Computer Architecture

Question 1

What are the internal components of a computer system?

Answer 1

• The internal components of a computer system consist of the hardware required to store and process data, and communicate with external, peripheral devices
• It contains the processor, main memory, I/O controllers
• These components are connected by the system bus (this is comprised of the address bus, data bus, control bus)

Question 2

What is the processor?

Answer 2

It is part of the computer that processes data by executing program instructions (these are low-level instructions in the form of machine code that the processor has been designed to handle, based on a specific processor instruction set)
- For the processor to be able to execute a program, the program instructions need to be transferred from secondary storage into main memory where they can be detached, decoded and executed. The data that needs to be processed is also loaded into main memory (from secondary storage) or provided by the input and output devices via the I/O controllers.

Question 3

What is main memory?

Answer 3

This is memory that can be accessed directly by the processor. Each memory location, where instructions or data are stored as binary sequences, has a physical address, which is a number used to locate that memory location and access it’s contents.

Question 4

Classifications of main memory

Answer 4

RAM, ROM

Question 5

What is RAM?

Answer 5

Random Access Memory is a type of computer memory that is used to temporarily store data that the computer is currently using or processing. RAM is volatile memory, which means that the data stored in it is lost when the power is turned off. RAM is typically used to store the operating system, application programs, and data that the computer is currently using.

Question 6

What is ROM?

Answer 6

Read Only Memory is a type of computer memory that is used to permanently store data that does not need to be modified. ROM is non-volatile memory, which means that the data stored in it is retained even when the power is turned off. ROM is typically used to store the computer’s BIOS (basic imputer/output system), which contains the instructions for booting the computer, as well as firmware for other hardware devices.

Question 7

What are I/O controllers?

Answer 7

They allow input data to be received for processing from input devices. The results of computation to be output from the system to output devices like display screens

Question 8

What are buses?

Answer 8

A bus is a communication system that is used to transfer data between components. The system bus is a set of parallel connections that allow internal components to communicate with each other and exchange data. There are also external buses that are used to connect the peripherals to the processor. These can be serial or parallel connections.

Question 9

Classifications of buses

Answer 9

Data, address, control

Question 10

What is a data bus?

Answer 10

The data bus is used to transfer data and instructions. The data bus is bidirectional; it allows a two-way connection between between internal components of the system allowing values to be written to or read from a location.

Question 11

What is the width of the data bus?

Answer 11

The width of the bus refers to its number of parallel lines and this determines the number of bits that can be transferred in one operation. If the width is 8 bits, then 8 bits can be transferred at one time.

Question 12

What is an address bus?

Answer 12

The address bus is used to specify the address of a memory location to either read data from or write data to that memory location

Question 13

What is the width of an address bus?

Answer 13

The width of this refers to its number of parallel lines which determines the number of bits that can be used to form an address of a memory location. If the width of the address bus is n bits then there are 2^n numbers that can be used to address memory locations; the max number of addressable memory locations.

Question 14

What is the control bus?

Answer 14

The control bus is used to send control signa,s that manage and orchestrate the operations that take place inside a computer system. This includes exchanging status signals between the components of the computer system, and transmitting clock signals required for the coordination of operation.

Question 15

What are the parts of a processor?

Answer 15

ALU, Control Unit, Clock, Registers,

Question 16

What is the ALU?

Answer 16

The ALU is responsible for performing arithmetic calculations and logical operations that include: addition, subtraction, multiplication, division, logical bit wise operation (AND, OR, NOT, XOR), comparison between values, shifting binary patterns to the left or right.

Question 17

What is the control unit?

Answer 17

This is charge of organising the sequence in which program instructions are executed followed by deciding the instructions. Decoding an instruction means that the opcode and operand of an instruction are analysed to determine what needs to be done to execute the instruction. This means that the control unit is responsible for directing the operations of all the other components of the of the processor:

• It uses control signals to enable data to be read from and written to the main memory
• It decodes every instruction that the processor will execute to determine what needs to be done (a calculation, logical operation, loading or storing data)
• It organises the sequence of micro-operations that need to be performed in order to carry out an inspection
• It uses control signals to determine the operation the ALU will carry out at each instance

Question 18

What is a clock?

Answer 18

The system clock — also simply referred to as the clock — generates
regular clock pulses by emitting a signal that continuously oscillates
between a low (or ‘0’) and a high (or ‘1’) state. The clock signal is used
to synchronise the operations of the processor components.
▪ If the processor needs to read a memory location, it sends a read
request via the control bus, along with the address of the memory
location via the address bus. These operations happen at the same
time (i.e. in the same clock cycle).
▪ Depending on how long it takes to access the memory, the processor
then receives the contents of that memory location via the data bus,
after a number of clock cycles

Question 19

What are registers and their classifications?

Answer 19

They are locations of computer memory within the processor that provide extremely fast access. Classifications include general-purpose registers, special purpose registers.

Question 20

What are general purpose registers?

Answer 20

Having to access the main memory can slow down the execution of instructions. Therefore, the processor uses registers to temporarily store and access the results of operations. The ALU is connected to a set of general-purpose
registers that are used to keep the results of the intermediate calculations that are produced as part of a larger computation.

