Practice Paper 2 (Cambridge International A-Level Computer Science)

A computer stores each character a user types as a 7-bit ASCII code.

The table shows three ASCII codes in denary.

(a) The user types the character 'e'. Show how the 7-bit ASCII code for 'e' is worked out and write the code in binary.

(b) A program converts the character 'e' to the character 'E'. Show how the ASCII code for 'E' is worked out from the ASCII code for 'e' and write the code in binary.

A photograph is stored as a bitmap image.

The photograph has a resolution of 4000 pixels wide by 3000 pixels high. The bit depth is 4 bytes.

Calculate an estimate for the file size of the photograph in megabytes.

Show your working.

Identify two elements of a bitmap image that can be changed to reduce its file size.

A video doorbell is attached to the front door of a house. The doorbell uses a motion sensor to detect when a visitor walks in front of the door. When the motion sensor is activated:

• The digital camera in the doorbell starts recording a video.
• A message is transmitted to a smartphone so that the person who lives in the house can watch the video.

The doorbell also has a button that can be pressed. When the button is pressed, a message is transmitted to a smartphone to play the doorbell sound.

The videos are stored on the doorbell’s internal secondary storage device and overwritten when the secondary storage device is full.

The video doorbell allows both real-time and on-demand bit streaming.

(i) State what is meant by bit streaming.

(ii) Give two differences between real-time and on-demand bit streaming.

A self-service ticket machine at a railway station has both Read Only Memory (ROM) and Random Access Memory (RAM).

A customer uses the machine to choose a journey and to pay for a ticket.

Explain why the ticket machine needs both types of memory.

Complete the truth table for the logic expression:

X = (A XOR B) NAND (A AND (B XOR C))

Draw the logic circuit for the logic expression:

W = P NAND ((Q OR NOT R) XOR (P XOR Q))

A programmer writes a program in assembly language. The processor cannot run this program until it has been translated.

(i) State the name of the software that translates an assembly language program.

(ii) State the name given to the translated program that the processor runs.

A building security system uses an 8-bit status register. Each bit reports one sensor. A bit is set to 1 when its sensor has been triggered and is 0 when it has not.

The table shows which sensor each bit reports.

The system must raise a full alarm only when the window sensor and the motion sensor have both been triggered.

Explain how bit masking is used to carry out this test. Your answer must include the 8-bit mask, the bitwise operation used, and how the result of the operation is interpreted.

Use the status register contents 01001010 as an example in your answer.

A computer is upgraded so that its processor has a larger amount of cache memory.

Explain how this can improve the performance of the computer.

A software developer is writing a computer program.

The developer uses an interpreter while writing the program code because it is easier for debugging.

Explain one reason why it is easier to debug the program code using an interpreter instead of a compiler.

The program is ready to be sold to customers.

The developer uses a compiler because it creates an executable file.

Explain the reasons why the need to create an executable file makes the complier the appropriate choice when the program is complete.

The programmer uses program libraries when developing the program.

Describe two benefits to the programmer of using program libraries.

A company stores customer data in a database.

Define the term data validation and the term data verification.

A hospital stores the medical records of its patients on a computer system.

Each statement below describes one of these three terms: security of data, privacy of data, integrity of data.

Statement 1: The hospital makes sure that a patient's record can only be read by the doctor who is treating that patient.

Statement 2: The hospital makes sure that a blood test result is stored in the record without any change to its value.

Identify the term that each statement describes.

A bank introduces an Artificial Intelligence (AI) system that reads loan applications and decides which of them a member of staff should look at first.

Describe one economic impact of this system on the bank.

A company stores its data in a relational database. The database management system (DBMS) uses Structured Query Language (SQL).

SQL has two parts.

(i) State the name of the part of SQL that the DBMS uses to create and change the structure of a database.

(ii) State the name of the part of SQL that the DBMS uses to add, change and query the data that is stored in a database.

State what is meant by each of the following terms in a relational database.

