Untitled Quiz

Secondary Memory

• Addresses limitations of main memory, which is too small for vast amounts of data.
• Demand for storage grows with technology advances.
• Substantial information (like comprehensive film archive) needs digitization and storage.
• Data can reach hundreds of terabytes, exceeding main memory capacity.

Memory Hierarchy

• Five-level hierarchy (Registers, Cache, Main Memory, Magnetic Disk, Optical Disk, Tape).
• Registers: Fastest, smallest storage (around 128 bytes) accessed at full CPU speed.
• Cache Memory: Larger than registers, ranging from 32 KB to a few megabytes, slightly slower than registers.
• Main Memory: Holds tens of megabytes to several gigabytes, with access times in the range of tens of nanoseconds.
• Magnetic Disks: Serve as primary means for permanent storage, providing several to tens of gigabytes with millisecond access times.
• Magnetic Tape and Optical Disks: Primarily for archival storage, with second-level access times and capacity limited only by budget.
• Access Time increases when going from registers to tape or optical disks.
• Storage Capacity increases downward (Registers → larger magnetic disks → tapes) moving down the hierarchy
• Cost per bit decreases as you move down the hierarchy

Magnetic Disks

• Storage device with platters coated in magnetizable material.
• Disk heads write/read data by magnetizing areas on surface.
• Originally large; now much smaller (3-12 cm).
• Track: Circular sequence of bits on the disk.
• Sector: Each track is divided into sectors (512 bytes of data each).
• Components: Preamble (for sync), data, ECC (error correction).

Zone Bit Recording

• Tracks divided into zones; outer zones have more sectors per track, increasing capacity.
• Manages read/write commands, arm movement, error correction, and remapping of bad sectors.
• Perpendicular Recording: Newer technique to increase data density by recording vertically.
• Winchester Disks: Sealed drives for dust protection ensuring high surface quality.

Floppy Disks

• Originally for mainframe maintenance, quickly became popular for personal computer software distribution.
• Physically flexible, hence the name "floppy".
• Organized into tracks and sectors.
• Unlike hard disks, heads directly touch the surface, resulting in more wear.
• Floppy disks were widely used for around 20 years, but newer storage media now replace them.

RAID

• Redundant Array of Independent Disks.
• Addresses slow disk performance relative to CPU by using multiple disks in parallel.
• Enhances disk performance and reliability.
• Unlike a Single Large Expensive Disk (SLED), RAID uses multiple disks; it appears as one large disk to the OS.

RAID Levels

• RAID Level 0 (Striping): Data split into strips and distributed across multiple drives for higher performance (lower reliability).
• RAID Level 1 (Mirroring): Data duplicated across primary and backup disks, offering high fault tolerance and high reliability (lower performance).
• RAID Level 2 (Hamming Code Parity): Data split into bits; Hamming code used for error correction; suitable for systems with many synchronized drives (high performance, high overhead).
• RAID Level 3 (Single Parity Disk): Uses one parity disk for error correction, all drives are synchronized. Can handle single drive failures, limited to handling one I/O request per time (high reliability, limited performance).
• RAID Level 4 (Striping with Dedicated Parity): Strips data with a dedicated parity disk, high fault tolerance, but small updates slow performance due to parity disk bottleneck.
• RAID Level 5 (Distributed Parity): Distributes parity information across all disks (eliminates bottleneck), and provides high fault tolerance (best for systems needing high reliability, high performance without parity disk bottleneck)

CD-ROMs

• Origins: Initially for television recording, soon popular for computer storage due to high capacity and low cost.
• LaserVision and Audio CDs: Early large-diameter optical disks were unsuccessful except in Japan; Philips and Sony launched the Compact Disc (CD) in 1980, becoming the first mass-market digital storage medium using this format.
• Red Book Standard: Published technical specifications enabling cross-compatibility among music publishers and electronics, ensuring CD compatibility with various players.
• Pit-Land Structure: A low-power laser reads pits (depressions) and lands (flat areas), identifying transitions between them to read binary data; ensuring reliable encoding.
• CD-ROM Development: Philips and Sony published the Yellow Book in 1984 for CD-ROM standards, enhancing error correction for data reliability.

CD-Recordables

• Emergence: Mid-1990s saw affordable and accessible CD recorders.
• Usage: Primarily for data backup, small-scale CD production, and as masters for duplication.
• Differences from CD-ROMs: Data is permanent once written, cannot be erased
• Structure: 120-mm polycarbonate blanks with grooves for laser guidance.
• Reflective Layer: Initially gold (later aluminum) creates reflectivity for data writing.
• Dye Layer: Cyanine (green) and pthalocyanine (yellow-orange) dyes simulate pits and lands.
• Writing Mechanism: High-powered laser creates dark spots on dye, mimicking data pits.
• Compatibility: Can be read by standard CD-ROM drives and audio CD players.