Question 21

What are special-purpose registers?

Answer 21

They are processor-based registers that are
used for a specific purpose. The registers used in the fetch-decodeexecute cycle are special-purpose registers because each one of them has a specific role to play in each phase of the fetch-decode-execute cycle.

Question 22

Classifications of special purpose registers?

Answer 22

Program counter, current instruction register, status register, memory address register, memory buffer register, accumulator

Question 23

What is the program counter register?

Answer 23

Holds the address of the next instruction to be executed by the processor

Question 24

What is the current instruction register?

Answer 24

Holds the current instruction that the processor is
executing.

Question 25

What is the status register?

Answer 25

Used to store information about the result of the last instruction
that the ALU executed. Each bit within the status register acts as a flag to indicate if
an error or exception has occurred within the process, or to enable or disable
interrupts to be raised:
o An error or exception is when the result of a calculation requires further
action. For example, it signifies if the result of a calculation is negative or
zero, or if a calculation produced an overflow or/and a carry.
o An interrupt is an event outside of the program process that requires the
attention of the processor. For example, indicating a hardware malfunction

Question 26

What is the memory address register?

Answer 26

Temporarily holds the address of the memory
location (in main memory) that the processor needs to access, either to read from or write to.

Question 27

What is the memory buffer register?

Answer 27

It temporarily,y holds the data that is read from or writer to the main memory.

Question 28

What is the accumulator register?

Answer 28

It stores the result of any calculation processed by the ALU. The processor accesses other general-purpose registers where temporary valves are stored while calculations are completed. Any result resides in the accumulator

Question 29

FETCH

Answer 29

▪ The program counter keeps the address of the next instruction to be
executed. The contents of the PC are copied into the memory address
register (MAR) which is connected to the address bus. The address of
the next instruction to be executed is placed on the address bus
▪ Once the address of the instruction is on the address bus, the control
unit instructs a memory read operation to allow the contents of the
memory location to be transferred to the processor. The instruction
that is stored at that address is transferred using the data bus from a
the main memory to the processor and is saved in the memory buffer
register
▪ Simultaneously the contents of the PC are incremented by one so that
they point to the address of the next instruction that needs to be
fetched.
▪ The contents of the MBR are copied to the current instruction register
(holds the next instruction that the processor is executing). This is to
ensure that the current instruction can be kept safe so that the MBR
can be used during the execute stage to store any additional dat

Question 30

DECODE

Answer 30

The control unit decodes the instruction that is kept in the CIR. This involves splitting in into operand and opcode to determine what type
of instruction needs to carried out

Question 31

EXECUTE

Answer 31

▪ The instruction is executed. The exact sequence of operations depends on the type of instruction that is being executed. For
example, for an arithmetic instruction (such as adding two numbers together) any required data are fetched from the main memory, then
the calculation is executed by the Arithmetic and Logic Unit (ALU), and the result of the instruction is stored in the accumulator, a generalpurpose register, or back into main memory

Question 32

What is Von Neumann architecture?

Answer 32

o The Von Neumann architecture used the idea of storing program instructions
and data in main memory and moving them between memory and processor
o It consist of a processor, memory unit that can communicate wit the
processor, connections for input and output devices, secondary storage for
saving and backing up data
o They also have buses

Question 33

What is Harvard architecture?

Answer 33

o On the other hand, Harvard architecture keeps instructions and data in
separate memories. The processor accesses these memories using separate
data and address buses; the processor is connected to the instructions
memory using a dedicated set of address and data buses
o This is used in embedded systems

Question 34

Comparison

Answer 34

o Harvard architecture uses separate memory units and buses for instructions and data which means that both memories can be accessed simultaneously,and this minimises the issue of keeping the processor waiting while loading
or saving data into memory which increases processor performance
o Von Neumann architecture uses the same address and data buses for both instructions and data which means that they both share the same pathways
o In Harvard architecture each memory can be adapted to meet the needs of a particular system; the instruction and data memories can be different sizes (the instructions memory can be implemented as read only which protects
programs from hacking). Von Neumann architecture allows for the instructions and data to be saved in the same memory which can be
exploited
o Von Neuman architecture enables a more flexible use of the main memory, which allows the processor to run a variety of programs that are not known in advance
o Von Neumann = general purpose
o Harvard = special purpose

Question 35

What is barcode reader?

Answer 35

▪ Barcodes are printed diagrams that consist of light and dark portions. They contain information which can be read by a computer using a barcode reader. There are two main types of barcode: 1D and 2D.
▪ 2D barcodes can contain more information in the same amount of space as a 1D barcode but require more processing in order for the information to be extracted. Barcode readers consist of a laser light source, a lens, photodiodes and a mirror. The mirror directs light from the laser onto a printed barcode. The light reflected by the barcode passes through the lens and is incident on the photodiode which turns light into electrical charge. This electrical charge can be measured and processed to form a digital signal
representing the content of a barcode. Light portions of a barcode reflect the most light while dark sections absorb incident light. The pattern of light and dark stripes in a barcode corresponds to binary 1s and 0s.
▪ Barcodes can have error detection and prevention methods such as parity
bits and check digits built in, allowing computers to tell whether a barcode has been read correctly. If a barcode fails to scan correctly, perhaps because the barcode is dirty, the reader will continue to scan until the barcode is read successfully. Barcode readers can scan barcodes 1000s of times a second, so the time delay caused by rescanning is hardly perceptible to humans

Question 36

What is a digital camera?

