What are the 2 types of memory
Primary
Secondary
What memory comes under primary
ROM
RAM
Cache
2 Types of secondary and what comes under them
Internal - HDD, SSD
External - DVDs/CD, Blu ray disc, USB memory stick, Removable hard drive.
Differences between primary and secondary storage
Primary:
Can be directly accessed by CPU
Only internal
Secondary:
Not directly accessed by CPU
Non volatile memory
Can be external or internal
What does the primary memory allow the cpu/computer to do
Primary memory allows the CPU to access applications and services temporarily stored
What is volatile memory
Contents of memory are lost when the computer is powered off
What is non volatile memory
Contents of memory aren’t lost when the computer is powered off.
Process of running a program from secondary storage
When you run an application or program data is retrieved from secondary storage and placed
temporarily into RAM
Features of RAM
Can be read from or written to
Stores data, files, programs, parts of the OS that are currently in use
Volatile
Uses of RAM
» the user may wish to program in their own routines; these new instructions would be stored in the RAM chip
» the RAM chip will store the data/instructions received from the remote control unit
What are the 2 types of RAM and full forms
DRAM - dynamic RAM
SRAM - static RAM
What is DRAM made out of
Millions of transistors and capacitors
What is a capacitor in DRAM
Holds the bits of information (0 or 1)
What is a transistor in DRAM
Acts like a switch which allows chip control circuitry to read the capacitor/change the capacitor’s value.
Which type of RAM needs to be constantly refreshed otherwise what happesn
DRAM
Otherwise capacitors would lose their values.
How does SRAM hold memory and what makes it different
Doesn’t need to be constantly refreshed
Uses flip flops to hold data.
What does “refresh” mean in DRAM
recharge every few seconds in order to maintain
charge
What does a flipflop mean in SRAM
electronic circuit with only two stable conditions
Where is SRAM preferred and why
CPU’s memory cache, since it is faster.
Diff between DRAM and SRAM
DRAM:
Uses capacitors and trasnsitors to store data
Needs to be constantly refreshed
Consumes less power
Higher memory capacity.
Cheaper to manufacture
SRAM:
uses flip flops to hold each bit of memory
doesn’t need to be constantly refreshed
has a faster data access time than DRAM
Difference between ROM and RAM
ROM:
Can only be read from.
Non-volatile memory
Permanent memory
Store the start up programs/routines of the system, eg: BIOS
RAM
Can be read from or written to
Volatile
Temp memory
Store programs/data currently in use
can be increased in size to improve operational speed of a computer
Uses of ROM
» storing the factory settings such as remote control frequencies
» storing the ‘start-up’ routines when the toy car is first switched on
» storing of the set routines; for example, how the buttons on the hand-held device control turning left, acceleration, stopping, and so on.
3 Types of secondary storage
magnetic
» solid state
» optical.
How is data stored in an HDD
Data is stored in a digital format on the magnetic surfaces of the disks
How is data accessed in an HDD
Read-write heads consist of electromagnets that are used to read data from or write data to the platters.
Format/structure of data stored in HDD (the parts in which it is stored)
Data is stored on the surface in sectors and tracks.
What is latency
the time it takes for a specific block of data on a data track to rotate around to the read-write head.
What leads to sectors in HDD become fragmented and impact on performance
HDD will undergo numerous deletions and editing which will cause gradual deterioration of the HDD’s performance.
How to combat fragmentation and what does it do
Defragmentation - tidies up sectors.
Why is SSD better than HDD and how
Solves the problem of latency they have no moving parts and all data is retrieved at the same rate.
