System Architecture (1.1)

Question 1

What is the CPU

Answer 1

(Central Processing Unit) is the hardware component responsible for processing and executing all the instructions inside of a computer.
- The speed is measured in Hz, so a 2Ghz CPU would process 2 billion instructions/CPU cycles per second

Question 2

How can clock speed affect performance

Answer 2

• The higher the clock speed, the faster the rate at which the CPU can execute instructions per second

Question 3

How can number of cores affect performance

Answer 3

• More cores results in instructions being executed in parallel per core , resulting in faster execution

Question 4

How can cache size affect performance

Answer 4

• A larger cache size means the CPU can access more temporary stored data which is much faster than if stored in RAM

Question 5

What is an embedded system

Answer 5

• a computer system built into another device. These are dedicated systems produced to be efficient at carrying out its specific task.
• They tend to contain more ROM than RAM, as they are specialised to
  carry out limited functions (cheaper to design and build)

Question 6

What are some examples of embedded systems

Answer 6

• Washing machine,
• MP3 player,
• Dishwasher
• smartwatch

Question 7

What are the CPU components

Answer 7

• Control unit (Directs the instructions within the processor)
• Arithmetic & Logic Unit (ALU) (Responsible for any arithmetic and logic calculations in the processor)
• Cache (Stores the most frequently accessed instructions from the RAM (faster than RAM, but holds much less data))
• Registers (Small amounts of highspeed memory located within the CPU)

Question 8

What are the 4 main Von Neuman Registers

Answer 8

• Memory address register (MAR) (Holds memory addresses about to be used by the CPU)
• Memory Data Register (MDR) (Holds the actual data or instruction to be used by CPU)
• Accumulator (Stores intermediate results of calculations in the ALU)
• Program Counter (PC) (Holds the memory
  address of the instruction for each cycle)

Question 9

What happens at the fetch stage of the cycle

Answer 9

• copy memory address from program counter to the MAR, and copy instruction from the MAR address to the MDR. Increase the program counter to point to next instruction.

Question 10

What happens at the decode stage

Answer 10

• instruction in MDR is decoded by the CU

Question 11

What happens at the execute stage of the cycle

Answer 11

• the instruction is performed/executed. This could be load data/write data to or from memory, or do a calculation or logic operation (using ALU).

Question 12

What is ROM

Answer 12

• The ROM is an internal hardware component which is part of the computers main memory
• ROM is non-volatile memory which means the data is saved/kept by the computer when the power turns off.
• ROM is used to store the BIOS (basic input output system) ʹ instructions needed to turn the computer on or the “bootup” sequence
  (bootloader)

Question 13

What is RAM

Answer 13

• The RAM is another internal hardware component which is part of the computer’s main memory
• RAM is used to store any running applications while the computer is ON
• The RAM is volatile memory meaning the data in the RAM is deleted/erased when the power turns off

Question 14

What is the difference between RAM and ROM

Answer 14

• A computer needs both RAM and ROM to function correctly. However, the ROM in a computer is difficult to upgrade or change, whereas the RAM can be easily upgraded and changed to hold more data
• RAM holds a lot more data than the ROM
• Typical RAM is 4GB and typical ROM is 4MB.

Question 15

What is virtual memory

Answer 15

• Virtual memory is memory which the computer uses by
  allocating a section of secondary storage to store
  running applications. This is only used when the RAM in
  a computer is full and runs out of capacity.

Question 16

How does virtual memory work

Answer 16

• CPU move data from RAM into the
  secondary storage, known as a “paging file”, so the CPU can continue with its execution of instructions from RAM. This is copied back into the RAM when it is needed

Question 17

What are the characteristics of virtual memory

Answer 17

• The virtual memory is slower than the RAM but allows the computer to continue functioning by using part of the HDD or SSD to store some data from the RAM.

Question 18

What is flash memory

Answer 18

• Flash memory is non-volatile memory which is used to store data and transfer this between a computer and another device. Flash memory can have its contents edited and changed according to the user’s needs, and it can also be electronically programmed

Question 19

What are examples of flash memory

Answer 19

• USB drives
• SD cards
• Solid State Drives (SSDs)

Question 20

Why could secondary storage be needed

Answer 20

• Secondary storage is needed to save data and programs that are needed after the computer is turned off. It is a form of non-volatile memory.
• Secondary storage can hold much greater capacity of memory than main memory, but is slower to access as it is not directly accessible by the CPU.

Question 21

What factors are there to consider about secondary storage

Answer 21

• Capacity (how much data can be stored)
• Speed (how fast the data can be read/written)
• Portability (is the device easy to move around and take with you)
• Durability (how will it be affected by drops, shocks, water etc)
• Reliability (chances of data always loading correctly)
• Cost (how much is the cost per GB)

Question 22

What is magnetic storage

Answer 22

• a type of secondary storage which is typically found in Hard Disk Drives (HDDs).
• Data is stored using magnetic dots which have a magnetic polarisation, on areas of the disk called sectors which are found within circular tracks.
• The data will have a positive or negative polarity, which is read by the read/write head on a moving arm.

Question 23

What are the positives/negatives of magnetic storage

Answer 23

Advantages: largest storage capacity, cheaper to produce than solid state drives
Disadvantages: more likely to be damaged by dropping due to moving parts, not as fast to read/write data as a solid state drive

Question 24

What is optical storage

Answer 24

• Optical memory is a type of secondary storage which uses lasers to read and write data.
• Examples of optical memory include CDs, DVDs and Blu-ray disks.
• Data can be read by using a laser which reads a series of pits and lands.
• The laser is shone onto the disk surface which is reflected, and this represents 0s and 1s.

Question 25

What are the positives/negatives of optical storage

Answer 25

Advantages: very cheap to produce (good for program distribution), much more lightweight and portable than magnetic disks, unaffected by shocks and water
Disadvantages: limited storage capacity (CDs hold around 700MB and DVDs upto 4.8GB), can also be damaged by scratches or by excessive use over a long period of time

Question 26

What is solid sate storage

Answer 26

• Solid State memory is a type of secondary storage which uses electricity and flash memory to store data.
• There are no moving parts in a solid state device, and the data is stored using electrical switches
• open switch represents a 1 (keeps charge) and a closed switch represents a 0

Question 27

What are the positives/negatives of solid state storage

Answer 27

Advantages: fastest type of storage (reading and writing), much more lightweight and less prone to damage than magnetic disks (no moving parts)
Disadvantages: most expensive form of storage (per GB of data)