Name and describe three buses used in the von Neumann model. Bus 1 Description Bus 2 Description Bus 3 Description The sequence of operations shows, in register transfer notation, the fetch stage of the fetch- execute cycle. MAR ← PC ← + 1 MDR ← [] CIR ← • denotes contents of the specified register or memory location • step 1 above is read as “the contents of the Program Counter are copied to the Memory Address Register” Describe what is happening at step 2. Describe what is happening at step 3. Describe what is happening at step 4. Describe what happens to the registers when the following instruction is executed: LDD 35 Explain what is meant by an interrupt. Explain the actions of the processor when an interrupt is detected.

9608_s15_qp_13

THEORY

2015

Paper 1, Variant 3

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The Von Neumann model uses a series of registers. Explain what is meant by the term register. Explain the purpose of the Memory Data Register (MDR). Name two registers, other than the MDR, that are used in the fetch-execute cycle. Register 1 Register 2 X is a register. The current contents of X are: The current contents of register X represent an unsigned binary integer. Convert the value in X into denary. The current contents of register X represent a Binary Coded Decimal. Convert the value in X into denary. The current contents of register X stores a two’s complement binary integer. Convert the value in X into denary.

9608_s18_qp_11

THEORY

2018

Paper 1, Variant 1

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A computer is designed using the Von Neumann model. Describe the role of the Arithmetic and Logic Unit (ALU) and Control Unit (CU) in the Von Neumann model. ALU CU Describe the role of the Status Register and Program Counter (PC). Status Register PC H is a register. The current contents of H are: The current contents of register H represent an unsigned binary integer. Convert the value in register H into denary. Convert the value in register H into hexadecimal. The current contents of register H represent a two’s complement binary integer. Convert the value in register H into denary. State why register H does not currently contain a Binary Coded Decimal (BCD).

9608_s18_qp_13

THEORY

2018

Paper 1, Variant 3

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A large warehouse stores goods that must be kept above a temperature of 15 degrees Celsius. The warehouse has six temperature sensors which are each placed at a different location in the warehouse. A computer system is programmed to turn on appropriate heaters when one of the sensors is below the minimum temperature. State the name given to the type of system described. Justify your answer to part . Sensors and heaters are two types of device used in this system. State two other devices that are used. Justify your choice. Device 1 Justification Device 2 Justification The computer system stores the temperature readings for the six sensors in six 8-bit memory locations. Six of the bits in an 8-bit register, LOWREG, are used to indicate whether a particular reading is below the minimum temperature. A value of 1 means the reading is below the minimum temperature. For example: This pattern of bits in LOWREG shows that sensor 5, sensor 4 and sensor 1 have readings below the minimum temperature. Not used Not used The following table shows part of the instruction set for a processor which has one general purpose register, the Accumulator (ACC), and an Index Register (. Instruction Explanation Op code Operand LDD Direct addressing. Load the contents of the given address to ACC. LDR #n Immediate addressing. Load the number n to IX. LDX Indexed addressing. Form the address from + the contents of the index register. Copy the contents of this calculated address to ACC. STO Store the contents of ACC at the given address. INC Add 1 to the contents of the register (ACC or . ADD Add the contents of the given address to the ACC. OR Bitwise OR operation of the contents of ACC with the contents of address. CMP #n Compare the contents of ACC with number n. CMP Compare the contents of ACC with the contents of . JMP Jump to the given address. JPE Following a compare instruction, jump to if the compare was True. JGE Following a compare instruction, jump to if the content of ACC is greater than or equal to the number used in the compare instruction. The code uses six memory locations to store the temperature readings. It stores readings for sensors 1 to 6 at addresses 8000 to 8005. At a particular time, the memory locations store the following data. Dry run the assembly language code starting at START and finishing when the loop has been processed twice. LOWTEMP LOWREG COUNTER ACC IX B00000000 Explain why the operand of the instruction labelled Q1 has the value 32. The code beginning at the instruction labelled HEATON must make the system turn on the heaters in those areas that are below the minimum temperature. Describe what this code will have to do.

