AS Level Computer Science WJEC.- Hardware - Memory

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What is Main Memory?
RAM, or Random Access Memory, a volatile form of memory that stores instructions and data. Retrieving data from main memory is slow, hence processors must waste clock cycles to retrieve information. This causes the Von Neumann Bottleneck.
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What is ROM?
Read-Only Memory stores Basic Input Output System, the software required to initialize the hardware, load settings, and initiate the operating system.
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What is a Cache?
Like RAM, a volatile form of memory, but they are smaller and act as a middle man between the CPU and Main Memory. The most used instructions are stored here, and the processor checks the cache first for the instruction it needs.
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Describe the three different levels of Cache.
Level 1 - Fast but very small. Embedded within the processor itself. Level 2 - Higher capacity than 1, hence is slower. Dedicated to 1 or 2 cores, and is located on a seperate chip so traffic on system bus does not slow it. Level 3 - All cores use it
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What is Secondary Storage?
Secondary storage is where data is stored permanently, and unlike RAM or Caches, they are not volatile, and therefore do not have all data wiped upon power being lost. They commonly store the OS, applications, and documents/files.
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Name the three main types of storage device.
Magnetic (Back-up tape and hard disc drives), Optical (CD, DVD, Blu-Ray), and Solid State (Memory sticks and Secure Digital [SD] cards)
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What is a Hard Disc Drive?
A hard drive is a high capacity Magnetic Storage Device. It stores data on a hard drive platter by introducing a small magnetic flux, which is remembered by the oxide on the disc. It has a fairly fast transfer and fast access rate, and a fair cost.
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How is data read/saved on a hard drive?
The reading and saving of data is managed by an arm with a special read/write head. The discs have several sectors, and the combined spinning of the discs and the movement of the arm allows every sector to be read. It then uses the flux to read/write
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What is a common speed for Hard Drives to operate at, and why is this important?
7200 Revolutions Per Minute (RPM). Due to how data is read, depending on the disc's spin, the higher the RPM, the faster data can be read from the disc.
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What is an SSD?
A Solid State Drive. They don't use magnetism to store data, and instead prompt for Electronically Erasable Programmable Read-Only Memory. While SSDs tend to have better performance than hard drives, they cost more and have lower capacity.
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What are optical drives?
Optical drives are discs that use lasers to store data by burning microscopic identations into them, which is done in a spiral pattern, starting from the middle. The indents and their absence create pits and lands respectively.
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How do we read data from Optical Drives?
Using the pits and lands, a laser is aimed at the disc and reflected back, causing interference with the original laser. The change in interference is how the optical drive can tell between pits and lands.
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What are Optical Drives typically used to store?
Software and multimedia (movies and music).
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What is RAID?
Redundant Array of Independent Discs. These are several drives brought together to act as one, and can be made up of either SSD and HDD. Typically, 1 of the subdrives will act as a parity drive, to correct errors by calculating what lost data was.
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What is Fragmentation and how does it occur?
Fragmentation is when files are split up and stored on differing parts of the storage medium's disc.
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How does Fragmentation occur?
This happens because as data is rewritten, it must erase old space or take up new space to fully hold all the data. This means that the gaps between chunks of data are filled in, as data is saved in a consecutive manner.
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Explain why Fragmentation is a problem.
The differing locations means, to read the data in order, as the hard disc should, the disc needs to make several revolutions, rather than just one. This makes retrieving data take much longer.
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What is Defragmentation?
The process of physically rearranging the data to make it all become consecutive and stored together, which removes fragmentation and improves retrieval speed.
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Other cards in this set

Card 2

Front

What is ROM?

Back

Read-Only Memory stores Basic Input Output System, the software required to initialize the hardware, load settings, and initiate the operating system.

Card 3

Front

What is a Cache?

Back

Preview of the front of card 3

Card 4

Front

Describe the three different levels of Cache.

Back

Preview of the front of card 4

Card 5

Front

What is Secondary Storage?

Back

Preview of the front of card 5
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