Chapter 6: Computer System and Networks

A computing device is a physical artifact that can run a program.
- Some examples include computers, tablets, servers, routers, and smart sensors.
The device must be able to take inputs, process the inputs, and then calculate results based on those inputs.
A computer is a computing device, but not all computing devices are computers.
A computing system is a group of computing devices and programs working together for a common purpose.
A computer network is a group of interconnected computing devices capable of sending or receiving data.

Each circle in the diagram above represents a computer system that is connected to another computer system, forming a computer network.
The larger circles represent systems that have a higher bandwidth capacity measured in bits per second.
The bandwidth of a computer network is the maximum amount of data that can be sent in a fixed amount of time.
A path between two computing devices on a computer network (a sender and receiver) is a sequence of directly connected computing devices that begins at the sender and ends at the receiver.
Routing is the process of finding a path from sender to receiver.
If the path from sender to receiver is broken, the path will be rerouted.
This fault-tolerant nature of the internet makes connections between computing devices more reliable.

Internet protocol (IP) is responsible for addressing and routing your online requests.
For a device to connect to the internet, it is first assigned an internet protocol address.

Transmission control protocol (TCP) is a protocol that defines how computers send packets of data to each other.
Data traveling in the internet is broken down into small chunks of data called packets.

User datagram protocol (UDP) is a protocol that allows computer applications to send messages without checking for missing packets to save on time needed to retransmit missing packets.
UDP is not as reliable as TCP, which does resend packets lost when transmitting.

When a system can support failures and continue to function, it is called fault tolerant.
- This is important because elements can fail at any time, and fault tolerance allows users to continue to use the network.
The process from computer D to computer K in the diagram above is called end-to-end architecture.
- This process involves the breaking down and assembling of the packets at each end.
- What happens to the packets in the middle is hidden from the user in an abstraction.

The internet refers to the hardware.
The World Wide Web, in contrast, refers to the software used on the internet.

Sequential computing is a computational model in which operations are performed in order one at a time.
A sequential solution takes as long as the sum of all of the steps.
A parallel solution takes at least as long as the longest branch in the program.

A problem is broken into discrete instructions.
These instructions are executed one by one by a single computing device having a single central processing unit (CPU).

A parallel computing solution takes as long as the longest of the tasks done in parallel.
A parallel computing solution takes as long as its sequential tasks plus the longest of its parallel tasks.
Parallel computing can consist of a parallel portion and a sequential portion.

Parallel computing is needed for real-world simulations and modeling.
Multiple processors can operate independently but share the same memory resources.

Distributed computing allows problems to be solved that could not be solved on a single computer because of either the processing time or storage needs involved.
Parallel computing uses a single computer with multiple processors.
Distributed computing uses multiple computing devices to process those tasks.