CIS 107a: Introduction to Hardware Concepts

Chapter 9: Multimedia Devices and Mass Storage

 

Objectives:

This chapter introduces the student to computer hardware. The objectives important to this chapter are:

  1. Multimedia devices: sound cards, cameras, MP3 players
  2. CD drives and DVD drives
  3. Devices used for backups and faulty tolerance
  4. Troubleshooting multimedia devices
Concepts:

A working definition of multimedia is offered: video, audio, and animation in addition to standard text and graphics capabilities to simulate reality. Multimedia capability is assumed in most computers. The author discusses the history of multimedia capable processors, mentioning Multimedia Extensions (MMX), Streaming SMID Extension (SSE), and Hyperthreading.

Robot going up a rampThe text begins a discussion of sound cards on page 382. In the course of the discussion, it is necessary to understand the difference between digital and analog systems. As an example, a ramp is analog in nature, because it changes in height in an infinite series of values across its length. Consider the image on the right:
As the robot travels up or down the ramp, it constantly changes its altitude, rising to many different heights.

Sound works like the ramp. Sound is an analog phenomenon, because it is caused by constantly changing waves of air pressure.


Robot in front of staircaseConsider the staircase behind the robot in the next picture. If the robot were to climb the staircase behind it, it would pass through a quantized series of altitude changes. You can make a case for the robot passing through each possible height, but the stairs themselves do not. The stairs represent abrupt changes in value without gradual transition between changes. Staircases are by nature, digital, having a series of discrete values. Computer files are digital in nature, since they are collections of bits, but they can store digital values that represent an analog reality.

In order to turn an analog event like sound into a digital file, sampling is done. The value of the event is measured (sampled) many times over the course of the event. A file is created that contains the collected series of values. The more times per second a sound wave is sampled, the more accurate the digital representation of it can be. Sampling a hundred times per second is more accurate than sampling ten times per second. Also, the more values that our sampling can sense, the more accurate the representation. Think of a staircase as an approximation of a ramp. The more steps there are in the staircase (not higher, just more steps), the more it can approximate a curve or a straight line, instead of a series of abrupt changes.

Sampling is measured in Hertz (Hz), also called cycles per second. The text tells us that the sampling rate for a digital version of a sound should be twice the frequency of the highest pitch tone you will capture. Since the human ear can hear from 20 to about 22,000 Hz, the sampling rate for music CDs is typically 44,100 Hz, which can also be written as 44.1 kHz. As noted above, a high sampling rate is improved by a larger number of possible values: if we can tell the difference between more frequencies, we will record a more realistic version of the source. So, the more bits we use for each sample, the greater the number of different frequencies we can sense and record.

Most multimedia technologies involve some sampling and some conversion between digital and analog formats. Sound cards are usually capable of sampling and recording sound, as well as providing a means of sending the digital contents of sound files to speakers or amplifiers. The text mentions that most sound cards have a Sound Blaster emulation mode, because the Sound Blaster line of sound cards (from Creative Labs) is considered a standard. Some sound cards have several input/output jacks which are often color coded, as indicated in the text. Even more color standards are available on Wikipedia's page about Microsoft's PC 99 Standard.

  • light blue - standard color for Line In jacks; this connects to the line out port of a music/sound source, like a CD player
  • lime green - standard color for Line Out jacks; plug in standard speakers or headphones here (A similar color may also be used for a keyboard port.)
  • pink - standard color for Microphone In jacks (may also be red); plug in an input microphone here
  • gray - standard color for Rear Out jacks; connect this to a set of rear speakers (This color is also used for some Firewire ports, and another sound port below.)
  • black - side speaker output (This color may also be used for USB ports.)
  • yellow-orange - Center or Subwoofer jack
  • gray rectangle, rounded on one end - Sony and Phillips Digital Interconnect Format (S/PDIF) fibre optic port
  • orange (the text says yellow) - Sony and Phillips Digital Interconnect Format (S/PDIF) coaxial port

The first three colors are common on sound cards, the black and yellow-orange jacks are found on more expensive models. Sound cards often have a game device port as well. Remember that sound cards usually include a wire that runs from the card to the direct audio connection on your CD drive.

Digital cameras have replaced film cameras for many users. The text suggests that we can think of a digital camera as a scanner that scans the area we point it at. Cameras vary in the methods they use to transfer images to computers and printers. Many cameras have USB or IEEE 1394 connections, while others use Flash memory cards of several designs. Each type of Flash memory retains data without power, which makes it practical to swap out the cards without losing data. Some kinds of cards can fit into shells that can be read by floppy drives, but it is also common to see computers and printers that have slots to accommodate one or two kinds of Flash card.

The text notes that photographic images are often saved as JPEG or TIFF files. Other formats are also common, but these are understood by most image processing software.

Web cameras are discussed briefly, with a short set of instructions for using web cameras to set up a video conference.

MP3 players are devices to store and play MP3 sound files, made popular by users sharing music files on the Internet. Sound files are notoriously large, but MP3 files can be compressed to a ratio of 1:24, saving a lot of space. The MP3 standard evolved from the Motion Picture Experts Group (MPEG) which developed several compression standards for different kinds of files.

