1.1 Systems Architecture Flashcards
CRAMMING AHHHHH (24 cards)
What is a computer?
An electronic device which takes input, processes data and delivers output
What is the purpose of the CPU?
To fetch, decode and execute instructions
Fetch-execute cycle: Fetch
1) PC is checked as it holds the address of the next instruction
2) The MAR uses this address to fetch the instruction from the main memory (RAM) into the CPU and brings it to the MDR (via the data bus)
3) The PC is incremented by 1 to point to the next instruction
Fetch-execute cycle: Decode
4) The CU decodes the instruction (inspects the instruction and works out what must be done)
Fetch-execute cycle: Execute
5) The instruction is executed (e.g. the ALU performs a calculation and stores the result in the ACC)
6) The process repeats
What does the Von Neumann architecture consist of?
CU, ALU, memory unit (typically RAM), inputs and outputs (or CPU and a single memory unit, connected by 3 buses)
How is data stored?
Data and instructions are all stored within the same memory unit (RAM) in address locations
def registers
tiny, fast pieces of onboard memory inside the CPU each with a very specific purpose
def arithmetic logic unit
performs calculations and logical decisions
def program counter
holds the address of the next instruction
def memory address register
stores the memory address where data is to be stored or fetched
def memory data register
holds data fetched from or to be written to main memory
def accumulator
holds the results of calculations
def control unit
decodes instructions and sends signals to control how data moves around the CPU
def cache
memory that provides fast access to frequently used instructions and data without having to go back to RAM
def clock speed
cycles per second, measured in hertz (Hz)
Clock speed
1) Measured in hertz (Hz)
2) Number of cycles per second
3) 3.2 GHz clock speed = 3.2 billion instructions can be fetched per second
4) Faster clock speed = more instructions can be fetched per second
Cache size
1) Temporary storage of data and instructions being read to and written from RAM
2) stores copies of frequently used data and instructions
3) quicker getting items from cache than RAM as cache is closer to the CPU than RAM (it costs time to go to and back from RAM)
Why does increasing cache size not always lead to improved performance?
A large cache might not increase speed as it is stored and searched linearly
Number of cores
1) a core is a complete copy of a CPU
2) so a quad-core processor would have 4 separate processing units, each with their own registers, ALU, ACC and CU
3) multiple cores allow multiple instructions to be executed at the same time
Why might doubling the number of cores not double the speed?
Doubling the number of cores doesn’t simply double the overall speed:
- CPU cores must communicate with each other which takes time
- many programs aren’t designed to make use of multiple cores
What is an embedded system?
A computer with a dedicated function within a larger mechanical or electrical system
Properties of embedded systems
1) low power consumption
2) small size
3) rugged operating ranges
4) low cost per unit
Examples of embedded systems
1) Washing machine
2) Coffee machine
3) Sat nav
4) Printer
5) Air conditioning
