Computer System Notes

Processor

• Also called CPU (Central Processing Unit), it is a critical device and the core of a computer.

• Computer Configuration:

  • Input device

  • CPU

    • Control device

    • Operation device

  • Main memory

  • Output device

  • Auxiliary storage devices

  • Peripheral devices

  • Flow of control

  • Flow of data

Basic Framework of CPUs

• Initially, CPUs comprised multiple chips.

• Advancements in technology enabled CPUs to be contained in a single chip called a “Microprocessor.”

• CPU incorporates "control" functions (sending instructions) and "operation" functions (performing calculations).

Types of CPU

Clock Frequency

• Definition: A cyclical signal that coordinates the timing of operations within the CPU or with external devices.

• Indicates the number of signals per second.

• CPUs with the same bits can have different throughput based on clock frequency.

• Higher clock frequency results in greater data processing capacity and faster speed.

• Measured in Hertz (Hz).

Bus Width

• Definition: A path used to exchange data between devices.

• Indicates the number of signal lines in the bus, measured in bits.

• Internal Bus: Exchanges data inside the CPU.

• External Bus: Exchanges data between the CPU and memory or peripheral devices.

Calculation of CPU Instruction Execution Count

• Example:

  • A CPU operates at 200MHz and executes one machine language instruction at an average of 0.5 clocks.

  • Calculation:

    • CPU clock frequency ÷ Clocks per instruction

    • $200MHz ÷ 0.5 clocks$

    • $= 200 \times 10^6$ clocks per second ÷ 0.5 clocks per instruction

    • $= 400$ million instructions per second

Storage Devices

• Definition: Devices that store data required for computer processing.

Memory

• Refers to devices used to store programs and data required for computer operation.

Types of Memory

• RAM

  • DRAM

  • SRAM

• ROM

  • Mask ROM

  • EPROM

  • EEPROM

RAM (Random-Access Memory)

• Volatile memory: Stored content is lost when power is off.

• Data can be read and written.

• Used as main memory or cache memory.

DRAM (Dynamic Random-Access Memory) vs. SRAM (Static Random-Access Memory)

ROM (Read-Only Memory)

• Non-volatile memory: Retains stored content after power is turned off.

• Used for data, programs, and rewriteable ROMs (flash memory or BIOS storage).

EPROM (Erasable Programmable Read-Only Memory) & EEPROM (Electrically Erasable Programmable Read-Only Memory)

Flash Memory

• Electrically rewriteable EEPROM.

• Used for BIOS storage or as an auxiliary storage device in computers.

BIOS (Basic Input/Output System)

• Program that controls input/output between the computer unit and peripheral devices.

• Stored in ROM and integrated into the motherboard.

• Abbreviation for “Basic Input/Output System.”

Memory Applications

Cache Memory Functionality

• Without Cache Memory:

  • Data is constantly exchanged between the CPU and main memory, leading to wait times and reduced efficiency.

• With Cache Memory:

  • Data is stored in the cache when the CPU reads it from main memory.

  • Subsequent access to the same data is faster since the CPU reads from the cache memory.

  • Improves processing efficiency.

Types of Main Memory

• Memory types vary based on the computer.

• Expanding main memory involves adding the correct type of memory.

SIMM and DIMM

• SIMM: Single In-line Memory Module

• DIMM: Dual In-line Memory Module

• Expansion memory is added to expand built-in standard memory.

Storage Media

• Devices that store created data and files.

• Also known as “auxiliary storage devices.”

Magnetic Disk

• Storage media that uses magnetization to read and write data.

Construction of Magnetic Disk

• Formatting (initialization) is required to organize the disk into tracks and sectors for data storage.

Sequence for Read/Write Operations of Magnetic Disks

1. Magnetic head moves to the target track.

2. Waits for the target sector to rotate into position (rotational latency).

3. Reads/writes data to/from the target sector (data transfer).

Fragmentation and Optimization (Defragmentation)

• Fragmentation: Occurs when data is stored across multiple regions of the hard disk due to repeated adding, deleting, and moving data.

• Optimization (Defragmentation): Repairs fragmentation to reduce seek operations and improve access speed.

