Computers Notes

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Hardware

The main components of a computer are:

  • CPU (Central Processing Unit)—the brain of the computer; it does all the calculations and data processing. A computer may have multiple processors, a processor may have multiple cores (acting like multiple processors in one package), and other devices may employ processors to reduce the demand on the CPU, e.g., a GPU (Graphics Processing Unit). Having multiple processors or cores may not make single tasks faster, but they can allow multiple tasks to be carried out at the same time (e.g., processing data and updating the display to show you its progress). The CPU’s main parameters are:
    • Model (e.g., Intel Core Duo) and
    • Clock speed (measured in Hertz), in addition to
    • The number of processors or cores.
  • Hard Disk Drive—this is where the computer stores data. Its main parameter is its capacity in Bytes, but its connection speed and internal access time become important in high-demand and live applications.
  • RAM (Random Access Memory)—this is temporary storage, like “scratch paper” for the CPU to use while it does its calculations. It can be accessed much faster than a hard drive, but it is not for permanent storage. Its main parameter is size, but its connection speed becomes more important in high-demand and live applications. More RAM won’t make a CPU work faster, but it will keep from slowing it down, as it would need to spend less time moving data to and from the hard drive.

More abilities are added to a computer via expansion slots (to install expansion cardsinside the computer’s case) and peripheral ports (to connect to external devices). Most devices fall into these categories:

  • Display adapter—connect your computer to an external display like an LCD monitor or projector. Most computers have one built in, but it is structured like an expansion card. Most display adapters can support one or two distinct video outputs. Its main parameters are:
    • The number of displays and connector formats supported,
    • The maximum resolution of the video signal, and
    • The amount of RAM on the card dedicated to graphics processing.
  • Audio interface—audio input and output. Most computers have one built in, but it is usually low-quality consumer grade, e.g., high impedance microphone inputs and unbalanced outputs. Some microphones and guitar cables have audio interfaces built-in, but they are usually lower (consumer) quality. The main parameters of an audio interface are:
    • The number of input and output channels,
    • Connection types supported,
    • Its resolution (in terms of maximum sampling rate and bit depth),
    • Extra features like microphone preamplifiers and phantom power, and
    • The bit rate of its connection to the computer, i.e., how much data it can send or receive at once.
  • MIDI interface (Musical Instrument Digital Interface)—to connect to music and audio hardware.
  • Network interface—this is how a computer connects with other computers or establishes wireless connections to devices. Its main parameters are the networking protocol used and the bit rate:
    • Ethernet—a hard-wired connection (i.e over a cable), making it cable of the highest data transfer speeds (bit rates), the longest ranges without significant signal loss, and the least susceptible to electromagnetic interference. Its main parameter is the maximum bit rate supported, usually either 10, 100, or 1000 Mbit/s (megabits per second—not megabytes)
    • Wifi (IEEE 802.11)—a wireless connection common for general networking (e.g., world wide web browsing). Some mobile devices can connect to your computer if they are both connected to the same wireless network. Its main parameter is the specific networking standard used (e.g., 802.11g, …n, etc. or just “wireless n,” etc.). Each standard has a different effective range and bit rate (typically ranging from 11 Mbit/s to about 7 Gbit/s).
    • Bluetooth—a wireless connection typically used to connect to peripherals like speakers with typical but rates ranging from 1 Mbit/s to 24 Mbit/s.
  • Input devices or controllers often send on/off data from switches, so they don’t need very fast connections. The most significant properties of an input device are the control features it offers (buttons, sliders, sensors, etc.), whether it is wired or wireless (usually USB or Bluetooth), and whether it requires an external power supply or can receive sufficient power through its data connection (like USB).
    • QWERTY keyboard (for typing text)
    • Mouse, track pad, track ball, etc. for controlling the cursor
    • Game controllers like game pads, joy sticks, Nintendo Wii Remotes and Microsoft Kinect sensor
  • Storage devices—including external hard disk drives and solid state flash memory drives
  • Connector formats. Sometimes connection format versions are updated so that the same physical connector can support better performance or more features, usually indicated by a version number (e.g., USB 3) or a reference to bit rate (e.g., Gigabit Ethernet, FireWire 800).

