T1 - Memory/ Secondary storage Flashcards
Types of Primary storage:
RAM
ROM
RAM:
Can be read from and written to
Access to RAM is much faster than a hard drive
RAM Stores:
OS first, then Software + Data
RAM holds copies of running programs from hard drive, when your computer is turned on
Volatile memory
When your computer is turned off, data stored is lost
Virtual memory:
Opened when there is not enough free space in RAM
is part of the hard drive used as an extension to RAM
VM Advantages:
Uses cheap secondary storage on the hard drive
Prevents error messages saying ‘out of memory’
VM Disadvantages:
very slow to access
Read-only memory (ROM)
Stores data even when a computer has no power
Data is read from ROM, but cannot be written to it
- non-volatile
non volatile memory
ROM = as the data isn’t lost if the power is off
ROM Stores:
- bootsrap
-bios
Bootstrap
- The initial program that is run when the computer is turned on + tells computer where OS is on hard drive
Basic Input/Output System (BIOS)
- It controls basic technical configuration of the computer
Secondary storage:
not directly accessible to CPU
non-volatile
Secondary storage: Uses: hard drive
Programs/data stored on hard drive
Secondary storage: Uses: Blu-rays
used to distribute films
Secondary storage: Uses: Memory sticks
used to transport data
Secondary storage: Uses: Magnetic tape or external hard drives
may be used for backup
Secondary storage: Uses: SD cards
can be used for additional storage on cameras and smartphones
Secondary storage: Types:
Hard Disk Drive (HDD)
Solid State Drive (SSD)
Offline secondary storage:
Compact Disc (CD), Digital Versatile Disc (DVD) or BluRay
Flash memory, SD cards
Removable HDD or SSD
Magnetic tape
Magnetic storage description
: Mechanical parts move over the disks surface to read and write data magnetically, or a drive head reads a magnetic tape
Magnetic storage Features:
Disk contains concentric circles called tracks
Each track is divided into sectors
Disk heads mounted on mechanical arms read and write the data
Magnetic storage used in
hard disks used PCs and laptops.
Magnetic storage Advantages:
large storage capacity, up to 6TB or more
relatively fast write speed
very cheap compared to SSD
USB can back up data
Magnetic storage Disadvantages:
Lots of mechanical parts,
durability an issue,
Not very portable
Optical storage description
: Lasers read and write data using light - uses songs, videos, films.
Optical storage Features:
Data is stored as pits and lands pressed into a spiral track
A laser beam passes over the pits and lands the level of reflection is measured
From this signal, 0s and 1s can be derived
Optical storage Advantages:
Cheap,
very easily portable,
takes up little space physically
Optical storage Disadvantages:
Less storage capacity compared to other types
Easily damaged / scratched, requires a CD reader
Slow write speeds
Pit size and wavelength: CD + Blu-ray
A CD has bigger pits and lands as red light has a
larger wavelength
The smaller Blu-ray pits and lands allow it to store more data
Solid State: description
Data is recorded onto solid memory chips without any moving parts
SSD Features;
non-volatile flash memory to store information
Flash memory:
Large electric current used to force electrons through a barrier and trap them on the other side
They remain on the other side until ‘flashed’ with a new current,
Low cost, portable, no moving parts, durable
Flash memory: Advantages:
Highly durable
very fast read/write speeds,
no noisy fan or drive arm,
faster start up times
Flash memory: Disadvantages:
More expensive
similar storage capacity as magnetic disks
How to access VM from hard drive
the existing data in RAM needs to be copied to the virtual memory, then data in virtual memory needs to be copied to RAM
