1. Theory Fundamentals
A section of Computer Science, 9608
Listing 10 of 304 questions
The environment in a very large greenhouse is managed by a computer system. The system uses a number of different sensors that include temperature sensors. In addition, the system controls a number of heaters, windows and sprinklers. State one other type of sensor that could be used with this system. Justify your choice. Sensor Justification Describe why feedback is important in this system. The system makes use of a number of parameters. These parameters are used in the code that runs the system. State one of the parameters used in controlling the temperature in the greenhouse. Explain how the parameter identified in part is used in the feedback process. There are eight temperature sensors numbered 1 to 8. Readings from these sensors are stored in four 16-bit memory locations. The memory locations have addresses from 4000 to 4003. Each memory location stores two sensor readings as two unsigned binary integers. Sensor 1 reading is stored in bits 8 to 15 of address 4000; Sensor 2 reading is stored in bits 0 to 7 of address 4000 and so on. The diagram shows that the current sensor 1 reading has a value of 97. Give the denary value of the current reading for Sensor 5. The following table shows part of the instruction set for a processor. The processor has one general purpose register, the Accumulator (ACC). Instruction Explanation Op code Operand LDD Direct addressing. Load the contents of the location at the given address to ACC. AND #n Bitwise AND operation of the contents of ACC with the operand. AND Bitwise AND operation of the contents of ACC with the contents of . XOR #n Bitwise XOR operation of the contents of ACC with the operand. XOR Bitwise XOR operation of the contents of ACC with the contents of . OR #n Bitwise OR operation of the contents of ACC with the operand. OR Bitwise OR operation of the contents of ACC with the contents of . can be an absolute address or a symbolic address. LSL #n Bits in ACC are shifted n places to the left. Zeros are introduced on the right hand end. LSR #n Bits in ACC are shifted n places to the right. Zeros are introduced on the left hand end. The reading for Sensor 5 is used in a calculation. The calculation is carried out by two assembly language instructions. The first instruction loads the contents of the 16-bit location that contains the value for Sensor 5. The second instruction moves the bits in Sensor 5 so that the 16-bit value is the value of Sensor 5. Complete the two instructions in the following code. Use the instruction set provided. LDD // load the contents of the 16-bit location containing the value for Sensor 5 into the Accumulator // move the bits in the Accumulator so that the Accumulator stores the value of Sensor 5 as an unsigned 16-bit binary integer
9608_w17_qp_32
THEORY
2017
Paper 3, Variant 2
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The bit depth of an image dictates how many different colours can be represented by each pixel. State the number of different colours that can be represented by a bit depth of 8 bits. One binary colour is represented by 0100 1110 Convert the unsigned binary number 0100 1110 into denary. Convert the denary number −194 into 12-bit two’s complement. Convert the Binary Coded Decimal (BCD) value 0110 1001 into denary. Identify one practical application where BCD is used. One example of a character set used by computers is ASCII. Describe how one character is represented in a character set. Data can be compressed using either lossy or lossless compression. Tick (✓) one box in each scenario to identify whether lossy or lossless compression should be used. Justify your choice. A program written in a high-level language. Lossy Lossless Justification A photograph that needs to be emailed to a friend. Lossy Lossless Justification You need to upload a video that you have created to a website. Lossy Lossless Justification
9608_w19_qp_11
THEORY
2019
Paper 1, Variant 1
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Different types of data can be represented in a computer system. Numeric is one type of data. Convert the following denary number into Binary Coded Decimal (BCD). Convert the following two’s complement binary integer into denary. Convert the following hexadecimal number into denary. AB Character is another type of data. The following tables show part of the ASCII code character set. Character Denary value Character Denary value A a B b C c D d E e Describe how the computer uses ASCII codes to represent characters. Convert the following string into ASCII codes. Bed Give the denary ASCII code for the following character. H
9608_w20_qp_12
THEORY
2020
Paper 1, Variant 2
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A car monitoring system provides information to the driver about the car’s performance and alerts the driver to possible problems. • Data about the car’s performance is stored in three memory locations with addresses 601 to 603. • Location 601 contains the distance travelled in kilometres for the current trip as a binary integer. • Location 602 contains the quantity of fuel used in litres for the current trip, as a fixed-point binary number with 5 places before the binary point and three places after the binary point. • The four least significant bits of location 603 are flags used to identify problems with the car, for example, the fuel is low. A flag is set to 1 if there is a problem, or 0 if not. These problems are: • Bit 0 - high engine temperature • Bit 1 - low oil pressure • Bit 2 - low battery • Bit 3 - low fuel • Bits 4 to 7 are not used The current contents of addresses 601 to 603 are: Most significant Least significant State the information that the current contents of addresses 601 to 603 