 Software

Software is data that instructs the hardware on what to do. The main types of software are:

  • Operating System—this is the main platform, dictating how a computer does its job. Most operating systems are fully functional, so the main factor for deciding among them is interoperability—what applications and hardware will work with it. The most common operating systems are:
    • Apple Mac OS—the operating system for Apple computers. Because of its exclusive use with one hardware manufacturer, Apple has had more control over both, often allowing simplifying matters by limiting choices, but that simplification may give users less control in the exact way they make use of their computers and devices.
    • Microsoft Windows—the operating system for personal computers evolving from IBM. Because of this evolution, many manufactures make hardware supporting Windows, but this degree of choice can result in requiring more research and customization on the part of the user to ensure everything works together without conflict.
    • Linux—a free, open source operating system. Because its source code is open to the public, it is very customizable and there are many variations on it. The tradeoff for this flexibility is that it often requires a deeper level of control from the user. Also, because it is these are commercial products, there is no vendor like Apple or Microsoft to be responsible for releasing updates to fix bugs or security holes. Applications that support Linux are also often free and open source with the same trade offs.
    • Mobile operating systems like Apple iOS, Google Android—used for smart phones,  tablets, and similar devices. They are often watered-down versions of the operating systems above, with limitations to enable simple operation of the device’s main features. Each hardware manufacturer chooses a different operating system and the amount of control it allows the user to take in customizing its settings and installed applications.
  • Device driver—many expansion cards and peripherals use communication standards that are fully compatible with an operating system, but some require their own software to enable the operating system to make full use of the device. This software is called a device driver. It is specific to each manufacturer, model, and operating system.
  • Application—this is a program that enables the computer to do something useful, for example creating and editing text, graphics, audio, transmitting data via the internet, or playing games. An installer is a specific kind of application that installs a device driver, application, or plug-in on a computer system, to make it ready for use.
  • Plug-in—this is software that can’t do anything on its own but instead adds functions to a software application, called the host application. This is common in audio editing: an audio editing application like Apple Logic can perform certain functions on its own (natively) and you can install plug-ins that add other functions like specific varieties of effects processors or synthesizers (called virtual instruments).
  • File—this is data stored on your computer. It may be an application file (the data that instructs the computer how to function as an audio editor, etc.) or a data file containing information you have created or can view or edit using an application, e.g., the audio you recorded or the text you wrote.

Media

Media refers to the data used for communicating, e.g, text, audio, or graphics files. Each media type has different characteristics an concerns.

