4.2 Representing Data Electronically

Data is represented in a computer by binary code.

Binary System: the basic data-representation method for computers uses just two numbers: 0 and 1, representing the off/on states of electricity or light pulses.

      

                          

Measuring Capacity

All data and program instructions in the computer are represented as binary.

•Bit: each 0 or 1 is a bit

•Byte: a group of 8 bits = 1 character, digit, or other value

•Kilobyte (KB): 1,000 (1,024) bytes

•Megabyte (MB): 1 million (1,048,576) bytes

•Gigabyte (GB): 1 billion (1,073,741,824) bytes

•Terabyte (TB):  1 trillion (1,009,511,627,776) bytes

•Petabyte (PB):  1 quadrillion bytes

•Exabyte (EB):  1 quintillion bytes

•Binary coding schemes assign a unique binary code to each character.

•ASCII (American Standard Code for Information Interchange)

•Requires 7 or 8 bits per character, depending on the version

•8-bit Extended ASCII provides 256 characters

•Commonly used for microcomputers

•Unicode

•Requires 16 bits per character

•Handles 65,536 characters—used for Chinese and Japanese

•EBCDIC (Extended Binary Coded Decimal Interchange Code)

•Requires 8 bits per character

•Used for IBM mainframes

•Machine Language: The computer’s “native language”

•A binary-type programming language (0s and 1s) built into the CPU that is run directly by the computer.

•Each CPU type has its own machine language; thus each computer’s machine language is brand-dependent.

•Language Translators: The computer’s system software converts higher-level language instructions and data into machine language so that the processor can “understand” what to do.

4.3 Inside the System Unit

Power Supply, Motherboard, & Microprocessors

TERM                         DEFINITONS

Bay                            Opening  in the computer cabinet used for the installation of electrical                                   equipment.

Power Supply            This converts AC to DC to run the computer.

Surge Protector         Protects the computer from being damaged by power spikes. Plug your                                  computer into one.

UPS                           Uninterruptible Power Supply. Battery-operated device that provides                                      power for a limited time when there is a blackout.

Motherboard             Main system board of the computer (also systemboard).

Microprocessor          Miniaturized circuitry of a computer processor.

Chipset                     Groups of interconnected chips on the motherboard that control                                              information flow between the microprocessor and other system                                                components connected to the motherboard.

                                                    

                                                     One View Of a Motherboard

Another View of a Motherboard

•Traditional microcomputer microprocessors are Intel and AMD.

•Multicore processors (2, 4, 6, 8) have more than one    

               processor “core” on a single silicon chip, which

               allows computers to run faster.

•Special processors are made for portable devices.

•   A graphics processing unit (GPU) is a specialized   processor used to manipulate three-dimensional   (3-D) computer graphics.

Processing Speeds

•Every microprocessor contains a system clock, which controls how fast all the operations within a computer take place (the chip’s processing speed).

•Older CPU processing speeds are in megahertz.

•1 MHz = 1 million cycles per second

•Current CPU processing speeds are in gigahertz.

•1 GHz = 1 billion cycles per second

•The faster a CPU runs, the more power it consumes, and the more heat it generates.

4.4 The Central Processing Unit & the Machine Cycle

•The CPU, for central processing unit, is the “brain” of the computer; it follows the instructions of the software (program) to manipulate data into information.

•The CPU consists of two parts—(1) the control unit and (2) the arithmetic/logic unit (ALU), both of which contain registers, or high-speed storage areas.

•All are linked by a kind of electronic “roadway” called a bus.

•For every instruction, the control unit carries out four basic operations, known as the machine cycle. In the machine cycle, the CPU (1) fetches an instruction, (2) decodes the instruction, (3) executes the instruction, and (4) stores the result

•The arithmetic/logic unit (ALU) performs arithmetic operations and logical operations and controls the speed of those operations.

•Arithmetic operations are the fundamental math operations: addition, subtraction, multiplication, and division.

•Logical operations are comparisons--the ALU compares two pieces of data to see whether one is equal to ( = ), greater than (>), greater than or equal to ( >= ), less than (<), less than or equal to ( <= ), or not equal to ( ≠ ) the other.

•The control unit and the ALU also use registers, special CPU areas that enhance the computer’s performance.

•Registers are high-speed storage areas that temporarily store data during processing. They

 may store a program instruction while it is being decoded, store data while it is being

 processed by the ALU, or store the results of a calculation.

•All data must be represented in a register before it can be processed.

•The number of registers that a CPU has and the size of each (number of bits) help

 determine the power and speed of a CPU.

•Buses are electrical data “roadways” through which bits are transmitted within the CPU

 and between the CPU and other components of the motherboard.

•In most computers, the bus width is the same as the computer’s word size, the number of

 bits that the processor can process at any one time. The more bits in a word, usually the

 faster the computer. A 32-bit-word computer will transfer data within each microprocessor

 chip in 32-bit chunks. A 64-bit-word computer is faster, transferring data in 64-bit chunks at

 a time. (Most, but not all, 32-bit software will run on a 64-bit system, but 64-bit software will

 not run on a 32-bit system.)

4.5 Memory

Memory

•Two type of storage: primary and secondary.

•Primary storage = “memory,” “main memory,” “RAM”; this type of memory is temporary and volatile.

•Secondary storage = hard disks and flash memory units; this type of memory is relatively permanent and nonvolatile.

