Computer Hierarchy

• The first generation of computers, from 1946 to about 1956, used vacuum tubes to store and process information.

• The second generation of computers, from 1957 to 1963, used transistors for storing and processing information.

Computer Hierarchy

• Third-generation computers, from 1964 to 1979, used integrated circuits for storing and processing information.

• Early to middle fourth-generation computers, from 1980 to 1995, used very-large-scale integrated (VLSI) circuits to store and process information.

• Late fourth-generation computers, from 1996 to the present, use grand-scale integrated (GSI) circuits to store and process information.

Computer Categories

• Supercomputers• Mainframe Computers• Midrange Computers• Workstations• Notebooks and Desktop Computers• Appliances

Hardware

• Hardware refers to the physical equipment used for the input, processing, output and storage activities of a computer system.

• Central processing unit (CPU) manipulates the data and controls the tasks performed by the other components.

• Primary storage internal to the CPU; temporarily stores data and program instructions during processing.

Hardware

• Secondary storage external to the CPU; stores data and programs for future use.

• Input technologies accept data and instructions and convert them to a form that the computer can understand.

• Output technologies present data and information in a form people can understand.

Hardware (Continued)

• Communication technologies provide for the flow of data from external computer networks (e.g. the Internet and intranets) to the CPU, and from the CPU to computer networks.

How the CPU Works

The Central Processing Unit

• Central processing unit (CPU) performs the actual computation or “number crunching” inside any computer.

• Microprocessor made up of millions of microscopic transistors embedded in a circuit on a silicon chip.

• Control unit sequentially accesses program instructions, decodes them and controls the flow of data to and from the ALU, the registers, the caches, primary storage, secondary storage and various output devices.

CPU (Continued)

• Arithmetic-logic unit (ALU) performs the mathematic calculations and makes logical comparisons.

• Registers are high-speed storage areas that store very small amounts of data and instructions for short periods of time.

How the CPU Works

• Binary form: The form in which data and instructions can be read by the CPU – only 0s and 1s.

• Machine instruction cycle: The cycle of computer processing, whose speed is measured in terms of the number of instructions a chip processes per second.

• Clock speed: The preset speed of the computer clock that times all chip activities, measured in megahertz and gigahertz.

• Word length: The number of bits (0s and 1s) that can be processed by the CPU at any one time.

• Bus width: The size of the physical paths down which the data and instructions travel as electrical impulses on a computer chip.

• Line width: The distance between transistors; the smaller the line width, the faster the chip.

Advances in Microprocessor Design

• Moore’s Law is that microprocessor complexity would double every two years as a result of the following changes:– Increasing miniaturization of transistors.

– Making the physical layout of the chip’s components as compact and efficient as possible.

– Using materials for the chip that improve the conductivity (flow) of electricity.

– Targeting the amount of basic instructions programmed into the chip.

Microprocessors & Microcontrollers

• The two most common microprocessor architectures are complex instruction set computing (CISC) and reduced instruction set computing (RISC).

• Microcontrollers are computer chips, embedded in products and technologies, that usually cost less and work in less-demanding applications than microprocessors.

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.

Memory Capacity

• Bit: Short for binary digit (0s and 1s), the only data that a CPU can process.

• Byte: An 8-bit string of data, needed to represent any one alphanumeric character or simple mathematical operation.

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

Secondary Storage

• Magnetic tape: A secondary storage medium on a large open reel or in a smaller cartridge or cassette.

• Sequential access: Data access in which the computer system must run through data in sequence in order to locate a particular piece.

• Magnetic disks: A form of secondary storage on a magnetized disk divided into tracks and sectors that provide addresses for various pieces of data; also called hard disks.

Secondary Storage

• Hard drives: A form of secondary storage that stores data on platters divided into concentric tracks and sectors, which can be read by a read/write head that pivots across the rotating disks.

• Direct access: Data access in which any piece of data be retrieved in a nonsequential manner by locating it using the data’s address.

• Magnetic diskettes: A form of easily portable secondary storage on flexible Mylar disks; also called floppy disks.

Optical Storage Devices

• Optical storage devices: A form of secondary storage in which a laser reads the surface of a reflective plastic platter.

• Compact disk, read-only memory (CD-ROM): A form of secondary storage that can be only read and not written on.

• Digital video disk (DVD): An optical storage device used to store digital video or computer data.

• Fluorescent multilayer disk (FMD-ROM): An optical storage device with much greater storage capacity than DVDs.

More Storage Options

• Memory cards: Credit-card-size storage devices that can be installed in an adapter or slot in many personal computers (i.e. memory sticks, thumb drives).

• Expandable storage devices: Removable disk cartridges, used as backup storage for internal hard drives of PCs.

Enterprise Storage Systems & RAID

• Enterprise storage system: An independent, external system with intelligence that includes two or more storage devices.

• Redundant arrays of independent disks (RAID): An enterprise storage system that links groups of standard hard drives to a specialized microcontroller that coordinates the drives so they appear as a single logical drive.

Storage Area Networks (SANs)

• Storage area network (SAN): An enterprise storage system architecture for building special, dedicated networks that allow rapid and reliable access to storage devices by multiple servers.

• Storage over IP: Technology that uses the Internet Protocol to transport stored data between devices within a SAN; sometimes called IP over SCSI or iSCSI.

Network-Attached Storage

• Network-attached storage (NAS) device is a special-purpose server that provides file storage to users who access the device over a network; plug-and-play.

Input and Output Technologies

• Input technologies allow people and other technologies to put data into a computer. The two main types of input devices are:– human data-entry devices include keyboards,

mouse, trackball, joystick, touchscreen, stylus and voice recognition;

– source-data automation devices input data with minimal human intervention (e.g. barcode reader).

• Speed up data collection;• Reduce errors;• Gather data at the source of a transaction or other event.

Input and Output Technologies (Continued)

• Output generated by a computer can be transmitted to the user over several output devices and media.– Includes monitors, printers, plotters and voice.

Multimedia Technology

• Multimedia technology is the computer-based integration of text, sound, still images, animation and digitized motion video.

• Merges capabilities of computers with televisions, VCRs, CD players, DVD players, video and audio recording equipment, music and gaming technologies.

Emerging Technologies

• Grid computing involves applying the resources of many computers in a network to a single problem at the same time.

• Utility computing (also called subscription computing and on-demand computing) is when a service provider makes computing resources and infrastructure management available to a customer as needed for a charge based on specific usage rather than a flat rate.

• Nanotechnology refers to the creation of materials, devices and systems at a scale of 1 to 100 nanometers (billionths of a meter).