  • Text—The letters, numbers, and symbols used for basic textual communication are well standardized and can be transmitted consistently with small file sizes. Adding metadata like font sizes and layout positions will increase the file size (although not significantly) and be more subject to variations in appearance across different viewing applications. For example, these properties explain why a text-only Wikipedia article typically loads faster than a YouTube video, but why both might appear slightly different in different web browsers.
  • Audio—Remember that sound requires changes over time, changing at rates between 20 Hz an 20,000 Hz, digital audio requires a steady and fast stream of data.   Its main parameters are:
    • Sample rate—how often the signal is updated. A wave can be misread if it is not sampled at least twice during one cycle (imagine charting the position of a clock’s second hand at a rate of one data sample every 59 seconds: it will appear to move backwards slowly—an erroneous reading due to a poorly chosen sample rate). The sample rate of CD-quality audio is 44,100 Hz, a good standard for humans, since it is at least twice our upper hearing limit of 20,000 Hz. Cheaper electronics (like toys) may try to get away with lower sample rates. Much higher sample rates allow greater precision in digital processing (e.g., avoiding errors caused by rounding numbers) but they result in larger file sizes.
    • Bit depth—each sample measures the amplitude of the audio at that time, represented by a number. The bit depth is the number of digits (a “bit” is one “binary digit”—one digit in a binary umber system that computers use) used to describe the amplitude. CD-quality audio uses 16 bits. Each bit doubles the dynamic range of a signal (the difference between the loudest and quietest amplitude it can represent), so 16 bits gives us about 96dB of dynamic range. However, we can hear ranges of 120 dB or more. Like sample rates, higher bit depths allow for more precise calculations during processing but make file sizes larger.
    • Number of channels—Most music is recorded in stereo (stereophonic), meaning two channels: left and right. Surround sound files will have more channels. Adding channels increases file size.
    • A sample file size calculation: at CD quality, 1 minute = 44,100 samples per second * 16 bits per sample * 2 channels  * 60 seconds = approximately 10 MB per minute (one Byte = 8 bits, and one MegaByte = 1024 Bytes), or when transmitted, a bit rate of 1.411 Mbit/s.
  • MIDI—Instead of transmitting or storing digital audio, a MIDI file stores instructions for performing, e.g., Note On, Note Off, and descriptive data like the Velocity (volume) of each note and the value of Continuous Controllers for musical expression. This makes file sizes very small and requires the hardware or applications to create digital audio by “performing” the instructions in the MIDI file.
  • Graphics
    • Raster images—this is the most common type of graphics file, in which an image is divided into columns and rows of pixels, each pixel contains one to four color channels to determine its color, and in the case of video, this still image constitutes one frame of a moving image. Its main parameters are the following, all of which increase file size as they increase in value:
      • Resolution—the number of pixels in a still image or single frame of video, expressed in columns and rows (e.g., 1920 x 1080), just the number of rows (if the aspect ratio of width to height is standardized, as in 1080p for HD video), or total number of pixels (e.g., 2.1 megapixel, a common convention for cameras).
      • Number of color channels—a file with only one color channel is grayscale, only indicating brightness. A typical color file requires three channels: Red, Green, and Blue. Some file formats support an additional channel specifying transparency, called alpha. Cameras don’t measure this, but applications can use it to aid in compositing images.
      • Color depth—like bit depth in audio, this specifies the level of precision in each color channel: how many binary digits are used to describe its value. 8-bit color yields 256 shades each of red, green, or blue.
      • Frame rate—the number of still frames meant to appear in one second, in order to create the illusion of movement. 24 Hz or fps (frames per second) is standard for film, 30 Hz for video. Like the sample rate in audio, higher frame rates allow for a better quality and reduced unwanted artifacts during processing but increases file size. Video frame rates may called progressive scan or interlaced. Progressive scan video draws each line in order, the same for each frame, like you might expect. Interlaced video will only update every other line with each frame; it’s a way of getting some of the effects of a higher frame rate while doing half the work of a progressive scan (in other words, progressive scan is generally better).
      • A sample size calculation: one frame of 1080-line HD Blu-Ray quality video = 1920 columns * 1080 lines * 3 color channels * 8 bits per color channel = 47.5 MB per frame
      • Another sample: one minute of 1080-line HD Blu-Ray quality video = 47.5 MB per frame * 24 frames pr second * 60 seconds = 66.75 GB per minute or in transition, a bit rate of 1,194 Mbit/s. Note: the Blu-Ray standard bit rate is really 40 Mbit/s—see Compression below to see how this works.
    • Vector graphics—this is a file that, like MIDI, describes how to draw the desired image (in terms of points, angles, and colors for large areas) instead of representing it in pixels. Also like MIDI, its size will be much smaller than a raster image, but it places demands on the processor to realize the image. Vector images have no resolution; they can be scaled continuously until they are rasterized by the output device, e.g., printer or monitor screen. Vector graphics make it simple to display perfect shapes but difficult ot achieve photorealistic detail. Adobe Illustrator is a vector graphics editor for 2D (flat, still) images. Vector graphics are used for fonts, Flash animations (not videos) and for 3D models.
  • Compression—Look at the bit rates of the media in this section and compare it to the bit rates of network and connection protocols above. Many connection speeds aren’t fast enough for full quality media, especially with cheaper consumer devices and for transmission over the internet, where network traffic also affects transmission speeds. So, it is common to compress media using one of several techniques called codecs (for “encode” and “decode”). Data compression can take some pressure off storage and transmission, but it is more demanding on processors to encode the data when recording and to decode it when playing it back.
    • Lossless compression—it is possible to reduce file sizes and allow them to be restored to full quality, for example looking for repeated patterns in the data and replacing them with short abbreviations and one “key” to decode them. However, there aren’t many lossless codecs, and they typically only reduce file sizes by half.
    • Lossy compression—most codecs are lossy, meaning they have to throw out some detail in the original media. Hopefully, it’s not detail that you would miss. Typical approaches are to cut out high audio frequencies or quiet details in sound or to make solid fields of a single color wherever pixels are already very close to the same color (this is often noticeable in black splotches in video). Dramatic reductions in file size are possible, but they result in great losses in quality. Lossy formats should be avoided whenever possible in production and professional work.
  • File formats
    • Uncompressed or with lossless compression, full-quality, suitable for production/editing
      • Audio: WAV, AIFF, or FLAC
      • Still graphics: BMP, GIF, PNG, RAW (which sometimes is only “near-lossless”)
    • Compressed, suitable for consumers
      • Audio: MP3
      • Still graphics: JPEG, sometimes GIF, PNG
    • Video: Since compression is so often necessary for video but we are highly sensitive to visual detail and different codecs perform better with different kinds of content, there are many, many video codecs to choose from. Video files are identified by their container, e.g., AVI, MOV (Apple), MPEG, WMV (Windows), and may employ any of several codecs. The container specifies what metadata is stored where within the file—metadata is information about the file itself, including resolution and the codec that should be used to play it.
    • Containers for other media (that could be uncompressed, lossless, or lossy, depending on the codec):
      • Audio: M4A
      • Still graphics: TIFF
    • Metafiles, suitable for consumers—PDF (Portable Document Format) is a metafile, a way of packaging several different kinds of media files into one. A PDF can include text, vector graphics, and raster graphics. It is convenient to deliver media in a single file, but since it relies on the viewer application to assemble all the media within the file, different viewer applications may not display it identically. RTF (Rich Text Format) is another metafile format.
    • Digital Rights Management (DRM)—some file formats include metadata and protocols for viewing that attempt to limit using the file in certain ways, like duplicating it or playing through devices like projectors, in order to avoid users violating the owner’s copyright over the material.

