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M150 – UNIT 6DATA, COMPUTING AND
INFORMATI1
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Unit 6
2UNIT 6: FIVE THEMES
Unit 6 sets the scene by providing you with some useful background
about the components of the computer that are involved when a
program is run, and some of the structures that programs employ.
Distinguishing: Computer as a system that is made up of Software,
Hardware and Firmware.
Describing: Functions of different components of a computer
( memory, OS, mother board, etc….).
Collaborating: Different computer components to process a computer
program.
Understanding: How computer understand our commands???!!!.
Introducing: The mechanism of how the software is going to skip or
repeat a sequence of instructions
EARLY COMPUTING MACHINES AND THEIR INVENTORS
From the time that numbers were invented humans have invented devices to help in manipulating them. The abacus, of which the oldest surviving example dates from 300 , is still used today. The Roman abacus, in use between the second and fifth centuries consisted of beads strung on a number of wires and the Roman word for the beads used, calculus, give us the modern word ‘calculator
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EARLY COMPUTING MACHINES AND THEIR INVENTORS
The first mechanical calculating device, which used a system of cogs, was invented by William Schickard in 1623. Schickard, like the famous astronomer Kepler, was born in Wu¨rttemberg, Germany, and Kepler used Schickard’s machine for his astronomical calculations. Because the six-digit numbers manipulated by the machine were insufficient for Kepler’s needs, the device came with a number of rings, which the operator could add to his fingers in order to keep track of higher order digits! Figure 1.2
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In 1694 the German mathematician and philosopher, Gottfried Wilhelm von Leibniz improved the Pascaline by creating a machine that could also multiply, but it was not until 1820 that Charles Xavier Thomas de Colmar, a Frenchman, invented a machine that could perform the four basic arithmetic operations
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EARLY COMPUTING MACHINES AND THEIR INVENTORS
HARDWARE, SOFTWARE AND COMPUTER SYSTEMS we will discuss what hardware, software, and computer systems are.
Then we will focus on how computer hardware and software components work together to execute computer programs.
The aims of this section are to: explain that a computer program is a sequence of instructions fo
performing a certain task on a computer; explain that hardware consists of the tangible parts of the computer; show that hardware and software solutions can be logically
equivalent – that is, a task carried out on a computer using software might be
reproducible using hardware, and vice versa; describe the information system model of a computer; describe the nature of data and instructions as they are stored in a
computer; recount the history of some early computing machines.
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SOFTWARE VS. HARDWAREYou will be learning about both hardware and software so
it is helpful to consider the relationship between them. Hardware consists of the tangible parts of the
computer system – ‘the parts that can be kicked’. Examples of hardware include the electronic circuits inside the casing, the keyboard and hard disk.
Software, on the other hand, is more abstract – it consists of sets of instructions that tell a computer how to perform a particular task. Examples of software are word-processor applications such as Microsoft Word, browsers such as Explorer or Netscape, and communications software such as FirstClass. The terms software and computer program are often used synonymously, though it could be argued that software is generally made up of a number of programs
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CONTINUE Although software and hardware are very different in nature,
they are also inextricably related. Any instruction performed by software can also be built directly into hardware, and instructions executed by hardware can often be simulated in software. As an illustration let us consider the multiplication of two numbers. One way of thinking about multiplication is to consider it as a number of additions: starting with nothing (zero) you need to add a particular number (one of the numbers to be multiplied) a specified number of times (the second number to be multiplied). For example, to multiply 3 by 4, we need to add 3 to 0, then add 3 to the result, and so on, until we have added 3 four times, as follows:
0 + 3 gives a result of 3 (first addition) 3 + 3 gives a result of 6 (second addition) 6 + 3 gives a result of 9 (third addition) 9 + 3 gives a result of 12 (fourth addition)
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CONTINUE
Now suppose that a computer has hardware (i.e. an electronic circuit) to carry out a simple arithmetic instruction such as ADD. Since multiplication is nothing more than repeated addition, we could construct a new circuit (or piece of hardware) made up of a number of ADD circuits that, working together, can multiply two numbers. Alternatively we could instruct the computer, using a computer program, to perform repeated addition using the existing ADD circuit .
The hardware and software solutions are logically equivalent – they both use repeated addition – but the hardware solution uses several ‘tangible’ electronic circuits, whereas the software solution uses the more abstract idea of ‘instructing’ the machine to use the same circuit repeatedly. The decision to implement some functions in hardware and others in software is based on factors such as speed, cost and reliability. You will learn how to write your own software (computer programs) in Units 7 to 10. 9
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UNIT 6: AGENDA
Hardware, Software and Computer system
The resources of a computer , and how they are managed.
