1-introduction

Question 1

What is a distributed system?

Answer 1

A collection of autonomous computing elements that appears to its users as a single coherent system.

Question 2

What are the two key characteristics of nodes in a DS?

Answer 2

1. They need to communicate with each other. 2. There is no global clock - each node has its own time.

Question 3

What is location transparency?

Answer 3

Users cannot tell where computation happens or where data is stored.

Question 4

What is replication transparency?

Answer 4

Users cannot tell whether data is replicated across multiple nodes.

Question 5

What is the difference between distributed and decentralised?

Answer 5

Decentralised systems have more redundant peer-to-peer connections. Distributed focuses on appearing as one coherent system.

Question 6

What is the Integrative view of building DS?

Answer 6

Adding a networked computer into a larger system.

Question 7

What is the Expansive view of building DS?

Answer 7

Extending one computer with more computers.

Question 8

What is the Architecture challenge in DS?

Answer 8

How do we organise? Client-server or peer-to-peer? Microservices? Layered architecture?

Question 9

What is the Process challenge in DS?

Answer 9

What kind of processes - threads

Question 10

What is the Communication challenge in DS?

Answer 10

RPC? API? Message queues? What protocols and middleware?

Question 11

What is the Coordination challenge in DS?

Answer 11

Synchronising actions of all the computers in the system.

Question 12

What is the Naming challenge in DS?

Answer 12

How do we identify resources?

Question 13

What is the Consistency challenge in DS?

Answer 13

We need data copies and we need to synchronise those copies across nodes.

Question 14

What is the Fault Tolerance challenge in DS?

Answer 14

Parts will fail - detect and fix without taking down the whole system.

Question 15

What is the Security challenge in DS?

Answer 15

Need authentication and encrypted communication.

Question 16

What is the Latency challenge in DS?

Answer 16

Need to minimise and hide network delay.

Question 17

What is the Processing Power challenge in DS?

Answer 17

Need to allocate enough processing power across nodes.

Question 18

What is the Storage challenge in DS?

Answer 18

How do we distribute storage across the system?

Question 19

Name 4 examples of distributed systems.

Answer 19

Internet, WWW, Cell networks, Cloud.

Question 20

What is parallel computing?

Answer 20

Multiprocessor/core vs multicomputer systems that can share memory or have private memory.

Question 21

What was Distributed Shared Memory (DSM)?

Answer 21

Implementing shared memory model on multicomputer using virtual memory techniques. Failed due to lower performance than true multiprocessors, now abandoned.

Question 22

How did DSM work?

Answer 22

Map all main memory pages to a single address space. OS traps and fetches pages from correct computer.

Question 23

What is Cluster Computing?

Answer 23

High-end systems connected locally (LAN). Same OS and hardware (homogeneous). Single program manages entire cluster.

Question 24

What is Grid Computing?

Answer 24

Lots of nodes anywhere. Flexible, secure, coordinated resource sharing. Virtual organisations share resources for common goals.

Question 25

What is the difference between Cluster and Grid computing?

Answer 25

Cluster: local, homogeneous, single admin. Grid: distributed, heterogeneous, multiple organisations.

Question 26

What are the 4 layers of Cloud Computing?

Answer 26

Hardware (unseen by users), Infrastructure (virtualisation), Platform (development/deployment), Application (cloud apps like office suites).

Question 27

What is Enterprise Application Integration (EAI)?

Answer 27

Allowing direct communication between applications in an organisation rather than having a client collate results.

Question 28

What does ACID stand for?

Answer 28

Atomic, Consistent, Isolated, Durable.

Question 29

What is Atomicity in ACID?

Answer 29

Transaction completes fully or not at all - never partial.

Question 30

What is Consistency in ACID?

Answer 30

Transaction brings database from one valid state to another.

Question 31

What is Isolation in ACID?

Answer 31

Concurrent transactions don't interfere with each other.

Question 32

What is Durability in ACID?

Answer 32

Committed transactions persist even after system failure.

Question 33

What is a Transaction Processing Monitor (TPM)?

Answer 33

Receives request, breaks into operations for different servers, sends and collects responses. All succeed → commit. Any fail → abort and rollback.

Question 34

What is RPC (Remote Procedure Call)?

Answer 34

Application calls function, RPC packages call and parameters into message, sends to remote server, result packaged and returned. Abstracted from programmer.

Question 35

What is MOM (Message Oriented Middleware)?

Answer 35

Asynchronous messaging - application publishes to queue, MOM holds it, subscribed apps receive and process.

Question 36

What is Ubiquitous Computing?

Answer 36

Embedded systems in your environment that operate autonomously, unobtrusively, without user interaction. System knows who/where/what you are.

Question 37

What is Mobile Computing?

Answer 37

Devices that move between different local services. No guaranteed connectivity or stable routing. Must discover what's nearby.

Question 38

What are the two approaches to mobile computing?

Answer 38

Cloud only (thin client, far away, can be slow) or Cloud with Edge (smaller server closer to client, some local processing).

Question 39

What are Sensor Networks?

Answer 39

Thousands of sensors on small battery-powered nodes with some memory and compute. Process locally or send to main database.

Question 40

What is the Cloud Edge Continuum?

Answer 40

Trade-off: closer to cloud = more reliable/compute but less mobile/responsive. Closer to edge = opposite.