Secondary key ...............................................................................................................

.................................................................................................................................

Foreign key ....................................................................................................................

.................................................................................................................................

An online bookshop uses a Database Management System (DBMS).

Two members of staff work with the database on the same day.

• Anika is a database developer. She needs to add a new table to the database and build a screen that other staff will use to type in new stock.
• Ben works in the warehouse. He needs a list of every order that was placed in March.

For each member of staff, identify the DBMS software tool they use and explain why that tool is the correct one.

A program stores the email addresses of new users.

The program must:

• input an email address
• check that the email address is valid
• store a valid email address in the next free element of a 1D array.

An email address is valid only if all three of these are true:

• it contains exactly one @ character
• there is at least one character before the @
• its last four characters are .com

Stepwise refinement is applied to the algorithm. The first refinement is:

Step 1 Input the email address.

Step 2 Check that the email address is valid.

Step 3 If the email address is valid, store it in the array at the next free index.

Step 4 If the email address is not valid, output an error message.

Step 2 is not yet at a level of detail from which the task may be programmed.

Outline the three steps that Step 2 refines into.

Do not use pseudocode statements in your answer.

A company hires out electric scooters in a city. A user unlocks a scooter using a mobile app, rides it, and then ends the hire by locking the scooter at any scooter parking point. The user pays for each minute of the hire.

An abstract model of the hire system is to be produced.

State four items of data that should be stored each time a scooter is hired.

State two operations that would be needed to process the hire data.

The diagram shows an Abstract Data Type (ADT) representation of a linked list after data items have been added.

• PS is the start pointer.
• PF is the free list pointer.
• Labels Df, Dc, Db and Dy represent the data items of nodes in the list.
• Labels Fg, Fh, Fm and Fw represent the data items of nodes in the free list.
• The symbol Ø represents a null pointer.

A program will be written to include a linked list to store alphanumeric user IDs.

The design uses two variables and two 1D arrays to implement the linked list. Each array element contains data of a single data type and not a record.

The statements below describe the design.

Complete the statements.

The two variables will be of type ........................................................................... .

The two variables will be used as ....................................................................... to the arrays.

The values stored in the two variables will indicate .............................................. .

The first 1D array will be of type ............................................................................. .

The first 1D array will be used to ............................................................................ .

The second 1D array will be of type ....................................................................... .

The second 1D array will be used to ...................................................................................... .

Refer to the insert for the list of pseudocode functions and operators.

A program is being developed in pseudocode before being converted into a programming language.

The following table shows four valid pseudocode assignment statements.

Complete the table by giving the data type that should be used to declare the variable underlined in each assignment statement.

A program writes a message to a log file each time an error occurs.

The text file ErrorLog.txt already exists and contains the messages from earlier runs of the program. These messages must not be lost.

The procedure AddError() takes one parameter Message of type STRING. It adds Message to ErrorLog.txt as a new line, then closes the file.

The first and last lines of the procedure are given.

Complete the procedure by writing the three pseudocode statements that are missing.

A program uses a stack to store the product codes of items as they are scanned at a checkout.

The stack is held in memory locations 700 to 707.

The operation of this stack may be summarised as follows:

• The TopOfStack pointer points to the last item added to the stack.
• The BottomOfStack pointer points to the first item on the stack.
• The stack grows upwards when items are added.

The diagram shows the current state of the stack.

Complete the following table by writing the answers.

One type of run-time error can cause a program to stop responding (‘freezing’).

Identify a particular type of programming construct that can generate this type of error and explain why it occurs.

Construct .......................................................................................................

Explanation.....................................................................................................

The function Process() contains a selection construct using a CASE structure.

Write pseudocode using a single selection construct with the same functionality without using a CASE structure.

Refer to the insert for the list of pseudocode functions and operators.

Four of the expressions used in the program are represented by pseudocode in the table.

Complete each pseudocode expression with a function or operator so that it evaluates to the value shown.

Any functions and operators used must be defined in the insert.