Higher Computing – Computer Systems : Computer Structure Homework
Homework 1 – The Processor
1.
2.
3.
Where does the control unit send signals to?
To Main Memory
1
Describe a logic operation carried out by the ALU.
AND both part of the condition must be true to take a certain action
OR
one part of the condition or the other must be true to take a certain action
1
Describe the purpose of the address bus.
The address bus holds the address of the memory location being accessed.
4.
A register will hold the address of the location to be written to.
Describe one other function of a register.
Hold data that is being transferred to or from memory;
Hold the instructions that are being carried out.
5.
1
What is the purpose of the control unit in a CPU?
1.
2.
3.
4.
6.
1
To control the timing of operations within the processor
To send out signals that fetch instructions from the main memory
To interpret these instructions
To carry out instructions that are fetched from main memory.
1
Describe the purpose of two signals found on the control bus.
Any two of;
 A read signal on the control lines instructs data to place data from the specified
memory address on the data bus.
 A write signal on the control lines instructs memory to take data on the data bus and
place it in the location specified by the address bus
 The Clock line is used to synchronize all the operations of the CPU. The pulses control
when each step in the fetch-execute cycle takes place. These timing pulses coordinate
and regulate the activities of the processor.
 A signal on the reset line returns the system to its initial state, stops all processes,
clears the registers and RAM.
 A signal on the interrupt line causes the current routine being carried out to be
suspended and gives control of the processor to another routine.
2
7.
State the purpose of registers in a microprocessor.



8.
Hold data that is being transferred to or from memory;
Hold the address of the location in memory which the processor is accessing to read or
write data;
Hold the instructions that are being carried out.
1
The processor and memory are linked by the address, data and control buses.
Give two examples (different from Q6) of the use of the control bus.
See answer to question 6
9.
1
The processor receives a signal on an interrupt control line. Explain what happens when the
processor receives the signal.
A signal on the interrupt line causes the current routine being carried out to be suspended and
gives control of the processor to another routine.
2
Total (11)
Homework 2 – The Bus System
1.
What is the function of
(a)
the data bus
(a)
(b)
2.
the address bus
The data bus allows data to be transferred between the processor and memory.
The address bus holds the address of the memory location being accessed.
2
What would be the effect of increasing the lines from 16 to 32 on
(a)
the address bus
(b)
the data bus
(a)
(b)
3.
(b)
The more lines on the address bus, the more locations the system can, in theory,
address.
System performance would be improved.
2
Why is the address bus uni-directional whereas the data bus and control bus are bidirectional?
Because the address bus only need to send data in one direction as opposed to the data bus and
control bus which have to take data to and from memory and the processor
1
4.
Describe a situation where the reset line will be used.
If the system stalls, a reset would get the machine moving again
5.
Why is the timing function of the clock line important to the operation of a processor?
1
The Clock line is used to synchronise all the operations of the CPU. The pulses control when
each step in the fetch-execute cycle takes place. These timing pulses coordinate and regulate
the activities of the processor.
1
Total (7)
Homework 3 – The Fetch Execute Cycle
1.
What is the function of
(a)
the address bus
(b)
in fetching data from memory.
(a)
(b)
2.


4.
The address bus holds the address of the memory location being accessed.
The data bus allows data to be transferred between the processor and memory.
2
Describe the stages of the fetch execute cycle. Your answer should refer to
appropriate buses and control lines.



