Unit 1 Characteristics of Contemporary Processors

What is an input device?

peripheral devices used to pass data into the computer (& allow users to communicate w/ computer)

Examples of input devices

• keyboard

• mouse

• biometrics

• temperature sensor

• cameras

• barcode scanner

• proximity sensor

• RFID scanner

• Infrared sensor

Describe a barcode

• representing data in a machine-readable form

• check digit at end of barcode

• when long code entered check digit calculated & compared to check digit at end of barcode

• if they do not match there was an input error

How do sensors work?

by converting an analogue signal into a digital form by an ADC (analogue to digital converter)

Main criteria for choosing an appropriate input device?

• cost

• speed

• accuracy

• reliability

Describe an RFID (Radio Frequency Identification)

• allows data to be transmitted wirelessly over radio waves

• made up of tags and reader

• tags = antenna(receiving & transmitting radio frequency sinals) & chip (processes signals)

• each tag = unique identifier

• reader transmits encoded radio signal to interrogate the tag

What is an output device?

peripheral devices used to report results of processing from a computer to the user (& allow the computer to communicate with the user)

Examples of output devices

• monitors

• printer

• speakers

• 3-D printers

• motors(actuator)

What is an actuator?

something that performs an action

3 different types of printers

• Inkjet(feel the ink)

• Laser (use lasers)

• Dot-Matrix (old,dots)

What are the two different types of memory?

• primary

• secondary

What is primary memory?

memory that can be directly accessed by the CPU

What type of memory are RAM and ROM?

primary storage

Features of RAM

• volatile (contents erased when no power)

• can be read from and written to

What is usually stored temporarily in RAM?

• user files

• applications software

• OS

Features of ROM

• non-volatile (contents remains with no power)

• read only

What is usually stored in ROM?

• OS

• BIOS bootstrap program

Secondary storage has slower… than RAM

access speeds

What are the 3 types of storage?

• Magnetic

• Optical

• Flash

Examples of magnetic storage devices

• hard disk drives

• magnetic tape drives

Examples of optical storage devices

• CDs

• DVDs

• Blu-ray discs

Examples of flash devices

• SSD (solid-state drives)

• USB flash drives

How do magnetic storage devices store data?

magnetising particles on a disk/tape

(two magnetic states representing binary 1 and 0)

How do optical storage devices store data?

using a laser to burn puts into the surface of the disc

How do solid state devices store data?

in flash memory cells

Hard Drive (Magnetic) advantages

• high capacity

• cheap

• reasonably quick

Hard Drive (Magnetic) disadvantages

• serial access - slow (one after the other)

• vulnerable to damage if dropped

Hard Drive (Magnetic) uses

• used in computers

Solid State Drive (Flash) advantages

• direct access - fast speed

• light and portable

• reliable

• not as vulnerable to damage if dropped

Solid State Drive (Flash) disadvantages

• more expensive than simple hard drive

• limited number of read/writes till they break

Solid State Drive (Flash) uses

• computers where speed is priority

CD, DVD + Blu - ray (Optical) advantages

• fast

• light and portable

• reliable

• not vulnerable to damage if dropped

• cheap

CD, DVD + Blu - ray (Optical) disadvantages

• limited capacity

• slow read write times

CD, DVD + Blu - ray (Optical) uses

distribution of software and films

USB pen drive (Flash) advantages

• cheap

• very portable

USB pen drive (Flash) disadvantages

• limited read write before stops working

USB pen drive (Flash) uses

carrying data from place to place

What is virtual storage?

storing data remotely so it can be accessed by any computer with access to the same system

Examples of virtual storage

• google drive

• microsoft one drive

Benefits of virtual storage

• scalability (easy to increase storage as capacity grows)

• accessibility(accessed from anywhere w/ internet)

• data protection (protects against lost data due to hardware)

• cost-effective (pay only for storage used)

Drawback of virtual storage

• dependence on internet

• security concerns

• ongoing costs (cost can add up overtime)

When a PC runs low on RAM it can move data from RAM → Hard Disc but what will this cause?

reduction in performance of PCs

reduced instruction set computers (RISC)

