CS50 Understanding Technology Flashcards
What number system do computers use to represent info?
Binary
How do computers implement the binary number system to represent 0’s and 1’s
Using switches called transistors
A turned off transistor represents what number
0
A turned on transistor represents what number
1
How do computers map numbers to characters
Using ASCII or Unicode
What does ASCII stand for?
American Standard Code for Information Interchange
How many bits are in a byte?
1 byte = 8 bits
Why is Unicode preferred over ASCII?
It uses more bits so it can map to more characters
ASCII: 7bit
Unicode: 8bit, 16bit, or 32 bit
Why are more cores on a CPU better?
The more cores, the more tasks a CPU can do at once
What is hyper-threading?
A single core presenting itself as multiple cores to a computer’s operating system
What is a System on a Chip (SoaC)?
A CPU and more are all interconnected rather than attached to a motherboard (phones, tablets, game consoles, Raspberry Pi)
Fast access memory that only stores data when the power is on
RAM (Random Access Memory)
What does 1.94 GHz mean?
The CPU can perform 1.94 billon operations per second
Slower but permanent computer data storage
Hard disk drive (HDD)
How does a HDD work?
Magnetic particles are used to store data where north pole orientation represents 1 and south pole orientation represents 0.
Metal platters physically spin around while reading heads move back and forth reading data from the device.
How does a SSD differ compared to an HDD?
An SSD uses electronic flash memory and has no moving parts.
SSDs are faster than HDDs but may not last as long.
A tiny amount of memory (bytes) where numbers are stored for operations
Registers
Memory built into the motherboard
L1, L2, L3 cache
Wireless internet
Wifi
Allows devices such as wireless keyboards and headphones to connect to your computer with a limited range
Bluetooth
ISP
Internet Service Provider
How to do home networks connect to the internet via the telephone infrastructure?
Cable modem, DSL modem, or FIOS device
This device could have built in wireless connectivity for your devices or you may need an additional home router
IP
Internet Protocol
.#.#.
What numbers are used in an IPv4 address?
Four numbers separated by dots of the values 0-255
What does an internet protocol address do?
They uniquely identify devices connected to the internet
Any device connected to the internet has an IP address
DHCP
Dynamic Host Configuration Protocol
How does your home computer get an IP address?
It’s assigned by your ISP using DHCP
What does DHCP do?
DHCP is Software that ISPs provide to allow your router to request an IP address
How do devices on your home network get an IP address?
The home router supports DHCP and assigns IP addresses to your devices
DNS
Domain Name Service
What does DNS do?
It converts domain names into IP addresses
How do computers communicate over a network?
Packets of data in binary format
What happens if the ISP’s DNS server doesn’t know a website’s IP address?
It will ask another DNS server.
There are root servers called “Authoritative Name Servers” that will know an IP if exists.
Why wouldn’t you send a large image in one packet?
Sending it in one packet could block internet traffic so it will be split up into smaller packets
TCP
Transmission Control Protocol
What is TCP/IP used for?
A set of conventions computers and servers follow to allow intercommunication
What does TCP do?
TCP ensures packets can get to their destination by allowing a computer to request a missing packet.
TCP standardized numbers that represent different services called ports
Port 80
HTTP
HTTP
hypertext transfer protocol
Port 443
HTTPS
Port 25
What is a protocol?
A procedure or system of rules for doing something.
UDP
User Datagram Protocol
How do TCP and UDP differ?
UDP doesn’t guarantee delivery
Why use UDP over TCP?
Use UDP when losing some packets is acceptable.
Use UDP when you don’t want buffering
Example: Video conferencing like Facetime
Why is this IP format #.#.#.# limited?
Each number is 1 byte or 8 bits
4 bytes * 8 bits = 32 bits
2^32 = About 4 Billion IP addresses which is too limited for all the devices in the world today
Why is IPv6 better than IPv4?
IPv6 uses 128 bits so it has many more available IP addresses
Why do private IP addresses exist?
Because your device is not a server so the public doesn’t need to see it
Examples:
10.#.#.#
192.168.#.#
172.16.#.#
What is a Subnet mask?
