Lectures 7 - 10

Question 1

What do threads provide?

Answer 1

A separate thread of execution

Question 2

Where and when do threads work?

Answer 2

They operate concurrently within the processor

Question 3

What functions do threads operate on?

Answer 3

They operate on small individual functions which are a subset of a larger process.

Question 4

What are some of the functions that the OS has in order to deal with multi tasking

Answer 4

• Interrupts
• Pipelining
• Superscalers
• Simultaneous Multi Threading (SMT)
• Symmetric and chip level multi threading (SMP/CMP)
• Direct memory access
• Graphics Processing Units (GPU’s)

Question 5

What do interrupts ‘tell’ the CPU?

Answer 5

That something of higher importance has happened

Question 6

What are the steps taken by the CPU when an interrupt is detected?

Answer 6

1: The event causes an interrupt request (IRQ)
2: A signal is sent to the processor through a reserved line
3: The processor saves its current state and loads the interrupt handler for that interrupt
4: Once the interrupt has been handled, the processor returns to its original task.

Question 7

What is pipelining?

Answer 7

When a process is broken down into a small series of steps, with which different circuitry does different parts

Question 8

What does pipelining allow?

Answer 8

It allows an instruction to be fetched while two others are being decoded and executed at the same time

Question 9

What happens in pipelining when a condition is encountered?

Answer 9

A likely outcome is selected so that it can be ready to be processed. However, if the unlikely outcome happens then the likely outcome will have to be wiped from memory.

Question 10

What is superscaling?

Answer 10

When a CPU uses its idle execution units (e.g. ALU) to complete more than one instruction per clock cycle

Question 11

What are superscalers often used in conjunction with?

Answer 11

Pipelines

Question 12

Why are superscalers often used with pipelines?

Answer 12

As it allows multiple instructions to be processed per pipeline instruction

Question 13

What three things does a computer need to know to access data on a HDD?

Answer 13

What cylinder it is on
Which head is currently in use
Which sector it is in

Question 14

What do sectors contain?

Answer 14

They contain (in order):

• A header
• Gap
• Data
• ECC
• Gap

Question 15

What does the header contain in a sector?

Answer 15

Contains addresses and error checking info

Question 16

What are the gaps for?

Answer 16

To allow the head to change operation

Question 17

What is the ECC?

Answer 17

Error Checking Code

Question 18

What does LBA stand for?

Answer 18

Logical Block Addressing

Question 19

What is the point of LBA?

Answer 19

It is how the OS knows where things are in a HDD (or other secondary storage device)

Question 20

What is the formula for LBA?

Answer 20

((C x HPC) + H) x SPT + (S-1)
Where: 
C = Cylinder
H = Head
S = Sector Number
HPC = Heads per cylinder
SPT = Sectors per Track

Question 21

What does RAID stand for?

Answer 21

Redundant Array of Independent Disks

Question 22

What is RAID?

Answer 22

It is a technique where data is split across multiple disks to improve reliability of a system

Question 23

What does RAID 0 do?

Answer 23

It strips the data: It spreads the data between all of the allocated disks.

Question 24

What does RAID 1 do?

Answer 24

It makes multiple disks contain the same data so that if one breaks then the data is still secure

Question 25

What does RAID 5 do?

Answer 25

It distributed the data across multiple disks along with their parity, meaning that if one of the disks were to fail then the other levels of data are not lost.