Answer 36

Digital cameras consist of a lens that focuses light onto a sensor. The path of
light between the lens and the sensor is regulated by a shutter.
▪ Two sensors commonly used in digital cameras are CMOS (complementary
metal oxide semiconductor) and CCD (charge coupled device) which both
convert incident light into electrical charge. Charge builds up in cells, each of
which represents a pixel in the image. Once the photograph has been taken,
the charge in each of the cells is measured and converted to a digital value
which is then processed by the camera and stored as a digital image.
▪ In colour cameras, there are multiple cells for each pixel, each of which has a
filter that only allows in certain wavelengths of light. This lets the camera
build up a separate image for the intensity of each colour of light which can
then be combined to form a full colour photograph.
▪ A Bayer filter is a special colour filter used in digital cameras that has the
same number of green filters as red and blue combined. Using a Bayer filter
produces an image that is a closer approximation of what the human eye,
which is most sensitive to green light, sees.

Question 37

What is a laser printer?

Answer 37

▪ A laser printer is an output device that produces images on paper from
digital signals. Laser printers, which print whole pages at a time, consist of a
laser light source, a mirror, a drum, a toner roller and fusers.
▪ When a document is printed, the drum is positively charged all over before
the laser is directed at its surface by the mirror. Areas on which the laser is
incident are discharged, leaving behind an impression of the page in
electrical charge on the drum. The toner roller dispenses negatively charged
toner (a type of plastic powder) onto the drum. As opposite charges attract,
toner is attracted to the positively charged portions of the drum. The toner
is then applied to the paper by the drum before the paper is heated by
fusers, fixing the toner to the paper. Colour printers apply the same process
with four different colours of toner: cyan, yellow, magenta and black (CYMK)
to achieve full colour prints

Question 38

What is RFID?

Answer 38

RFID, which stands for radio frequency identification, is a method of
transferring information wirelessly between a tag and a reader. RFID is used
in contactless credit and debit cards as well as in some hotel room cards.
Inside an RFID tag is a chip which contains a small amount of memory. The
chip is attached to a coil of wire which acts as an antenna. Most RFID tags
are passive, meaning that they induce enough power wirelessly from the
reader to operate the chip. However, active tags (which contain a small
power supply like a battery) also exist. Active tags can be used much further
away from readers than passive tags which must be held within a few
centimeters of their reader.
▪ When an RFID tag is scanned, the reader emits radio waves which are picked
up by the tag’s antenna (stage 1). The power induced in the tag’s antenna
from these waves is enough to power the chip (stage 2) which then uses its
antenna to emit its own radio wave (stage 3), which contains the
information held on the chip. This wave is picked up by the reader which
decodes the information and returns the information to a computer.

Question 39

Advantages of RAM

Answer 39

• Speed: RAM in much faster than other types of storage, such as hard drive or solid-state drive, which means that the computer can access the data stored in RAM , more quickly.
• Flexibility: RAM is go,a tile memory, which means that the data stored in it can be easily modified or deleted. This makes it ideal for storing data that the computer is currently using or processing
• Capacity: The capacity of RAMa can be easily upgraded, which allows the computer to store more data in memory and thus improve performance
• Power Management: RAM consumes less power compared to hard drives and solid-state drives which makes it an ideal memory for portable devices

Question 40

Disadvantages of RAM

Answer 40

• Volatility: RAM is volatile memory, which means that the data stored in it is lost when the power is turned off. This can be a problem for important data that needs to be preserved, such as unsaved work or files that have not been backed up
• Capacity: The capacity of RAM is limited, and although it can be upgraded if may still not be sufficient for certain applications or tasks that require a lot of memory.
• Cost: RAM can be relatively expensive compared to other types of memory, such as hard drives or solid-state drives, which can make upgrading the memory of a computer more costly

Question 41

Advantages of Read Only Memory

Answer 41

• Non-volatility: ROM is non-volatile memory, which means that the data stored in it is retained even when the power is turned off. This makes it ideal for storing data that does not need to be modified, such as the BIOS or firmware for other hardware devices
• Reliability: Because the data stored in ROM is not easily modified, it is less prone to corruption or errors than other types of memory
• Power Management: ROM consumes less power compared to other types of memory, which makes it an ideal memory for portable devices

Question 42

Disadvantages of ROM

Answer 42

• Limited Flexibility: ROM is read-only memory, which means that the data stored in it cannot be modified. This can be a problem for applications or firmware that need to be updated or modified
• Limited Capacity: The capacity of ROM is typically limited, and upgrading it can be difficult or expensive.
• Cost: ROM can be relatively expensive compared to other types of memory, such as hard drives or solid-state drives, which can make upgrading the memory of a computer or device more costly.