Java Software SolutionsInput/Output DevicesPeripheralsMain Memory and Secondary MemoryCharacteristics of Main MemorySecondary Memory DevicesTwo Other Common Terms for Memory DevicesOther Memory DevicesCentral Processing UnitCPU - moreSlide 11NetworksLocal Area Networks (LAN) and Wide Area Networks (WAN)The InternetIP Address vs Internet AddressThe Domain Name SystemThe World Wide WebHypertext and BrowsersUniform Resource LocatorsAnother Sample URLSlide 21World Wide WebProgrammingProblem Solving – Know this!How do these Steps Apply to You?The Java Programming LanguageA Java ProgramWhat to Notice in Lincoln.javaWhat to Notice (2)The println() MethodAnother Look at Lincoln.javaThe Method Named main()CommentsTwo Types of Comments1/73Java Software SolutionsChapter 1.2Computer Systems(continued)2/73Input/Output DevicesFor our purposes, the primary I/O devices will be the keyboard and the monitor.Output on a monitor is achieved by breaking the screen picture into small pieces called picture elements (pixels). The pixels are represented in the computer as numbers (as is everything else) and each pixel has a specific ‘screen address.’A typical monitor can display a number of ‘screen resolutions’ such as 640x480, 800x720, 1280 x 1024 and others… These numbers represent the number of pixels used to display the screen information.3/73PeripheralsAlmost all devices in a computer other than the CPU and main memory are called peripherals.Controllers are devices that coordinate the activities of specific peripherals.A unit with several disks attached will have a disk controller for timing, contention, data access, …Input/Output (I/O) devices and secondary memory devices are considered peripherals.4/73Main Memory and Secondary MemoryMain memory is made up of a series of consecutive memory locations called addresses.Associated with each memory location is a unique address.On many computers, each memory location consists of 8 bits, or one byte of information.The storage capacity of a device such as main memory is the total number of bytes it can hold.A kilobyte (KB) is 1,024 bytes or 210 bytes.Larger units are a megabyte (MB), a gigabyte (GB), and a terabyte (TB).It is usually easier to think about these capacities by rounding them off.5/73Characteristics of Main MemoryWhen data is stored in a main memory location, it overwrites (thus destroying) any information that was previously stored there.Main memory is usually volatile.The information stored in it will be lost if its electrical power is turned off. (meaning of volatile in this context)You should frequently save your work onto a secondary memory device (such as a disk) in case the power goes off.6/73Secondary Memory DevicesA disk is a direct access (also referred to as random access) device since the read/write head can move very quickly to the information needed.In the prerequisite to this course, you have seen pictures of disks and how they operate.Disk is both a direct access device and can be accessed sequentially just like a tape unit.A tape must be sequentially processed / rewound / or fast-forwarded to get to the desired information.A tape is thus a considered a sequential access device.While tapes used to be the medium of choice when disks were expensive and access was controlled to those types of applications really needing disks, tapes now are almost exclusively used for backup storage.Very inexpensive and can store huge quantities of data – often archival.7/73Two Other Common Termsfor Memory DevicesRandom Access Memory (RAM)The terms RAM and main memory are basically interchangeable. Sometimes called primary memory.RAM should probably be called read-write memory since data can be both written to it and read from it.Read-Only Memory (ROM)After information is stored on ROM, it cannot be altered (easily). Data in ROM is ‘burned’ into the chipsCan sometimes be reprogrammed (PROMs) and sometimes we have Erasable Programmable Read Only Memories (EPROMs) (Need special equipment)ROM chips are often embedded into the main circuit board to provide the preliminary instructions when the computer is initially turned on.8/73Other Memory DevicesAdditional memory devices include CD-ROM, CD-Recordable (CD-R) drives, CD Rewritable (CD-RW) discs, and DVD devices.(Know the differences)The speed of a CD drive is expressed in multiples of x, which represents a data transfer speed of 153,600 bytes per second.Due to improvements in technology, storage capacity approximately doubles every 18 months.9/73Central Processing UnitThe ‘processor’ interprets and executes your program’s instructions one at a time – sequentially.Consists of the arithmetic and logic unit, the control unit, and the registers (usually in the ALU and Control Units)Control unit dissects the instruction and directs the ALU to perform the calculations / comparisons using the registers.In CPU there are additional registers:Instruction register; program counter, more10/73CPU - moreThe notion of a stored-program computer – a von Neumann machine – stored both program instructions and data together in main memory. Fetch-decode-execute cycleFetch instruction from primary memory (RAM)Decode instruction (to see what it is to be done)Execute the instruction using registersRepeat11/73CPU - moreCPU on a chip called a microprocessorMain circuit board also contains communications sockets, etc. for connection with video displays, etc.Main circuit board also contains the system clock which pulses.Instructions are in synch with these pulsesSome take a single pulse; others, more.Often called clock speed.12/73NetworksA network is two or more computers connected together so they can exchange information.Each computer of a network has its own network address.One technique to improve network speed is to divide large messages into segments, called packets.Packets have fixed formats and other constraints…Then send the individual packets across the network intermixed with pieces of other messages sent by other users.13/73Local Area Networks (LAN) and Wide Area Networks (WAN)A local-area network (LAN) is designed to span short distances and connect a relatively small number of computers.Within a building or small areaYou may connect to the LAN here in this classroom and see these
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