Midterm 1 Flashcards
LCD
liquid-crystal display
Processor
- a CPU consists of Memory Unit (RAM), Control Unit (coordination), Arithmetic Logic Unit (logic and calculations)
- a processor accepts digital data as input, performs the basic arithmetic, logical, control and input/output (I/O) operations according to instructions stored in a program.
Primary computer memory
stores data and instructions being worked on
data is lost when power is off
Secondary computer memory
- flash memory
- non-volatile
- data is permanently stored even if power is switched off.
- slower than primary memory
- CPU does not directly access it, transferred to main first
- e.g. flash drive, CD, ROM, PROM, EPROM
cache
Stores data so future requests for that data can be served faster
Random vs. Sequential access
- Random access - An item of data is accessed by an address among a population of addressable elements
- Sequential access - A group of elements (such as data in a register, a file, magnetic tape) is accessed in a predetermined, ordered sequence
5 Steps of Programming
- Requirements
- Design
- Implementation
- Verification
- Maintenance
Abstraction, Generalization, Analytical thinking
- Abstraction is a technique for managing complexity of computer systems, working at higher levels of the system, rather than the more complex details below the current level. It captures the most important aspects of a concept and ignores unimportant details. e.g. how does a user enter a number
- Generalization is applying/designing an idea or program to increasingly wider range of users, or applications
- Analytical Thinking - (algorithmic thinking) involves gathering relevant information and applying a step-by-step approach for breaking down complex problems into single and manageable components to arrive at appropriate solutions
Synchronous and asynchronous
synchronous - has a common clock that triggers the sender and receiver to be active at the same time
asynchronous - is the transmission of data without a common clock. typically, a protocol establishes the timing of reading data. Sending and receiving occur at different times
Broadcast and point-to-point
broadcast - message is sent out to all devices simultaneously
point-to-point - a communication connection between nodes where information is transferred from one device to a device at a specific address
Internet protocol
The Internet Protocol is responsible for addressing hosts and for routing datagrams (packets) from a source host to a destination host across one or more IP networks.
An Internet protocol address is a numerical label assigned to devices in a computer network
IPv4
IPv4 has 32bit addressing system typically written in the dotted-decimal notation 169.192.1.1
The address space is (2^32) addresses.
The most significant octet of the address is the network identifier or prefix
The rest is the host identifier
A number of IP address are reserved for special purposes:
- 0.0.0 host internal address (loop back)
- 254.0.0-.254.255 link-local address (local address space)
IPv6
The growing number of devices connected to the internet has exhausted the IPv4 address space.
IPv6 has 128bit number addressing written as dotted-hex notation 2001:db8:0:1234:0:567:8:1
The address space is (2^128) addresses.
The loopback address, 0000:0000:0000:0000:0000:0000:0000:0001
Abbreviated to ::1 as leading zeros are ignored
link local addresses are preceded by the octet fc00::
Purpose and role of a DNS server
Domain Name System (DNS) acts a kind of lookup table for mapping the domain name hierarchy to the IP address space.
Server respond to browser’s queries returning which IP maps to which URL.
TCP/IP
TCP/IP uses the client/server model of communication
A computer user (a client) requests and is provided a service (such as sending a Web page) by another computer (a server) in the network.
TCP/IP communication is primarily point-to-point
TCP
Transmission Control Protocol is responsible for breaking data down into small packets before they can be sent over a network, and for assembling the packets again when they arrive
TCP guarantees delivery of data and the same order in which they were sent
TCP can detect lost or corrupt packets and request them to be resent
IP
Internet Protocol takes care of the communication between computers
It is responsible for addressing, sending and receiving the data packets over the Internet
Packet Switching
Messages are divided into packets before they are sent
Each packet is then transmitted individually and can even follow different routes to its destination
Once all the packets forming a message arrive at the destination, they are recompiled into the original message.
World Wide Web
The World Wide Web in a service over the Internet
WWW is an open source information space
Documents and other web resources are identified by Universal Resource Locator (web address)
Documents are interlinked by hypertext links.
Challenges with the vast amounts of information available on the Internet
Velocity - it moves fast through multiple channels
Variety - It is made of f many types of data
Volume - Users generate immense amounts of data
Complexity - It must be able to traverse multiple data centers, the cloud and geographical zones
Big question is how to get meaningful values from big data.
Hypertext Markup Language (HTML)
Hypertext Markup Language (HTML) is a language for describing how a web page appears in a web browser.
Debugging
the process of determining why a system does not work properly
The Four Key Steps in Debugging
1) Check that the error is reproducible.
Computers are deterministic. Make sure you know exactly how to reproduce the error.
2) Do not jump to conclusions.
The actual cause of the error may be many steps removed from the visible symptoms.
3) Check all the “obvious” sources of error.
You would be surprised how often a cable is not plugged in…
4) Isolate the problem
The goal is to make good assumptions and divisions of parts that you know are working and others that need investigation.
- Be careful! It is often parts (including yourself) that you assume are working that really are not.
- Make sure assumptions are backed up by tests.
Common HTML Errors
Open with no matching close tag
<a>…
Non-matching quotes
<img></img> (open with “, close with ‘)
<img></img> (HTML does not like smart quotes)
Missing attribute or incorrect attribute name.
Incorrect tag name (which may result in non-matching tags).
Incorrect file name or hyperlink address.
Forgot required tags like , , .
Forget to stop escape sequence with a semi-colon</a>
