Unit 3.3 - data storage Flashcards
What is primary storage?
Internal computer memory that can be accessed directly by the CPU.
E.g. ROM, RAM
What is RAM?
Random access memory temporarily stores data and programs that are currently being used.
- fast to access
- volatile (loses its content when power is removed)
- capacity of 8-32 GiB
- more RAM = better performance
- data can be read from and written to RAM
What is ROM?
Read only memory contains the first instructions/BIOS (basic input output system) set during manufacturing of chip. The instructions it contains are vital for when the computer is turned on/booting.
- data can be read from ROM but not altered/deleted
- not useful for storing user data
- non-volatile
- capacity of 4-8MiB
What is secondary storage?
Storage devices that are not directly accessible by the CPU.
- non-volatile
- can hold both programs and data
- greater capacity than primary memory
- removable
- ideal for storing all of user’s data and programs permanently.
Loading file vs saving file
Loading file : from secondary storage to primary storage
Saving file: from primary storage to secondary storage
What are off-line storage devices?
Storage devices that you remove from your computer.
What is magnetic storage?
A type of storage that stores data by applying a magnetic charge to a magnetized material.
Stores binary data in sectors on disk/tape coated with material where different areas on surface can be magnetized North or South to store binary digits 1 or 0.
How does a hard disk drive store data?
In an HDD, there are many disks called platters, which spin constantly when the computer is running. A read/write arm moves in and out across the disk surface and using an electromagnet, it reads & writes the data on(to) the disk.
+ cheap, fast & can hold large amounts of data
- durability (moving part will fail), reliability (data could be wiped by powerful magnet), loud, high power consumption.
How does solid state storage work?
Solid state storage devices store data by using electronic circuits (created using transistors). The state of transistors (whether they hold charge or not) represents binary data.
Different types of transistors are used in solid state devices - NOR flash technology in older ones and NAND flash technology in modern ones. The switch to NAND was because they took up less physical space. Transistors use control gates (set transistor charge) and floating gates (retain charge when disconnected from power).
Examples of solid state devices & advantages and disadvantages
Examples: SSD (solid state drive), SD memory card, USB flash drive. All these use flash memory.
+ small, lightweight, quick to access data, durable (because it has no moving parts), less heat production, less power consumption
- noisy, limited read/write cycles, lower storage capacity than magnetic storage, data cannot be changed, expensive
How does optical storage work?
It uses light to read and write data - in disc surface, there are tiny low points (pits) and high points (lands). When a laser is pointed at a disc surface, lands reflect light while pits scatter light. This information is interpreted as binary data by a light sensor. To write data, the laser creates lands/pits in a layer of material on the disc.
+ portable, cheap to produce
- small memory capacity and data transfer, easily damaged
Give 3 examples of optical storage devices
- CD - slowest data transfer speed and smallest data capacity. Application: music/software
- DVD - middle data transfer speed & data capacity. Application: movies
- Blu-Ray - fastest data transfer speed & largest data capacity. Application: movies/console games
6 important properties of storage devices
- Capacity - amount of data that can be stored
- Portability
- Durability - how well it lasts, how prone to damage it is
- Reliability - consistency in performance
- Access speed - how quickly data can be read from or written to device
- Cost - price per mb of data stored
What is virtual memory & what is it used for?
An area of memory in secondary storage created when RAM is full; when it’s full, there needs to be a way for the CPU to execute instructions not currently available in RAM.
Currently unused pages of instructions in RAM are moved to virtual memory, called paging out.
Pages of required instructions are copied from virtual memory to RAM, called paging in.
Advantages and disadvantages of virtual memory
+ allows operating system to run programs than require more RAM than available.
- very slow access of data and program execution, inefficient, causes disk thrashing
What are operating systems?
Software which manages a computer system’s CPU, memory, storage and devices.
What is local storage?
Storage devices which are directly connected to a computer system (e.g. hard disk)
What is cloud storage and how does it work?
A modern type of storage that uses servers on the Internet to store data.
When data is saved, it is sent across Internet to server where it is stored. When user opens file, a request is sent to server to retrieve file.
Servers used for cloud storage are located in huge data centers that house 1000s of servers
Use of cloud storage + pros & cons
Use: data backup, shared live files for group work, streaming services, photo/video uploads for easy access/sharing
Examples: OneDrive, Google Docs, etc
+ data is accessible from any device at any time
- no internet = no access, can be expensive, vulnerable to cyber crime
Local vs cloud storage
Local storage +: data is accessible with no Internet, faster access speed, no monthly costs, data is fully under user’s control
Local storage - : risk of hardware failure, data can only be accessed on local computer, back-ups are user’s responsibility
Cloud storage +: users can access data from any computer, low initial cost, backing up data is cloud provider’s responsibility, easy collaboration, additional storage capacity can be added easily
Cloud storage -: needs Internet connection, monthly fees, data may be stored in different countries with different privacy laws, slower, at risk of unauthorized access, environmental impacts
