Topic 2.1 - Hardware and Components

Question 1

What is word length and what are some usual word lengths of processors?

Answer 1

The word length is the number of bits that a processor can handle/transfer as a unit. Common word lengths are now 32/64

Question 2

Examples of main (primary) memory:

Answer 2

• RAM

- ROM

Question 3

Examples of secondary storage:

Answer 3

• SSD
• HDD
• Magnetic Tape
• Flash drive

Question 4

Describe RAM

Answer 4

Random Access Memory temporarily stores currently being used programs and data including the OS so it accessible by the processor.

• If there is not enough RAM, data must be sent back to secondary storage to free up space (less efficient)
• Volatile
• Random Access, given a unique address
• Made of cheap silicon

Question 5

What is the difference between DRAM and SRAM

Answer 5

Dynamic RAM is cheaper and more can be stored in a smaller space however data must be reloaded. Static RAM is more expensive, larger and doesn’t need reloading.

Question 6

What components are found inside the CPU?

Answer 6

• ALU (Arithmetic Logic Unit)
• PC (Program Counter)
• Control Unit
• MAR (Memory Address Register)
• MDR (Memory Data Register)
• CIR (Current Instructor Register)
• SR (Status Register)
• System Clock

Question 7

What busses are used in the Von Neumann architecture?

Answer 7

• Address bus
• Control bus
• Data bus

Question 8

What’s the difference between the address bus and the data bus?

Answer 8

The address bus is uni-directional and sends the addresses to memory so they can be retrieved whereas the data bus is bi-directional and send data to be stored/fetched.

Question 9

What is the definition of a bus?

Answer 9

It is a set of parallel wires that connect the different parts of the computer and to send data/addresses to different parts of the computer.

Question 10

What happens in the fetch part of the fetch-decode-execute cycle?

Answer 10

• The program counter is copied to the memory address register
• The program counter is incremented
• The address is sent down the address bus and the data at that address is sent back via the data bus into the memory data register,

Question 11

What happens in the decode-execute part of the fetch-decode-execute cycle?

Answer 11

• The contents of the memory data register are copied to the current instruction counter
• The CIR decodes the opcode and that operation is carried out with the operand to update the necessary register or accumulator

Question 12

What is the status register used for?

Answer 12

The status register stores the state of the values of the outcomes of some operations such as:

• Overflow, underflow, zero, negative, positive
• Parity
• Interrupts (enabled disabled)

Question 13

What are the problems with the Von Neumann architecture?

Answer 13

• Data bus is slower than the CPU’s clock speed

- Data and instructions share the same memory location so there is a risk of accidentally over-writing code

Question 14

What is the Harvard model?

Answer 14

The Harvard model splits memory into two parts, one section for programs and one section for data. This means the CPU can both fetch instructions and data at the same time.

• Less chance of program corruption
• Used for ABS as the system must respond really quickly

Question 15

Why is Cache memory needed?

Answer 15

As fetching from memory is a lot slower than the speed of the processor, cache is required to make up this difference and increase efficiency.

Question 16

How does cache memory work?

Answer 16

• Stores regularly used data and instructions
• Holds intermediate data whilst processing is carried out
• Cache is made out of logic devices and so is more expensive and therefore only is found in small amounts

Question 17

What are the different types of cache memory?

Answer 17

L1 - Embedded in the CPU (fast but expensive)
L2 - Located between the processor and memory
L3 - Located on the memory
- L2 and L3 have their own bus

Question 18

What is the purpose of the cache controller?

Answer 18

The cache controller decides what to store in the cache memory and works off the 80/20 rule. The 80/20 rule states that 80% of the time that the program is running, the same 20% of the code is being used.

Question 19

What is parallel processing?

Answer 19

Where multiple calculations occur simultaneously to perform a single task

• Use of multiple cores
• Complex to design/write
• Large problems divided into smaller ones
• Use of concurrency
• Speed of program found using Amdahl’s law

Question 20

What is concurrency?

Answer 20

Executing parts of a program out of order

Question 21

What is Amdahl’s law?

Answer 21

T(n) = T(1)(B+1/n)(1-B)

• n = number of cores or threads
• B = fraction of program which is sequential

Question 22

What is FTP?

Answer 22

File Transfer Protocol

• Allows transfer of large files over a network
• In-built error checking and re-transmission is used to ensure the file is transferred

Question 23

What is HTTP?

Answer 23

Hypertext Transfer Protocol

• Allows transfer of multimedia web-pages over the internet
• Allows different browsers to display and format the pages as the author intended

Question 24

What is SMTP?

Answer 24

Simple Mail Transfer Protocol

• Allows emails to be sent over a network
• Provides standard way of transferring emails between two different servers

Question 25

What is IMAP and POP3?

Answer 25

Internet Message Access Protocol and Post Office Protocol 3

• Way of uploading/downloading email between PC and the server
• IMAP stores data on server saving device storage space
• POP3 downloads the message and then deletes from the server so isn’t as useful

Question 26

What is DHCP?

Answer 26

Dynamic Host Control Protocol

• Temporarily leases IP addresses to devices
• Ensures unique addresses are allocated
• If a device is no longer accessing the internet, the DHCP will return their IP address to the pool of addresses.

Question 27

What is UDP?

Answer 27

Universal Datagram Protocol

• For video applications and streaming
• Has error checking facilities
• But doesn’t re-send packets as slight drops in quality are acceptable in order to keep the video playing.

Question 28

What is TCP/IP?

Answer 28

Transmission Control Protocol / Internet Protocol

• Allows networked computers to connect with one another
• Specifies how signals are routed round a network and reduces need for gateways to convert signals into different protocols.

Question 29

What is handshaking?

Answer 29

• Exchange of signals between devices to establish their readiness to transfer data.

Question 30

What is fragmentation?

Answer 30

When storing a file on a HDD, there might not be enough space ‘together’ on the disc to store it all in one place. Therefore, files are fragmented and spit up to different parts of the HDD which slows down the HDD access speed.

Question 31

What is defragmentation?

Answer 31

Where fragmented files are moved closer together so preferably they are on the same track. This will reduce the movement of the read/write head, increasing access speeds and the life of the disc.