The System Unit:

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Chapter 3

• The System Unit
• Processing and Memory

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Learning Objectives

• Understand how data and programs are represented
  to a computer and be able to identify a few of
  the coding systems used to accomplish this.
• Explain the functions of the hardware components
  commonly found inside the system unit, such as
  the CPU, memory, buses, and expansion cards.
• Describe how new peripheral devices or other
  hardware can be added to a PC.

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Learning Objectives, Contd.

• Understand how the computer systems CPU and
  memory components process program instructions
  and data.
• Name and evaluate several strategies that can be
  used today for speeding up the operations of
  computers.
• List some technologies that may be used in the
  future PCs.

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Overview

• This chapter covers
• How computers represent data and programs
• How the CPU, memory, and other components are
  arranged inside the system unit
• How the CPU works
• Strategies to speed up a computer and create
  faster computers

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Data and Program Representation

• Computers today are mostly digital
  computersdevices that can only understand two
  states.
• The two states of a digital computer are
  typically represented by 0s and 1s that is, in
  binary form.
• Computers do all processing and communications in
  binary form, so natural-language input and output
  are translated to and from binary by the computer.

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The Binary Numbering System

• We normally use the decimal numbering system,
  which uses 10 symbols (0, 1, 2, 3, 4, 5, 6, 7, 8,
  and 9).
• Computers use the binary numbering system, which
  represents all numbers using just two symbols (0
  and 1).

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Coding Systems for Text-Based Data

• ASCII and EBCDIC
• Fixed-length codes that can represent any single
  character of data as a string of eight bits.
• Unicode
• A longer (32 bits per character is common) code
  that can be used to represent text-based data in
  virtually any written language.

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Coding Systems for Other Types of Data

• Graphics dataoften stored as a bitmap which the
  color to be displayed at each pixel stored in
  binary form.
• Audio datawaveform audio is common MP3
  compression makes audio files much smaller.
• Video datarequires a great deal of storage
  space, but can be compressed.

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Machine Language

• Machine language is the binary-based code used to
  represent program instructions.
• The basic set of machine language instructions
  that a CPU can understand is that CPUs
  instruction set.
• Most programmers rely on language translators to
  translate their programs into machine language
  for them.

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Inside the System Unit

• The system unit of a PC is the case that houses
  processing hardware and other hardware.
• All of the hardware contained within the system
  unit is connected to the system board or
  motherboard.

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CPU

• The CPU (central processing unit) does the vast
  majority of processing for a computer.
• CPUs contains a variety of circuitry and
  components and are connected to the motherboard.
• Also called the processor or microprocessor.

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CPU, Contd.

• Processing speed (clock speed) is measured in
  megahertz (MHz) or gigahertz (GHz) and measures
  the number of clock ticks per second.
• A computer word is a group of bits or bytes that
  a CPU can manipulate at one time.
• Other factors that affect the speed of the
  computer include the amount of RAM and cache
  memory, bus width, and bus speed.

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Memory RAM

• RAM (random access memory) is the computers main
  memory and is used to temporarily storage
  programs and data with which it is working.
• RAM is volatile (erased when the power to the PC
  goes off).
• RAM comes in a variety of types, speeds, and
  size. Types of RAM include

DRAM SRAM SDRAM
DDR SDRAM RDRAM DDR-II SDRAM
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Memory Other Types

• Cache memoryfast memory chips located on or
  close to the CPU chip (L1, L2, and L3).
• Registershigh speed memory built into the CPU.
• ROM (read-only memory)non-volatile chips inside
  which data or programs are stored.
• Flash memorynon-volatile memory that can be
  erased and reused. Used both within the PC and
  for portable storage media (e.g digital cameras).

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Buses

• Buses are electronic paths that data travels
  around on a computer system.
• Internal buses move data around within the CPU.
• Expansion buses establish links with peripheral
  devices.
• ISA, PCI, AGP, USB, FireWire.

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Expansion Slots and Cards

• Expansion for desktop PCs.
• Expansion cards can be inserted into expansion
  slots on the motherboard.
• Some external devices can be plugged into
  existing USB or FireWire ports without adding
  another expansion card.
• PC cardsused with notebook PCs.
• Expansion for handhelds and mobile devicescan
  have proprietary, PC card, or SDIO slot.

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Ports

• Connectors to which devices can be attached.
• Common ports

• Serial
• Parallel
• SCSI
• USB
• FireWire
• Network

• Keyboard
• Mouse
• Monitor
• Modem
• MIDI
• IrDA
• Game

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How the CPU Works

• The CPU is a collection of electronic circuits
  and components.
• Impulses from an input device passes through RAM
  and enters the CPU via a system bus.
• Within the CPU the impulses move through the
  circuits and components to create new impulses.
• Eventually, a set of electronic impulses leaves
  the CPU for an output device.

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Typical CPU Components

• Arithmetic/logic unit (ALU)
• Control unit
• Registers

• Prefetch unit
• Decode unit
• Internal cache
• Bus interface unit

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The System Clock and the Machine Cycle

• The system clock synchronizes the computers
  operations.
• The machine cycle is the series of operations
  involved in the execution of a single,
  machine-level instruction.
• Fetch
• Decode
• Execute
• Store

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Making Computers Faster Now and in the Future

• Speeding up your system today.
• Add more memory.
• Perform system maintenance.
• Buy a larger or second hard drive.
• Upgrade your Internet connection.
• Upgrade your video card.
• Upgrade your CPU.

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Making Computers Faster Now and in the Future
Contd.

• Strategies for making faster computers.
• Moving circuits closer together.
• Faster and wider buses faster memory.
• Improved materials (copper, SOI, new materials).
• Pipelining.

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Making Computers Faster Now and in the Future,
Contd.

• Strategies for making faster computers, contd
• Multiprocessing (multiple CPUs, each working on a
  different job) and parallel processing (multiple
  CPUs working together to make one job finish
  sooner).
• Hyperthreading.
• Improved instruction set design.

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Future Trends

• Nanotechnologycomputer chips thousands of times
  smaller than todays components built at the
  atomic and molecular levels.
• Organic computerscomputers
• containing organic matter (biotechnology).
• Quantum computinguses atoms or nuclei working
  together as quantum bits (qubits).

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Future Trends, contd.

• Optical chipsuse light waves to transmit data.
• 3-D chipsuse multiple layers of circuitry or the
  circuitry stands vertically.

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Summary

• Data and program representation
• Inside the system unit
• How the CPU works
• Making computers faster now and in the future