Unit 1: System Architecture

Question 1

What is the CPU and what is its role?

Answer 1

Internal hardware component of the computer that is responsible for executing instructions of programs. It is made up of many important components, each with its own role.

Question 2

What is the function of the CU?

Answer 2

• Manages the fetching, decoding and executing of program instructions. (Fetch, Decode Execute)
• Controls the flow of data inside the CPU (to registers, ALU, cache) and outside the CPU (to main memory and input/output devices)

Question 3

What is the function of the ALU?

Answer 3

• Performs logic operations (AND, OR, NOT) and binary shifts.
• Performs arithmetic calculations including adding, subtracting, comparing sizes of numbers, multiplication and division.
• Contains the accumulator register.

Question 4

What is the function of the Cache?

Answer 4

• Very fast memory in the CPU (Slower than registers, faster than RAM)
• Stores regularly used data so it can be accessed quickly by the CPU when it’s needed. (When the CPU request data, it checks the cache first before fetching it from the RAM)
• Has a very low capacity and is expensive compared to RAM and secondary storage.
• 3 levels of Cache memory - L1 is quickest but has lowest capacity, L3 is slowest but holds the most.

Question 5

What is the Von Neumann Architecture?

Answer 5

A system where the CPU runs programs stored in memory. Program consists of instructions and data which are stored in memory addresses.

Question 6

What is the function of the MAR?

Answer 6

Holds the memory address of the current instruction, and then the data that it uses, so that these can be fetched from memory.

Question 7

What is the function of the MDR?

Answer 7

Holds the actual instruction, and then the data that has been fetched from memory.

Question 8

What is the function of the PC?

Answer 8

Holds the address of the next instruction to be executed.

Question 9

What is the function of the Accumulator?

Answer 9

Stores intermediate results of calculations in ALU before it is transferred from memory.

Question 10

To summarise, what are the steps involved in the fetch, decode, execute cycle?

All information in GoodNotes

Answer 10

CPU operates by repeating three operations:
FETCH - Causes the next instructions and any data involved to be fetched from main memory.
DECODE - Decodes the instruction.
EXECUTE - The instruction is executed.

All information in GoodNotes

Question 11

What are embedded systems and how are they mainly used?

Answer 11

Embedded systems are computers built into other devices.
* E.G Dishwashers, Microwaves, TVs
* Often used as control systems - monitor and control machinery in order to achieve a desired result. E.G In a dishwasher, the embedded system could control the water pumps and water release mechanisms.
* Due to them being dedicated to a single task, they are often easier to design, cheaper to produce, and more efficient at doing their task than a general purpose computer.

Question 12

What is the purpose of a computer and a computer system?

Answer 12

COMPUTER - Takes data, processes it, then outputs it.
COMPUTER SYSTEM - Hardware and software that work together to process data/complete tasks.

Question 13

What does volatile and non-volatile memory mean?

Answer 13

VOLATILE - Temporary memory - requires power to retain its data.
NON-VOLATILE - Permanent memory - keeps its content even when it doesn’t have any power.

Question 14

What is RAM?

Answer 14

Random Access Memory is used as main memory in a computer. It can be read and written to and is volatile.
* Main memory is where all data, files and programs are stored while they’re being used.
* When a computer boots up, the operating system is copied from secondary storage to RAM or when a software application is opened, the same process occurs. They stay in RAM until the application is closed
* Slower than CPU cache, faster than secondary storage.

Question 15

What is virtual memory and when is it used?

Answer 15

1. Computers have limited amounts of RAM and as applications are opened, RAM fills with data.
2. When RAM is full, data that hasn’t been used recently is moved to a location on secondary storage (virtual memory)
3. Virtual memory is needed if there are too many applications open at once or if a particularly memory intensive application is being used (or both)
4. If the CPU needs to read data stored in virtual memory, it must move the data back to RAM which is slow as data transfer rates are much slower on secondary storage than RAM.

Question 16

How can using virtual memory affect system performance?

Answer 16

• Using virtual memory can make a computer slower to respond when switching between applications (as data for one application in virtual memory is swapped with the other)
• When using memory-intensive applications (due to data constantly moving between virtual memory and RAM just to keep the program running)

Question 17

What is ROM?

Answer 17

Read Only Memory is non-volatile memory and contains all the instructions a computer needs to properly boot up which are called (BIOS) Basic Input Output System. BIOS is a type of firmware - hardware specific software built into a device.
1. As soon as the computer is powered on, CPU reads instructions from ROM which tells the CPU to perform self checks, and set up the computer. e.g test the memory is working ok, see what hardware is present and compy the OS into RAM.

Question 18

What is CPU performance dependent on?

Answer 18

• Clock Speed
• Number of Cores
• Cache Size

Question 19

What is Clock Speed and how does it affect CPU Performance?