3.
the data bus
The memory address of the next instruction is placed on the address bus;
A read signal is activated on the Read Lines;
The data stored at the addressed memory location is placed on the data bus and
transferred to a register which holds it until it is executed
The processor interprets the instruction;
The processor carries out the instruction.
5
Complete the two missing stages of the fetch-execute cycle.
1.
The memory address of the next instruction is placed on the address bus.
2.
A read signal is activated on the Read Lines;
3.
The instruction is transferred to the processor on the data bus.
4.
The processor interprets and carries out the instruction.
2
Data is to be transferred from the processor to main memory using a write operation.
Describe how a processor would perform a write operation. Your answer should mention
the buses or control lines used at each stage.
The steps involved in a memory write operation are:
o Address bus is set up with the address to be written to.
o Data bus is set up with the data to be written
o Write line (on control bus) is activated.
o Place data in appropriate memory location
4
Total (13)
Homework 4 – Computer Memory
1.
What is a bootstrap loader?
It is a part of the OS that is stored in ROM and starts up the computer
2
2.
How is memory organized so that data can be stored and retrieved by the processor?
Computer memory is divided up into memory locations.
3.
1
When Carolyn switches on her computer, system software in ROM finds and loads the OS.
Name this system software in ROM.
Bootstrap loader
4.
1
Ernie’s computer has 16mb of cache memory. Describe how the use of cache memory may
improve system performance.
When the processor attempts a read from memory, it checks cache first. If the data is
already stored there it is transferred directly to the processor. This saves a read operation
which is much slower than accessing cache.
2
5.
A new computer system has a 3GHz processor with a 64-bit data bus and a 32-bit
address bus. Calculate the maximum amount of memory that can be addressed by this
computer. Show all working and express your answer in appropriate units.
2a*d
232 * 64
4,294,967,296 * 64
274,877,906,944/8
34359738368/1024
33554432/1024
32768/1024
32 Gb
6.
3
A palmtop computer has a processor with a 24 bit address bus, 32 bit data bus and 8
control lines. The palmtop computer accepts flash cards as additional storage.
Calculate the maximum amount of memory that the palmtop computer can address.
Express your answer in appropriate units. Show all working.
2a*d
224 * 32
16,777,216 * 32
536,870,912/8
67108864/1024
65536/1024
64 Mb
3
Total (12)
Homework 5 - Performance
1.
How does the use of cache memory improve system performance?
When the processor attempts a read from memory, it checks cache first. If the data is
already stored there it is transferred directly to the processor. This saves a read operation
which is much slower than accessing cache.
2
2.
Is the clock speed on its own a reliable indicator of system performance?
No, other factors such as the size of the data bus must be considered
3.
1
Why is measuring the number of FLOPS a better approach than measuring MIPS?
FLOPS is an objective approach measuring the number of clearly definable, arithmetical tasks
that can be carried out per second
Whereas MIPS does not take into account the size and complexity of the instructions being
carried out and is a rough indication of performance.
2
4
Why are application-based tests seen as reliable indicators of a system performance?
This is the actual time that a computer would take to carry a specific set of tasks
5.
2
Why is the rate of data transfer to and from peripherals important to system
performance?
Peripherals are slower than the processor but they transfer data at different speeds and the
quicker the data is transferred the quicker the computer can process the data.
1
6.
Why is a system with a 64-bit data bus width not necessarily twice as fast as one with a 32-bit
data bus width?
You will have to consider other factors such as the size of cache. Also it would depend on the
complexity of the instructions being dealt with
1
7.
Explain how word size affects system performance.
The word size indicates the number of bits that can be transferred in parallel to and from
memory.
1
8.
Processor clock speed is one factor which affects system performance. Name one other
factor and describe how it affects system performance.
•
Memory
• Data in RAM does not have to be fetched from slower disc.
• Some memory chips enable faster memory reads.
•
9.
More RAM allows more/larger programs, more multi-tasking
•
The width of the data bus;
• The width of the data bus indicates the number of bits that can be transferred
in parallel to and from memory.
•
The use of cache memory;
• Processor can get this data quicker than locating it in main memory.
•
The rate of data transfer to and from peripherals.
• All peripherals operate at slower speeds than the processor.
• This slows down processing if reading from a disk/cd etc.
• Selecting a drive with a faster transfer rate can improve the overall
performance of your system.
Explain the effect of a cache on the performance of a computer.
The larger cache is, the fewer fetches required from main memory as more data cached
10.
(a)
(b)
Clock speed may only be accurately used to compare processors of the same type
A more powerful processor may achieve more in a shorter number of pulses 2
Name and describe one other measure of processing power.



data bus width
cache memory
rate of data transfer to an from peripheral devices
Mercury ZX
3.7 GHz Ami Processor
1 Mb Cache memory
32 bit Data Bus
24 bit Address Bus
512 Mb RAM
200 Gb Hard Disk
(a)
1
Describe two weaknesses of “clock speed” as a measure of processor
performance.


11.
2
1
Phantom IV
3.9 GHz Storm Processor
2 Mb Cache memory
32 bit Data Bus
24 bit Address Bus
512 Mb RAM
320 Gb Hard Disk
Explain one technical reason why the Phantom IV may give the best
performance.
One of the following;
 Faster clock speed will mean more instructions fetched in a fixed time OR
 Larger cache means (more instructions can be stored) reducing fetches to main
memory
1
(b)
State one technical reason why the Mercury ZX may give the best
performance.







12.
Do not know the architecture of the machines/ CPUs.
Mercury might have more efficient/effective instruction set.
Phantom IV may be CISC, Mercury may be RISC.
Mercury may have reason more registers within the CPU than the Phantom IV.
Mercury may process more instructions per second than the Phantom (may be
expressed in terms of mips/flops).
Mercury may have a faster hard drive speed than the Phantom IV.
Any one from the above or other valid
Two methods of measuring performance are application based tests and MIPS.
(a)
Explain why MIPS may be the better measure of processor performance than
application based tests.
2
(b)
State one other measure of processor performance.
1
Clock speed, FLOPS
13.
1
Explain why increasing the number of registers could improve system performance.
It would allow more data to be stored within the processor avoiding the need for it to be got
from cache or RAM
1
Total (22)