Memory & Storage Flashcards
All 36 cards in this deck
What is main memory?
Any memory that the CPU can access directly, apart from cache and registers. RAM and ROM are main memory.
Why does a computer need main memory?
So the CPU can quickly access the instructions and data of the programs currently being run.
What is cache memory?
High-speed volatile memory built into the processor that temporarily holds data and instructions the processor is likely to reuse.
Why does cache memory speed up processing?
The processor does not have to wait to fetch the data and instructions from the slower RAM.
True or false? Cache memory is slower than RAM but much larger.
False. Cache is faster than RAM, but it is very small and more expensive to build.
What is RAM?
Volatile main memory: it can be read from and written to, and loses its contents when the power is switched off.
What is ROM?
Non-volatile main memory: it keeps its contents when the power is switched off, and can be read from but not written to.
What does RAM hold while a computer is running?
The operating system and the programs and documents currently open/in use.
What is usually stored in the ROM of an embedded system?
The start-up instructions and the firmware: the program that controls the device, which rarely or never needs to change.
What is secondary storage?
Any non-volatile storage that is not directly accessible by the CPU. It keeps data, files and programs long term, including when the computer is switched off.
Why does a computer need secondary storage?
Because RAM is volatile and limited in size, so data and programs must be stored permanently somewhere with a large capacity.
Give two differences between main memory and secondary storage.
Main memory is faster and directly accessible by the CPU; secondary storage is slower, non-volatile, not directly accessible by the CPU and has a much larger capacity.
True or false? A program stored on a hard disk must be loaded into main memory before the CPU can run it.
True. The CPU fetches its instructions and data from main memory, not directly from secondary storage.
What are the two main types of secondary storage in a modern computer?
Solid state (e.g. a solid state drive, SSD) and magnetic (e.g. a hard disk drive, HDD).
Give two examples of magnetic storage devices or media.
Hard disk drive (HDD) and magnetic tape.
Give two examples of solid state storage devices or media.
Solid state drive (SSD) and USB memory stick (also SD/memory cards).
How does solid state storage store data?
It uses electrical circuits (flash memory) to store data persistently. It has no moving parts, and keeps its data when the power is off.
True or false? Solid state storage contains moving parts.
False. It has no moving parts, which makes it robust and portable. A solid state drive (SSD) is also faster to read from and write to than a magnetic hard disk drive.
Give one advantage and one disadvantage of a solid state drive compared with a magnetic hard disk drive.
Advantage: faster access with no moving parts, so more durable and lower power. Disadvantage: higher cost per gigabyte.
Why is flash (solid state) memory suitable for tablets, smartphones and digital cameras?
It is small and light, has no moving parts so is robust, uses little power and is fast to read from and write to.
Which type of storage is most suitable for backing up very large amounts of data as cheaply as possible?
Magnetic storage (hard disk drive or magnetic tape) — large capacity at a low cost per gigabyte.
Give two drawbacks of storing data in the cloud rather than locally.
You need internet access (speed depends on the connection), and you have no control over security, relying on the provider; there may also be an ongoing subscription cost.
Give two advantages of storing data remotely (in the cloud) rather than locally.
Data can be accessed from anywhere with an internet connection and shared easily; no need to buy and maintain your own storage hardware.
What is the purpose of ROM in a general purpose computer?
It stores the BIOS: the start-up (boot) instructions the CPU runs when the computer is switched on, which check the hardware and load the operating system into RAM.
Why are a computer's start-up instructions stored in ROM rather than RAM?
ROM is non-volatile, so the instructions are still there when the power comes on. RAM loses its contents when switched off.
Which typically has the larger capacity, an HDD or an SSD?
An HDD.
What limits the lifespan of the flash memory in an SSD?
It can only be rewritten a limited number of times before it starts to wear out.
What is cloud storage?
Storing data at a remote location, on servers that use magnetic and/or solid state storage, accessed over the Internet rather than held on the user's own device.
What is volatile memory? Give an example.
Memory that loses its contents when the power is turned off, e.g. RAM, cache or registers.
What is non-volatile memory? Give an example.
Memory that keeps its contents when the power is turned off, e.g. ROM (secondary storage is also non-volatile).
Put registers, cache and RAM in order from fastest to slowest.
Registers (fastest, inside the CPU), then cache, then RAM. The faster the memory, the smaller and more expensive per byte it tends to be.
How does a magnetic hard disk drive store data?
On spinning platters coated in magnetic material. A read/write head on a moving arm magnetises tiny areas in one of two directions, which represent 0 and 1.
How does a magnetic hard disk drive read data?
As the platter spins, the read/write head moves to the right position and detects the direction of magnetisation of each tiny area beneath it, giving the 0s and 1s.
Why can storing data in the cloud raise legal concerns?
The provider's servers may be in another country with different data protection laws, and it may be unclear who is responsible if the data is breached.
Why is data in cloud storage protected if the user's device is lost, stolen or destroyed?
The data is held on the provider's remote servers, and the provider backs it up, so it is not lost along with the local device.
When the CPU needs an instruction or data that is not already in one of its registers, where does it look first?
In the cache. Only if the item is not there is it fetched from the slower RAM.