• aim to use simple instructions that will execute within one clock cycle

• MULT would be separated into a number of simpler commands

adv/dis RISC

• complier does more work to translate high level code into machine code

• more RAM required

• pipelining is possible as each instruction takes one clock cycle

• cheaper

• low energy requirement - portable devices

• less complex hardware - more room for cache

complex instruction set computers (CISC)

• large instruction set - MULT

• aim is to try and accomplish tasks in as few lines of assembly code as possible

• these instructions are built into the hardware

• used in embedded systems

adv/dis CISC

• compiler does less work to translate high level code into machine code

• less RAM required since code is shorter

• more complex hardware

  • more power hungry

• more expensive

• code is executed in more cycles due to instruction complexity

• cant make use of pipelining

multi core processor

• processor contains 2 or more cores

• each core can FDE on its own

• enhance multicore processors further

  • on chip shared cache

  • inter-core communication

• 2X cores doesn’t mean 2X performance

  • overheads with inter-core communication

  • some programs cant take advantage of it

parallel processing

• processes instructions by dividing them between multiple process or cores

• achieved by assigning different cores to different stages of the FDE cycle

advantages of parallel processing

• improves speed and performance by executing multiple instructions simultaneously

• reducing overall processing time

• efficient as tasks that can be divided into smaller, concurrent operations

limitations of parallel processing

• task being carried out

• if software has been designed to make use of parallel processing / multiple cores

graphics processing unit (GPU)

• type of co-processor - secondary processor that is used for a specific set of tasks, enhancing the performance of the main CPU by offloading duties - working concurrently

• has lots of independent processors which work in parallel making it very efficient at completing repetitive tasks such as image processing and machine learning

difference between CPUs and GPUs

• GPUs have thousands of processors but run slower than a CPU core

• GPUs are highly specialised and are faster in certain tasks

  • simple operations on large data sets

• CPUs are all rounders

  • complex operations on small data sets

What is the ALU?

The Arithmetic Logic Unit is a part of the CPU that performs arithmetic and logical operations on data for the computer programs.

What type of arithmetic operations does the ALI do?

Mathematical operations such as addition and subtraction on fixed or floating point numbers.

What type of logical operations does the ALU do?

Boolean logic operations such as AND, OR, NOT and XOR.

What is the CU?

The Control Unit is a part of the CPU that controls and manages the operations of the CPU

What does the CU do?

It:

• controls and coordinates the activities of the CPU

• manages the flow of data between the CPU and other devices

• accepts the next instruction to be decoded

• decodes the instruction

• stores the resulting data back in the memory

What are registers and what are they used for?

Registers are small memory cells that operate at a very high speed and can be accessed quickly.

They are used to temporarily store data and all arithmetic, logical and shift operations that occur in these registers (essentially control information).

Name all 5 of the registers.

• Program Counter (PC)

• Accumulator (ACC)

• Memory Address Register (MAR)

• Memory Data Register (MDR)

• Current Instruction Register (CIR)

What is the purpose of PC?

The program counter is a special purpose register that holds the address of the next instruction to be executed.

What is the purpose of the ACC?

The accumulator is a special register which temporarily stores the results of operations performed by the ALU.

What is the purpose of MAR?

The Memory Address Register is a special register which holds the address of a location that is to be read from or written to.

What is the purpose of MDR?

The Memory Data Register is a special register which temporarily stores data that has been read or data needs to be written.

What is the purpose of CIR?

The Current Instruction Register is a special register which holds the current instruction being executed, decoded and divided up into operand and opcode.

What are buses?

Buses are a set of parallel wires which connect two or more components in the CPU. They carry groups of bits between several components of a computer.

What is the width of a bus?

The number of parallel wires the bus has

What does the width of the bus affect?

It is directionally proportional to the number of bits that can be transferred simultaneously at any one time. They are typically 8, 16, 32 or 64 wires wide.

Name the three buses in the CPU.

• Data Bus

• Control Bus

• Address Bus

What is the data bus?

The data bus is a bi-directional bus (meaning bits can be carried in both directions) which transports data and instructions between components (e.g. processor and memory).

What is the control bus?

The control bus is a bi-directional bus which carries control signals between internal and external components, to synchronise access and use of data.