CD-Rewritables (CD-RW)

• Purpose: Provides a rewritable CD-ROM alternative, meeting demand for reusable media.
• Material: Uses an alloy of silver, indium, antimony, and tellurium; which has two stable states (crystalline and amorphous) with different reflectivities.
• Laser Functionality: Three Levels:
• High Power: Converts crystalline to amorphous state, creating low-reflectivity "pits"
• Medium Power: Reverts alloy to crystalline state, restoring high-reflectivity "lands"
• Low Power: Reads data without altering material state.
• Cost: CD-RW discs are often more expensive than CD-Rs.
• Accidental Deletion: CD-R is preferred for backups due to its write-once nature, reducing the risk of accidental data loss.

DVD

• Background: Developed to meet demand for high-capacity, high-quality optical storage.
• DVD Evolution: Derived from CD technology but optimized for larger storage and multimedia.
• Core Improvements: Smaller pits, tighter spiral, red laser, enabling higher data density.
• Capacity Increase: Up to 4.7 GB for single-layer DVDs (7x a CD's capacity).

DVD Formats

• Standard DVD Formats: Single-sided, single-layer: 4.7 GB
• Single-sided, dual-layer: 8.5 GB
• Double-sided, single-layer: 9.4 GB
• Double-sided, dual-layer: 17 GB

DVD Capabilities

• Multimedia Capabilities: High-resolution video (720 x 480), supporting up to 133 minutes of content with MPEG-2 compression, plus audio and subtitles in up to 8 languages, and subtitles in 32 languages.

Blu-Ray

• Successor to DVD, named for its shorter wavelength blue laser.
• Improved Focus: Blue laser allows for smaller pits and lands, enabling higher data density.
• Storage Capacity: Single-sided Blu-Ray: 25 GB, Double-sided Blu-Ray: 50 GB.
• Data Transfer Rate: ~4.5 MB/sec, higher than DVD but slower than modern magnetic disks.
• Expected Replacement: Likely to phase out CD-ROMs and DVDs due to higher capacity and performance.
• Adoption Timeline: Full transition expected to take several years.

Input/Output (I/O)

• Computer system components = CPU, memories (primary/secondary), I/O equipment.
• I/O equipment: Printers, scanners, modems.
• I/O equipment connects to the rest of the system via buses.

Buses

• Definition: A communication system that transfers data between components within a computer or between computers.
• Motherboard Components:
• CPU (Central Processing Unit): Brain of the computer, executing instructions.
• DIMM (Dual In-line Memory Module) Slots: Slots for RAM modules allowing memory expansion.
• Support Chips: Manage functions like memory control and interfacing.
• Bus System: A pathway etched onto the motherboard connecting CPU, memory, and I/O devices.
• Structure of I/O Devices:
• Components (Controller): Contains most electronics for managing the I/O device (e.g., hard drive, printer, scanner).
• Device Itself: The physical unit.
• Function of Controllers: Translate CPU commands into actions for the I/O device.
• Direct Memory Access (DMA): Allows data transfer between I/O devices and memory without CPU intervention, streamlining handling and improving efficiency.
• Interrupt Mechanism: Controller sends an interrupt signal to the CPU, halting current operation; execute an interrupt handler routine to process I/O completions.
• Bus Utilization: Shared resource used by CPU and I/O controllers.
• Bus Arbitration: A component (bus arbiter) controls bus access ensuring orderly device access.
• Priority Scheme: I/O devices receive priority to prevent data loss, especially hard drives. The CPU can use the bus exclusively when no I/O requests are present
• Cycle Stealing: I/O devices request bus access, interrupting CPU processes, which can slow overall system performance.
• Performance Challenges: Increasing speeds of CPUs and components have led to bus contention issues, creating bottlenecks.

Legacy and Modern Bus Technologies

• Legacy Buses: ISA Bus (Industry Standard Architecture)- becoming obsolete due to limitations in speed and bandwidth, EISA Bus- enhancement of the ISA bus maintaining backward compatibility with improved performance.
• Modern Bus Technologies: PC Bus (Peripheral Component Interconnect)- designed for high-speed data transfer and ease of use, widely used to connect CPU with high-bandwidth peripherals.

Terminals

• Computer terminals consist of a keyboard and a monitor (often integrated in older systems).

