Section 1 Components Of A Processor Flashcards
State 4 components of the CPU
ALU
Buses
Control unit
dedicated registers
What does the control unit do?
Controls and coordinates data flow between CPU and other devices
Accepts the next instruction, decodes it into several sequential steps eg fetching addresses and data from memory, manages its execution and stores the resulting data back in memory or registers
What are buses made of?
A set of parallel wires connecting 2 or more components of a computer
It typically consists of 8,16,32 or 64 lines
How many buses connect the processor to main memory and what are they called? What directions can data flow through each?
3, the data bus, the address bus, and the control bus
Data and control buses have 2 way signal flow, the address bus is one way
What are the 3 buses known as as a collective?
The system bus
What is the purpose of the control bus? Give some examples (4) of signals it transmits
transmit command, timing and specific status information between system components
Bus Request indicates a device is requesting use of the data bus
Bus Grant indicates the CPU has granted access to the data bus
Clock signals synchronise operations
Interrupt request indicates a device is requesting CPU access
What is a “word” in terms of memory?
Units memory is divided up internally into, as a fixed size group of digits (16,32,64 bits)
What does the data bus transmit?
Data and instructions between system components via a bi-directional path
What does the address bus transmit?
memory addresses of words that are used as operands in program instructions, so the data can be retrieved and sent back to the processor
What is the function of the ALU? What operations can be carried out?
Performing arithmetic and logical operations on the data
ADD, SUBTRACT, MULTIPLY and DIVIDE on fixed or floating point numbers
Boolean logic operations eg. AND, OR, XOR, NOT comparing 2 values
What are registers?
Special memory calls that operate at a very high speed
Results of all arithmetic, logic or shifts are stored here
What is the accumulator register?
One that stores the results of all operations in the ALU
What are 4 registers (minus the ACC) and their function
Program counter (PC) holds the address of the next instruction to be executed which can be the next one in a sequence, or the address to jump to in a branch/jump instruction copied from the CIR to the PC
Current instruction Register (CIR) holds current instruction being executed, divided into opcode and operand
Memory Address Register (MAR) which holds the address of the memory location from which data (or instructions) can be fetched or to which data can be written
Memory data register (MDR) is used to temporarily store data read from / written to memory (AKA memory buffer register)
What is the FDC cycle?
The sequence of operations involved in executing an instruction and can be divided into 3 phases, fetch, decode, execute
Repeats as each inst. is executed.
How are registers used in the fetch execute cycle? (6)
Fetch
1 Address of next instruction is copied from PC to MAR
2 Instruction held at that address is copied to the MDR, and the PC content is incremented simultaneously so it holds the address of the next instruction
3 The contents of the MDR are copied to the CIR
Decode
4 Instruction held in the CIR is decoded. The instruction is split into opcode and operand, where the opcode is used to figure out what hardware to use to execute that type of instruction
The operand holds either
the address of data to be used with the operation, copied to MAR,
the actual data to be operated on, copied to the MDR or the ALU/ACC
Execute
The appropriate instruction /opcode is carried out on the operand
Factors affecting processor performance
Clock speed
Number of cores linked together on a single chip
Amount and type of cache memory
How does clock speed affect processor performance
All processor activities begin on a clock pulse, some may take more than one clock cycle to complete
1 clock cycle = 1Hertz
Greater clock speeds lead to faster instruction execution
What is the typical speed for a PC processor, and how many clock cycles occur per second
2 to 4GHz
2 to 4 billion cycles per second
How does an increase in the number of cores affect processor performance, and how might it not affect speed in the desired way
Each core can theoretically process a different instruction simulatneously with it’s own fetch execute cycle
Software may not be able to take full advantage of more processors
What does it mean when a computer has multiple cores?
when a computer has two or more processors linked together in the same integrated circuit
3 levels of cache?
level 1, extremely fast, small - between 2-64KB
level 2, fairly fast, medium sized - 256KB-2MB
some have a level 3 cache
define cache
A small amount of expensive very fast memory inside the CPU where frequently fetched instructions or data are held
how does amount and type of cache memory affect processor performance?
more allows for more frequently fetched instructions to be accessed faster than from main memory
if too large, searching may take long
if level 1, it’s faster than levels 2 and 3
why does the width of the address bus limit the maximum possible memory capacity of the system?
Each word in memory has its own specific address
When a processor reads a word of data, from memory, it first put the address of the desired word on the address bus
