1. Computer Review
Video and Sound Cards

2. Integrated Card Overview
Both sound and video cards are used to expand upon functionality typically already on the motherboard
The motherboard’s video and audio cards are called onboard or integrated cards
These use part of the computer’s memory and sometimes it’s processor to function
Usually the cheapest and least powerful solution
Good for low-stress systems, like data processing workstations
Motherboard documentation can tell what onboard components are offered, or the ports on the back panel will let us know

3. Dedicated Video Cards
Consist of a GPU, or graphics processing unit, very high-speed dedicated graphics memory, and, depending on how powerful the card is it could also include a heatsink and fans.
A high-end video card will likely be the second hottest component in your computer, after the CPU
Can be very expensive, ranging from $30 all the way up to $1000

4. Display Connectors
Speed and price aren’t the only factors to consider when selecting a video card. Display connectors are very important since that will limit what can be connected to the computer
Popular ports include VGA, DVI, S-Video, HDMI and display ports
While adapters can be used, it’s best to match the video card port to the display device port

5. Display Capabilities
After making sure that the card has the correct video ports, it is important to make sure that the card is powerful enough to perform the job it is intended for
Some parameters to consider are:
resolution (the number of pixels output to the screen)
refresh rate (number of times the screen is refreshed each second)
support for multiple monitors
Support for Virtual Reality hardware

6. Graphic Card API
Software will communicate to the GPU through an API, or an Application program Interface
DirectX and OpenGL are two of the most common APIs for 3D graphics
Because of differences in which API is used, as well as differences in driver capabilities, different graphics cards that show comparable specifications may behave drastically different in different applications, and may even have drastically different performance when paired with a different brand CPU
For example: A graphics card that uses memory very efficiently could out perform a more powerful card that has more memory and a faster processor for a program that has poor memory use optimization

7. Dedicated Graphics Card Specific Issues
While the parameters we discussed so far affect both integrated and dedicated graphics cards, there are two factors to consider that only apply to dedicated graphics card
Bus Type
You need to make sure that the motherboard has the right expansion bus type for the card. Most dedicated video cards use PCIe x16, but depending on the make and model, PCI or PCIe X1 could be used
Multi-GPU Support
Some video cards have the capability to link together identical video cards to share the graphical processing load. This is very expensive and typically only done to support high end video processing, running multiple high end programs at once, or to support a large number of multiple monitors

8. Making Sure the Rest of the Computer is Compatible
After making sure that the motherboard and graphics card match, there are still system requirements to match
You have to make sure that your computer has a compatible operating system, and in higher end cards, enough ram
For higher end graphics cards you’ll have to make sure your power supply has the correct connections and is outputting enough watts. High end graphics cards can put a lot of strain on weaker power supplies. Weaker graphics cards will simply accept the power coming from the PCI port

9. Selecting the Correct Graphics Card
When selecting a graphics card to run specialized software such as games or image/video editing software, use minimum and recommended system requirements to determine an appropriate graphics card
Be careful of bottlenecks! Just because your graphics card is powerful enough, you may not be able to run the software without the correct operating system, enough RAM or a powerful enough processor

10. Specialized Graphics Card Abilities
Aside from adding specialized graphics processing, there are other capabilities that graphics cards can provide
TV tuners can allow your computer to accept TV Input to watch and record live TV
Video capture cards allow for computers to accept video signals from a third party, such as a video game console

11. Audio Cards
Audio cards were once a necessity for any computer that wanted to run games or output video, but modern computers only need audio cards for specialized purposes
Such as
Outputting 7.1 sound for use as a home theater
Sound recording
High quality gaming audio

12. Analog Audio
Sound is an analog signal naturally. It is transmitted through the air in the form of sound waves caused by air vibrating
This creates alternating regions of high and low pressure, which can be mapped over time like this

13. Digital Audio
The process a computer uses to store these analog signals as digital data is called sampling
How accurate this digital data matches the analog signal is called its fidelity
There are two different factors to a digital signal’s fidelity:
Bits per sample affect how many different values there are to approximate the value of the sounds amplitude
Sample rate is how often the analog signal is sampled. The more often the sound is sampled, the larger the file but the more accurate the graph would be

15. Audio Compression
The goal of audio compression is to retain the fidelity of the audio file while reducing its size
There are many ways to do this. Most compression algorithms cause the file to lose some of its data. This is called lossy compression. Compression algorithms that maintain perfect fidelity from the original file are called lossless compression
An example of lossy compression mpeg2 audio layer 3 (or MP3) can compress an audio file to 9% of its original size, whereas FLAC (free lossless audio codec) can typically only reduce the original file to 50 or 60% of its size

16. Choosing an Audio Card
Just like choosing a video card, selecting an audio card with the proper ports is important
Most audio cards will have multiple 3.5mm jacks for audio, including line in, microphone and speaker out. These will typically be color coded and have an appropriate symbol or label next to the port
Audio cards could also have a coaxial or optical port for higher quality digital sound
The number of channels an audio card supports is also important, as each distinct speaker is going to be one channel. Most cards, including integrated audio cards, will include 2 channels, while higher end cards will include support for up to 7.1 channels. 7 speakers and a subwoofer on an LFE channel (Low Frequency Effect)

17. Troubleshooting Audio Devices
Like any other troubleshooting, go from least invasive to most
First, check that the sound is un-muted and the volume is raised, both at the software level and at the hardware level
Make sure that the speakers are connected to the correct port on the computer and, if necessary, plugged into the power strip
If these steps do not work, then it is time for more advanced troubleshooting
Use playback devices from the sound applet to see if the correct audio device is chosen and enabled
Use the device manager to see if the hardware is detected and configured appropriately
If only certain audio sources won’t play, like certain videos or sound files, then make sure that the correct codec (compressor-decompressor) is installed

