Coa

Front 1

Advantages of Direct Mapped Cache

Back 1

-Simple to implement

-Easy and fast to find item

Front 2

Disadvantages of Direct Mapped Cache

Back 2

-very prone to cache thrashing

-lowest hit rate

Front 3

Advantages of N-way set associative cache

Back 3

-less cache thrashing

-higher hit rate

Front 4

Disadvantage of N-way set associative cache

Back 4

-more complex design

-longer search time

Front 5

What is cache thrashing

Back 5

Same block being replaced frequently

-leads to lower hit rate

-cache memory not fully utilised

Front 6

What is locality of space

Back 6

Code/data stored close together will likely to be accessed together

Front 7

2 tasks that cache need to do

Back 7

Storage

Retrieval

Front 8

Locality of time

Back 8

Recently executed code/data will more likely to be executed again

Front 9

Disadvantage of LRU

Back 9

LRU needs to maintain access history for each block, slows down cache

Front 10

Benefit of random replacement policy

Back 10

It never thrashes

Front 11

What are dirty blocks

Back 11

Blocks that have been updated while they are in the cache

Front 12

What is write through

Back 12

Updates cache and main memory simultaneously on every write

Front 13

What write back

Back 13

Updates memory only when the block is selected for replacement

Front 14

Advantage of write through

Back 14

No cache coherency issue

Front 15

Disadvantage of write through

Back 15

More traffic on system bus

Front 16

What is cache coherency

Back 16

Content in cache is different from the equivalent address in the main memory

Happens when CPU writes to cache but not to main memory

Front 17

Effective Access Time (EAT) formula

Back 17

EAT = H x AccessC + (1-H)x(AccessC + AccessMM)

Front 18

Order of CPU Memory Access

Back 18

CPU -> Cache -> Main Memory -> Disk

Front 19

Purpose of cache

Back 19

Store recently used data near to CPU so that access can be faster and improve system performance

Front 20

What does virtual memory do

Back 20

Extend address space

Front 21

Disadvantages of having virtual memory

Back 21

- more virtual memory means longer access time (copy to main memory may be needed)

Front 22

What is segmentation

Back 22

Dividing virtual address space into variable length segments

Front 23

What is memory fragmentation

Back 23

Occurs when small unusable clusters of memory addresses are created

Front 24

How is memory fragmentation caused

Back 24

By paging and segmentation

Front 25

Paging causes internal or external fragmentation

Back 25

Internal

Front 26

Segmentation causes internal or external fragmentation

Back 26

External

Front 27

Advantages of virtual memory

Back 27

- Allows system to run programs that are bigger than main memory

- Frees application from having to manage a shared memory space in physical memory

-Virtual address space can be seen as contiguous but it is actually spread across fragmented blocks in physical memory

Front 28

What is Translated Lookup Buffer (TLB)?

Back 28

It is a cache data table containing the recent page lookup values

Front 29

How is data stored in HDD

Back 29

Data is stored on the concentric rings called tracks.

Front 30

Why are there gaps between tracks

Back 30

To minimise interference from adjacent tracks

Front 31

What does the stored data of HDD consist of

Back 31

Header, data, trailer

Front 32

HDD - what is seek time

Back 32

Time taken for head to move to correct track

Front 33

HDD- what is rotational delay

Back 33

Time taken for the disk to rotate until the head reaches the starting position of the sector

Front 34

Hdd- what is access time

Back 34

Time from request to the time the head is in position

Front 35

Hdd - What is transfer time

Back 35

Time required to transfer the required data after head is positioned

Front 36

Formula for average rotational delay

Back 36

Front 37

Hdd- formula for transfer time

Back 37

Front 38

What are the 2 addressing scheme for HDD

Back 38

- Cylinder Head Sector (CHS)

- Logical Block Addressing (LBA)

Front 39

Disadvantage of CHS

Back 39

Cannot handle large address ranges

Front 40

Advantage of LBA

Back 40

Simple linear addressing

Front 41

2 techniques to extend the life of SSD

Back 41

- wear levelling

- use external RAM as buffer

Front 42

What is wear levelling

Back 42

Distributing data and erase/write cycle evenly over the entire disk

Front 43

How does external RAM help to extend life of SSD

Back 43

Minimise the number of writes to FLASH in SSD

Front 44

Formula for chance of failure

Back 44

Front 45

Problems in HDD

Back 45

- access times for moving the heads lowers the transfer rate

- mechanical device, suffer from crash

Front 46

Purpose of RAID

Back 46

Improve reliability and performance

Front 47

Explain RAID level 0

Back 47

No redundancy

Best performance

No fault tolerance

Needs minimum of 2 disks

Data striped as blocks across all disks

Front 48

Explain RAID level 1

Back 48

-Mirrored disk

-100% redundancy

-Data is written to both disks

-Write throughput is slower because every drive must be updated

-need minimum of 2 disks

Front 49

Advantages of RAID Level 1

Back 49

- Easy to recover data

- Faster read operation

Front 50

Disadvantages of RAID level 1

Back 50

Write throughput is slower

Expensive

Front 51

Explain RAID Level 5

Back 51

- Block level striping with single distributed parity

- Data on single failed drive can be reconstructed from surviving data and parity info

- commonly used in network server

Front 52

Explain RAID level 6

Back 52

- May recover from multiple disk failures

- uses block level striping with double distributed parity

Front 53

Advantage and disadvantage of RAID level 6

Back 53

Advantage: high data availability

Disadvantage: significant write penalty

Front 54

Explain RAID level 10

Back 54

Combines protection of RAID 1 with performance of RAID 0

More expensive