1.2 Memory and Storage Flashcards
What is Primary Storage?
Holds data and instructions which CPU needs access to while a computer is running. The CPU can quickly acess data from primary storage than from secondary storage,
e.g. RAM, ROM, Registers, Cache
Does Primary Storage have a high storage capacity?
No. It has a relatively small storage capacity compared to secondary devices
What is secondary storage?
Secondary storage – non-volatile storage used to save data.
E.g. hard disk - measured in terabytes (TB)
What is ROM?
Small piece of read-only memory located on the motherboard. It contains the very first instructions of the computer.
Non-volatile
Uses – firmware, and BIOS information.
What is RAM?
Temporary storage of instructions and data for programs executed by the processor.
Uses – holds operating system and programs in use by CPU while computer is running. It is volatile (contents lost when power is turned off). Large compared to ROM.
Internal components of a computer
RAM, ROM, CPU, Hard Drive
What is the POST?
Power on Self Test - wakes up all the connected components and makes CPU aware of their existence
What is Virtual Memory?
Virtual memory allows computers to use hard disk space as an extension of RAM - when there is not enough physical RAM to store the open programs.
What happens when instructions are needed again?
A different program can be swapped out of RAM into virtual memory to make room for instructions now needed.
What happens when RAM is not executed?
Programs are transferred out to virtual memory and when RAM is needed, programs are transferred back to RAM from virtual memory.
Why is Secondary storage needed?
ROM is read-only and RAM is volatile. It is needed for storage of programs and data when power is turned off, semi-permanent storage of data that can change, backup of data files and archive of data files
What is the drive?
The device that reads and writes data from secondary storage
Media
What the data is actually stored on
What is optical storage?
`Consists of CD-R, CD-RW. DVD-RW, Blu-Ray
Low capacity compared to other types of storage, slow to access data
How do optical drives work?
By shining a laser at the media and processing the reflection from the media
What are pits and lands?
Where the surface of the disc is physically burned by the laser. Suitable for storing zeros and ones.
What is magnetic storage?
Consists of a hard disk drive, and tape. High storage capacity. Quick to access data. Has moving parts, which eventually fail. Hard disks perform better if defragmented
Disadvantages:
Slow access times, prone to scratches
Advantages:
Cheap, thin, light weight, portable
Advantages of magnetic storage:
Cheap, large capacity
Disadvantages of magnetic storage:
slow access times, fragile
What is solid state storage?
Consists of SSD, Memory sticks, Flash memory cards. Medium storage capacity. Very quick to access data. No moving parts, very reliable, no noise, low power, no need to defragment. Expensive compared to other types of storage
Advantages:
Durable, Fast access times
Disadvantages:
Cost, Limited read and writes
What is a bit (b) or binary digit?
Everything must be stored with only ones and zeros
What is a nibble?
4 bits or half a byte
What is a byte?
1 byte (B) = 8 bits
What is a kilobyte?
1 Kilobyte (KB) = 1024 bytes - 2^10 : 1000 ~~ bytes - 10^3
What is a megabyte? (1000KB)
1 MB = 1024^2 bytes - 10^6 - 1,000,000 bytes
What is a gigabyte? (1000MB)
1 GB = 1024^3 bytes = 10^9 = billion bytes
What is a terabyte? (1000GB)
1 TB = 1024^4 bytes = 10^12 = trillion bytes
Petabyte (1000TB) :
1 PB = 1024^15 bytes = 10^15 = quadrillion bytes
Why is data converted into binary to be processed through the computer?
With just two states, electronic components are easier to manufacture, therefore cheaper and more reliable. Examples of using two states to store data include RAM - capacitors with a charge or no charge - Optical disk - light reflected or not - Hard disk with magnetic disk representing north and south polarity and Memory stick - flash memory
What is a binary digit?
A 0 or a 1.
What is so special about bits?
With combining a series of bits, it’s possible to represent any kind of data, text, images, sound and commands.
How do you calculate a text file?
Bits per character x Number of characters
How to calculate a sound file?
Sample rate X Duration (s) x Bit depth
How to calculate an image file?
Colour depth x Image height (px) x Image width (px)
How to convert from denary to binary?
Divide by two method or binary number line method
How to convert from binary to denary?
Add together the columns that have 1s in. e.g. 01100110 = 64+32+4+2 = 102
What is the rule in adding binary?
0 + 0 = 1
0 + 1 = 0
1+ 1 = 0 carry 1
1+1+1 = 1 carry 1
What is an overflow?
When the total from adding binary numbers can not be stored within the registers of a CPU. The largest number we can store in 8 bits is 255.
How do we fix an overflow error?
Add an extra column on the left beyond the 128 with a weighting of 256 to store this number
What is the denary number range?
0 - 255
What is the binary number range?
00000000 - 11111111
What is the hexadecimal range?
00 - FF
Why ix hexadecimal used?
They are useful for representing large binary numbers in a smaller number of digits. They are used in computer science to represent colours, memory address, MAC addresses and much, much more
What is Most Significant Bit?
The left-most bit in any representation - 128 is biggest value
What is the Least Significant Bit?
The right-hand side is the least significant bit - 1 is lowest value
What is binary left shift?
Multiplying (by 2)
What is binary right shift?
Dividing (by 2)
What is a character set?
A defined list of characters recognized by the computer hardware and software. With each character being represented by a single number.
What is each character represented by?
A binary number
Well known character sets:
ASCII - a 7 bit character set with 2^7 characters = 128
What is Extended ASCII?
an 8 bit character set with 2^8 characters = 256
What is Unicode?
24-bit character set with 2^24 characters > 16 million