Running a program.
Types of programming languages.
The structure of computer programs.
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UNIT 6: HARDWARE, SOFTWARE AND COMPUTER SYSTEM
Hardware vs. Software
Computer Hardware and Software components work together in order to execute computer program
Hardware: describes the physical parts of computer that can be touched.
Software: describes the information or the programming the computer uses, you can't touch it .
Firmware is the term used to refer to a sequence of instructions (software) etched into the read-only
memory (ROM) of the computer, usually to perform some system function. Because these
instructions are on a chip they form a permanent part of the computer and could be viewed as a
combination of hardware and software.
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UNIT 6: FIRMWARE a software program or set of instructions programmed
on a hardware device (usually in the ROM)
It provides the necessary instructions for how the device communicates with the other computer hardware
can be thought of as "semi-permanent" since it remains the same unless it is updated
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UNIT 6: EXAMPLE1"I bought a 100-pack of empty DVD discs and tried to burn a
video to a few of them but it would not work".
I contacted my DVD drive manufacturer and they suggested that I update the firmware on the DVD drive.
The updated Firmware had a new set of computer code for my drive instructing how to write to the DVD I’m using
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UNIT 6: HARDWARE VS. SOFTWARE Although Hardware and Software are different in
nature, there are related.
A solution to a computer problem can be implemented using either Hardware or Software.
Hardware uses several tangible electronic circuits.
Software uses instructions to use same circuits.
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UNIT 6: REFLECTION 1EX: 2.3
A book could be thought of as being made of paper and ink, or
it could be thought of as being a collection of words and sentences.
Which view is analogous to Software and which to Hardware?
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UNIT 6: COMPUTER AS A SYSTEM
The tutor asked us to define computer, after a discussion the result was a computer is a machine that Accepts input, Process Input then it gives a result as an Output.
So every machine that Accepts input, Processes that input, and produces Output is called a system
Perfect
Then my mother’s Washing machine is a system
Yes
Or
No
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UNIT 6: AGENDA Hardware, Software and Computer system
The resources of a computer, and how they are managed.
Running a program.
Types of programming languages.
The structure of computer programs.
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UNIT 6: REFLECTION 2EX:3.1
In what form are the data and Instructions stored in a computer?
Well, it is the easiest question so far , All data and instructions saved inside the computer ( in Memory) , read and accessed by CPU in order to execute these instructions are in Machine language ( 0/1) – Digital form .
COMPUTER SYSTEM : One simple view of an information system is that it is a machine
that can solve problems by carrying out a sequence of instructions, usually on a given set of data. The data provided is usually referred to as input, and the solution (or results) produced is referred to as the output.
Our view is that a computer differs from a calculating device in that it includes a mechanism that stores not only the data but also the instructions for processing that data, and the results that are to be output. If we have a computer at the heart of our information system we can extend our model as
( Input --- ( Process/ Storage) -- Out put
This is what we call information system based on computer . The word ‘process’ has a very particular meaning in some areas of
computing. In this unit we are using it to refer to all the processing (or manipulation) of the input so as to produce the output.
So far , system is what ever accepts ( input) , process this input ( execute, compute ) accordingly by executing specific instructions , then produce result .
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ACTIVITY 2.2
Use two online dictionaries (they could be the ones mentioned in Activity 2.1, or any others) to look up the term ‘computer’. Compare the two definitions.
Discussion The whatis.techtarget.com website has the following definition: A computer is a device that accepts information (in the form of digital data) and
manipulates it for some result based on a program or sequence of instructions on how data is to be processed.
Complex computers also include the means for storing data (including the program, which is also a form of data) for some necessary duration. (accessed 11 July 2003)
The webopedia website defines a computer as: A programmable machine. The two principal characteristics of a computer are: It responds to a specific set of instructions in a well-defined manner. It can execute a prerecorded list of instructions (a program). The first definition emphasizes the digital nature of the data that is manipulated by the
program, and it also mentions the storage of instructions and data, but only for ‘complex’ computers. The second definition does not mention digital data or storage, but it requires that the computer must respond to the instructions in a well-defined manner. Both definitions agree that a computer executes a list of instructions called a program.
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A computer is a device that accepts data and manipulates it by carrying out a sequence of instructions (a program), so as to produce some output. A computer also has the means of storing the input, the output and the program.
Input, output and instructions: The input to a computer process starts off as words or numbers entered from a
keyboard. However it can take other forms, such as images, sound, or digital information from scientific instruments. Sometimes data will already be available in the computer as a file, in which case the input might be via mouse clicks or some other input device.