Calculating the Capacity of Magnetic Disks

• Storage Capacity Formula:

  • Storage capacity per sector $\times$ No. of sectors per track $\times$ No. of tracks per surface $\times$ No. of storage surfaces

• Example #1:

  • Floppy disk specifications:

    • No. of tracks per surface: 80

    • No. of sectors per track: 18

    • Sector length (bytes): 512

    • Storage surface: Both sides

  • Answer:

    • $512 \text{ bytes} \times \frac{18 \text{ sectors}}{1 \text{ track}} \times \frac{80 \text{ tracks}}{1 \text{ surface}} \times 2 \text{ surfaces} = 1,474,560 \text{ bytes} = 1.4 \text{ MB}$

• Example #2: Disk divided into 120-cylinder zones with sectors of different zones containing 200, 240, 280, and 320 sectors. Each sector contain 4096 bytes. What is the disk capacity.

  • $120 \times 200 + 120 \times 240 + 120 \times 280 + 120 \times 320 = 124,800 \text{bytes}$

  • $124800 \text{ bytes} \times 4096 \text{ bytes} = 511,180,800 \text{bytes}$

Number of Sectors Needed to Store Data Formula

• Formula:

  • Data length ÷ Storage capacity per sector

• Example #3:

  • For a floppy disk with 512 bytes per sector, how many sectors are needed to store 500, 1400, and 1600 bytes of data?

• Answer:

  • 500 bytes ÷ 512 bytes = 0.976 (1 sector)

  • 1,400 bytes ÷ 512 bytes = 2.734 (3 sectors)

  • 1,600 bytes ÷ 512 bytes = 3.125 (4 sectors)

  • Total: 1 + 3 + 4 = 8 sectors

Optical Disks

• Storage device that uses laser optics to read and write data.

• Types:

  • CD-ROM: Compact Disc Read-Only Memory

  • CD-R: Compact Disc Recordable

  • CD-RW: Compact Disc Rewritable

  • DVD-ROM: Digital Versatile Disc Read-Only Memory

  • DVD-RAM: Digital Versatile Disc Random Access Memory

  • DVD-R: Digital Versatile Disc

  • DVD-RW: Digital Versatile Disc Rewritable

Other Storage Media than Magnetic Discs

• Streamer (Magnetic Tape Drive):

  • Continuously reads and writes data.

  • Stores tens to hundreds of GB.

• MO Device (Magneto-Optical Disk Drive):

  • Writes data using laser optics and magnetism.

  • Capable of repeated rewriting.

  • Stores hundreds of MB to several GB.

• Flash Memory:

  • Non-volatile, rewriteable storage that retains content after power off.

  • USB Memory:

    • Reads and writes data using flash memory.

    • Stores tens of MB to tens of GB.

  • SD Memory Card:

    • Reads and writes data using flash memory.

    • Used in digital cameras and mobile phones.

    • Stores tens of MB to tens of GB.

Storage Hierarchy

• A pyramid-shaped hierarchy illustrating the structure of storage devices used by computers.

• Storage devices are stacked by data access speed.

• Faster access speeds are at the top, closer to the CPU.

Input and Output Devices

• Computers connect to peripherals (printers, scanners) using matching interfaces.

Input/Output Interfaces

• Intermediary device/system for exchanging data between two points.

Types of Data Exchanged

• Analog:

  • Electronic signal with a wave-like pattern.

  • Expressed as a continuous value.

• Digital:

  • Electronic signal with a bar graph pattern (numerical value conversion).

  • Expressed as a concrete numerical value.

Serial Interface

• Transfers data one bit at a time.

• Uses fewer signal lines and is less prone to signal variation.

• IEEE 1284:

  • Connects a computer to a printer.

• SCSI:

  • Connects a computer to peripherals.

  • Up to seven external peripherals can be connected in a daisy chain method.

Daisy Chain Method

• Diagram illustrating the connection of multiple SCSI devices (hard disks, CD-ROM drive, MO drive, printer, scanner) to a computer unit; uses terminators at the end.

Wireless Interface

• Transfers data using infrared or wireless transmission technology.

• Transmission speed varies depending on distance.

Standards for Wireless Interfaces

• IrDA:

  • Uses infrared communication.

  • Distance: within two meters.

• Bluetooth:

  • Uses 2.4GHz band.

  • Transmission speed: 1Mbps.

  • Range: 10 meters.

Device Driver

• Software that enables the use of a peripheral.

• Modern operating systems are “plug and play,” automatically enabling peripherals upon connection.