9608_w17_qp_31

THEORY

2017

Paper 3, Variant 1

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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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A large warehouse stores goods that must be kept above a temperature of 15 degrees Celsius. The warehouse has six temperature sensors which are each placed at a different location in the warehouse. A computer system is programmed to turn on appropriate heaters when one of the sensors is below the minimum temperature. State the name given to the type of system described. Justify your answer to part . Sensors and heaters are two types of device used in this system. State two other devices that are used. Justify your choice. Device 1 Justification Device 2 Justification The computer system stores the temperature readings for the six sensors in six 8-bit memory locations. Six of the bits in an 8-bit register, LOWREG, are used to indicate whether a particular reading is below the minimum temperature. A value of 1 means the reading is below the minimum temperature. For example: This pattern of bits in LOWREG shows that sensor 5, sensor 4 and sensor 1 have readings below the minimum temperature. Not used Not used The following table shows part of the instruction set for a processor which has one general purpose register, the Accumulator (ACC), and an Index Register (. Instruction Explanation Op code Operand LDD Direct addressing. Load the contents of the given address to ACC. LDR #n Immediate addressing. Load the number n to IX. LDX Indexed addressing. Form the address from + the contents of the index register. Copy the contents of this calculated address to ACC. STO Store the contents of ACC at the given address. INC Add 1 to the contents of the register (ACC or . ADD Add the contents of the given address to the ACC. OR Bitwise OR operation of the contents of ACC with the contents of address. CMP #n Compare the contents of ACC with number n. CMP Compare the contents of ACC with the contents of . JMP Jump to the given address. JPE Following a compare instruction, jump to if the compare was True. JGE Following a compare instruction, jump to if the content of ACC is greater than or equal to the number used in the compare instruction. The code uses six memory locations to store the temperature readings. It stores readings for sensors 1 to 6 at addresses 8000 to 8005. At a particular time, the memory locations store the following data. Dry run the assembly language code starting at START and finishing when the loop has been processed twice. LOWTEMP LOWREG COUNTER ACC IX B00000000 Explain why the operand of the instruction labelled Q1 has the value 32. The code beginning at the instruction labelled HEATON must make the system turn on the heaters in those areas that are below the minimum temperature. Describe what this code will have to do.

9608_w17_qp_33

THEORY

2017

Paper 3, Variant 3

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Von Neumann is an example of a computer architecture. The diagram has registers used in Von Neumann architecture on the left and descriptions on the right. Draw one line to match each register with its correct description. Register Description Current Instruction Register Memory Address Register Program Counter Memory Data Register Stores the address of the memory location about to be written to or read from Stores the address of the next instruction to be read Stores the address of the input device from which the processor accesses the instruction Stores the instruction that is being decoded and executed Stores the data that has just been read from memory, or is about to be written to memory Many components of the computer system transfer data between them using buses. One example of a bus is an address bus. Name two other buses that exist within a computer and give the purpose of each. Bus 1 Purpose Bus 2 Purpose State the benefit of increasing the address bus width from 16 bits to 32 bits. The following statements describe features of a low-level language. Complete the statements by writing the appropriate terms in the spaces. A is a sequence of instructions that are given an identifier. These instructions may need to be executed several times. A is an instruction that tells the assembler to do something. It is not a program instruction. The processor’s instruction set can be put into several groups. One of these groups is .

9608_w19_qp_11

THEORY

2019

Paper 1, Variant 1

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The following incomplete table shows descriptions relating to computer architectures. Complete the table by inserting the appropriate terms. Description Term A • There are several processors. • Each processor executes different sets of instructions on one set of data at the same time. B • The processor has several ALUs. • Each ALU executes the same set of instructions on different sets of data at the same time. C • There is only one processor. • The processor executes one set of instructions on one set of data. D • There are several processors. • Each processor executes a different set of instructions. • Each processor operates on different sets of data. State three characteristics of massively parallel computers.

9608_w19_qp_31

THEORY

2019

Paper 3, Variant 1

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The following incomplete table shows descriptions relating to computer architectures. Complete the table by inserting the appropriate terms. Description Term A • There are several processors. • Each processor executes different sets of instructions on one set of data at the same time. B • The processor has several ALUs. • Each ALU executes the same set of instructions on different sets of data at the same time. C • There is only one processor. • The processor executes one set of instructions on one set of data. D • There are several processors. • Each processor executes a different set of instructions. • Each processor operates on different sets of data. State three characteristics of massively parallel computers.

9608_w19_qp_33

THEORY

2019

Paper 3, Variant 3

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Complete the following statements about CPU architecture by filling in the missing terms. The Von Neumann model for a computer system uses the program concept. A program is a series of instructions that are saved in . The processor each instruction, it and then it. The processor uses several to store the data and instructions from the program because they can be accessed faster than main memory. The following table shows assembly language instructions for a processor that 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. LDM #n Immediate addressing. Load the denary number n to ACC. LDI Indirect addressing. The address to be used is at the given address. Load the contents of this second address to ACC. STO Store contents of ACC at the given address. ADD Add the contents of the given address to ACC. CMP Compare the contents of ACC with the contents of . OUT Output to screen the character whose ASCII value is stored in ACC. INC Add 1 to the contents of the register (ACC or . JPE Following a compare instruction, jump to if the compare was True. JPN Following a compare instruction, jump to if the compare was False. END Return control to the operating system. The current contents of the main memory are: Address Instruction LDD 80 ADD 80 STO 80 LDD 82 INC ACC STO 82 CMP 81 JPN 50 LDD 80 OUT END … ASCII code table (Selected codes only) ASCII Code Character & ‘ ( ) * Assembly language instructions can be put into groups. Tick (✓) one box in each column to identify the appropriate instruction group for each of the three assembly language instructions. Instruction group Assembly language instruction STO 80 JPN 50 INC ACC Input and output of data Data movement Arithmetic operations Unconditional and conditional jump instructions Compare instructions

9608_w20_qp_12

THEORY

2020

Paper 1, Variant 2

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