18. Introduction to Networks
Wireless Architecture

19. Wireless Network Devices
Before we discuss a wifi network’s architecture, let's look at its components
STA
A device with a wireless network card installed is often called an STA, or a station. Sometimes we refer to the host itself as the STA, but actually it's the wireless network interface in the host
This means you could have two wireless network interface cards in one host, in which case it would be identified as two different STAs or stations AP
An Access Point, sometimes called a wireless AP (WAP), is the device that coordinates all communications between wireless devices, as well as the connection to the wired network
Many WAPs also include ports to connect the wireless network to the wired network
It acts as a hub on the wireless side and a bridge on the wired side
It also synchronizes the stations within a network to minimize collisions

20. Ad Hoc Network
There are two different modes of operation in a wireless network.
In an Ad Hoc network multiple wireless devices are configured to communicate directly with each other
An ad hoc network uses a physical mesh topology. If multiple devices need to send information to each other, they communicate directly with each other in a mesh topology. However they use a logical bus topology
As you add devices, each device has to keep track of every other device within the network to communicate. Because of this, ad hoc configurations aren't widely implemented
They have limited scalability and require more work to administer, especially if we want to connect to a wired network. Typically, they are only used to establish temporary connectivity, such as to copy data from one system to another

21. Infrastructure Network
An infrastructure network uses a wireless access point, unlike ad hoc mode
The wireless access point acts like an Ethernet hub, meaning an infrastructure network uses a star physical topology with the access point in the middle
A device that needs to send data to another device sends it first to the access point, and then the access point forwards that message on to the intended device. Since there is no way to send a message to a specific host, the network is using a logical bus topology
You can easily add hosts without increasing administrative efforts, and the AP can be connected to a wired network easily, allowing clients to access both wired and wireless hosts
An infrastructure network is recommended for all but the smallest of wireless networks

22. BSS
The smallest networking unit of a wireless network is called a BSS (basic service set)
The BSS is a collection of all the devices that communicate together using the same channel, or portion of the wireless frequency that all devices use
If you are using an ad hoc network, the BSS would include all of the individual wireless devices that communicate together, and in an infrastructure network, the BSS includes all of the wireless devices and the wireless access point
All devices that communicate with a single access point are in the same BSS

23. Extended Service Set
In large environments, you can implement multiple wireless access points within the same wireless network. All clients and the wireless access point they connect to form a separate BSS, and a collection of multiple basic service sets is referred to as an extended service set (ESS). The ESS is identified by a name that's called the service set identifier (SSID). This is what we commonly refer to as the network’s name
Remember that the key difference between the two BSSs is that they use a different channel, even though they are on the same network
Wireless clients who want to connect to the ESS are configured with the SSID and look for an access point that is configured with the same SSID

24. Roaming
This configuration allows a wireless host in one BSS to roam, or move, to another BSS. The wireless client is configured with the SSID and connects to the access point using the appropriate channel, and identifies the access point using its basic service set identifier (BSSID)
The BSSID is usually configured automatically through the AP MAC address
When a wireless client joins the network, it uses the SSID to find an appropriate access point within its location. It automatically chooses the channel to use for that BSS and then communicates directly with the AP
When the wireless client moves outside of the range of the current BSS, it uses the SSID again to locate an access point in range that's part of the same SSID. In this case, a different channel will be used, so the client will change channel to communicate with the other BSS. It will use the BSSID to

25. The Backhaul
You can connect the ESS together with a wired network. In this case, the wireless access points are acting as bridges connecting the wireless clients to the wired clients on the wired network
The link between the access points and the wired network are called the backhaul. The backhaul allows the wireless access points to communicate with the wired clients and other wireless clients in a separate BSS.
This can also be called the distribution system

26. Management of Media Access
Wireless networks use a physical star topology centered on the AP, but they use a logical bus topology. This means a message sent to one device is actually received by all devices
For this reason, wireless networks only operate in half-duplex mode. Devices can send and receive, but not at the same time, they have to take turns using the transmission medium
Wireless networks use the Carrier Sends Multiple Access Collision Avoidance (CSMA/CA) media access method to keep data collision at a minimum
If you remember the media access method used by Ethernet on a hub connection, CSMA/CA will look very similar
When a wireless device needs to transmit on the network, it first senses the media by listening to see if any other device is already transmitting

27. Request to Send Message
If the medium appears to be free, the transmitting device sends a Request To Send message (RTS) to the receiving device. The RTS message indicates that the sender would like to transmit a message, and includes information such as the duration that the message will take to transmit
Remember that, on a wireless network, all messages transmitted can be received by any other devices in the area. This means that if one host sends out an RTS message, all hosts on the BSS will know that there is a device out there that will be transmitting for the specified period of time
Host use the time period within the RTS to know how long the transmission medium will be busy

28. Clear to Send and Acknowledgement
When the destination device receives the RTS, it transmits back a Clear To Send (CTS) message
The CTS message indicates that the device is ready to receive and effectively locks in the time that the sending device is going to use the transmission medium
After the RTS and the CTS, the device sends the messages to the destination device. Then it waits for an acknowledgement (ACK). If the acknowledgement isn't received, then the sending device assumes that there was a collision on the network and it retransmits the original data
After the time specified in the RTS has expired, the other wireless devices can go through the same process to see if it's okay for them to send. They'll sense the media, send an RTS, wait for the CTS, send the data, and receive the ACK