In modern computers, all data, including the instructions that make up a computer program, are stored in the computer as binary digits (bits) – sequences of zeros and ones. The branch of mathematics that defines the rules governing the manipulation of entities with only two states, such as bits, is called binary logic (or Boolean algebra – after the Englishman, George Boole, who developed it in the middle of the nineteenth century).
It is important to be aware that at a fundamental level computer processing is simply the application of logic to binary numbers.
Of course in order to make the results readable by humans, the binary representations of the output need to be ‘translated’ back into an appropriate format.
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EXERCISE 2.5
Hardware, software and computer systems In History snippet 2 you learned about Babbage’s analytical machine.
(a) Could this be described as a computer according to the two website definitions given in the discussion following Activity 2.2?
(b) Does it fulfil the M150 course definition, as given after the same discussion?
Discussion (a) Babbage’s machine could respond to a series of instructions in a well-
defined way, and so it could be described as a computer according to the webopedia definition. However, the analytical machine did not process digital data and so it is not a computer according to the whatis.techtarget definition.
(b) According to the M150 definition, a computer must be able to store data, instructions and results. The analytical machine did not have storage space for the instructions (they were to be input using punched cards) and so it cannot be considered to be a computer according to our definition.
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INSIDE THE COMPUTER SYSTEM :
You learned that the circuits at the heart of a computer system consist of switch-like electronic components and that all data and instructions are stored in the computer as sequences of binary digits (bits), which are manipulated using binary logic. You read about some of the early machines which are considered to be the forerunners of today’s computers.
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THE HEART OF THE COMPUTER – THE CENTRAL PROCESSING UNIT (CPU)
Computer processes manipulate binary representations of data, using instructions that are themselves stored in binary format. The component of the computer in which this manipulation of binary data takes place is referred to as an arithmetic/logic unit (ALU). Movement of data between the ALU and other parts of the computer is coordinated by the control unit.
The terms ‘processor’, ‘microprocessor’ and ‘CPU’ are often used interchangeably. The term ‘microprocessor’ usually refers to the chip on which the processor is implemented.
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CONTINUE Within both the ALU and the control unit are small
numbers of memory locations known as registers which are used to hold single pieces of data or single instructions immediately before and after processing. The ALU and the control unit along with their registers are together referred to as the central processing unit (CPU) or processor of a computer. A much larger area of memory, known as main memory, is where the data and instructions that are not immediately required are held, and where results are eventually stored.
Individual pieces of data and instructions are moved from main memory into the registers as required. The registers are built from more efficient (and expensive) memory than main memory, thus allowing fast access and transfer of data.
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CONTINUE
The processor of a PC is usually on a single microchip,(or microprocessor) which can contain several tens of millions of circuits. Processors come in ‘families’, such as the Pentium 4, Celeron, AMD Athlon XP. Each family of processors has what is termed an instruction set. This is the collection of basic instructions, called machine language instructions, which a particular processor understands .
The terms ‘machine language’ and ‘machine code’ are synonymous, but we will be using machine language in this unit.
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The CPU together with the way in which memory, internal communications and input/output are organised define an architecture for a computer that has been well established since the 1940s when it was first described by the
mathematician John von Neumann. Characteristic of the von Neumann architecture is the fact that the program instructions are stored in the main
memory along with the
data.
Figure 3.2 shows how data
moves between the various
components. The data flow is
coordinated by the control unit,
through the sending and
receiving of control signals.
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UNIT 6: HARDWARE :CPU – THE HEART OF COMPUTER
The Central Processing Unit: (CPU also called processor) is the part of the computer that executes program instructions. It consists of two parts:
1. The Arithmetic and Logic Unit (ALU) is where all calculations and logical operations are performed.
a- Arithmetic operations involve addition, subtraction, multiplication, and division.
b- Logic operations basically consist of comparing or combining two values:• All ALUs can compare >, <, and =.• Some ALUs can also compare >=, <=, and <>.• Comparisons can be combined using the logical operations NOT, AND and OR.
Truth tables are used to formally define these logical operations.
2. The Control Unit (CU): The control unit interprets program instructions. The control unit communicates with main memory and with input and output device controllers. The control unit directs the ALU to execute program instructions.
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UNIT 6: CPU – THE HEART OF COMPUTER
The CPU Registers : are high-speed storage locations within the CPU, used for specific tasks:
Memory Data Register (MDR) is used to hold data that are being transferred to or from primary storage.
Memory Address Register (MAR) indicates the location of the data to be stored or retrieved from primary storage.
Instruction Register (IR) holds the instruction being executed.
Program Counter (PC) holds the primary storage address of the next instruction to be executed.
The address held in the PC ,instruction cycle insures sequential execution of instructions. Jumps to another part of the program are achieved by
instructions, which reset the contents of the program counter.
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UNIT 6: CPU – THE HEART OF COMPUTER
Accumulator (AC) holds the results of ALU operations.
Program Status Register (PS) contains binary flags that signal the results of the previous operation.
For example the carry bit will be set to 1 if the last arithmetic operation lost a carry bit, and to 0 otherwise. Other condition codes indicate whether the last result was negative, zero or overflowed.
General-purpose registers are used for different purposes.
The first three registers are used by the control unit and are not accessible to the programmer.
The arrangement of registers define the processor architecture.
REGISTERS
We stated that registers are very fast, efficient areas of memory that are located in the CPU and used as a holding area for all the data and other information needed during the processing of a program. In fact there are a number of different types of register, some located in the ALU, some in the control unit, and each designed to hold a particular type of information .
Arithmetic/logic unit (ALU) The arithmetic/logic unit is the part of the CPU where the
arithmetic and logical operations are carried out. It contains a number of registers where data is held directly prior to and following processing. Among other things, the ALU can:
add subtract compare multiply and divide (which may be derived from adding and subtracting). 31
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INSTRUCTION CYCLE
Each computer's CPU can have different cycles based on different instruction sets.
1. Fetch the instruction from main memory
The CPU presents the value of the program counter (PC) on the address bus. The CPU then fetches the instruction from main memory via the data bus into the memory data register (MDR). The value from the MDR is then placed into the current instruction register (CIR), a circuit that holds the instruction temporarily so that it can be decoded and executed. 32
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INSTRUCTION CYCLE Decode the instruction The instruction decoder interprets and implements
the instruction. The instruction register (IR) holds the current instruction, while the program counter (PC) holds the address in memory of the next instruction to be executed. the machine cycle or instruction cycle is generally divided into four parts:- 1)Fetching a instruction 2)Decoding a instruction 3)Executing a instruction 4)storing the instruction
2. Fetch data from main memory Read the effective address from main memory if the
instruction has an indirect address. Fetch required data from main memory to be processed and placed into registers.
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INSTRUCTION CYCLE 3. Execute the instruction From the instruction register, the data forming the
instruction is decoded by the control unit. It then passes the decoded information as a sequence of control signals to the relevant function units of the CPU to perform the actions required by the instruction such as reading values from registers, passing them to the Arithmetic logic unit (ALU) to add them together and writing the result back to a register. A condition signal is sent back to the control unit by the ALU if it is involved.
4. Store results Also called write back to memory. The result generated by
the operation is stored in the main memory, or sent to an output device. Based on the condition feedback from the ALU, the PC is either incremented to address the next instruction or updated to a different address where the next instruction will be fetched. The cycle is then repeated.
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SUMMARY the instructions in a computer program are processed by the
CPU, that data and instructions are stored in main memory, but moved to registers in the CPU as required, and that operations such as adding and logical comparisons are carried out by the ALU. We can summarise the steps carried out by the CPU in the execution of a computer program as follows:
This cycle continues, as shown in Figure 4.1, until all the instructions in the computer program have been carried out.
get an instruction from the program; find and transfer any data necessary to perform the
instruction; carry out the instruction (which may involve saving a result
for later use).
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During each cycle the CPU must: 1 locate the next (or if execution has just started, the first) instruction in the program, which is stored in main memory; 2 transfer this instruction into the processor by placing it into an appropriate register; 3 decode the instruction to see what it is to do (what this involves will be
discussed in more detail in Subsection 4.2); 4 locate (in main memory) any data the instruction refers to, and fetch it into the processor by placing it into an appropriate register; 5 do the processing on the data that the instruction requires (e.g. add a number to another number); 6 place the result in an appropriate register; 7 if necessary move the result back to main memory so that it can be used later in the processing; 8 update the program counter to hold the memory address of the next instruction
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MAIN MEMORY
A computer has a number of different types of memory (or data storage). As a computer user you are probably most familiar with main memory, often referred to as RAM, and file storage memory, such as that provided by a hard disk. Main memory is used to store a program of instructions and the data needed by the program while it is running. Its contents are volatile, i.e. they are lost when the computer is switched off. File storage memory is memory that is used to store large amounts of data for use at some later date. Unlike main memory, it is non-volatile, i.e. the data is persistent – it is not lost when the computer is turned off.
We will consider only main memory in this subsection. Main memory can be envisaged as a large collection of
sequentially ordered pigeon-holes, each of which can hold the same number of bits, equivalent to the word size of the computer. 37
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MAIN MEMORY The word size refers to the number of bits that the CPU can
manipulate at one time. It is determined by the size of the registers in the CPU and the number of bits that can be moved round the computer as a single unit. When people refer to computers as being ‘32-bit’ or ‘64-bit’ machines they are referring to word size. Older personal computers (including 386, 486 and Pentium PCs) had a word size of 32 bits. Newer processors such as the Itanium series have a 64-bit (or 8-byte) word size.
Locations in main memory are sequentially numbered, so that each one has a unique ‘address’ by which it can be directly accessed. This is why this type of memory is sometimes referred to as random-access memory (RAM).
The addressable nature of main memory makes the retrieval of data much faster than if there was a need to search sequentially through each ‘pigeonhole’ in turn until the right one was found. Furthermore, random access means that each memory location takes the same amount of time to access, regardless of its address.
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UNIT 6: MEMORY (also called primary storage, internal storage, or main memory).
Memory is the part of the computer that holds data for processing, programs, and information waiting to be output to secondary storage.
There are three main characteristics of memories:
The capacity of the memory varies in different computers and is measured in bytes.
A byte consists of 8 binary digits called bits. Each bit can represent binary 0 or binary 1. Each byte represents one
character in memory. There are four commonly used units of memory capacity:
QUESTIONS :List two characteristics of main memory. It is randomly accessible (or addressable). It is volatile.
Suppose a computer is described as having 128KB (i.e. 128 kilobytes) of RAM. (a) How many bytes of memory does it have? (b) If the word size of the processor is 64 bits, how many words can the memory
store? You learned about bits, bytes and words in Section 3 of Unit 3. In particular you
should recall that a byte contains 8 bits, and a kilobyte contains 1,024 bytes.
Discussion (a) There are 131,072 bytes of memory. As a single kilobyte is 1,024 bytes, 128 kilobytes is 128 6 1024 bytes, i.e. 131,072 bytes. (b) The memory can hold 16,384 words. As each byte contains 8 bits, a 64-bit
word is equivalent to an 8-byte word. There are 131,072 bytes in all, so the number of words is 131,072/8, i.e. 16,384.
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UNIT 6: MEMORY
There are two types of memory chips:
Random access memory (RAM): Data and programs must be loaded from external storage (such as disk) into RAM before it can be used by the processor. RAM is volatile (temporary).
Read only memory (ROM): chips have programs built into them at the factory and cannot be changed by the user, thus they are not volatile. programmable ROMs (PROM) that can be programmed by the
user using special devices to save his own information. ROM typically contains special instructions to start up the
computer, give keyboard keys their special control capabilities and put characters on the screen.
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UNIT 6: MEMORY HIERARCHY Memory hierarchy: there is a memory hierarchy
consisting of primary memory (CPU internal registers, cache memory, main memory) and secondary memory (external devices such as disks)
Cache memory: is a high-speed expensive RAM memory used to store copies of the most frequently accessed information in main memory.
Virtual memory: Virtual memory is a memory system used to increase the effective size of the computers physical main memory.
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UNIT 6: SECONDARY (EXTERNAL) STORAGE
We mentioned before that the main memory is volatile (temporary). If the power is turned off program and data disappear. External storage is nonvolatile (permanent). External storage also has much more capacity than the primary
memory. There are two approaches to external storage:
sequential access and direct access.
The most widely used external storage media are -- floppy disks, -- hard disks,
-- optical disks and -- magnetic tapes.
Disks are direct access storage media, while tapes are sequential access storage media.
THE OPERATING SYSTEM We have briefly examined the important hardware
components of a computer: the processor, memory and peripheral devices. Managing these resources to effectively coordinate and carry out all the computer’s tasks is the job of the operating system. Common operating systems for personal computers include Linux, Mac OS (for the Apple Macintosh) and the various versions of Windows, e.g. Windows 2000 and Windows XP.
An operating system is a complex piece of software that acts as an interface between the user (or an application program) and the computer hardware. It essentially enables the user to carry out a variety of complex tasks on the computer, without the need to know anything about what goes on ‘inside the box’. The functions of the operating system include the following.
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CONTINUE Provision of a user interface The user interface is the software that enables us to communicate with
our computers. It provides us with a means of inputting data and instructions, and presents output in a way that we can understand.
The user interfaces of early operating systems such as CP/M and DOS were text based, requiring the user to learn a set of commands which needed to be typed in following precise rules. Output to the screen also consisted entirely of characters. Today most PC operating systems provide graphical user interfaces (GUIs), the most common example of which is Microsoft Windows. GUI-based operating systems make use of icons, menus and other graphical widgets, with which the user interacts via a pointing device, usually a mouse. Most people find graphical interfaces more intuitive, quicker to learn, and easier to use than sequences of commands. A further advantage of GUIs is their availability for use by programs other than the core software provided by the operating system. For example, application programs (e.g. word processors, spreadsheet packages), even those produced by companies other than Microsoft, can ‘hook in’ to the Windows user interface to provide a consistent look and feel. This makes it much easier for users to learn how to use new applications.
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QUESTION :
Name four functions of an operating system? You could have given any four of the
following: providing a user interface; managing the allocation of memory; controlling peripheral devices; scheduling access to the processor; providing an interface between a computer
and an application; providing basic utilities.
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UNIT 6: OPERATING SYSTEM Is the most important system software component. It interacts between the application software and the computer
and manages the computer’s internal resources.
Within the OS, besides the kernel, there is a group of other programs called utility programs, that perform common tasks, such as formatting disks, copy files from other disks, backup disks, remove and rename files, and others.
Mainframes and minicomputers have powerful OS, including virtual memory, multiprogramming and multiprocessing, where many users can run different programs at the same time. Microcomputer OS focus on a single user.
The most important operating systems are: DOS, Microsoft Windows, Unix, Linux and MAC.
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UNIT 6: OPERATING SYSTEM
The Operating system has the following functions; Provision of user interface Management of the memory Coordination and control of peripheral devices. Scheduling access for the processor Interface between Hardware and computer
applications. Provide basic utilities (disk formatting, file
management, etc….).
The bootstrap loader: is a program that is stored permanently in the computer’s electronic circuitry in ROM. This process is called booting.
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UNIT 6: AGENDA Hardware, Software and Computer system
The resources of a computer , and how they are managed.
Running a program.
Types of programming languages.
The structure of computer programs.
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UNIT 6: THE FETCH/EXECUTE CYCLEDuring the program execution the CPU do the following steps:
Get an instruction from the program.
Find and transfer any data necessary to perform instruction.
Carry out the instruction.
The process of locating, transferring and carrying out a single instruction during execution is called fetch/execute cycle.
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UNIT 6: CONTINUEDuring each cycle the CPU must:
Locate the next instruction in the program which is stored in the main memory (first one is used if the execution has just started).
Transfer the instruction in to the processor by putting it in a register.
Decode the instruction. Locate any data located in the main memory which refers to the
instruction. Do the processing. Place the result in an appropriate register. If needed move result back to the main memory to be used later. Increment the program counter by 1.
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UNIT 6: EXAMPLE EXECUTING PROGRAM Executing Program
Data 2 3 ?
Memory location of data
501 502 503
InstructionLDA 501
ADD 502 STO 503 HLT 000
Memory location of instructions
701 702 703 704
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UNIT 6:CONTINUE
LDA 501
operator operand
LoaD Accumulator
address of a memory location
???
The Accumulator
3? ?2
502500 503501
part of the computer's memory
Before LDA executes
2after LDA executes
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UNIT 6:CONTINUE
ADD 502
operator operand
ADD to Accumulator
address of a memory location
2
The Accumulator
3? ?2
502500 503501
part of the computer's memory
before ADD executes
5after ADD executes
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UNIT 6:CONTINUE
STO 503
operator operand
STOre Accumulator in memory
address of a memory location
5
The Accumulator3? ?2
502500 503501
computer's memory before STO
before STO executes
5after STO executes
3? 52
502500 503501
computer's memory after STO
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UNIT 6:CONTINUE
HLT 000
operator operand
HaLT
dummy value - not used
No effect on accumulator or memory
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UNIT 6: AGENDA Hardware, Software and Computer system
The resources of a computer , and how they are managed.
Running a program.
Types of programming languages.
The structure of computer programs.
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UNIT 6: TYPES OF PROGRAMMING LANGUAGES. Five Generations of Programming Languages
GENERATION NAME SAMPLE STATEMENT First Machine 10010001 Second Assembly ADD A, B JMP L Third Procedural and structural Overtime:= 5 0; Fourth Object oriented FIND NAME "JONES“ Fifth Natural IF patient is dizzy, THEN check
temperature and blood pressure
Computer professionals talk about levels or generations of program ming languages, ranging from ‘low’ to ‘high.’ Programming languages are called lower level when they are closer to the language the computer itself uses.
The computer understands the 0s and 1s that make up bits and bytes. Programming languages are called higher level when they are closer to the language humans use that is, for English speakers, more like English.
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UNIT 6: MACHINE LANGUAGES: THE FIRST GENERATION We mentioned earlier that a byte is made up of bits, consisting of 1s and 0s.
These 1s and 0s may correspond to electricity’s being on or off in the computer.
They may also correspond to a magnetic charge’s being present or absent on storage media such as disk or tape.
Data represented in 1s and 0s is said to be written in machine language.
To see how hard this is to understand, imagine if you had to code this :
111100100111001111010010000100000111000000101011
Machine languages also vary according to computer design - another characteristic that makes them hard to work with
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UNIT 6: ASSEMBLY LANGUAGES: THE SECOND GENERATIONAssembly languages have a clear advantage over the 1s and 0s of
machine language because they use abbreviations or mnemonics. These are easier for human beings to remember. The machine language code we gave earlier could be expressed in
assembly language as:
ADD A, B
JMP L Assembly language is also considered low-level.
Assembly languages also vary from computer to computer.
With the third generation, we advance to high-level languages, many of which are considered portable languages.
That is, they can be run on more than one kind of com puter—they are “portable” from one machine to another.
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UNIT 6: HIGH-LEVEL PROCEDURAL LANGUAGES: THE THIRD GENERATION
People are able to understand languages that are more like their own (e.g., English) than machine languages or assembly
languages. These more English-like programming languages are called “high-level” languages.
However, most people still require some training in order to use higher-level languages. This is particularly true of procedural languages.
Procedural languages are programming languages with names like BASIC, Pascal, C, COBOL, and FORTRAN.
They are called “procedural” because they are designed to express the logic—the procedures—that can solve general problems.
For a procedural language to work on a computer, it must be translated into machine language Depending on the language, this translation is performed by either a compiler or an interpreter.
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UNIT 6: HIGH-LEVEL PROCEDURAL LANGUAGES: THE THIRD GENERATION
A compiler converts the programmer’s procedural language program, called the source code; into a machine language code, called the object code.
An interpreter converts the procedural language one statement at a time into machine code just before it is to be executed. No object code is saved.
What is the difference between using a compiler and using an interpreter?
When a program is run, the compiler requires two steps. The first step is to convert the entire program’s source code to object code.
The second step is to run the object code. The interpreter, in contrast, converts and runs the program one line at a time.
The advantage of a compiler language is that once the object code has been obtained, the program executes faster.
The advantage of an interpreter language is that programs are easier to develop.
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UNIT 5: PROBLEM-ORIENTED LANGUAGES: THE FOURTH GENERATION
Third-generation languages are valuable, but they require training in program ming.
Object-oriented languages, also known as very high-level languages, require little special training on the part of the user.
Unlike general-purpose languages, object-oriented languages are designed to solve specific problems. Some of these fourth-generation languages are used for very specific applications. Many consider Lotus 1-2-3 and dBASE to be flexible fourth-generation languages.
Query languages: Query languages enable nonprogrammers to use certain easily understood commands to search and generate reports from a database. An example is the commands used on an airline reservations system
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UNIT 6: NATURAL LANGUAGES: THE FIFTH GENERATION
Natural languages are still being developed.
They are designed to give people a more human (“natural”) connection with computers.
The languages are human languages: English, French, Japanese, or whatever.
Researchers also hope that natural languages will enable a computer to learn — to “remember” information, as people do, and to improve upon it.
Clearly this area is extremely challenging.
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UNIT 6: AGENDA Hardware, Software and Computer system
The resources of a computer , and how they are managed.
Running a program.
Types of programming languages.
The structure of computer programs.
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UNIT 6: THE BASIC BUILDING BLOCKS OF COMPUTER PROGRAMS All programs can be built from three logical building blocks
Sequence
• Take the first left
• Take the second right
• Take the third exit at the roundabout
Repetition/loops
• while you have not yet reached the turnoff for Little Whamping
•go straight ahead at each roundabout
• Selection/ifs
• If the traffic in the high street is heavy
•take the first left
•take the first right
•take the first left
• else
•follow the high street to the end
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UNIT 6:CONTINUE Let's not worry about the programming language for a while
The syntax for how you do sequence, selection and repetition varies from programming language to programming language but the basic structures stay the same.
Once you have the concepts clear you can apply them to any language (JavaScript, Java, Visual Basic, C#, C++, Perl etc etc)
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UNIT 6: SEQUENCE The only thing to worry about is getting the instructions in the correct order
buy a stamp
buy a birthday card write in the birthday card
address the envelope
post the envelope
Put these instructions into a logical sequence for Robbie the willing but slightly dim robot!
put the card in the envelope
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UNIT 6: SELECTION A selection instruction allows you to write programs (and remember programs are basically just plans) that will operate in different ways depending on circumstances
If I win the lottery this Saturday I'll tell my boss what I think of her on Monday otherwise I'll start an OU degree and get a better job in a
couple of years
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UNIT 6: TRUE OR FALSE Selection always includes a condition that can be evaluated when the program runs (i.e. the plan is executed) to be true or false (this is called a Boolean expression).
The truth or falsity of the condition determines which path is taken.
I win the lottery this Saturday
tell my boss what I think of her on Monday
start an OU degree
True FalseThe condition is like a fork in the
road determining
which path you take
a "flow chart"
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UNIT 6: SELECTION EXERCISES If Charlton Athletic stay in the premiership next season I'll renew my season ticket. Otherwise I'll spend my money on getting Sky instead.
Identify the condition and draw a flow chart diagram
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UNIT 6: REPETITION A repetition instruction allows one or more instructions to be repeated a number of times.
While I've got a chance of winning I'll keep putting one
foot in front of the other
I've got a chance of winning
put one foot in front of the other
False
Sorry Paula!
True
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UNIT 6: REPETITION EXERCISEI'm getting Robbie to plant tulip bulbs in the garden. I've given him a bag of bulbs and told him that while there are still any left in the bag he should take one out, dig a hole for it and put it in.
Draw a flow chart representing my instructions to Robbie.
What's wrong with these instructions for Robbie To make cups of tea for the family repeat the
following actions: put milk in cup put teabag in cup pour in boiling water
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UNIT 6: CONDITIONS AGAIN Important observation: both selection and repetition are controlled by conditions that can be evaluated to true or false (i.e. Boolean expressions). Selection - which path should I follow? Repetition - how often should I go round the loop?
Because Boolean expressions are of crucial importance a considerable chunk of Unit 6 section 6 is devoted to them.
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UNIT 6: COMPOUND CONDITIONS Often we want to combine separate conditions when using them to control a selection or a repetition e.g.
if (the customer is over 64 or the customer is under 18)
charge them reduced rate
else charge them full rate
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UNIT 6: EVALUATING COMPOUND CONDITIONS You have to evaluate the separate parts and combine them
according to rules in order to evaluate the truth or falsity of the overall expression
(the customer is over 64 or the customer is under 18)
true/false true/false
true/false
The rules used to combine the separate parts depend on the operator used. In this case the operator is or.
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UNIT 6: EVALUATING OR EXPRESSIONS If either or both of the sub-expressions are true then the whole expression evaluates as true. Only if both the sub-expressions are false does the whole expression evaluate to false.
Evaluate (the customer is over 64 or the customer is
under 18) When
a) the customer is 17b) the customer is 65c) the customer is 63
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UNIT 6: ANOTHER OR EXERCISEif (the patient is over 12 or the patient is under 60)
prescribe the adult dosage
else
prescribe reduced dosage
What will happen when the patient is:
a) 16
b) 11
c) 70
Is there a problem here?
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UNIT 6: EVALUATING AND EXPRESSIONSIf (the sky is purple and there is a shower of dead frogs)stay under the duvet
elseget up and go to work
If either or both of the sub-expressions are false then the whole expression evaluates as false. Only if both the sub-expressions are true does the whole expression evaluate to true.
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UNIT 6: AN AND EXERCISEIf (the date is an odd number and there's an "r" in the month)
drink Coffeeelse
drink Tea
What's to be drunk on:a) May 11th
b) March 21st
c) September 22nd
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UNIT 6: MIXING IT EXERCISE If ((gender = "male" and age > 64) or
(gender = "female" and age > 59))charge reduced rate
elsecharge full rate
What will happen for:
a) a male of 63b) a female of 60c) a male of 25
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UNIT 6: MIXING IT EXERCISE 2if (monthly income > 2000or (monthly income > 1000 and
monthly outgoings < 500))grant credit
elserefuse credit
What will happen for:
a) someone with monthly outgoings of 1800 and a monthly income of 2100
b) someone with a monthly income of 900 and monthly outgoings of 200
c) someone with a monthly income of 1200 and monthly outgoings of 600
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WHAT’S NEXTUnit 7: An introduction to programming using
JavaScript
Introduction
Getting started
Programming for selection: the if statement
Programming for repetition: the while statement
Programming for repetition: the for statement
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SOME REVIEW QUESTIONS What is assembly language? Write using assembly language a program that
adds 2 numbers. Using your program describe what is meant by operator and operand .Also describe what happens to in the computer hardware as the program is executed? In this case you can assume that the first number is stored at memory location 400 is 3 and the second number is stored at 401 is 4. Also assume that the starting memory location is 700.
Define virtual and cache memory? Describe using an example the meaning of low and
high level language? What is meant by compiler and interpreter?