Memory Chips                Explanation

  RAM                                     Random Access Memory chips are volatile and                                            hold:

         sSoftware instructions

                                             sData before & after the CPU processes it

  ROM                                  Read Only Memory

         sCannot be written on or erased without special                                     equipment

         sAre loaded at factory with fixed (permanent) start-                               up instructions (BIOS), that tell the computer how                               to load the operating system

  CMOS                                Complementary Metal Oxide Semiconductor

         sPowered by a battery

         sContains time, date, calendar, boot password

  Flash                                  Nonvolatile memory that can be erased and                                                  reprogrammed more than once

                                    sDoesn’t require a battery

         sUsed in newer PCs for BIOS instructions 

    

Speeding up Processing: Cache

•The CPU works much faster than RAM, so it often must wait for information

•Cache temporarily stores instructions and data that the processor uses frequently to speed up processing

•Level 1 cache is part of the microprocessor

•Holds 8 to 128 KB

•Faster than Level 2 cache

•Level 2 cache is external cache

•Holds 64 kb to 16 MB

•Level 3 cache is on the motherboard

•Comes on very high-end computers

•Holds 2 to 8 MB

•Virtual Memory—also used to speed up processing.

•This type of memory is unused hard disk or optical (CD) space that the processor uses to extend the capacity of RAM.

•The processor goes first to L1 cache, then L2 cache, then RAM, then virtual memory.

Each type of memory is slower than its predecessor.

4.6 Expansion Cards, Bus Lines, & Ports

1) Expansion cards are circuit boards that provide more memory or that control peripheral devices (for graphics, sound, video, network interface, wireless connection, etc.).

Expansion Cards: If a computer uses closed architecture, no expansion  cards can be added; if the computer uses open architecture, expansion cards can be inserted in expansion slots inside the computer, connected to the motherboard.

2) Buses connect the expansion cards to ports.

An expansion bus is not the same as the frontside bus:

•Frontside bus: The bus that connects the CPU within itself and to main memory.

•Expansion bus: Buses that connect the CPU with expansion slots on the motherboard and thus via ports with peripheral devices.

Types of expansion buses:

•PCI: High-speed bus that has been widely used to connect PC graphics cards, sound cards, modems, and high-speed network cards.

•PCI Express: Doubles the speed of the original PCI bus . PCIe is the latest standard for expansion cards available on mainstream personal computers.

•Accelerated Graphics: Transmits data at twice the speed of a PCI bus and is designed to support video and 3-D graphics.

•Universal Serial Bus (USB): Does away with the need to install cards in expansion slots. USB devices can connect one to another outside the system unit, and then the USB bus connects to the PCI bus on the motherboard.

Firewire: Resembles the USB bus but is used for more specialized purposes, such as to connect audio and video equipment to the motherboard.

3) A port is a connecting socket or jack on the outside of the computer unit or device into which are plugged different kinds of cables that connect peripheral devices.

Port Type

  Serial port               Used to transmit data slowly over long distances          

         sSends data sequentially, one bit at a time

                                    sUsed to connect older keyboards, mouse, monitors, dial-up                                       modems

  Parallel port            For transmitting data quickly over short distances

         sTransmits 8 bytes simultaneously

         sConnects printers, external disks, tape backups

  USB port                  Universal Serial Bus high-speed hardware standard for interfacing                                    peripheral devices,   such as scanners and printers, to computers                                    without a need for special expansion   cards or other hardware                                          modifications to the computer. USB is replacing many varieties   of                                  serial and parallel ports.

FireWire                    Intended for multiple devices working with lots of data and requiring                                  fast transmission   speeds, such as DVD drives, digital video                                                cameras, and gaming consoles.

Ethernet                        Supports a network standard for linking a wired local area network                                      and connecting it to a   DSL or a cable modem for high-speed                                              Internet access.

Graphics                       Connects digital monitors and multimedia digital devices, such as                                       TVs and DVD players.

eSATA                           External Serial Advanced Technology Attachment; allows the                                               attachment of an eSATA hard   disk, which has fast data transmission                                 speeds.

Bluetooth                     Connects devices that use short-range radio waves that transmit up                                    to 30 feet.

IrDA                         Transfers data via infrared light waves between directly aligned                                           devices, as between a   smartphone and a desktop computer.

HDMI                       High-Definition Multimedia Interface; carries both video and audio                                      signals and is used for   connecting HDTVs, DVD players, and game                                    consoles to computers, laptops, and other   devices.

MIDI                             Musical Instrument Digital Interface; used to connect electronic                                          musical instruments to a   sound card that converts the signals to                                        digital instructions that can be saved or   manipulated.

  

4.7 Secondary Storage

Hard Disks: Still the major secondary-storage                          device for desktop/tower computers.

•Thin, rigid metal, glass, or ceramic platters covered with a substance that allows data to be held in the form of magnetized spots.

•The more platters there are, the higher the drive capacity.

•Store data in tracks, sectors, and clusters.

•Formatting creates a file allocation table that maps files to clusters.

•Drive heads ride on .000001” cushion of air, and can crash!

•Important data should always be backed up!

                                

 

•Hard Disk Types: 

•Nonremovable hard disk – Also known as a fixed disk; is housed in the microcomputer system unit and is used to store nearly all programs and most data files. Usually consists of several metallic or glass platters, from 1 to 5.25 inches (most commonly 3.5 inches) in diameter, stacked on a spindle, with data stored on both sides. Read/write heads, one for each side of each platter, are mounted on an access arm that moves back and forth to the right location on the platter.

•External hard disk – Freestanding disk drive (portable); usually connected via USB.

•RAID – redundant array of independent disks; for large computer systems.