Fundamentals of Computer Organisation and Architecture Flashcards
Describe Von Neumann architecture
Shared memory space for instructions and data, with both stored in the same format.
A single processor follows a fetch - decode - execute cycle, with one instruction at a time.
Registers are used as a fast access to instructions and data.
Describe Harvard architecture
Instructions and data are stored in separate memory units, with each having its own bus. This means the next instruction can be fetched whilst simultaneously reading and writing data.
It is faster, but more expensive as more hardware is required.
What is the opcode of an instruction?
A machine code instruction that can be executed by the processor.
Describe the Fetch Execute cycle
The contents of the Program Counter (PC) are transferred to the Memory Address Register (MAR) using an Address bus.
The address in the Memory Address Register is transferred to the Address Memory using an Address bus.
Simultaneously, the Program Counter is incremented.
Next, contents of the Addressed Memory are transferred to the Memory Buffer Register (MBR) using a Data bus.
These contents are then transferred from the MBR to the Current Instruction Register (CIR) using a Data bus.
The contents of the CIR are decoded and then executed.
The Status Register (SR) is checked for any flags and an Interrupt Service Routine is ran if necessary.
The cycle then begins again.
What is the operand of an instruction?
The data that is manipulated by the processor according to the given opcode.
What is direct addressing?
Requires a reference to a memory location or register.
What is immediate addressing?
The data is immediately available in the operand.
Explain what happens when an interrupt occurs.
The volatile environment, including the contents of the PC and register, is placed within a stack frame which is pushed onto a stack. The memory location of the first instruction of the interrupt service routine is copied to the program counter. Once the interrupt has been serviced, the top frame is popped off the stack, and the memory location of the next instruction is copied to the PC, allowing the original program to continue running.
What is the role of the control unit.
Synchronises communication around the CPU.
What are the factors affecting the performance of the CPU.
Clock speed:
Increasing clock speed also increases the speed of the processor. However, it will cause more heat to be generated, which means a cooling system is required.
Cache:
Hold a copy of data inside a small piece of memory inside the processor. Before looking for data in memory, check if it is already in cache.
Multiple processors working together.
What is the purpose of a barcode reader, state the four types.
Extract the information stored inside a barcode.
Pen-style readers
Laser scanners
Charge-Coupled Device (CCD) readers
Camera based readers
Describe how a digital camera works
A sensor, comprised of millions of tiny light sensors arranged into a grid is used. The senor can either be a CCD (higher quality, more power) or a CMOS.
The shutters open and light enters the camera. An image is projected onto the sensor at the back of the lens. Each tiny sensor measures the brightness of each pixel, and this is turned into an electrical signal stored as binary. The digital recreated image is greyscale.
Describe the two types of barcodes.
1D barcode (linear):
Most often seen on goods in shops, holds a limited amount of information.
2D barcode (QR):
Most often used to take users to websites, can encode more complex information.
What is a barcode used for?
Used to uniquely identify millions of products.
Used for tracking delivery items, tickets, items in shops, luggage tags, etc.
How do pen-styled readers work?
Physically looks like a pen that you drag across a barcode. A photo diode in the tip of the pen measures the intensity of light reflected back at it, and produces a waveform. This is translated to a digital format and can be looked up.
