Peripherals

• Everything outside the "core" of the computer (CPU and RAM) is called a peripheral.
• Peripherals connect to the motherboard either through a connector built onto the motherboard, or through a connector built into an interface board which itself connects to the motherboard.
• there are a few standard types of wired connectors, including
• Serial, older standard for mouse and external modem and other "slow" devices
• USB (Universal Serial Bus), increasingly popular for variety of slow and fast devices
• FireWire, another increasingly popular serial connection for fast devices
• Parallel, older standard for printers and other "faster" devices
• RJ-45, telephone-like connectors for use with high-speed networks
• We will look at peripherals as three categories:
• input devices, intended primarily for bringing data into the computer
• output devices, intended primarily for data/information output from the computer
• storage devices and media

Input Devices

A major issue is digitizing: converting image, sound, movement, position, etc into binary (digital) form

Digital camera:

• image captured on rectangular grid of charge-coupled devices (CCD)
• each CCD represents one pixel.
• CCD transforms light into signal which is digitized into 24-bit (3 byte) code representing its color.
• Each image has millions of pixels (camera resolution given in megapixels).
• Image saved in raw format of 4 megapixel camera requires 12 megabytes to store (3 times 4 million).
• Image saved in compressed format, such as JPEG, will require much less (about one-tenth as much)
• JPEG compression loses a little quality and resulting size will vary depending on complexity of image
• Note that digitizing occurs in the camera because it has its own storage

The web page http://www.immigration-usa.com/html_colors.html has a chart showing selected colors and their 24-bit numerical codes (given in hexadecimal, base 16) used by HTML, the language for writing web pages.

Output Devices

Identification and brief discussion of output devices such as printers, monitors, sound card with speakers, MIDI

Color: additive (color producing devices like monitors: red/green/blue) and subtractive (color reflecting devices like printers: cyan/magenta/yellow) (demo of both) - will return to this in chapter 6 on graphics and multimedia

Other storage devices and media

• Examples are floppy and Zip disks, CD-ROMs, tapes.
• These are removable, and therefore easily distinguishable from the devices that operate them.
• Hard drives and some other devices use media which are permanently attached to or an integral component of their operating device.

• floppy disks of various sizes
• a floppy disk drive
• some platters from an old hard drive
• a newer hard drive
• a couple types of magnetic tapes

By contrast, RAM is volatile. When the power is turned off, it loses all its values.

Magnetic Disk Storage

• disks are rotating devices. Typical hard drive rotates at 5400 or 7200 RPM
• Data are stored in concentric circles. Each such circle is called a track.
• there are also dividing lines that radiate out from the center to the edge. These divide the disk surface into sectors.
• the surface is thus sliced up into slightly curved rectangles
• a specific address on the disk is identified by its track number and sector number combined
• the read/write head is mounted on an arm which can slide back and forth from the edge of a disk toward its center. This movement selects the track. The rotating disk allows access to the desired sector.
• the disk is thus a random access device too
• hard drives normally have 2 or more platters that allow multiple bits to be read/written at once.
• disk storage is usually characterized by its capacity, expressed in MB or GB, or perhaps TB (terabytes, or trillions of bytes)
• it is secondarily characterized by rotational or data access speed

Magnetic Tape storage

• data are stored as magnetic charges on ribbons of tape
• one piece of data is stored across the width of the tape
• tapes are sequential access, not random, because to get from address X to address Y, every address on the ribbon between X and Y has to pass across the read/write head.
• tapes permit slower access than disks
• tapes are cheaper per unit of storage than disks, so tapes used for backup and long term storage

Optical storage

• data are read and written using lasers (concentrated light beams) rather than magnetic devices
• data are stored as physical "pits", with a pit representing 1 and no-pit representing 0
• thus it is fundamentally harder to write than it is to read
• hard disks have much higher capacity per square inch of surface
• hard disks are also much less portable

• CD-ROM : Compact Disc - Read Only Memory
• CD-R : Compact Disc - Recordable (write once)
• CD-RW : Compact Disc - Re-Writable
• DVD-ROM : Digital Versatile Disc - Read Only Memory
• DVD-R, DVD+R : Digital Versatile Disc - Recordable (write once)
• DVD-RW, DVD+RW : Digital Versatile Disc - Re-Writable

• To handle "-ROM" operations requires only a weak laser to detect pit/no-pit.
• To handle "-R" operations requires a second stronger laser to "burn" pits
• To handle "-RW" operations requires a third laser (stronger than read, weaker than write) to "erase" pits
• There are several competing DVD writeable and re-writable formats, so be wary

• Because the media are removable (like floppies) their capacities are fixed.
• CDs hold about 650 MB of data. The basic DVD holds 4.7 GB (more focused laser) but this can be doubled by using a second layer or both sides, and quadrupled by using both.
• CD drive read speeds are rated as a multiple of how much faster it reads data compared to the first generation of CD drives (150 KB per second). A "32X CD-ROM" reads data up to 32 times faster than the original drives.
• CD-RW drives often have three sets of "X" speeds, listing, in order, the recording speed for CD-Rs, the recording speed for CD-RWs, and the read speed (e.g. 6X/4X/24X).

Solid state storage