What does CPU stand for
Central Processing Unit
What components does the CPU consist of
Control Unit (CU)
Arithmetic and logic unit (ALU)
Registers
Busses
What does the CPU do
execution or processing of all the instructions and data in a computer
What is the Von Neumann architecture
A type of computer architecture which introduced the concept of stored programs in 1940s
What made the Von-Neumann architecture different
The concept of a CPU
The CPU could access memory directly
Computer memories could store programs AND data
stored programs were made up of instructions which could be executed in sequential order
What is an ALU
The component of the CPU that carries out all arithmetic and logical operations
Examples of arithmetic operations that are carried out by ALU
+, -, logical shifting ( multiplication and division)
Examples of LOGIC operations that are carried out by ALU
AND and OR
What is a register
A temporary component in the CPU which can be
general or specific in its use; it holds data or instructions as part of the Fetch–Decode–Execute cycle
Types of special purpose registers
Current Instruction register - CIR
Accumulator - ACC
Memory Address Register - MAR
Memory Data Register - MDR
Program counter - PC
What is an ACC (register)
Accumulator - Temporary stores the results of the calculation from the ALU
What is a PC (register)
Program Counter - This register stores the address where the next instruction to be read can be found
What is the MAR
Memory Address Register - Stores the address of the memory location currently being read from or written to
What is the MDR
Memory Data Register - Stores data which has just been read from memory or data which is about to be written to memory
What is the CIR
Current information register - this register stores the current instruction being decoded and executed
How does the MDR differ from the MAR
The MAR stores the location of the data/instruction
The MDR actually holds the data/instruction itself.
Flow of registers
PC –> MAR –> MDR
What is the Control unit
CU - ensures synchronisation of data flow and programs throughout the computer by sending out control signals along the control bus
What is a bus
what does each wire do
Busses are used in computers as parallel transmission components; each wire in the bus transmits one bit of data
3 main types of busses
Address
Control
Data
Which busses have two way flow
Control
Data
What does the address bus do
direction
Carries addresses throughout the computer system
Unidirectional between CPU and memory
How does width of a bus affect the bus (address)
Wider the bus the more memory locations can be directly addressed at any given time.
What is a memory location
a numbered place in memory where values can be stored
What is an address
a label for a memory location used by the CPU to track data
What is a data bus
the system bus that allows data to be carried from CPU to memory (and vice versa) or to and from input/output devices
What is a word
a group of bits used by a computer to represent a
single unit
Modern computers word length
64-bit
How does width affect data bus
Wider the bus, the larger word can be transported
What is the control bus
the system bus that carries signals from control unit to all other computer components
Usual width of control bus
8 bits wide
What is the FDE
Fetch-decode-execute cycle - a cycle in which instructions and data are fetched from memory, decoded and finally executed
What happens in the fetch stage
Next instruction is fetched from the memory address stored in the MAR and the instruction which are stored at that address are then temporarily stored in the MDR.
Then the contents of MDR are copied to CIR.
Finally PC is incremented by 1 so that next instruction can be processed
What is the decode stage
Instruction is decoded so it can be interpreted in the next part of the cycle
What is the execute stage
Instruction carried out in a logical sequence since the CPU passes the decoded instructions as a set of control signals to the appropriate components within the computer system.
What is the system clock
produces timing signals on the control bus to ensure synchronisation takes place
What is the clock cycle
vibrational frequency of the system clock which
sends out pulses along the control bus
How is clock cycle measured
Gigahertz GHz
What is overclocking
changing the clock speed of a system clock to a value higher than the factory/recommended setting
What is the BIOS
Basic Input/Output system - suite of programs on firmware that are used to initialize a computer system during the boot up process.
What is cache memory
Temporary memory hold instructions that are freq repeated.
What is an IAS (full form and function)
Immediate Access Store
Memory that holds all the data and programs that need to be accessed by the Control Unit
What is the Backing store
A secondary storage device used to store data permanently even when the computer is powered down
Examples of backing store memory
HDD
SSD
What is a core
a unit on a CPU made up of an ALU, control unit and
registers
Names and number of cores of CPUs
Dual core - 2 cores
Quad core - 4 cores
How to increase the speed and performance of a computer
Increasing the bus width (data and address)
Increasing the clock speed
The use of cache memory
Use of multicore CPUs
Problems with overclocking
unsynchronised operations which would lead to frequent crashes and the computer becoming unstable
Serious overheating of the CPU - unreliable performance
Why does increasing the number of cores not always lead to an increase in performance
The CPU needs to communicate with a larger number of cores which could reduce overall performance
