Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
28 Cards in this Set
- Front
- Back
|
Secondary Storage |
Any kind of permanent storage to which the contents of ROM/RAM are copied |
|
|
Magnetic Storage |
Secondary storage that works by magnetising parts of a substance as north and south poles to represent binary 1s and 0s |
|
|
Optical Storage |
Secondary storage that works using differences in light reflection from a material |
|
|
Solid State Storage |
Secondary storage that works by storing charge (electrons) or 'flash' memory |
|
|
What represents 1s and 0s in Magnetic Storage |
The north and south poles |
|
|
What represents 1s and 0s in Optical Storage |
Shinier or more reflective parts of the disk represent 1s or 0s |
|
|
What represents 1s and 0s in Solid State Storage |
Represents 1s and 0s by little pools of trapped electrons on a microchip |
|
|
Examples of magnetic storage |
Hard disks and magnetic tape storage |
|
|
Examples of optical storage |
CDs and DVDs |
|
|
Examples of solid state |
USB memory sticks or SD cards |
|
|
Features of secondary storage |
More permanent (non volatile) Slower to access Cheaper Higher storage capacity Do not require power |
|
|
How do hard disks work? |
Inside a hard disk there are stack of disks (platters) which have a magnetic coating on each surface There are magnetic recording heads on the end of an arm that float above the spinning disk Data is recorded on each disk, along circular tracks which are split into sectors |
|
|
What happens when data is read in a hard disk |
Arm moves to above the right track Required sector come under the head Magnetised surface induces a tiny current in the head Disk controller translates into binary |
|
|
Does data come immediately from a hard disk? |
No, it takes time
Arm moving above track time taken is called seek time Time taken for sector to arrive under head is called latency |
|
|
DVDs structure |
|
|
|
DVD (optical) |
|
|
|
Lasers (DVD) |
Two lasers used by the player
1. To write data on the disc 2. To read the data on the disc |
|
|
Writing (DVD) |
Laser heats the recording material Creates non reflective depressions on the surface (pits) Slow process - heating and cooling takes time |
|
|
Reading (DVD) |
Laser reflects differently off the surface and this is detected by a light sensor Spiral track is longer on the outside, so rotation speed os reduced so data is passed at a constant speed |
|
|
When data is read, disc wise (DVD) |
Disc spins in the drive Tracking mechanism moves the laser into correct position Laser shines on the disc Is reflected on to a light sensor Signals are turned into binary |
|
|
Flash Drives (electrical/solid state) |
Uses chips (NAND Flash) --> has special kinds of transistors, that trap electrons in a pool |
|
|
Pools (solid state) |
Electrons IN a pool = 0s Empty Pools = 1s |
|
|
Features of Solid State Devices |
Small (billions of transistors on a chip) High capacity Fast access |
|
|
Reading data (solid state) |
Control Signals (identify which bit and apply a small voltage) If electron pool empty --> transistor on and 1 (vice versa) Control signals are changed |
|
|
Writing data (solid state devices) |
Control signals Apply a high voltage Pulls electrons into the pools Record 1 or 0 |
|
|
Erasing Data (solid state) |
Higher voltage Remove electrons from pools High voltage from erasing and writing cause transistors to break down |
|
|
How many times can flashdrives be rewritten |
1 million before transistor breaks down |
|
|
Flash Drive Diagram |
|