How is data stored and retrieved in SSD
store data by controlling the movement of electrons within NAND or NOR chips. The data is stored as 0s and 1s in millions of tiny transistors within the chip
at a junction what are the 2 types of transistors (SSD) and what tech do they use
Floating gate
Control gate
use CMOS (complementary metal oxide
semi-conductor) NAND technology
What allows SSD to be non volatile
A dielectric coating separates the two transistors, which allows the floating gate transistor to retain its charge
Benefits of SSD over HDD
More reliable and durable
Lighter
Lower power consumption
Run much cooler
Very thin
Access data faster
Drawback of SSD
SSD Endurance - the total guaranteed number of times\
data can be written to or read from a solid state drive (SSD) in its usable life cycle
Charge leaks away from SSD which leads to data loss
Main advantage of USB Drives
very small, lightweight devices, which make them very suitable as a method for transferring files between computers
Diff between a dongle and a normal usb flash drive
what does a dongle prevent
The dongle contains additional files that are needed to run the software.
Without this dongle, the software won’t work properly.
It therefore prevents illegal or unauthorized use of the software, and also prevents copying of the software since, without the dongle, it is useless.
What kind of software is a dongle used to store
Complex or expensive software, such as financial planning software
What are the optical storages
CDs
DVDs
Blu ray
What do CDs and DVDs use to store data
Structures on them to store data
How is data accessed
Both CDs and DVDs use a thin layer of metal alloy or
light-sensitive organic dye to store the data.
The data is stored in ‘pits’ and ‘lands’ on the spiral track.
A red laser is used to read and write the data.
What makes DVDs different
How are they made diff
potential for dual-layering, which considerably increases the
storage capacity
Two layers of a standard DVD are joined together with a transparent (polycarbonate) spacer, and a very thin reflector is also sandwiched between the two layers.
Why do DVDs have a larger storage size than CDs
‘pit’ size and track width are both smaller - more data can be stored on the DVD surface
DVDs use laser of the shorter the wavelength of the laser light, the greater the storage capacity of the medium.
Wavelength of laser of DVDs and CDs
DVDs use lasers with a wavelength of 650nanometres;
CDs use lasers with a wavelength of 780nanometres.
Main diff between DVDs and Blu ray
Laser
What is the laser’s wave length
Structure
Layers
Transfer rate
a blue laser, rather than a red laser - wavelength is shorter (480)
Allows pits and lands to be much smaller
Blu-ray disks automatically come with a secure encryption system that helps to prevent piracy and copyright infringement
the data transfer rate for a DVD is 10Mbps and for a Blu-ray disc it is 36Mbps
(this equates to 1.5hours to transfer 25GiB of data).
Can come in single or duel layer
What is virtual memory
a memory management system that makes use of secondary storage and software to enable a computer to compensate for the shortage of actual physical RAM memory
What is a page and another name
fixed-length contiguous block of data utilised in virtual memory systems
Data blocks
Benefits of virtual memory
» programs can be larger than physical memory and still be executed
» there is no need to waste memory with data that isn’t being used
» it reduces the need to buy and install more expensive RAM memory
What is disk thrashing
a problem in a hard disk drive (HDD) caused by excessive swapping in and out of data causing a high rate of head movements during virtual memory operations
What is the thrash point
The point at which the execution of a program
comes to a halt because the system is so busy moving data in and out of memory rather than actually executing the program
What is cloud storage
method of data storage where data is stored on remote servers.
3 types of clouds and explanations
Public cloud – this is a storage environment where the customer/client and cloud storage provider are different companies
» Private cloud – this is storage provided by a dedicated environment behind a company firewall; customer/client and cloud storage provider are integrated and operate as a single entity
» Hybrid cloud – this is a combination of the two above environments; some data resides in the private cloud and less sensitive/less commercial data can be accessed from a public cloud storage provider.
Benefits of using cloud
Can access data at anytime, from anywhere in the world provided they have internet
here is no need for a customer/client to carry an external storage device with them or carry the same computer
the cloud system offers almost unlimited storage capacity
Allows data to be recovered if it is lost on the internal storage of the client.
Disadv of using cloud
f the customer/client has a slow or unstable internet
connection, they would have many problems accessing or downloading their data/files
the potential failure of the cloud storage company is always possible – this poses a risk of loss of all back-up data
