1.1 Systems Architecture Flashcards
What is the Program Counter
Holds the address of the next instruction to be executed and adds one each time so that it points to the next instruction
Fixed program machine
Has one purpose - eg. calculator
Stored program machine
Has changeable programs
What is the Accumulator (Acc)
a special purpose memory location that holds the results of any calculations performed by the arithmetic logic unit (ALU)
What is the Memory Data Register (MDR)
Holds data or a program instruction temporarily when it is fetched from memory or data that is waiting to be written to memory
What is the Memory Address Register (MAR)
Holds the address (location in memory) of where the data is to be fetched from and then where it is to be stored
How is instruction data and program data stored in the computer
In Binary form
What is the Random Access Memory (RAM)
The main memory of the computer. Acts as storage for programs and data while the programs are being executed
What does the ALU do?
It does the arithmetic calculations & logic and shift operations
What are buses
They are the wires that carry all the data around
What is a cache
Temporary storage that provides fast access to frequently used instructions and data. It is used to avoid taking extra time going all the way to RAM
What are registers
A superfast memory location within the CPU, used in the execution of instructions
What three things can affect the performance of the CPU?
- Clock speed
- Cache size
- Number of cores
What is a gigahertz? (GHz)
1 billion cycles per second
How does clock speed affect the CPU?
Clock speed is the number of instruction cycles that a CPU can do per second so a faster clock speed means a faster CPU
How does cache size affect the CPU?
There are three cache sizes:-
Fastest - Can hold the least amount of data - most expensive
Slower - can hold more data
Slowest - Can hold the most data at a time - least expensive
How does the number of cores affect the CPU?
The more cores there are, the faster the computer can work. This is because parallel processing can take place with more than one instruction being executes simultaneously. However, double the core does not equal double the speed.
What is a core
A complete copy of the CPU each with its own components (ALU, Acc, etc).
What is a quad-core processor
a processor with 4 cores
What is an embedded system
An embedded system is a computer system with a dedicated or single function and is usually found within a larger mechanical or electrical system. It often has a very basic or no user interface.
what is a register
a very fast memory location within the CPU used in the execution of instructions
What is the purpose of the CPU
It fetches, decodes, and executes instructions & manages the rest of the hardware
What happens in the Fetch-Decode-Execute cycle
FETCH
- The Program Counter is loaded with the location of the next instruction to be executed.
- This address is then loaded into the Memory address register (MAR) which is connected directly to the address bus. What this means is that the address bus is now pointing to the instruction in RAM The Pc is then incremented by one so that it holds the address of the next instruction to be executed - This instruction is copied from RAM on to the data bus which then allows the Memory Data Register (MDR) to store a copy of it.
DECODE
The purpose of the decode phase is to look at the content of the MDR and work out if it is a relevant instruction that the CPU can carry out.
• Check to see if the MDR contains a valid CPU instruction - if it does, load the instruction register with the instruction. If it is not valid, then ideally an error is flagged so that the program can deal with it.
EXECUTE
- actually carrying out the instruction present in the instruction register.
- results of processing are held in the accumulator
What does the Control Unit do?
Coordinates all the activities inside the CPU and regulates and controls processor timing
What is Clock Speed
The speed at which a processor operates. Measured in Hertz (cycles per second).
Main Characteristics of an Embedded system
- Program which controls the equipment can’t be changed
- Has a very limited operating system
- Very simple to no user interface
Common CPU compoents
ALU
CU
Cache
Registers
What is Von Neumann architecture
the design upon which many general purpose computers are based
A processor based on Von Neumann architecture has which five special registers
- Program counter
- MAR
- MDR
- Accumulator
(- CIR)
Examples of embedded systems
- central heating systems
- engine management systems in vehicles
- domestic appliances, such as dishwashers, TVs and digital phones
- digital watches
- electronic calculators
- GPS systems
- fitness trackers
computer A has a 3.2 GHz processor
computer B has a 1.2 GHz processor
explain why computer A will usually run faster than computer B
- it will have a higher clock speed
- so it will be able to complete more fetch-execute cycles per second
- therefore more instructions can be completed per second
