Computer Science Unit 4 computer systems

What does the CPU do?

The CPU carries out processing on the computer, it does this by fetching and executing instructions

Types of operation carried out by the ALU

Arithmetic operations, Logic operations

What does ALU stand for?

Arithmetic logic unit

1st step in the Fetch-Decode-Execute cycle

store data in memory, Processor fetches the next instruction to be executed from main memory

2nd step in fde cycle

instruction is decoded by control unit

3rd + 4th step in fde cycle

instruction is executed and cycle repeats

What does the bus do?

used transfer data/instructions from one component of CPU to another

What does the clock do?

Controls the number of instructions per second, allows CPU to synchronise operations

Factors that affect CPU performance

Clock speed, cache size, number of cores

What does the control unit do?

Decodes instructions, controls fetching + writing of data

What does the register do?

Specific purpose in FDE cycle, special purpose small memory location on CPU

What does the cache do?

Very fast memory, close to/on CPU, stores frequently used data

How does cache size affect CPU performance?

Bigger the cache, the more instruction it can hold - processor waits less time for instructions to be fetched

How does number of cores affect CPU performance?

More cores, more instructions CPU can process, each core is capable of fde its own instructions

What is the purpose of the Operating System?

To provide an interface between user + hardware

What is the purpose of the Applications Management?

Allocate memory space, determine time needed by processor for app to run, provides interface for running programs, manages execution

What is the purpose of the Processor management?

multitasking only if OS can support it

What is the processor?

electronic circuit that performs the calculations that run a computer

What is the purpose of security management?

allows users to be created/deleted, access levels to be given, logs files users touch, audits it

How does the OS communicate with Input /output devices?

through drivers

what is a device driver?

acts as a translator for the signals between the OS and the device, contains instruction on how to control a device

What are input and output devices called?

Peripherals

Advantages of using a device driver are…

any device can be used with OS as long as it has a driver for it, it can be updated

Characteristics of a high level language

Similar to spoken/written human language

Examples of high level languages

Python, Java, C++

Characteristics of low level language

language similar to computer’s instruction set

Examples of low level language

Machine code, assembly language

What is machine code also known as?

binary code

Advantages of machine code

able to specify items, code is directly executed, allows certain functions

Disadvantages of machine code

difficult to write in, relevant to single consistent architectures

Advantages of assembly language

Direct access to hardware, short easy to remember instructions, optimized code for specific hardware

Disadvantages of assembly language

machine dependant, lengthy code, cannot be transferred to computers of different makes

What are translators?

Programs that convert source code to object code

What does an assembler do?

translates assembly language to machine code all in one go

Advantages of using an assembler

Allows developers more control, portable as it is smaller and has no library, more accessible than machine code

Disadvantages of assemblers

difficult to write and debug, difficult to read, slower and less efficient, machine dependant, prone to errors

5 main parts of CPU

Control unit, cache, clock, ALU, bus

4 types of memory

Register, RAM, ROM, cache

What is RAM

Random Access Memory

Characteristics of RAM

High speed, volatile

Why doesn’t the CPU access programs and other data from the hard drive directly?

Data speed from hard drive is very slow, CPU clock is not synchronised with hard drive and can not be incorporated directly

What is often stored in RAM?

Data and instructions that are currently in use?

What is often stored in ROM

Instructions that tell the computers how to perform basic functions such as initialising hardware components

Average bytes for a hard drive

128 GB

What does ROM stand for?

Read only memory

Characteristics of ROM

Cannot write to it, non volatile, primary

How does increasing the amount of RAM affect the performance of PC?

Improves the speed, it would allow the storage of more files and programs,

Types of primary storage

RAM and ROM

Types of secondary storage

Hard disk drive, Solid state drive

Types of offline secondary storage

Compact disc, Digital Versatile Disc, BluRay, Flash memory, SD cards, removable HDD or SDD, magnetic tape

Characteristics of secondary storage

non volatile, internal or external, not directly accessible by the CPU

Magnetic disc with a solid platter

hard disc

magnetic disc with a soft plastic platter

floppy disc

basic functions of a magnetic disk

concentric circles called tracks which are divided into sectors, disk heads mounted on mechanical arms that read and write data

How are magnetic hard discs used

Used in PCs and laptops

Pros of magnetic hard discs

very large, very cheap compared to SSD

Portable external hard disc?

Connected to computer by USB, used for backing up and transporting data

Pros of magnetic storage

cheap, large storage, relatively fast write speed

cons of magnetic storage

lots of mechanical parts so not very durable, not very portable

capacity of magnetic storage

500GB -12TB or more

Basic features of optical storage

data is stored as pits and lands which are burned or pressed into a spiral track, laser beam passes over and the level of reflection is measured, 0s and 1s are derived from this signal

Pros of optical storage

cheap, very portable, take up little space physically

cons of optical storage

less storage compared to others, easily damaged, slow write speeds

uses of optical storage

songs, videos, multi media storage, backup and archiving of data

types of optical storage

CD, DVD, Blu Ray

Order of smallest to highest storage capacity of optical storage

CD, DVD, BluRay

Basic features of SDD

use non volatile flash memory to store, no mechanical moving parts

Pros of SSD

Highly durable, very fast read/write speeds, faster start up timeD

Cons of SSD

more expensive than magnetic hard disc, similar storage as magnetic disc

SSD uses

Laptop, higher end computers, smartphones and tabletscap

capacity of SSD

100GB-16TB

Pros of flash memory

low cost, portable, durable

Cloud storage

saving data in an offsite storage system maintained by a third party

Pros of cloud storage

easy use, backups, scalable, capacity convenient

Cons of cloud storage

cannot be accessed without internet, speed is variable, security

characteristics of storage devices

capacity, speed, portability, durability, reliability and cost