1.1 Systems Architecture Flashcards
What is a Computer?
What are two critical components that you can see when you lift the lid of a computer?
Computer - An electronic device which takes input, processes data, and delivers output. To process data a computer follows a set of instructions called a computer program.
- If we take the lid off a computer we can identify two critical components:
- Memory e.g. RAM
- CPU - Central Processing Unit
How does a computer carry out an instruction?
The computer carries out it’s instruction by fetching, decoding and executing them.
What happens during Fetch stage?
Fetch:
- Fetching the next instruction from the main memory (RAM)
- Brings the instruction back into the CPU
What happens during the Decode stage?
Inspects the instruction and works out what needs to be done.
What happens during Execute stage?
Carries out the instruction
This could be things such as:
- Going back to main memory and grabbing some data
- Performing a calculation
- Storing back into main memory
What are the four parts the CPU is made of and what do they do?
ACRC
- *Control Unit**
- Sends Signal to control how data moves around the CPU and co-ordinates the CPU’s operations.
- *Arithmetic Logic Unit**
- Carries out Arithmetic calculations
- Makes logical decision
- *Cache**
- Provides fast access to frequently used instruction and data. It is very fast.
- *Registers**
- These are super fast pieces of onboard memory inside the CPU. Each has a specific purpose:
- Accumulator
- Memory Address Register(MAR)
- Program Counter(PC)
- Memory Data Register(MDR)
What is a Fixed Program Computer?
What is a Stored Program Computer?
Fixed program computers had fixed programs. e.g. Calculator
Stored programs computers is one that has changeable programs
What are the key characteristics of Von Neumann Architecture?
What does the internal clock do?
- Central Processing Unit(CPU)
- Single Control Unit(CU)
- Arithmetic Log Unit(ALU)
- Onboard cache - Small amounts of highspeed memory that helps the control of instructions.
- Internal Clock - Which provides a pulse at a constant rate to synchronise components.
What is the purpose of the Program Counter(PC)?
Holds the address of the next instruction to be executed in memory
Whilst we fetch this address. We increment its contents by 1 so it points to the next instruction.v
What is the purpose of the Memory Address Register(MAR)?
MAR Holds the address of where data is to be fetched or stored.
What is the purpose of the Purpose of the Memory Data
Register?
MDR Holds the data fetched from, or to be written to memory.
What is the purpose of the Accumulator?
Holds the results of calculations in ALU
Show me what a typical Fetch/Execute cycle looks like?
- The program counter is checked as it holds the address of the next instruction to be executed.
- This address is used by the MAR in order to fetch the instruction needed from Main Memory (RAM) and bring it into Memory Data Register (MDR).
- The address in PC is then incremented to point to the next instruction.
- Now the instruction is in the CPU the CU decodes the instruction to see what has to be done.
- Now we know what to do we can execute the instruction.
What we actually do depends on the instruction is e.g.
- We could be asked to head back to Main Memory(RAM) and fetch some data and add it to the accumulator.
- We could be asked to jump to another instruction
- We could be asked to writer data held in the accumulator back into Main Memory(RAM)
What are the factors that affect the Speed of the CPU?
What might be problems of having multiple cores?
- Clock Speed
- Measured in Hertz(Hz)
- Number of cycles per second
- Modern Processors operate at billions of Cycles per second,(GHz)
- 3.2 GHz = 3.2 Billion instructions Fetched per second.
- Cache Size
- Temporary Storage of Data and instructions being read to and written from
- Located on the board or very near CPU
- Stores copies of recent data and instructions
- Much quicker getting items from the cache than from main memory(RAM)
- Trying to avoid going and getting instructions and data from memory if we don’t need to as it costs time.
- Number of Cores:
- A core is a complete copy of a CPU
- So a quad-core processor would have 4 separate processing units, each with its own:
Registers
ALU
Accumulator
CU - Doubling the number of cores doesn’t simply double the overall speed
- CPU Cores have to communicate with each other and this takes time.
- Many programs are not designed to make use of multiple cores.
What is an embedded system?
An embedded system is a computer with a dedicated function within a larger mechanical system.