Keyboards

• Original IBM PC: Snap-action switches for tactile and audible feedback.
• Cheaper Keyboards: Simple mechanical contact for key activation.
• Advanced Methods: Some keyboards use magnets and coils to detect key presses.
• Operation: Key press generates interrupt; handler reads register for key code; release also triggers interrupt.
• Software handling: Multikey sequences (SHIFT, CTRL, ALT) processed by software for enhanced functions.

CRT Monitors

• Structure: Cathode ray tube (CRT) and power supplies housed within a box.
• Functionality: Electron gun emits electron beam towards phosphorescent screen, producing images via raster scanning.

CRT Raster Scanning Process

• Horizontal Sweep:Electron beam sweeps horizontally across screen with a controlled voltage increase.
• Vertical Sweep: Electron beam returns to the left side after completing horizontal sweep with vertical deflection plates.
• Refresh Rate: The screen is repainted at 30-60 times per second.

CRT Grid Function

• Grid controls electron acceleration; positive voltage allows passing (glowing screen); negative voltage repels and prevents glow.
• Visual Output: Binary control converts electrical signals into displayed pixels (bright/dark spots) illustrating an image.

Flat Panel Displays

• Transition from CRT to LCD: CRT monitors are too bulky for portables, leading to LCD adoption; lightweight and slimmer.
• Liquid Crystal Technology: Organic molecules that flow like liquids, but have structured arrangement; allowing light manipulation based on molecular alignment.

Flat Panel LCD Structure

• Basic Structure: LCD consists of two glass plates with a liquid crystal sandwiched between, transparent electrodes, and light sources to illuminate the screen. Polarizing filters (polaroids) are attached to both sides to manage light polarization

Twisted LCD Structure

• Twisted Structure: TN (Twisted Nematic) display features horizontal/vertical grooves on the rear/front plates which causes liquid crystal molecules twist.

Flat Panel Display Matrix Configurations

• Passive Matrix Displays: Use perpendicular wires to create a grid.
• Active Matrix Displays: Incorporate TFTs (Thin Film Transistors) at each pixel, enabling independent voltage control for better image quality.

Video RAM

• Purpose: Used in CRT and TFT displays for refreshing the screen.
• Information for each screen image is stored in a bitmap.
• Storage Requirements: For 1600x1200 resolution, requires storage for the RGB values in bytes.
• Color Palette Option: Indexed color can be used to reduce memory requirements.

Video RAM (Bandwidth and AGP)

• Bandwidth Challenges: High screen resolution/video playback requirements exceed older bus architectures like (E)ISA and PCI
• AGP Bus Introduction: To address limitations, Intel developed AGP (Accelerated Graphics Port); for higher-speed graphics performance.

Mice

• Evolution of Computer Users: Early computers were operated by experts; now minimal technical knowledge.
• Why a Mouse: Early interfaces used command lines; point-and-click interfaces (Windows/Macintosh) eased navigation.
• Mechanical Mouse: Features two perpendicular rubber wheels/rolling ball for tracking movement.
• Optical Mouse: Uses LED and photodetector, no moving parts; tracks by sensing grid lines crossed on special pad.
• Optomechanical Mouse: Combines mechanical and optical elements, using a rolling ball and light pulse encoders.
• Data Transmission: Data packets for mouse movement and button states sent serially to the computer.

Printers

• Matrix Printers: Technology uses print heads (7-24 needles) forming dots arranged in matrices; for efficiency on large forms, receipts, and multipart continuous forms with carbon paper.
• Inkjet Printers: Technology uses piezoelectric or thermal crystals to control individual droplet sizes for various printing qualities; usually affordable.
• Laser Printers: Technology utilizes a rotating drum; charged and exposed to a laser, creating light/dark spots for toner application; excellent for high-quality/fast printing, sometimes combining printing/copying/faxing functions.

Color Printers

• Color Representation: Monitors use RGB; printers use CMYK
• Gamut and Calibration: Devices have limited color ranges that require calibration to match screen(RGB) and printed colors (CMYK)
• Inkjet Printer Types: Dye-based, pigment-based; common ink cartridges.
• Solid Ink Printers: Uses melted wax ink, offers stable color over time but with long startup time

Advanced Color Printers

• Color Laser Printers: Uses CMYK toners; large memory, high quality but may need time, best for lasting color
• Wax Printers: Uses heated wax ribbons for vibrant color.
• Dye Sublimation Printers: Vaporizes dye for near-continuous colors without halftoning; best for use for high quality photograph.

