Intro computers

Introducing Computer Systems

Introducing Computer Systems

The Computer Defined

• Electronic device

• Converts data into information

• Modern computers are digital– Two digits combine to make data

• Stores data in its own memory unit .

• It can accept data (input), manipulate data (process), and produce information (output)

Computer ArchitectureComputer Architecture

Parts of the Computer System

• Computer systems have four parts– Hardware– Software– Data– User

Parts of the Computer System

• Hardware– Mechanical devices in the computer– Anything that can be touched

• Software– Tell the computer what to do– Also called a program– Thousands of programs exist

Parts of the Computer System

• Data– Pieces of information– Computer organize and present data

• Users– People operating the computer– Most important part– Tell the computer what to do

Components of a Computer

• Computers use the same basic hardware

• Hardware categorized into four types– Processor– Output/Input– Memory– Storage

Components of a Computer - Processor

Processor – Brain of the computer– Carries out instructions from the program– Manipulate the data– Most computers have several processors– Central Processing Unit (CPU)– Processors made of silicon and copper

Components of a Computer - Memory

• Two basic categories of computer memory: Primary storage and secondary storage. – Primary stores small amounts of data and

information that will be immediately used by the CPU.

– Secondary stores much larger amounts of data and information (an entire software program, for example) for extended periods of time.

How the CPU Works

Hierarchy of Memory Capacity• Kilobyte (KB): approximately one thousand

bytes.• Megabyte (MB): approximately one million

bytes (1,048,576 bytes, or 1,024 x 1,024).• Gigabyte (GB): actually 1,073,741,824

bytes (1,024 x 1,024 x 1,024 bytes).• Terabyte: One trillion bytes.• Petabyte: Approximately 1015 bytes.• Exabyte: Approximately 1018 bytes.

Primary Storage• Primary storage or main memory stores three types

of information for very brief periods of time:– Data to be processed by the CPU;– Instructions for the CPU as to how to process the data;– Operating system programs that manage various aspects of

the computer’s operation.

• Primary storage takes place in chips mounted on the computer’s main circuit board, called the motherboard.

• Four main types of primary storage: register, random access memory (RAM), cache memory and read-only memory (ROM).

Main Types of Primary Storage• Registers: registers are part of the CPU with

the least capacity, storing extremely limited amounts of instructions and data only immediately before and after processing.

• Random access memory (RAM): The part of primary storage that holds a software program and small amounts of data when they are brought from secondary storage.

• Cache memory: A type of primary storage where the computer can temporarily store blocks of data used more often.

Primary Storage (Continued)

• Read-only memory (ROM): Type of primary storage where certain critical instructions are safeguarded; the storage is nonvolatile and retains the instructions when the power to the computer is turned off.

• Flash memory: A form of rewritable read-only memory that is compact, portable, and requires little energy.

Secondary Storage

• Memory capacity that can store very large amounts of data for extended periods of time.– It is nonvolatile.– It takes much more time to retrieve data because

of the electromechanical nature. – It is cheaper than primary storage.– It can take place on a variety of media

• The two main storage technologies are magnetic and optical.

Optical storage devices are:

• Compact Disk Read-Only Memory (CD-ROM)

• Digital Video Disk Read-Only Memory (DVD-ROM)

• CD-Recordable (CD-R)

• CD-Rewritable (CD-RW)

Magnetic storage are:

• Diskettes (floppy disks)

• Hard disks

• High-capacity floppy disks

• Magnetic tape

Formatting

• Before a magnetic disk can be used, it must be formatted—a process that maps the disk's surface and determines how data will be stored.

• During formatting, the drive creates circular tracks around the disk's surface, then divides each track into sectors.

• The OS organizes sectors into groups, called clusters, then tracks each file's location according to the clusters it occupies.

Formatted Disk

Hard Disks

• Hard disks use multiple platters, stacked on a spindle. Each platter has two read/write heads, one for each side.

• Hard disks use higher-quality media and a faster rotational speed than diskettes.

• Removable hard disks combine high capacity with the convenience of diskettes.

Read/write heads

Optical Storage Devices

• How Optical Storage Works

• CD-ROM

• DVD-ROM

• Other Optical Storage Devices

CD-ROM

• In PCs, the most commonly used optical storage technology is called Compact Disk Read-Only Memory (CD-ROM).

• A standard CD-ROM disk can store up to 650 MB of data, or about 70 minutes of audio.

• Once data is written to a standard CD-ROM disk, the data cannot be altered or overwritten.

Other Optical Storage Devices

• A CD-Recordable (CD-R) drive lets you record your own CDs, but data cannot be overwritten once it is recorded to the disk.

• A CD-Rewritable (CD-RW) drive lets you record a CD, then write new data over the already recorded data.

DVD-ROM

• A variation of CD-ROM is called Digital Video Disk Read-Only Memory (DVD-ROM), and is being used in place of CD-ROM in many newer PCs.

• Standard DVD disks store up to 9.4 GB of data—enough to store an entire movie. Dual-layer DVD disks can store up to 17 GB.

• DVD disks can store so much data because both sides of the disk are used, along with sophisticated data compression technologies.