Why do we need primary storage
For faster access speed. Reading and writing from a hard disk is is a very slow compared to the speed of the processor so we use RAM to act as a temporary storage for programs and data while the program is being executed by the CPU
Key characteristics of ROM
- non-volatile
- used to store the bootstrap loader which is required to start up the computer
- memory can only be read NOT written to
Key characteristics of RAM
- Volatile
- Stores the user data/programs that are currently in use
- memory can be both read and written to
Why is virtual memory needed
Sometimes when RAM isn’t big enough to hold all the open programs and data in use, virtual memory will be used. This is a small section of the hard disk that is used like RAM. However, in order for the programs or data to be used, they have to be switched back over into RAM which is time consuming and can cause disk thrashing.
Why is secondary storage needed
Because ROM is read only and RAM is volatile
- storage of programs and data when the computer is turned off
- backup and archive of data files
What are the 3 common types of storage
- Optical
- Magnetic
- Solid State
What is the portability of secondary storage
How easily it can be unplugged and carried away, whether it fits in a pencil case or needs a larger bag
What is the durability of secondary storage
how easily it can be damaged
What is the reliability of secondary storage
how long it will last
Advantages and disadvantages of Magnetic storage (6)
- very large capacity
- faster than optical but slower than SSD
- not very portable as they are either built into the computer or would fit into a very large pocket
- not durable due to moving parts
- very reliable as they can write to the disk an infinite number of times
- relatively cheap per unit of storage
Advantages and disadvantages of Solid State storage (6)
- medium capacity
- very fast speed
- very portable (light and thin)
- Very durable
- very reliable
- considerably more expensive than other types
Advantages and disadvantages of Optical storage (6)
- Small capacity
- Quite slow
- very portable
- scratches can affect data (durability)
- reliable over medium terms but degrades over time
- medium cost
Units of data storage in order
- bit
- nibble
- byte
- kilobyte
- megabyte
- gigabyte
- terabyte
- petabyte
why must data be stored in binary
Because the computer understands the 1 to be on or true and the 0 to be off or false
Equation to work out sound file size
sound file size = sample rate x bit depth x duration (secs)
Equation to work out image file size
image file size = colour depth x image height(px) x image width(px)
Equation to work out text file size
text file size = bits per character x number of characters
what is an overflow error
when two binary numbers are added and the number is valued as more than 255 so the 8 bit binary can no longer store it
How are characters represented on a computer
as binary
What is a character set
all the different characters a computer can represent, encoded using a given number of bits
Number of bits per character in ASCII and therefore maximum number of characters in the set
7
128
Number of bits per character in Unicode and therefore maximum number of characters in the set
16
65,000+
Advantages and disadvantages of Unicode
- wide range of characters available
- larger amount of storage needed per character
How are images represented by binary
Every image is a series of pixels and each pixel is a specific colour, represented by a specific code
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1.1 Systems Architecture31
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1.2 Memory and storage44
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1.3 Computer networks, connections and protocols90
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1.4 Network Security34
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1.5 Systems software30
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1.6 Ethical, Legal and Cultural, and environmental Impacts of digital technology24
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2.1 Algorithms16
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2.2 Programming Fundamentals29
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3rd Year10
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Retest17
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not on flashcards1
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2.3 Key terms18
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2.3 Producing robust programs27
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2.4 Boolean Logic1
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2.5 Programming languages and integrated development environments20
