T1 - Architecture of the CPU/ Performance Flashcards
CPU
- The CPU processes instructions
Stored program concept
- In 1943-44, von Neumann had the idea of storing the program
instructions/data in memory
Von Neumann architecture
- Program instructions and data are both stored in the same memory
Control unit
- coordinates activities in CPU
-sends signals to control how data moves around
Receives signals from the system clock
Directs timing + controls other parts of the CPU
Arithmetic logic unit
- actual arithmetic operations are done
Carries out logical operations: AND, OR and NOT
Registers -
very fast memory location in the CPU
Cache
- it is slower to access than registers but faster than RAM
Types of Registers: Program Counter (PC)
- holds the address of the next instruction to be executed
Types of Registers: Memory Address Register (MAR) -
holds the memory address of the current instruction, so that these can be fetched from memory
Types of Registers: Memory Data Register (MDR)
holds the actual instruction, and data that has been fetched from memory
Types of Registers: Accumulator
- holds the result of an instruction before it is transferred to memory
-result if alu
FDE cycle
FETCH – fetches the next instruction + data involved to main memory
DECODE – decodes the instruction
EXECUTE – the instruction is executed
PC : role
holds the address of the next instruction to be executed
incremented (increased by 1) as soon as that instruction has been fetched = moves onto next instruction.
ACC : role
where arithmetic/ logic results are temporarily stored
MAR during FETCH stage:
address of the next instruction is copied from PC to MAR.
MDR during FETCH stage
instruction at that address is fetched from memory + copied to MDR
Then the Control Unit during FETCH stage
decodes the instruction and decides if data needs to be fetched
Factors affecting CPU performance:
Clock speed
- Cycles per second measured in hertz
Processor cores -
The number of duplicate processing units (cores) placed in one CPU
Cache
Memory on the CPU that is faster than RAM but slower than registers
Factors affecting CPU performance:
cache
processor cores
clock speed
clock speed role
Everything in a computer happens on the pulse of the internal clock
The faster the clock speed, the faster the instructions are processed
Processor speed: Hz, KHz, MHz, GHz
One cycle per second = 1 hertz (Hz) = 1 instruction carried out each second
1 kilohertz (kHz) = 1000 cycles per second
1 Megahertz (MHz) = 1,000,000 cycles per second
1 Gigahertz (GHz) = 1,000,000,000 cycles per second
Multi- core processors:
A dual-core processor
- can perform two instructions at the same time
- allows twice as many instructions to be executed,
- each core is theoretically able to process a different instruction at the same time with their own FDE cycles
Cache Memory: role
a small amount of very fast, expensive memory in the CPU
It can be accessed faster than regular main memory (RAM)
Quickens fetch stage
Level 1 cache -
extremely fast but small (between 2-256KB),
located on the CPU. Each core will have its own level 1 cache
Level 2 cache -
usually also given to each core.
Is fast, but a little slower than level 1 cache.
The typical size is 256KB-8MB
Level 3 cache -
slowest type of cache, but still faster than RAM.
It is usually located on the CPU
Stores 4MB-50MB.
is cache shared
The cache is shared between all the cores on the processor
Embedded Computers:
a single microprocessor:
that includes RAM, ROM and a CPU
frequently used to control a device using simple inputs