Making Decisions

These are some guidelines for making hardware and software decisions based on your intended use. Keep in mind that as time passes and technical abilities rise, software and media demand more resources, so aiming higher than the minimum requirements will make your resources viable longer.

  • Determine what applications (or at least what types of applications) you plan to use.Find system requirements published by the manufacturer, and use that as a minimum guide to your CPU, RAM, and storage specifications.
  • Consider the dimensions of the media you’ll be dealing with: audio, video, resolution, number of simultaneous audio or video signals. Use this to determine suitable hard disk storage capacity and connector formats and network protocols for transmitting files. Use these requirements to find suitable expansion cards and peripherals. Check the system requirements of those items to adjust the minimum specifications of your computer.
  • Consider the number of expansion cards and peripherals you need, and find a computer with enough expansion slots and peripheral ports.
  • As mentioned above, more RAM won’t make your computer run faster, but it will prevent more functions from slowing it down. It is wise to buy a computer that has room to add more RAM later, so you can lower your initial cost and still upgrade one time, before buying a whole new computer.
  • Regarding cost: better hardware is always available, but there is usually a sharp increase in price at some point (e.g., watch the dollars per Gigabyte ratio for your RAM options): the point just below that jump is usually an optimal compromise. Still, be sure that point will actually meet your needs, and aim high within reason, to ensure your system will remain viable for longer.

Protecting Your Computer

  • Surge protector—attempts to block or divert spikes in electrical power, e.g., caused by large equipment shutting off or lightning
  • Power conditioner—attempts to provide “clean” power: consistent voltage and current alternating with a pure sine wave shape, in order to avoid strain on equipment
  • UPS (Uninterruptible Power Supply)—a rechargeable battery to avoid or delay sudden power loss. If a blackout lasts for more than a moment, a UPS will give you enough time to save files and shut the computer down safely before losing power.
  • Static electricity—static shocks can damage electronics, so try to discharge yourself by touching a large metal object before touching your computer, and make sure it is plugged in and grounded (easy to forget for portable computers and mobile devices) before connecting it to the house PA or projector.
  • Cooling—CPUs generate a lot of heat, so cooling fans, vents, and the space around them must be kept clear for air to flow.
  • Physical damage (drops, liquids, dirt)—moving parts like hard disk drives and the many delicate connections inside your computer can be broken if dropped or hit hard. Liquids can cause short circuits. Dirt can block cooling measures or corrode connections and components.
  • Theft—take measures to physically secure your computer. Many computer cases and peripherals support Kensington format lock cables.
  • Malware—files received from sources you don’t trust may contain software that may try to steal or destroy your data or commandeer your computer to attack others. Seek anti-malware software applications and practice common sense when exposing your computer to other computers and files. In performance situations, however, be prepared to minimize activity by anti-malware software so it doesn’t interfere with performance.
  • Software updates, BUT…—vendors often release updates to software in order to fix bugs or security holes. In general, you always want to keep your software up to date, but before you update anything, check for interoperability problems that might result (e.g., does your video editor support the new version of the operating system yet?), and avoid updates up to a month before a performance or deadline when you can. Updates may cause tricky interoperability problems that could wreck your project.
  • Firewall—use your operating system’s security settings to restrict incoming network connections from other computers to avoid attacks.
  • Backup—make copies of your installers, software license information, and media files in case of loss due to hardware failure, physical damage, theft, or malware. Fixed storage media like DVDs aren’t keeping up with media file sizes, so this can be tricky. Consider a constant backup service like cloud-based Carbonite, Crash Plan, Dropbox, or Google Drive in addition to a long term archive approach like large external storage drives kept in a safe place or an internet hosting service like DreamHost or Go Daddy.