will provide to the driver. A car has low oil pressure and low fuel. It has travelled 80 kilometres and used 7.25 litres of fuel. Complete the contents of the addresses to record this information. The following table shows the assembly language instructions for the car performance monitoring system. There is one general purpose register, the Accumulator (ACC). Table 8.1 Instruction Explanation Label Op code Operand LDM #n Load the number n to ACC LDD Load the contents of the location at the given address to ACC STO Store the contents of ACC at the given address AND #n Bitwise AND operation of the contents of ACC with the numeric operand CMP #n Compare the contents of ACC with the number n JPE Following a compare instruction, jump to or if the compare was True JMP Jump to or : Labels an instruction Note: # denotes immediate addressing B denotes a binary number, for example B01001010 & denotes a hexadecimal number, for example &4A Write assembly language instructions to set the contents of addresses 601 and 602 to zero, and set all four least significant bits of the contents of address 603 to one. Use the instruction set from Table 8.1. A program continuously checks the flags. If a flag is set, the program moves to the error-handling routine at the specified label. For example, if the engine temperature is high, the program jumps to the label for the error-handling routine HIGHTEMP. The error-handling routine instructions have not been provided. A programmer has written most of the instructions for the program in the following table. There are four missing operands. Complete the assembly language program by writing the four missing operands. Label Op code Operand CHECKFLAGS: LDD AND &0F STO TEMP AND &01 CMP &01 JPE HIGHTEMP LDD TEMP AND &02 CMP JPE LOWOIL LDD TEMP AND CMP &04 JPE LOWBATT LDD AND &08 CMP &08 JPE LOWFUEL JMP TEMP:
9608_w20_qp_32
THEORY
2020
Paper 3, Variant 2
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Convert the following two’s complement binary integer into denary. Show your working. Working Answer Convert the following unsigned binary integer into hexadecimal. Convert the following denary integer to Binary Coded Decimal (BCD). Give two examples of practical applications of BCD. An encryption routine replaces each character in a short message with a different character. For example, the following table shows how the routine encrypts the word ‘HELLO’ by adding 3 to the ASCII denary value of each character. Original character H E L L O ASCII denary value ASCII denary value + 3 Encrypted character K H O O R The ASCII value of the character A is 65. Complete the table to show how the routine will encrypt the word ‘WANDS’. Original character W A N D S ASCII denary value ASCII denary value + 3 Encrypted character
9608_w21_qp_13
THEORY
2021
Paper 1, Variant 3
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A group of students broadcast a school radio station on a website. They record their sound clips in advance and email them to the producer. Describe how sampling is used to record the sound clips. The students use software to compress the sound clips before emailing them. Circle your chosen method of compression and justify your choice. Lossy / Lossless Justification: Students also email images to the radio station for use on its website. These are compressed before sending using run-length encoding (RLE). Explain what is meant by run-length encoding. The following diagrams show: • the denary colour code that represents each colour • the first three rows of a bitmap image Colour symbol Colour code B W B B B B B B B B B B W W W B B B B B B B B B B B B W W W W W W B B B B B B B B W W W W W W W W W … Show how RLE will compress the first three rows of this image. Row 1: Row 2: Row 3:
9608_s16_qp_11
THEORY
2016
Paper 1, Variant 1
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A group of students broadcast a school radio station on a website. They record their sound clips in advance and email them to the producer. Describe how sampling is used to record the sound clips. The students use software to compress the sound clips before emailing them. Circle your chosen method of compression and justify your choice. Lossy / Lossless Justification: Students also email images to the radio station for use on its website. These are compressed before sending using run-length encoding (RLE). Explain what is meant by run-length encoding. The following diagrams show: • the denary colour code that represents each colour • the first three rows of a bitmap image Colour symbol Colour code B W B B B B B B B B B B W W W B B B B B B B B B B B B W W W W W W B B B B B B B B W W W W W W W W W … Show how RLE will compress the first three rows of this image. Row 1: Row 2: Row 3:
9608_s16_qp_12
THEORY
2016
Paper 1, Variant 2
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A computer has a microphone and captures a voice recording using sound recording software. Before making a recording, the user can select the sampling rate. Define the term sampling rate. Explain how the sampling rate will influence the accuracy of the digitised sound. Sampling rate Explanation The computer also has bitmap software. Define the terms pixel and screen resolution. Pixel Screen resolution A picture has been drawn and is saved as a monochrome bitmap image. State how many pixels are stored in one byte. A second picture has width 2048 pixels and height 512 pixels. It is saved as a 256-colour image. Calculate the file size in kilobytes. Show your working. The actual bitmap file size will be larger than your calculated value. State another data item that the bitmap file stores in addition to the pixel data.
9608_s17_qp_11
THEORY
2017
Paper 1, Variant 1
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Questions Discovered
304