Telecommunication Equipment

• Most computers connect to a network (often the Internet).
• I/O equipment required for network communication

Modems

• Definition: Modulates and demodulates data for transmission over phone lines.
• Purpose: Connects computers over telephone lines, enabling communication between various devices,
• Challenge: Raw digital signals don't transmit well; need modulation.
• Digital Signal Transmission Issue: Digital signals distort.
• Solution: Modulation (using carrier sine wave, 1000-2000 Hz). which carries data with minimal distortion

Modem (Modulation/Demodulation)

• Modulation: Converting digital data into analog signals for transmission.
• Demodulation: Converting received analog signals back into digital data to retrieve original information.
• Types of Modulation: Amplitude Modulation (AM), Frequency Modulation (FM), Phase Modulation (PM).

Modem (Advanced Techniques)

• Dibit Phase Encoding: Transmits 2 bits per time interval, using different phase shifts for encoding.
• Baud and Bit Rate: Baud rate refers to signal changes per second; bit rate can be higher if multiple bits are sent per baud.

Modem Data Transmission

• Serial Transmission: 8-bit characters sent serially over single-channel telephone lines.
• Start and Stop Bits: Each character preceded by a start and followed by a stop bit, increases bit count to 10. (example given 9600baud)
• Types of Data Transmission Modes:
• Full-duplex: Simultaneous, two-way transmission using different frequencies.
• Half-duplex: Data travels in one direction at a time.
• Simplex: Data travels only in one direction.

Modem Capabilities

• Data Rates: 28,800 bps to 57,600 bps with low baud rates; advanced techniques combine modulation methods for higher bit rates.

Digital Subscriber Line (DSL)

• Overview: High-speed Internet access technology over traditional telephone lines.
• ADSL: Asymmetric DSL, higher download speeds than upload speeds.
• Broadband Concept: Offers broader bandwidth compared to earlier dial-up, often marketed as "Broadband".
• Voice Optimization: Traditional phone lines designed for voice, bandwidth is limited to 3000 Hz.

Wireless Technologies

• Wireless has become ubiquitous and increasingly important.
• Wi-Fi: Uses radio waves for data transfer; widely used in homes and offices for high speed data access.
• WiMax: A wireless broadband wireless solution that works via radio towers for longer distance communication; used today; often used by businesses or in public areas;
• Mobile Networks: Wireless communication networks have become more important as mobile devices have proliferated.
• Cellular Technologies: Many different cellular technologies exist today.

Digital Cameras

• Overview: Peripherals that capture images electronically, mainly using a CCD sensor array.
• Mechanism: Uses a lens to focus an image onto a CCD (Charge-Coupled Device) array replacing film. Analog-to-digital converter reads intensities to generate digital data. 
• CCD Array: Converts light into electrical charges with values from 0-255.
• Color Filtering: A Bayer filter separates light into red, green, and blue components within the CCD array. Each pixel consists of four CCD sensors for full color capture
• Interpolation: Software combines pixel data to create a full-color image.

Digital Cameras Image Capture Functions (Processes)

• Focus: Adjusts lens based on image detail.
• Exposure: Determines optimal light intensity.
• White Balance: Adjusts color based on light source spectrum.
• Storage: Saves data in camera's RAM (high-end SLRs may use more) for rapid frame capture

Digital Camera (Post-Capture Processing)

• White Balance Correction: Adjusts colors to reflect true tones.
• Noise Reduction: Reduces image noise.
• Sharpening: Enhances edges to improve detail.
• Compression: JPEG format compresses images, reducing filesize with potential detail loss.

Digital Cameras (Image Storage/Transfer)

• Storage Media: Saved on flash memory; Micro drives.
• Image Transfer: Connects to computers via USB, FireWire, etc
• Editing Software: Tools exist for further editing (e.g., Adobe Photoshop).

Digital Cameras Embedded Computing

• Embedded System: Modern digital cameras have powerful processors
• Capabilities for managing functions: lens/flash, real-time display, controlling buttons/settings. 

ASCII (American Standard Code for Information Interchange)

• Character encoding standard used primarily in early computers.
• Bit Length: 7 bits per character; has 128 possible characters (including control characters).
• Purpose: Represents text in computers/telecommunication.
• Examples: SOH, STX, ETX, EOT (used for control in data transmission)

UNICODE

• Formed by companies, developed as a universal standard.
• 16-bit encoding assigns a unique code point for every character.
• 65,536 code points cover many world languages and symbols
• ASCII compatibility; Latin 1 has code points 0-255, mapping to ASCII.
• Code Point Allocation: Divided into blocks of 16, organized by script and helps with various language challenges.
• Diacritical Marks: Each mark has it's own code point; software combines them to create new symbols
• UNICODE Challenges: Script-based sorting issues; requires external tables; dynamically growing language (new words/names).
• Cultural Sensitivity and Controversies: Number of code bits for some languages vary (Han ideographs) and reflects cultural inclusion in allocation.