7 - Fundamentals of Computer Organisation and Architecture

Question 1

What is the difference between von Neumann and Harvard architectures?

Answer 1

In von Neumann architecture, instructions and data share the same memory which the processor communicates with over a shared bus called the system bus. In Harvard architecture, instructions and data are allocated separate memories. The processor is connected to both memories by separate buses so that each memory can be accessed simultaneously.

Question 2

What are the advantages of Harvard architecture.

Answer 2

• Instructions and data are handled quicker as they do not have to share the same bus.
• Avoid bottleneck of single data/address bus.
• Instructions and data memory can have different word lengths.
• Avoids possibility of data being executed as code, which is one method that can be exploited by hackers.

Question 3

Where is von Neumann architecture used?

Answer 3

Von Neumann architecture is used extensively in general purpose computing systems.

Question 4

Where is Harvard architecture used?

Answer 4

Harvard architecture is extensively used in embedded systems such as digital signal processing (DSP) systems.

Question 5

What is meant by the stored program concept?

Answer 5

A program must be resident in main memory in order to be executed. Instructions are fetched and executed one at a time by the processor. Programs can be moved in and out of memory.

Question 6

What does an opcode represent?

Answer 6

It indicates the basic machine operation.

Question 7

What does an operand represent?

Answer 7

The value that the instruction operates on.

Question 8

What is an instruction set?

Answer 8

The set of bit patterns for which machine operations have been defined. An instruction set is processor specific.

Question 9

What is the difference between direct and immediate addressing?

Answer 9

Direct addressing means that the operand is the memory address or register number of the datum whereas immediate addressing means the operand is the datum.

Question 10

How does the addressing mode relate to the operand of an instruction?

Answer 10

It indicates how the value in the operand should be interpreted.

Question 11

Describe the principles of operation of a bar code reader and how the software in the barcode reader will use the check digit.

Answer 11

For a photodiode system a laser is shone at the bar code. A moving mirror moves the light beam across the bar code and the light is reflected back. White bands reflect more light than black bands. A light sensor measures the amount of reflected light which is converted into an electrical signal and analysed to determine the value encoded in the bar code.

The data digits are passed through a function to calculate a check digit. The result is compared against the check digit read in. If they don’t match an error is indicated. If they match the bar code is accepted and processed.

Question 12

Explain the purpose of the check digit in a bar code.

Answer 12

To check the bar code is valid.

Question 13

Describe the principles of operation of a laser printer.

Answer 13

The print drum is coated in static charge. The printer generates a bitmap image from the data. Laser beam is directed on the print drum via a rotating octagonal mirror. The laser is modulated and neutralises electric charge on the drum where image should be dark. Toner is given charge and the charged drum picks up toner. There is one drum mechanism for each colour. Toner is then transferred from drum to paper. The toner is then fused to the paper by heated rollers.

Question 14

A RFID system is made up of a transponder built into an RFID tag and an interrogator or reader. Explain the principle of operation of this RFID system.

Answer 14

The RFID reader transmits a signal to the antenna of the RFID tag. The RFID tag is energised by the signal from the reader. The transponder in the tag sends the data signal which is received by the reader.

Question 15

Describe the principles of operation of a digital camera.

Answer 15

Lens focuses light onto an array of sensors on the sensor chip. Each sensor produces an electrical signal. The signal represents a pixel. The image is captured when the shutter is pressed. An ADC converts measurement of light intensity into binary data. Firmware performs data processing to “tidy up” image. Colour filter is used to generate data separately for red, green, blue colour components. Image is recorded as an array of pixels.

Question 16

Describe the principles of operation of a solid state drive (SSD)

Answer 16

Most commonly uses NAND flash memory. Data is stored using floating gate transistors. This is a type of transistor that can trap and store charge. Data must be read in pages and written/erased in blocks. Can use single-level cells that store one bit or multi-level cells that store two bits.

Question 17

Describe the principles of operation of a hard drive

Answer 17

The hard disk is a magnetic medium. Binary digits are represented by magnetising spots on the disk. The hard disk is made up of platters that are divided into tracks (which are concentric circles) and sectors. The drive head moves radially, while the disk continually spins at a high speed. Data is read/written as correct sector passes under the read/write head. There is one head per platter and the head is parked when not in use.

Question 18

What are the development in the design of hard disk drives that has enabled an increase in storage capacity?

Answer 18

• More platters
• Greater density of each platter
• More tracks on a platter
• Change to perpendicular magnetic domains
• Ability to write smaller magnetic domains
• Use of different alloy materials for the platter

Question 19

What are the hardware components of a solid-state drive?

Answer 19

• NAND memory
• Controller
• SATA interface

Question 20

What are the differences between primary and secondary storage?

Answer 20

• Secondary storage is non-volatile
• Secondary storage is not directly accessible to the processor
• Capacity of primary store is limited by width of the address bus whereas there is no limit on capacity of secondary store
• Data in primary store can be accessed more quickly than data in secondary store

Question 21

Describe the principles of operation of an optical disk drive that is used to read data from an optical disk, such as CD-ROM or DVD-ROM

Answer 21

With optical disks, data is stored on a spiral track. The disk spins at constant linear velocity. A low power laser is shone at the disk. Light is focussed on spot on track. Some light is reflected back from the disk. The amount of light reflected back is measured. Continuation of land/pit on the disk reflects light whereas transition between land and pit scatters light. Transition between land and pit indicates a 1 and continuation of land/pit represents 0.

Question 22

Explain why a laser printer with a built-in wireless network adapter is likely to be a
suitable choice of printer for a small office.

Answer 22

Laser printer is suitable because it prints many pages per minute and there is a low cost per printed page as toner is cheaper than ink.

Having a wireless network adapter is suitable means its easy to share printer between many devices, can print directly from computers with WiFi and WiFi should be fast enough for likely number of users (as small office).