What are the different types of control signal?

• bus request - a device is requesting use of the data bus

• bus grant - CPU has grants access to the data bus

• memory write - data is written to the addressed location

• memory read - data is read from the addressed location and placed on the data bus

• interrupt request - a device is requesting access to the CPU

• clock - used to synchronise operations

What is the address bus?

The address bus is a unidirectional bus which transports the address that data is to be read from/written to from the CPU to memory.

What is the significance of the width of the address bus?

It’s proportional to the number of addressable memory locations

What is assembly language?

Assembly language is a low-level programming language that uses mnemonic codes to represent machine instructions e.g. ADD = Addition. It is a simplified way of representing machine code.

How do buses relate to assembly language programs?

The instruction in the CIR is split into two parts:

• Opcode = tells computer what to do e.g. add or subtract

• Operand = provides what the operation should use, either actual data or the location of the data

For example: ADD A, B

• Opcode - ADD (tells the computer to add two values)

• Operand - A and B (the values or memory locations being added)

What is opcode?

The instruction to be executed

What is operand?

The data or the memory address where the data is held that the instruction is being executed upon

What is pipelining?

Pipelining is the process of completing the fetch, decode and execute cycles of multiple separate instructions simultaneously (essentially when one instruction is being executed, another is being decoded and another is fetched).

Why do we use pipelining?

To reduce the amount of the CPU that is idle at any one time, thus increasing the processing speed

What is the FDE cycle?

The fetch-decode-execute cycle is the sequence of operations that are completed in order to execute an instruction.

What happens in the F?

Fetch: the next instruction is fetched from memory - where the address from the PC is copied to the MAR, this instruction then is copied to the MDR by the data bus while also the contents of the PC is increased by 1 and then the value held in the MDR is copied to the CIR

What happens in the D?

Decode - the instruction is split (decoded) into opcode and operand in the CIR

What happens in the E?

Execute - the decoded instruction/ opcode is carried out on the operand; the CPU carries out the required instructions

What are the three factors affecting CPU performance?

• Clock speed

• Number of cores

• Amount and type of cache memory

What is clock speed?

Clock speed is the frequency at which the internal clock generates signals switching between 0 and 1. It controls how often instructions are executed and data is fetched (essentially the speed at which a computer’s CPU executes instructions).

What are cores?

A core is an independent processing unit that is able to run its own FDE cycle.

So essentially, the more cores a computer has, the more FDE cycles it can complete at any given time e.g a dual core processor can complete two FDE cycles simultaneously, so runs theoretically twice as fast.

Why is multi-core processing not always n times faster than single core?

• Not all programs are able to utilise multiple cores efficiently, so may only rely on one core

• Some instructions rely on results of others, so could pause operations until another instruction is complete, which causes a slight delay

What is cache?

Cache is a small, fast and expensive memory onboard the CPU used to store instructions and data that are used regularly so it can access them quicker. As cache fills up, unused instructions are replaced.

What are the three types of cache?

• Level 1 cache

• Level 2 cache

• Level 3 cache

List the three levels of cache from quickest and smallest capacity to slowest and largest capacity:

• L1

• L2

• L3

What is Von Neumann Architecture?

Von Neumann Architecture is a computer design/architecture where a single control unit manages program control via a linear sequence of FDE cycles (essentially it handles everything by following a step-by-step process to run programs)

What is Harvard Architecture?

Harvard Architecture is a computer design/architecture that stores data and instructions in separate memories to allow the next instruction to be read while data is currently being read or written.

What is the main difference between Von Neumann Architecture and Harvard Architecture?

Whether memory is separate for data and instructions or they are stored in one memory

Advantages of Von Neumann Architecture

• cheaper to develop as the control unit is easier to design

• programs can be optimised in size

Advantages of Harvard Architecture

• quicker execution as data and instructions can be fetched in parallel

• memories can be different sizes which can make more efficient use of space

What is contemporary processing?

Contemporary Processing is a combination of Von Neumann and Harvard Architecture. Von Neumann is used when working with data and instructions in main memory, but uses Harvard architecture to divide the cache into instruction cache and data cache.