28

How are strings represented in a computer?

Answer 28

Strings are a sequence of characters represented using some character encoding like ASCII or Unicode.

Question 29

How are graphics and colors represented in a computer?

Answer 29

Images are represented as a grid of square pixels which each display one color.

Colors are often represented in RGB format and consist of 3 numbers, each representing a shade of red, green, and blue respectively. These numbers are often given in hexadecimal.

For example, 0x70EF5A uses 8 bits per color. The first 8 bits (0x70 or 112 in decimal) correspond to the amount of red, the second group of 8 bits (0xEF or 239 in decimal) correspond to the amount of green, and the last 8 bits (0x5A or 90 in decimal) correspond to the amount of blue.

Question 30

Define the AND, OR, NOT, NAND, NOR, and XOR operators.

Answer 30

AND: outputs True only when both inputs are True
OR: outputs True as long as at least one of the inputs are True
NOT: has a single input, outputs the negation of the input (True -> False, False -> True)
NAND: the negation of AND. Outputs True unless both inputs are True.
NOR: the negation of OR. Only outputs True when both inputs are False.
XOR: outputs True if EXACTLY one of the inputs is True (outputs True if the inputs are different).

Question 31

Construct truth tables using the logical operators AND, OR, NOT, NAND, NOR, XOR

Example: complete the following truth table:

Answer 31

Example solution:

Question 32

Construct a logic diagram using AND, OR, NOT, NAND, NOR, and XOR gates.

Example: draw a logic circuit represented by the following truth table.

Answer 32

You do not need to memorize the shape of the logic gates, you can just draw circles and write the name of the gate.

Example solutions: