OCR H446 A-Level Computer Science

Transcription

1 Name: Class Teacher: Date: OCR H446 A-Level Computer Science REVISION BOOKLET 1.2 SOFTWARE AND SOFTWARE DEVELOPMENT Content in H446 A-Level Computer Science: 1.1 The characteristics of contemporary processors, input, output and storage devices 1.2 Software and software development 1.3 Exchanging data 1.4 Data types, data structures and algorithms 1.5 Legal, moral, cultural and ethical issues 2.1 Elements of computational thinking 2.2 Problem solving and programming 2.3 Algorithms

2 1.2.1 SYSTEMS SOFTWARE TOPIC The need for, function and purpose of operating systems Memory management: Paging Segmentation Virtual memory Interrupts, the role of interrupts and Interrupt Service Routines (ISR), role within the fetch-decode-execute cycle Scheduling: Round robin First come first served Multi-level feedback queues Shortest job first Shortest remaining time Distributed, embedded, multi-tasking, multi-user and Real Time operating systems BIOS Device drivers Virtual machines, any instance where software is used to take on the function of a machine: Including executing intermediate code or running an operating system within another

3 1.2.1 SYSTEMS SOFTWARE FUNCTION AND PURPOSE OF OPERATING SYSTEMS MEMORY MANAGEMENT PAGING SEGMENTATION VIRTUAL MEMORY INTERRUPTS ROLE OF INTERRUPTS INTERRUPT SERVICE ROUTINES (ISR)

4 ROLE OF INTERRUPTS IN THE FETCH-DECODE-EXECUTE CYCLE SCHEDULING ROUND ROBIN FIRST COME FIRST SERVED MULTI-LEVEL FEEDBACK QUEUES SHORTEST JOB FIRST SHORTEST REMAINING TIME

5 OPERATING SYSTEMS DISTRIBUTED EMBEDDED MULTI-TASKING MULTI-USER REAL-TIME BIOS

6 DEVICE DRIVERS VIRTUAL MACHINES RUNNING AN OPERATING SYSTEM WITHIN ANOTHER

7 1.2.2 APPLICATIONS GENERATION TOPIC The nature of applications, justifying suitable applications for a specific purpose Utilities Open source vs Closed source Translators: Interpreters Compilers Assemblers Stages of compilation: Lexical analysis Syntax analysis Code generation Optimisation Linkers and loaders and use of libraries

8 THE NATURE OF APPLICATIONS APPLICATIONS GENERATION UTILITIES OPEN SOURCE VS CLOSED SOURCE TRANSLATORS INTERPRETERS COMPILERS ASSEMBLERS

9 STAGES OF COMPILIATION LEXICAL ANALYSIS SYNTAX ANALYSIS CODE GENERATION OPTIMISATION LINKERS AND LOADERS USE OF LIBRARIES

10 1.2.3 SOFTWARE DEVELOPMENT TOPIC Understand software development lifecycles including: Waterfall Agile methodologies Extreme programming Spiral model Rapid application development The relative merits and drawbacks of different methodologies and when they might be used Writing and following algorithms

11 SOFTWARE DEVELOPMENT LIFECYCLES WATERFALL SOFTWARE DEVELOPMENT AGILE METHODOLOGIES EXTREME PROGRAMMING SPIRAL MODEL RAPID APPLICATION DEVELOPMENT

12 ADVANTAGES/DISADVANTAGES OF DIFFERENT METHODOLOGIES WRITING AND FOLLOWING ALGORITHMS

13 1.2.4 TYPES OF PROGRAMMING LANGUAGE TOPIC Need for and characteristics of a variety of programming paradigms Procedural languages Assembly languages: Including following and writing simple programs with the Little Man Computer instruction set Modes of addressing memory: Immediate Direct Indirect Indexed Object-oriented languages with an understanding of: Classes Objects Methods Attributes Inheritance Encapsulation Polymorphism

