- Job can often be done even if the instructions are not followed precisely
Somewhere between human language such as English and Computer languages.
Precise enough to describe what is meant without being tedious.
Computer Science can be considered as the study of algorithms including
A PC is a general-purpose informationprocessing device. It can take information from a person (through the keyboard and mouse), from a device (like a pendrive or CD) or from the network (through a modem or a network card) and process it. Once processed, the information is shown to the user (on the monitor), stored on a device (like a hard disk) or sent somewhere else on the network (back through the modem or network card).
Addition, Subtraction etc on binary numbers in a way similar to that of decimal numbers
0+0 = 0
1+0 = 1
0+1 = 1
1+1 = 0 with carry 1
The different type of data have different form: - text -> code tables - numerical ->diff. dig. formats - picture, sound -> spec. formats - audio, video ---> Via a process of digitization.
The programs are stored also in digitized format.Representation of Data
Change state: based on circuit at each TIME STEP.
Memory is the functional unit of computer thatstores instructions and data.
Memory is divided into fixed size units called cells, currently 8 bits --- called byte
Each memory cell has an address. Note that k bits can beused to address 2k memory cells/bytes.Comments: Memory
The capacitor in a dynamic RAM memory cell is like a leaky bucket.It needs to be refreshed periodically or it will discharge to 0.
This refresh operation is where dynamic RAMgets its name. Dynamic RAM has to be dynamically refreshed all of the time or it forgets what it is holding. The downside of all of this refreshing is that it takes time and slows down the memory.
1. Computer is processingdatasequentially.
The machinecarries out instructionsonebyone. Neumann thought, electriccomputerscould be fastenoughwithoutparallelism. However most of today’scomputersaresequential, therearemultiprocessorcomputersabletoperformmultipletaskinthesametime.
2. Computer usesbinaryquotation and it is fullyelectronic.
Binaryquotationcan be implementedwith 2-state circuits (1-higher voltage, 0-lower voltage) withtheuse of vacuumtubes, transistors, complexintegratedcircuits.
3. Computer has internalmemory.
Neumann suggestedusinginternalmemorytostorepartialresultsinordertomake computer capable of carrying out a set of operationswithoutanyuserinteraction. Nowadaysweusesemi-conductormemorycontainingintegratedcircuits.
4. Stored program concept.
Instructionscan be denotedwithnumbers, sotheycantreatedasdata and can be storedinmemory. Inthisway, computer canworkonitsown, itretreivesdata and instructionsfromthememory. Naturallythedata and theinstructionsarelocatedindifferentparts of thememory.
5. Computer is universal.
There is no needtomakespecialdevices, machinestoperformdifferent computer tasks. Turing proovedwithmathematicallogicaltoolsthat a machinecapabletoperformsomeelementaryoperationscancarry out anykind of calculations.
Control Unit --- brain of the CPU. It decides which operations are to be performed and when.
CPU repeatedly executes the instruction cycle.
1. Fetch the instruction from memory
2. Decode the instruction
3. Execute the instruction (including the setting up for the next instruction to be executed)(Control signals are used to select which operation is to be done.)
What does it mean?The disk is turning, while the read and write head is moving over the disk surface
Nearly every desktop computer, laptop and server in use today contains one or more hard-disk drives. Every mainframe and supercomputer is normally connected to hundreds of them.
Hard disks store digital information in a relatively permanent form.
Data is stored on the surface of a platter in sectors and tracks. Tracks are concentric circles, and sectors are pie-shaped wedges on a track, like this:
A typical track is shown in yellow; a typical sector is shown in blue. A sector contains a fixed number of bytes -- for example, 256 or 512., sectors are often grouped together into clusters.
Keyboard, Monitor, printers, speakers, etc.