  • The MPEG-1 standard is used on audio CDs, and MP3 is based on it.
  • MPEG-2 is used for video on DVDs.
  • MPEG-3 is an example of a standard that was bypassed by its successor before it was used. We do not use MPEG-3.
  • MPEG-4 is used on the Internet for transmitting video.

This edition of the text discusses MIDI (musical instrument digital interface) devices. MIDI devices may connect to a computer through a USB port, or through a 5-pin DIN port (similar to an old style keyboard port).

Video capture cards are described as devices that allow us to input data to a computer from a video recorder, a video camera, cable TV, etc. Such cards may use USB or IEEE 1394 ports, and are often sold with video editing software.

A compact disk is read by a laser that senses pits and lands on the surface of the disk. A pit is a where another laser actually burned away some of the disk material. The pit should not go all the way through the disk, so I hesitate to call it a hole. When viewed from the other side of the CD disk, a pit will look like a bump. (See Marshall Brain's discussion on How Stuff Works. He has some very clear and informative animations for this.) A land is an area on the disk where nothing was burned away. A CD reader interprets the transitions from a pit to a land (or a land to a pit) as a 1 bit, and no transition as a 0 bit. (See reference.) Other devices, such as CD-R and DVD drives work a little differently. (See below.)

It is good to know that you can generally open a CD drive, even if it has no power, by inserting an unfolded paper clip into a small hole on the front of the drive. In testing this fact, I found that the distance that you must insert the paper clip varies. You may have to insert it two or more inches.

A CD drive may attach to your computer in a number of ways. Sometimes, a connection to a sound card is required. Some guidelines are offered about the order of installation of devices:

  • if your CD drive attaches to a SCSI bus, install the host adapter first
  • if your CD drive uses a proprietary adapter, install it and the drive together
  • if your CD drive attaches to an existing IDE channel, install as you would a hard drive

You may encounter jumper pins on a CD drive. On a SCSI CD drive, the jumpers may set the SCSI address, enable or disable parity checking, or enable or disable a terminator on the drive. On an IDE drive, the choices may be Cable Select, Master, or Slave. For an enhanced IDE drive, the choices may be primary master, primary slave, secondary master, or secondary slave.

Be aware that installing a CD drive on the same IDE channel as a hard drive may cause the hard drive to slow down.

The text warns that you may find a port on the CD drive that is meant to connect to an input port on your sound card. If so, do not mistake it for a power port. Applying power to this port can destroy the drive. In your text, it is identified by the label RGGL, standing for the Right and Left sound lines, and two grounds (Right, Ground, Ground, Left).

A CD-R (CD-Recordable) drive is one that is meant to be able to write to a CD-R disk. These disks are different, in that the drive does not actually melt pits into the disk. This laser causes a change in chemicals on the disk that changes how they reflect light. Such a change can only take place once for any bit on the disk. Like a regular CD, a CD-R disk is recordable once.

This is similar to a CD-RW drive (CD-Rewriteable), which is able to change the chemical state on its own kind of disks multiple times. A CD-RW disk is rewritable, information can be recorded to it several times.

DVD (Digital Video Disk or Digital Versatile Disk) standards allow the storage of about 8.5 GB of data per disk, compared to 600 to 700 MB per CD. DVD data is packed closer together, and DVDs can have two layers. (If only one layer is used, a DVD may only hold about 4.7 GB of data.) Several standards exist for recordable and rewritable DVDs, notably DVD-R and DVD+R. Both are common, but often they are not compatible.

The chapter changes topics to discuss backups. Any system that holds important data should be backed up regularly. The question is simply how to do it. The chapter discusses several alternatives:

  • tape drives - internal or external, intended to make copies of hard drives
  • removable hard drives - can be used as primary hard drive or to make a copy of the primary
  • jump drives - typically small compared to hard drives, ranging from 16 MB to 1 GB, used more for convenience to transport files
  • Zip drives - typically 100 MB or 250 MB capacity, displaced by jump drives due to their ease of use (no special hardware required)

RAID systems use multiple hard drives for better performance, fault tolerance, or both. Follow this link to a nice summary of RAID level features not listed in these notes.
RAID levels and features:

  • RAID-0 - Disk striping writes to multiple disks, does not provide fault tolerance. Performance is increased, because each block of data in a stream is written to the next device in the array. Failure of one device will affect all data. This will provide a performance enhancement by striping data across multiple disks. This will not improve fault tolerance, it will decrease fault tolerance.
  • RAID-1 - Mirroring and Duplexing provide fault tolerance by writing the same data to two drives. Two mirrored drives use the same controller card. Two duplexed drives each have their own controller card.
  • RAID-5 - provides fault tolerance by a different method. Data is striped across several drives, but parity data for each stripe is saved on a drive that does not hold data for that stripe. Workstations cannot use this method. It is only supported by server operating systems.

Students should review the troubleshooting information at the end of the chapter, to get tips for several kinds of problems.