F453 Computing Questions and Answers

Explain why interrupts are used in a computer system (2) Interrupts are used to obtain processor time for a higher priority task. They are also used to avoid delays. Other answers include: Avoid loss of data As an indicator to the processor That a device needs to be serviced

State two sources of interrupts and explain why these sources have different job priorities (4) SOURCE 1 – User interrupt – for example new user log on request SOURCE 2 – Power Failure/system failure REASON – New user can wait but the data must be saved before the power fails. Other answers include: Clock interrupt Software interrupt Peripheral interrupt i.e.. Printer empty.

Describe two reasons why scheduling is used. Maximise number of users… with no apparent delay Maximise number of jobs processed… As quickly as possible. Other answers include Obtain efficient user of processor time dependant upon priorities

Explain why jobs are given different priorities when in a job queue Some jobs are more urgent than others Priorities are used to maximise the use of computer resources

Assembly language and machine code are languages used in computing Assembly language and machine code are languages used in computing. Describe the term assembly language (2) It is a lower level language/machine specific that uses descriptive names for data stores and mnemonics for instructions. Other answers include Uses labels to allow selection Each instruction is generally translated into one machine code instruction May use Macros

Describe the term Machine Code (2) Binary notation Where instructions operate on bytes of data Other answers include Set of all instructions available To the architecture.

State three of the tasks performed by an assembler when producing machine code. (3) Reserves storage space for instructions and data Replaces mnemonic opcodes by machine codes Create symbol table to match label to addresses Checks syntax

Either an interpreter or compiler may be used with a HLL program Either an interpreter or compiler may be used with a HLL program. Describe one feature of an interpreter. (2) Translates one line/statement… Then allows it to be run before translation of the next line OR Reports error at a time.. And stops.

State two features of a compiler (2) Translates whole program as a unit Creates executable program/intermediate program Other answers include: May report a number of errors at the same time Optimisation.

Lexical analysis is one stage of compilation Lexical analysis is one stage of compilation. Describe what happens during lexical analysis. (8) Once the programmer has written the code, the source program is then used as the input and tokens are created from individual symbols and from the reserved words in the program. Tokens are a fixed length string of binary digits. Once this has taken place, the variable names are loaded into a symbol table and all redundant characters such as spaces and comments are removed. The final stages of this involves error diagnostics and the code is then prepared for the syntax analysis.

State the three stages in order, of the machine cycles in classic Von Neumann Architecture. (2) Fetch Decode Execute

Two computer architectures are reduced instruction set computer (RISC) and Complex instruction set computer (CISC) architectures. Complete the table below.

Compare the number of machine cycles used by RISC and CISC to complete a single instruction (2) RISC – each task may take many cycles CISC – a task may be completed in a single cycle As instructions may be more complex that individual instructions in RISC

An array processor is used in some systems An array processor is used in some systems. Explain the term array processor. (2) A processor that allows the same instruction to operate simultaneously On multiple data locations Other answers include: The same calculation on different data is very fast Single instruction multiple data.

Weather forecasting or airflow simulation around new aircraft. Give one example of the type of task for which an array processor is most suitable (1) Weather forecasting or airflow simulation around new aircraft.

A list of cities is: Aberdeen, Belfast, Cardiff, Glasgow, Oxford, York A list of cities is: Aberdeen, Belfast, Cardiff, Glasgow, Oxford, York. Show the steps of a serial search for York in the list. (2) Start at Belfast Look at each word in turn Until York is found.

A list of cities is: Aberdeen, Belfast, Cardiff, Glasgow, Oxford, York A list of cities is: Aberdeen, Belfast, Cardiff, Glasgow, Oxford, York. Show the steps of a binary search for York in the list. (3) Look at the middle (Cardiff. Glasgow,) York is in second half of list Repeat halving Until York is found.

Explain one advantage of a binary search compared with a serial search when searching for an item in any large set of data (3) Usually faster because Half the data is discarded at each step/fewer items are checked.

Add data item at position ‘pointer’ A stack contains a number of data items. List the steps needed to attempt to add one data item to the stack. (3) If stack is full Report error and stop Increment pointer Add data item at position ‘pointer’

Explain how a quick sort can be used to put a set of numbers into ascending numerical order. You may use the following set of numbers: 30 9 46 14 22 (5)

Give the name for one other method of sorting used in computing (1) Insertion sort

State the traversal that should be used to obtain the reverse polish notation form from a binary tree. (1) Post order

Other than a binary tree, state what data structure may be associated with RPN (1) Stack

State a symbol, often used in mathematical expressions that is not required when working with RPN Brackets

A program in a particular assembly language includes the instructions: JMP CD (jump to instruction labelled CD) and CD ADD 41 ( add number 41 to number in accumulator) Explain the term opcode and give one example from information given. (2) Opcode is the mnemonic part of the instruction and it indicates what is it to do. The example given is JMP/ADD

State the type of addressing used by the instruction AND 41 (1) Immediate

State the meaning of the term symbolic addressing and give one example from the information given. The use of characters to represent the address of a store location. The example is CD.

Explain the purpose of the accumulator (2) Temporary storage within ALU and it holds the data being processed. IT also deals with the input and output in the processor.

Describe indexed addressing (3) Uses the index register and an absolute address to calculate addresses to be used

State the meaning of direct addressing (1) Instruction gives to address to be used.

Explain why it is not possible to only use direct addressing in assembly languages (2) Because the number of addresses available is limited by the size of the address field. Code is not relocatable.

Explain the term data dictionary and give two examples of the information stored.(4) A data dictionary is a file containing descriptions of data in the database it is used by database managers when altering the database structure. It may include names of tables/columns and may define access rights. Other examples may include: Identifies foreign keys Identifies indexes Meaning of data columns Relationship between data.

Data description Language DDL It has been decided to start selling pet toys. Details of toys and their suppliers need to be added to the database. State the language used to create the table TOY (1) Data description Language DDL

Give three benefits to a relational database compared with flat files Avoid data duplication Easier to change data Data can be added easily