Components of a computer (unit 1) (finished) Flashcards
(1.1) What is a CPU?
Central processing unit
(1.1)What are some of the components of a CPU?
Control unit
Buses
ALU
Dedicated registers
(1.1) What does the control unit do?
Coordinates the activity of all other components
(1.1) What do buses do?
used for transporting data, tiny wires that transfer signals between components
(1.1)How many different system buses are there, and what are they called?
3-
Control bus- Signals from the control unit to other parts of the processor
Data bus- carries data from one place to another
Address bus- carries location address where the data is going (to or from)
(1.1) What control signals are there?
Memory read Memory write Bus request Bus grant clock
(1.1)What does the ALU do?
Arithmetic logic unit
This component performs arithmetic, logical and shift operations on data
Arithmetic operations: Add, Subtract, Multiply and Divide
Logical operations include: AND, OR, NOT, XOR
Shift operations: Move bits to the left or right within a register
(1.1) What does the ACC do?
Single general purpose register used to store values of recently done calculations
(1.1)What are some dedicated registers used by the processor?
Program counter (PC) – holds the memory address of the next instruction to be executed
Current Instruction Register (CIR) – holds the current instruction, which is split into opcode and operand
Memory Address Register (MAR) - holds the address in memory where the processor is required to fetch or store data from or to
Memory Data Register (MDR) – temporarily holds data moving between the processor and main memory
Accumulator (ACC) – to hold intermediate results of an instruction
(1.1) What is the fetch decode execute cycle? (FDE)
The order in which processors carry out program instructions:
Fetch- retrieves the data
Decode- decodes the data
Execute- carries out the decoded data
(1.1) detailed version of FDE cycle
Fetch:
1.The address of the next instruction is copied from the PC to the Memory Address Register (MAR)
2.The instruction held at that address is copied to the Memory Data Register (MDR)
3.Simultaneously, the contents of the Program Counter (PC) are incremented by 1
4.The contents of the MDR are copied to the Current Instruction Register (CIR)
Decode:
5.The instruction held in the CIR is decoded
6.It is split into operand and opcode to determine the type of instruction it is. Additional data, if required, is fetched from memory…
7.and passed to the accumulator
Execute:
8.The instruction is executed and the result held in accumulator or stored in memory
(1.2) What is a word?
A word is the unit of data that memory is divided into
Word length is usually 8, 16, 32 or 64 bits
(1.2) What is the address bus, and why is it important?
carries location address where the data is going (to or from)
The width of the address bus determines the maximum possible memory addresses of the system
(1.2) What is special about the data bus?
The data bus is bi- directional
(1.2) How close is assembly language to machine code?
Very closely related, usually have a one to one correspondence
(1.2) What are some factors that could affects processor performance?
Clock speed- determines the cycles of FDE per second
Number of cores
Amount/type of cache memory
(1.2) What is a co-processor?
A co-processor is a second, less powerful processor that runs alongside the regular processor
This is uncommon due to the hardware complexity
(1.2) What is parallel processing?
Using several processor cores working at the same time
Each different core can work on a different part of the same task (this isn’t always possible due to some instructions having to be processed sequentially)
(1.2)What are the levels of memory storage in order of speed?
CPU registers
lvl1 cache
lvl2 cache
RAM
(1.2) What sections is lvl1 Cache memory split up into?
Instruction cache and data cache
(1.2)What is pipelining?
Pipelining is the process of overlapping stages in the FDE cycle
One example of this is as soon as one part of the process has been completed for one part, it is started for the part after.
(1.3)Who were the first people to suggest a stored program concept?
John von Neumann and Alan Turing
(1.3)What is the stored program concept?
A program must be loaded into main memory to be able to be reached by the processor (and then executed)
The instructions are fetched one at a time, decoded and executed sequentially/in order by the processor. This is the FDE cycle.
The sequence of instructions can only be changed by a conditional or unconditional jump instruction. This is sometimes called a branch
(data and instructions are both logically the same, which makes them interchangeable.) (von Neumann is built around this principal, which is why they have the same storage space)
(1.3)What is the Von Neumann architecture?
Instructions and data are stored in a common main memory and transferred using a single shared bus
(1.3)What is the Harvard architecture?
Different sized memories and word lengths can be used for data and instructions
Mainly used in embedded systems, where speed takes priority
(1.3)Advantages of the von Neumann architecture
Owing primarily to cost and programming complexity, almost all modern computers are based on von Neumann’s ideas
It is easier to share information with other computers that use the same processing methods
It simplifies the job of the Control Unit
Data from memory and from external devices are accessed in the same way
(1.3)Von Neumann vs Harvard architecture comparison
Von Neumann:
Used in PCs, laptops, servers and high performance computers
Data and instructions share the same memory. Both use the same word length
One bus for data and instructions is a bottleneck
One bus is simpler for control unit design
Harvard:
Used in digital signal processing, microcontrollers and in embedded systems such as microwave ovens and watches
Instructions and data are held in separate memories which may have different word lengths. Free data memory can’t be used for instructions, and vice versa
Separate buses allow parallel access to data and instructions
Control unit for two buses is more complicated and expensive