14 1.2.4 TYPES OF PROGRAMMING LANGUAGE CHARACTERISTICS OF A VARIETY OF PROGRAMMING PARADIGMS PROCEDURAL LANGUAGES ASSEMBLY LANGUAGES FOLLOWING AND WRITING LITTLE MAN COMPUTER INSTRUCTIONS MODES OF ADDRESSING MEMORY IMMEDIATE

15 DIRECT INDIRECT INDEXED OBJECT-ORIENTED LANGUAGES CLASSES OBJECTS METHODS

16 ATTRIBUTES INHERITANCE ENCAPSULATION POLYMORPHISM

17 EXAM QUESTIONS QUESTION 1 Intensive Care Units in hospitals are for patients in need of round the clock monitoring and support. Computerised systems can be used to monitor patients vital signs (temperature, heart rate, blood pressure and breathing). They can then alert medical professionals to any significant changes. These systems usually run on an embedded, real-time, operating system. i. State what is meant by the term real-time. [1] ii. Explain why a real-time operating system would be suitable for Intensive Care Units. [2]

18 QUESTION 2 The program, as shown in Fig 1 below, is written in assembly code using the Little Man Computer instruction set. It is supposed to take in two numbers and output the higher. INP STA NUMA INP STA NUMB SUB NUMA BRP NOTA LDA NUMB BRA QUIT NOTA LDA NUMA QUIT OUT HLT NUMA DAT NUMB DAT Fig 1. a. State what type of translator program would be needed to convert the code above into machine code. [1] b. Explain how you would correct the program so it outputs the higher of the two numbers entered. [2]

19 c. The program does not work correctly. Describe what the program actually does, using the numbers 4 and 9 being entered as an example. [2] d. Programs can also be written in high level languages. In pseudo code, write a procedural program that takes in two numbers and outputs the higher of them. [4]

20 QUESTION 3 A software development company is building an operating system for a mobile phone that is in the process of being designed. a. Give one reason the phone needs an operating system. [1] b. Explain how the developers could use virtual machines. [2] c. One of the developers is responsible for writing the code for what happens when the CPU receives an interrupt. Outline what the code must do. [6]

21 d. The developers follow the waterfall lifecycle. List three stages of the waterfall lifecycle [3] Justify why the waterfall lifecycle is suited to the development of the operating system. [2] Give one disadvantage of using the waterfall lifecycle to develop the operating system. [1]

22 e. The code is written using an object-oriented programming (OOP) language. Discuss the advantages and disadvantages to the team of developers of using OOP over procedural programming. You should refer to inheritance, encapsulation and polymorphism in your answer. [9]

23 QUESTION 4 The owner of a small shop has bought some new stock-handling software and is setting up a computer system in order to run it. The owner will use a number of pieces of utility software. State the purpose of each of the following types of utility software and describe how the owner would use them. File Handlers [3] Hardware Drivers [3] Backup Utility [3]

24 QUESTION 5 An operating system uses scheduling. One method of scheduling is first come, first served. a. Explain why the first come, first served scheduling method may not be efficient. [2] b. Describe one other scheduling method. [2] c. Explain why scheduling is necessary. [4]

25 d. Explain why memory management is necessary. [3] e. Paging may be used in memory management. Describe paging. [3]

26 QUESTION 6 A computer uses a Von Neumann processor. Describe the fetch-decode-execute cycle that this architecture uses. Fetch Decode Execute [3]

27 QUESTION 7 a. A burglar alarm runs on a processor with the Little Man Computer (LMC) instruction set. One of the instructions in the set is Branch if Positive (BRP). Describe what the instruction BRP does. [2] b. A numeric PIN code entered into the burglar alarm is compared with the code stored at the memory location passcode. If the codes match, the program jumps to the part of the program labelled deactivate. If the codes do not match, the program jumps to the part of the program labelled alarm. Write the LMC code to meet the requirements above. (You don t have to write the code for labels deactivate and alarm, as you can assume this has already been written elsewhere). [4]