It’s used to determine if a device is on the same network
The subnet mask separates the IP address into the network and host addresses.
Another name for a router?
Gateway
What is a routers purpose?
To forward data in the direction of a destination via other routers
What is the internet?
A network of networks each with their own routers
Can packets take different paths across the internet?
Yes. Because of internet traffic the fastest path may change
A program that sends packets to each router on a path to a destination, reporting the time it takes to reach that router
Traceroute
RJ11
Phone jacks
RJ45
Ethernet cables
Coaxial cable
Cable tv
Programs can synthesize the musical instruments for notes stored in these types of files
MIDI
An early sound format using uncompressed data storage allowing high quality
WAV
Audio format that uses compression to significantly reduce how many bits are necessary to store a song
MP3
It discards 0s and 1s that humans can’t necessarily hear
What does lossy compression mean?
You lose quality in the compression process
File format on iTunes
AAC
How do streaming services like Spotify work?
They don’t transfer a file to you but rather stream bits of information to you
The number of times per seconds we take a digital snapshot of what a person would hear
Sampling Frequency
The number of bits used for individual snapshots of what a person would hear
Bit depth
The number of bits necessary to store one second of music
Sampling frequency x Bit depth
What is a graphic?
horizontal and vertical pixels
RGB
Red Green Blue
No color
Black
All color
White
The most common format for RGB values
Hexadecimal (base-16, contains 16 digits)
How many bits are used to store a hexadecimal value?
4 bits
The largest number in 0-15 is 4 bits
What is a single row in a graphic image?
A scan line
Image type originally used by Windows
BMP (Bitmap)
Image type that only supports 8-bit color and is usually used for low quality images but can also be animated
GIF
Image type that uses 24-bit color and lossless compression
JPEG
Image type that uses 24-bit color and is typically used for high quality images
PNG
A bunch of images shown quickly in succession to create the illusion of motion
Video
What are video file formats?
Containers that store multiple types of data.
A video track, audio track, a secondary audio track (for different languages), closed captions, etc.
Video file format mostly used on Windows
AVI
Video file format often used to stream video or audio on the internet
MPEG-4 Part 14 or MP4 is a digital multimedia container format most commonly used to store video and audio, but it can also be used to store other data such as subtitles and still images.
Like most modern container formats, it allows streaming over the Internet.
Video file format used on MacOS
Quicktime
A device or computer program which encodes or decodes a data stream or signal
Codec
A spherical video image
3D video
Data that tells programs, applications, and browsers how to display the image
Metadata
Keeping people away from things you don’t want them to see
Privacy
What does it mean to delete a file off of a hard drive?
An operating system doesn’t actually delete it from the hard drive it only forgets that the file exists.
Little values a web server puts on a user’s browser
Cookies
What are cookies used for?
They are used to remember if a user has visited a website before.
What can happen if a hacker could obtains a cookie?
A session hijacking attack.
What happens if you clear browser history and cookies?
Your history will be wiped clean and websites will forget you visited.
How are session hijacking attacks prevented from wireless intercept?
Encryption scrambles the session cookie.
What does Incognito Mode do?
Browser history is automatically removed.
How many possible combinations for a 4 digit password with the values 0-9?
10 x 10 x 10 x 10 = 10,000 possible combinations
0000-9999
Why will you will have to wait for an amount of time if you have entered a bad passcode?
It slows down the process of someone guessing.
Software that stores on your phone or hard drive all usernames and passwords in an encrypted way
A password manager.
A device that displays a unique value that is synced with a server used for 2FA
An RSA device
Why is public WiFi sometimes dangerous?
Everything you do on http sites can be seen, but https or secure websites will still be private.
A server that allows you to establish an encrypted connection to communicate for you.
A VPN (Virtual Private Network)
Why can using a VPN can slow down speed?
Because we are encrypting data through an algorithm.
Software that helps prevent people from accessing your computer
A firewall
Cryptography using two keys, one public and one private
Public Key Cryptography
An attack where an adversary sends a somewhat official-looking email
Phishing
Malicious software
Malware
