GCSE OCR J277- COMPUTER SCIENCE MEMORY AND STORAGE TEST QUESTIONS WITH 100% CORRECT ANSWERS

Primary Memory Memory that can be addressed and accessed directly by the processor. 2 types of primary memory ->RAM (Random Access Memory) -> RAM (Read Only Memory) Brainpower Read More Previous Play Next Rewind 10 seconds Move forward 10 seconds Unmute 0:03 / 0:15 Full screen RAM (Random Access Memory) -> Stores parts of the OS currently being used by the computer for access by the CPU -> Stores programs currently running for access by the CPU -> Stores programs currently being used for access by the CPU -> High-speed volatile memory ROM (Read Only Memory) -> Stores programs permanently in the same location -> Contains instructions for boot-up (BIOS- Basic Input Output System) -> The boot up program in stored in the ROM -> Non-volatile memory Difference between RAM and ROM RAM is volatile, ROM is non-volatile. RAM is read/write, ROM is read only. RAM is fast, ROM is slower. RAM is big, ROM is small. Virtual Memory -> Part of the secondary storage used as (temporary RAM) -> It is used when RAM is full -> Data can be moved from the RAM when it is full to the VM so the RAM can be filled we data- when you need the data it is transferred back from the VM to the RAM which is slower. Disadvantages of Virtual Memory -> The read/write speed of a hard drive is much slower than RAM, and the technology of a hard drive is not geared towards accessing small piece of data at a time -> VM is slower to access than the RAM directly so moving data between the RAM and VM takes processor time -> OS has to constantly swap information between RAM and hard disk which operates all the time. This causes thrashing and reduces the execution of programs How does Virtual Memory work An application that is no longer in use is swapped out of the RAM into virtual memory in the hard drive. Space for a new application to load is made. Old application can be swapped back if needed Secondary Storage -> Long-term/non-volatile storage of data/files -> External/auxiliary storage of data Why do we need Secondary Storage? -> For long-term/non-volatile/permanent storing when the device is turned off -> To store data/files -> For transferring data/files to another device 3 types of storage -> Optical -> Magnetic -> Solid State Optical Storage A laser light creates marks in a pattern on a disk A laser light detects where the marks are and translates this into a readable format Magnetic Storage Read/write head (on an actuator arm) moves across a stack of magnetized disks and change how magnetized that part of the medium is. Solid State Storage This is made of microchips (switches). The state of the switches determine if a 1, or 0 is stored. Optical Storage types -> CD (compact disk) -> DVD (digital versatile disk) Magnetic Storage types -> Magnetic tape -> Floppy disk Solid Stage Storage types -> Flash Memory -> SSD (Solid State Drive) Characteristics of storage devices capacity, speed, portability, durability, reliability and cost Optical Storage characteristics lower capacity, relatively slow speed, small lightweight but easily scratched, limited rewrites, cheap per disc but not practical for large amounts of data. Magnetic Storage characteristics higher capacity, relatively fast, moving parts but can be portable, durable, reliable, and cheap for large amounts Why do computers use binary? Computers consist of transistors which only have two values-on or off. Solid State characteristics higher capacity, faster access times, considerably lighter so portable, no moving parts, expensive for large amounts of storage. Units of data storage Bit- 1 Nibble- 4 bits Byte- 2 nibbles (8 bits) Kilobyte- 1000 bytes Megabyte- 1000 kilobytes Gigabyte- 1000 megabyte Terabyte-1000 gigabyte Image file size formula image file size = color depth x image height (px) x image width (px) Sound file size formula sample rate x duration (s) x bit depth Text file size formula bits per character x number of characters Overflow error Loss of accuracy as it "loses" the rightmost bit which it can't store anywhere. Character set The characters/symbols a computer uses/understands/displays. ASCII (American Standard Code for Information Interchange) -> 7 bits per character -> It is used to represent letters and symbols as numbers, with each character given a unique a number from 0 to 128. -> Most computers use ASCII codes to represent text, which makes it possible for computers to communicate easily with each other. Extended ASCII -> However, the extended ASCII has larger characters sets that use 8 bits which gives them an additional 128 characters. -> The extra characters are used to represent non-English characters, graphic symbols and mathematical symbols. Unicode -> Unicode uses 16 or 32 bits and is usually shown in hexadecimal (FFFF). -> Unicode can have a larger character set as it uses more bits to represent each character. -> Introduced as a Universal code so all languages and characters can be represented. -> It can continuously be extended. Resolution ->The number of pixels we use is known as the resolution (width*height of an image) -> ADVANTAGE- The quality of an image is improved as it is closer to the original image -> DISADVANTAGE- The more pixels that need to be stored, the larger the file size on the disk. Colour depth -> The number of bits to represent the color of a pixel. -> ADVANTAGE- The more realistic colors- more binary digits means more colors available. -> DISADVANTAGE- The more data that needs to be stored and the larger the file size on the disk Metadata + examples Metadata is the data alongside image to tell the computer how to display it. (DATA ABOUT DATA) Examples of metadata- -> Height -> Width -> Number of bits per pixel -> Colours used -> Location -> Date -> File type. Describe how bitmap images are represented in binary. An image is made of/split up into pixels. Each pixel given a binary code Which represents the colour of that pixel. Each colour is given a different/unique binary code. Metadata is stored alongside this image. Sampling Height/amplitude of a waveform is sampled/measured Converted to/stored as binary/digital Samples/Measurements are taken at regular intervals/set intervals/by sensible example ( 44,100 times per second) Sample rates The number of samples/measurements of the sound are taken each second. 44.1KHz is average sample rate Advantages + Disadvantages of high sample rates Benefit of high sample rate- Higher sample rate means that the sound measured is more accurate so it is closer to the original sound that our ears hear. Disadvantage of high sample rate- Higher sample rates mean we have to store more samples which means the file size will be bigger. This will use up more storage and will take longer to send over the internet. Advantages + Disadvantages of low sample rates Benefit of low sample rate- Lower sample rate means fewer samples are stored so less file space is needed and it will take less time to send over the internet. Disadvantage of low sample rate Lower sample rate means fewer samples are taken which means the audio is not as close to the original.