Answer 19

Number of instructions a single processor core can carry out per second (Hz) - This is usually around 3.5 GHz for most desktop computers.
The clock sends a pulse at fixed intervals to trigger the next stage of the fetch, decode, execute (FDE) cycle.
* The higher the clock speed, the greater number of instructions that can be carried out per second.
* CPUs can be overclocked to make them run at a higher clock speed than the factory-set rate. But if not done properly, it can make CPUs overheat, cause crashing or permanent damage to the system. - High performance cooling systems are often needed.

Question 20

What is Cores and how does it affect CPU Performance?

Answer 20

• Each core in a CPU can process data independently of the rest.
• The more cores, the more instructions it can carry out at once, so the faster it can process a batch of data.
• PCs and smartphones have 4 or more cores these days.

Question 21

What is Cache and how does it affect CPU Performance?

Answer 21

• A larger CPU cache gives the CPU faster access to more data it needs to process.

Question 22

Generally, what does a higher clock speed, number of cores and cache size mean for a CPU?

Answer 22

They will have better performance but will be more expensive.

Question 23

What can too little RAM mean for a computer?

Answer 23

The computer may run slowly due to the use of virtual memory being needed.

Question 24

What does more RAM mean for a computer?

Answer 24

• The more applications or more memory-intensive applications it can run smoothly, making it faster overall.
• RAM can easily be upgraded by replacing RAM sticks with higher capacity or higher speed ones.
• If a computer already has plenty of RAM to run everything the user wants, increasing RAM won’t make a difference to performance.

Question 25

What is the role of GPUs?

Answer 25

* Graphics processing units are specialised circuits for handling graphics and image processing which can reliev processing load on the CPU, freeing it to do other things. * Computers have basic GPUs integrated on the motherboard or CPU but for better graphics performance, a dedicated graphics card (GPU) is used. * Using high-end graphics cards can greatly improve performance in graphics-intensive applications.

Question 26

What is Primary Storage?

Answer 26

Memory areas that the CPU can access very quickly, like CPU registers, cache, ROM and RAM. It has the fastest read/write speeds and is mostly volatile. **Primary storage is the memory in which the computer can store the data or instructions that are currently in use.**

Question 27

What is Secondary Storage?

Answer 27

It's where all data (OS, applications and user files) are stored when not in use. Includes magnetic hard disk drives, solid state drives, CDs, SD cards. Non-volatile and read/write speeds are much slower compared to primary.

Question 28

What are Hard Disks (HDDs) and what is there function?

Answer 28

* Traditional internal storage found in PCs/Laptops - often called hard drives. * Made of stack of magnetised metal disks spinning thousands of times a second. * Data stored magnetically in small areas on the disk's circular track - a moving arm can access these areas and read/write data. * Portable HDDs are popular for backing up/transporting large amounts of data * Generally long lasting and reliable but can be damaged by large impacts e.g being dropped.

Question 29

What are Solid State Drives and what is there function?

Answer 29

* Used for the same purpose as HDDs - internal/external storage. * Most use a type of flash memory (common type of non-volatile memory) * Have significantly faster read/write times than HDDs and cna give quicker times for bootingup/opening programs and files.

Question 30

What are advantages of SDDs?

Answer 30

* Faster * Don't need defragmenting * More shock-proof than HDDs * Silent whereas HDDs make more noise

Question 31

What are advantages of HDDs?

Answer 31

* Cheaper * Have a higher capacity (than SDDs) * Longer read/write times than SDDs which can only be written a certain number of times before they deteriorate.

Question 32

What is Memory (Primary Storage) used for?

Answer 32

**Memory (Primary Storage)** * Holds digital data/instructions * Uses on/off electricity signals * Needs electricity to work * Faster access * Volatile

Question 33

What is Storage (Secondary Storage) used for?

Answer 33

**Storage (Secondary Storage)** * Holds digital data/instructions * Uses a method of storage that does need electricity * Keeps a copy of data and instructions when they are not in use * Slower access

Question 34

What are optical disks and their function?

Answer 34

* CDs, DVDs, Blue-Ray disks * Come in three forms: read-only, write-once, rewritable. * As internet speeds have increased, streaming and download services like Netflix, Spotify and Steam have removed the need for optical disks. * Modern devices (phones/tablets) don't have optical drives. * Used to be popular for backing up data but have a low capacity per disk, very slow read/write speeds and poor reliablility compared to flash storage devices. * Very cheap, portable and won't be damaged by water or shocks but are easily scratched.

Question 35

What are magnetic tapes and their function?

Answer 35

* Greater storage capacity than HDDs * Extremely low cost per GB * Often used by large organisations in archive libraries to store huge amounts of data. * Comes in plasic cassettes requiring a special tape-drive for read/writing. * Read/written sequentially, meaning it is read/written from beginning to end, or until stopped by the computer meaning it's very slow at finding specific data stored on it, but fast read/write speed once it is in the correct place to begin read/writing.

Question 36

What is a processor?

Answer 36

A processor is a special component that processes data and instructions to control other components within the computer. Two main processors: GPU, CPU

Question 37

What is a general purpose system?

Answer 37

General purpose systems are capable of performing many different tasks.