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Computers (Secondary Storage (Definition Internal/external memory, not…
Computers
Secondary
Storage
Definition
Internal/external memory, not under direct CPU control
Internal - Hard Disk, External - CD/DVD
Used for long term data storage after Comp switched off
Optical Storage
Use lens, light beams to R/W data
CD: ~700 MB DVD: ~4.7 GB Blu-ray: ~50 GB
+ High portability, cheap, fairly durable
+ CD-R, DVD-R types are read only
- Relatively small capacity to other types
- Blu-ray (& similar) require special drive
Magnetic Storage
Use magnets on rotating metal plates (hard disk etc.)
+ Large storage, fast access to R/W, fairly cheap
- Data transformed by magnetic field/ mech problems
- Can suffer wear, tear w. moving parts
Solid State Storage
Flash memory, force e- into readable data positions
+ Fast, durable (no move parts), very compact, hi capacity
- Expensive, ltd no. of R/W from wear & tear (still Ks or Ms)
Factors
Capacity - Amount of data that can be STA
Speed - Rate of data transfer
Portability - Whether data can be carried
Durability - Time before device starts failing
Reliability - If data STA w/o common errors
Cost - Manufacture cost for device
Cloud Storage
Online, on remote servers (Dropbox, OneDrive etc.)
Can be just like local storage devices; can auto backup
+ Minimal Hardware = less local maintenance, only internet
+ Features, App integration, auto data sync
Flash Memory
Non-volatile, no moving parts (Solid-state)
Made by Dr Fujio Masuok (80s) for Toshiba
Flash for erasing data was like camera flash
Cells of storage transistors w/ logic gates
Binary = +ve, -ve charges (USB, SD etc.)
(USB = Universal series bus; SD = secure digital)
Components
Buses
Address - tells location of data in memory
Control - communicates w/ other components
Data - transport data for computation in CPU
ALU
Does arithmetic, logical calc, results stored in registers
Temporary holding place for data, instructions being processed
Inc. register to store current results during calc (accumulator)
Accumulator (ACC)
Accumulates results of calc to stop the ALU
from having to store current results in Main,
slowing the operation
Control Unit (CU)
Directs flow of inputs, outputs, communicating w/ data bus
Controls, monitors hardware; controls memory, devices, ALU
to be able to respond to instructions
Program Counter (PC)
Holds address of next instruction, keeps hold of CPU's places in a sequence, aka IP (instruction pointer)
or IAR (Instruction Address Register), also a CIR
Current Instruction Register, holds current instruction address
FDE
Cycle
Instruction
Specific form of binary, agreed-upon protocol
Opcode - instruction for CPU
Operand - place where CPU should execute
Fetch
Value placed in PC of next instruction given to MAR
Instruction, data located by sending value to memory
Use address bus; data sent to MDR w/ data bus
Decode
CPU has a set of codes/instructions (machine language )
It can understand to decode instructions
Execute
Action required by instruction take place
Calculations etc.
Storage
RAM
Where all current programs, data is STA
Allows comp to quickly access w/ fastest storage
Volatile: data lost w/ no power - hard disk needed
Any location can be directly accessed in RAM
(Random Access Memory) no serial search needed
ROM
Computer doesn't write to memory, permanent data
Non-volatile: data not lost w/o power; STA 'boot up' program
RAM vs. ROM
RAM
- Stores current programs, data
ROM
-Stores only boot-up program
RAM
- Volatile;
ROM
- Non volatile
RAM
- larger capacity;
ROM
smaller capacity
RAM
- Can be written, read on;
ROM
- Read only memory
Cache
Built-in CPU memory, 3 Levels
L1 closest, fastest; L3 furthest, slowest
Computer
Definition
Takes inputs, processes, outputs result (can STA output)
Use Hardware,Software; system has CPU, memory & others
Components
Hardware - Physical computer parts
Software - Programs used by computer
Memory - where hardware stores data
CPU - main unit for processing instructions
GPU - Renders images, animation, videos
(Graphics Processing Unit)
First Computer
Electronic Numerical Integrator and Computer (ENIAC)
Made 1943-46 made by John Mauchly & J Presper Eckert
At Uni of Pennsylvania, solve large-scale arithmetics
US Army use for logistics
Computer
System
IPO Model
Simplest computer design - input, processor, output
Maybe Main memory, secondary storage added
Main (RAM) closer to P than Secondary (Hard Disk etc.)
Comp prioritises data often used to put in Main memory
FDE Cycle
Stored Program Concept - Programs stored in memory
Programs loaded from Secondary to main before use
Programs contains Ks to Ms of instructions
Fetches one at a time, place in processor, decode, execute
CPU processes data & instructions for this reason
FDE Steps
PC holds address of next instruction
Address copied to MAR (memory address register)
Data found in MAR taken to MDR (memory data register)
MDR content copied to CIR (Current Instruction Register)
PC contents incremented
CIR content divided (opcode, operand) CU interprets opcode
Address of instruction copied (CIR to MAR)
Data in MAR copied to MDR; Operation performed
Embedded
System
Embedded vs. General Purpose
G-P, many diff. functions, central 'brain' (CPU)
Embed, built into hardware, very specific functions
Small IPO processor, built into daily appliances
Cars (<50 inside), Washing machine, Insulin pumps etc.
Uses
Device can auto one function
Smaller hardware/device needed for processor
Reduce price, G-Ps would have unnecessary functions