Chapter 9 I/O Peripherals

Hard Disk Layout

Constant Angular Velocity l Number of bytes per sector is same regardless of track position l Since disk rotates at fixed speed, transfer time is constant l Density of bits per track varies from track to track l Hard/floppy disks store data in CAV format

Accessing Data

Disk Characteristics

Block (Sector) Format 512 bytes/sector IRG

Header Record

Data Transfer l Disk controller has an I/O Buffer for data that is being read/written l Transfer rate between disk-buffer is slower than buffer-memory l Generally multiple blocks are read/written l As head rotates over IBG, data is transferred between buffer and memory via DMA

Disk Interleaving

I/O Process

CD ROM

CD-ROM Characteristics l Block - 2,352 bytes l 16 byte header w/4 byte ID l ID: Minute, Second, Sector, Mode l 75 sectors/sec * 60 secs * 60 mins l 270,000 blocks l 288 bytes for parity checks l 550 MB total capacity l w/o error correction mode, 630 MB

CD ROM Read Process

DVD ROM l Formatted similarly to CD ROM l Shorter light wavelength allows increased density of storage l Laser can be focused such that 2 layers of data can be recorded on same side of disk - 1 beneath the other l Both disk sides may be used l 4.7 GB/layer/side

Video Monitor- Resolution l 15” Monitor - 9” x 12” l Suppose 768 x 1024 pixels l Then each pixel is 9/768 or 12/1024 in size => ” or about 0.28mm l 1024 x 1280 => 0.24 mm

Video Memory l Pixel - RBG w/levels of intensity l 4 bits/color => 16x16x16 - 4,096 colors (Requires 12 bits/pixel) l 8 bits/color => 16,000,000+ colors (Requires 24 bits/pixel) l At 12 bits/pixel (4,096 colors) w/ 768 x 1024 resolution => 768K x 12 bits of data storage => 1.125MB

Video Memory Color Transformation Table - 4,096 colors l A palette (color transformation table) is created with 256 rows (representing all combinations of R/B) l Each row then specifies Green color, say l Note 1 byte can be used to represent pixel color - rather than 12 bits => 0.75MB l Palette is stored in video memory l Video card transforms pixel byte into screen color via palette l 3 bytes per pixel are required for true color => 3.75 MB for 1024 x 1280 resolution

Color Transformation Table

Raster Scan Display Pixels displayed one row at a time and refreshed 30 times/sec Video Memory Scan generator controls both memory scanner and video scanner that locates pixel on monitor. Video memory can be modified concurrently by CPU as data is being scanned for display.

Cathode Ray Tube (R/B/G) (ensures beam strikes correct color phosphor) Screen is coated with phosphors that glow when struck with electronic beam strength of beam determines color intensity

Liquid Crystal Display

Active/Passive Matrix LCD l Active Matrix - one transistor for each cell in matrix guarantees each cell receives strong charge - resulting in excellent picture expensive and difficult to manufacturer l Passive Matrix - one transistor for each row and column with scanner to activate cell charge is applied less often and therefore is lower => dimmer picture

Grey Scale for Printing

Laser Printing Process

Trends - Laser l Trends - better paper handling, higher speed (8-12ppm) l US Sales 2.0M (1997), 3.7M (1998), 2.9M projected (2003) l Pros - great speed, perfect text, low cost per page, great paper handling l Cons - monochrome only (color laser new), more expensive to buy, hard to fit on desktop

Ink Jet Printer l Ink Reservoir and set of nozzles l Dot is produced by heating ink behind a nozzle which forces ink to spray onto paper l Multiple reservoirs are used for color printing

Trends - Ink Jet l Trends - better quality on plain paper, higher speed (2-4 ppm), 11X17 paper l US Sales 11.3M (1997), 14.9M (1998), 15.6M projected (2000)23.6M(2003) l Pros - cheap, near photo-quality color, near laser-quality text, images close to original l Cons - slow, costly cartridges, frequent and tedious cartridge changes, smudging, weak paper handling l 2 out 3 printers are ink-jet