Chapter 9

I/O Peripherals

Hard Disk Layout

Constant Angular Velocity

Number of bytes per sector is same regardless of track position

Since disk rotates at fixed speed, transfer time is constant

Density of bits per track varies from track to track

Hard/floppy disks store data in CAV format

Accessing Data

Disk Characteristics

Rotational Speed Latency Seek Time Buffer Transfer Rate

3.5"Floppy 360 rpm 83 msec 95 msec 54 KB/sec

100 MB Zip 2941 rpm 29 msec 10 msec 1.4 MB/sec

10 GB HD 5400 rpm 5.6 ms 9.5 msec 2 MB

20.4 GB HD 7200 rmp 4.2 ms 9.0 msec 1 MB 66 MB/sec80 GB HD 7200 rmp 5.6 msec 9.5 msec 2 MB

Block (Sector) Format

512 bytes/sector

IRG

IRG

Header Record

Data Transfer

Disk controller has an I/O Buffer for data that is being read/written

Transfer rate between disk-buffer is slower than buffer-memory

Generally multiple blocks are read/written As head rotates over IBG, data is

transferred between buffer and memory via DMA

Disk Interleaving

I/O Process

CD ROM

CD-ROM Characteristics

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

CD ROM Read Process

DVD ROM

Formatted similarly to CD ROM Shorter light wavelength allows

increased density of storage Laser can be focused such that 2

layers of data can be recorded on same side of disk - 1 beneath the other

Both disk sides may be used 4.7 GB/layer/side

Video Monitor- Resolution

15” Monitor - 9” x 12” Suppose 768 x 1024 pixels Then each pixel is

9/768 or 12/1024 in size =>0.0117” or about 0.28mm

1024 x 1280 => 0.24 mm

Video Memory

Pixel - RBG w/levels of intensity 4 bits/color => 16x16x16 - 4,096 colors

(Requires 12 bits/pixel) 8 bits/color => 16,000,000+ colors

(Requires 24 bits/pixel) At 12 bits/pixel (4,096 colors)

w/ 768 x 1024 resolution => 768K x 12 bits of data storage => 1.125MB

Video MemoryColor Transformation Table - 4,096 colors

A palette (color transformation table) is created with 256 rows (representing all combinations of R/B)

Each row then specifies Green color, say Note 1 byte can be used to represent pixel color -

rather than 12 bits => 0.75MB Palette is stored in video memory Video card transforms pixel byte into screen color

via palette 3 bytes per pixel are required for true color

=> 3.75 MB for 1024 x 1280 resolution

Color Transformation Table

Raster Scan DisplayPixels displayed one row at a time

and refreshed 30 times/sec

Video Memory

Scan generator controls bothmemory scanner and video scanner that locates pixel on monitor.

Video memory can be modifiedconcurrently by CPU as data isbeing 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 beamstrength of beam

determines color intensity

Liquid Crystal Display

Active/Passive Matrix LCD

Active Matrix - one transistor for each cell in matrixguarantees each cell receives strong charge - resulting in excellent pictureexpensive and difficult to manufacturer

Passive Matrix - one transistor for each row and column with scanner to activate cellcharge is applied less often and therefore is lower => dimmer picture

Grey Scale for Printing

Laser Printing Process

Laser Printing Process

Trends - Laser

Trends - better paper handling, higher speed (8-12ppm)

US Sales 2.0M (1997), 3.7M (1998), 2.9M projected (2003)

Pros - great speed, perfect text, low cost per page, great paper handling

Cons - monochrome only (color laser new), more expensive to buy, hard to fit on desktop

Ink Jet Printer

Ink Reservoir and set of nozzles Dot is produced by heating ink

behind a nozzle which forces ink to spray onto paper

Multiple reservoirs are used for color printing

Trends - Ink Jet

Trends - better quality on plain paper, higher speed (2-4 ppm), 11X17 paper

US Sales 11.3M (1997), 14.9M (1998), 15.6M projected (2000)23.6M(2003)

Pros - cheap, near photo-quality color, near laser-quality text, images close to original

Cons - slow, costly cartridges, frequent and tedious cartridge changes, smudging, weak paper handling

2 out 3 printers are ink-jet