OCR GCSE COMPUTER SCIENCE PAPER 1 TEST QUESTIONS AND ANSWERS.

what is the purpose of the CPU? to process data by following the fetch-decode-execute cycle, it's incharge of searching, sorting, calculating and decision making what happens at the fetch stage? the CPU fetches data and instructions from RAM and then stores them in it's own temporary memory called registers Brainpower Read More Previous Play Next Rewind 10 seconds Move forward 10 seconds Unmute 0:00 / 0:00 Full screen what happens at the decode stage? the CPU understands what the instructions mean, the CPU decodes the instructions and gets to the next step what happens at the execute stage? the CPU carries out the instructions on the data define bus information travels along a bus from one part of the CPU to another define address bus a one way bus that requires data from an address in memory define data bus moves data in both directions as data is both read and written to memory define control unit responsible for timing on the CPU, uses the clock to ensure operations happen in the correct sequence define arithmetic logic unit does all arithmetic calculations and logical operations define registers Small temporary storage spaces inside the CPU define accumulator stores the results from the ALU temporarily until they're written to memory define program counter stores the memory address of the next instruction, is incremented by 1 at each new cycle define instruction register current instruction is stored in this register define memory address register stores the memory address of the current instruction being executed define memory data register stores the data that was read/written to memory what is the function of the ALU? performs basic arithmetic operations (addition, subtraction, multiplication, and dividion) and logical operations (AND, OR, NOT). what is the function of the control unit? manages and monitors hardware, manages the input and output signals, uses clock signals to synchronise the running of the fetch-decode-execute cycle what is the function of the cache? a small amount of storage that temporarily holds instructions that the CPU is likely to reuse, it's close to the CPU and so is fast to access what are the 3 factors affecting CPU performance? clock speed, cache size, number of cores How does clock speed affect CPU performance? the speed of the f-d-e cycle is determined by the CPU's clock chip, the clock speed is measured in hertz (cycles per second), the greater the clock speed, the more instructions are processed per second what's the issue with increasing clock speed? the CPU can overheat (overclocking), so you need to use heat syncs How does cache size affect the performance of the CPU? if the cache is larger it's more likely the next required instruction has already been transferred from the RAM to the CPU, improving process time how does the number of cores affect the CPU? they can carry out parallel processing - the same program can have two instructions carried out at once. they can carry out multi-tasking - different program's instructions are carried out at the same time what is an embedded system? An embedded system is a small computer that forms part of a larger system. it takes input, processes data and delivers an output. it doesn't need an operating system, the input is just a button or set a control, makes devices easier to use and increases reliability what is primary storage? and examples memory areas that the CPU can access very quickly, has fastest read/write speeds, mostly volatile. eg. CPU registers, cache, RAM, ROM what is secondary storage? and examples non-volatile where all data is stored when not in use, read/write speeds are much slower. eg. solid state, CD, SD cards what is tertiary storage? used for long term data storage, mainly used for archives and backups of massive amount of data what is RAM needed for? stores programs currently in use, helps to enable 'multi-tasking' (by copying data needed so it's passed through the CPU), stores all instructions from open programs properties of RAM? volatile (loses data when no power), faster than hard drive, internal how does RAM store data? uses capacitors and transistors, capacitor is a 1 or 0, transistors tell computer what's in capacitors properties of dynamic RAM? 1 transistor, 1 capacitor per bit, limit to how fast data can be read, power is always needed properties of static RAM? 4-5 transistors wired together for each bit data, doesn't lose its charge, much faster, but more expensive, needs constant power what is the purpose of ROM? stores BIOS and boot up program what are the properties of ROM? it's a memory chip, non-volatile (stores data without power), primary storage (directly accessed by the CPU), fast access rates what type of memory do modern ROM chips use? flash memory how does flash memory work? a large electrical current forces electrons through a barrier into fixed positions, the different arrangements give data what is virtual memory? a small portion of secondary storage which acts as RAM in the event of the RAM becoming full Why is virtual memory needed? it allows the computer to continue to function even though the RAM is full (albeit much slower) what happens to the performance of the CPU with smaller/larger amounts of RAM? smaller = limited multitasking and greater use of slower virtual memory larger = greater storage of programs, faster performance, effective multi-tasking what is cache memory? a small amount of memory located next to the CPU, it stores frequently used instruction, it supplies the CPU with data at high speeds properties of cache? small capacity, volatile, used in f-d-e cycle how does magnetic storage work? it uses different patterns of magnetisation in a magnetisable material to store data. magnetised points represent 1 and demagnetised points represent 0 how does optical storage work? a laser is used to burn 'pits' into shiny surfaces. a laser is used to read it, when it hits 'land' the beam is reflected (0), when it hits a 'pit' it isn't reflected (1) how does solid storage (flash) work? a large electrical current forces electrons through a barrier into fixed positions, the different arrangements give data what is the use, capacity, speed, portability, durability, reliability and cost for hard disk (hard drive)? desktop computers to store large files, programs and operating systems; 750GB - 3TB (large); fast read/write speeds; heavy; dropping can cause damage; can be reused but has has a limited life; quite cheap what is the use, capacity, speed, portability, durability, reliability and cost for magnetic tape? backing up vast amounts of data;; 1 - 5TB (very large); fast write speeds but slow read speeds; small and light but reading device is heavy; fairly durable; can be used again and again; cheap what is the use, capacity, speed, portability, durability, reliability and cost for CD-ROM? storage of small media files and documents; 650MB (small); moderate read/write speeds; portable and light; can be scratched/snapped but fairly durable; CD-R are written ones but CD-RW can be reused; very cheap what is the use, capacity, speed, portability, durability, reliability and cost for blu-ray/DVD-ROM? storage of larger media files and documents; 4.37GB (DVD) 25GB(blu-ray) (small); moderate read/write speeds; very portable and light; fairly durable but can be scratched; DVD-Rs are written once but can be re-read; very cheap what is the use, capacity, speed, portability, durability, reliability and cost for solid state drive? desktop computers, laptops and tablets store large files, programs and operating systems; 64GB - 480GB (moderate); super fast read/write speeds; very small and lightweight; no moving parts so is durable; can be reused many times; very expensive what is the use, capacity, speed, portability, durability, reliability and cost for flash SD cards? in phones, cameras - can function on the move; 16GB-64GB, super fast read-write speeds; extremely portable; no moving parts so is durable; can be reused many times; expensive what is the use, capacity, speed, portability, durability, reliability and cost for flash memory stick? backing up/transferring documents and small media files from computer to computer; 1GB-64GB, super fast read/write speeds; extremely portable; no moving parts so is durable; expensive what is the use, capacity, speed, portability, durability, reliability and cost for a NAS drive? a stand alone external hard drive at the centre of a network allows users to read/write files; 750GB-3TB (large); high read/write speeds but the network can cause slow access speeds; very heavy; dropping causes damage; can be reused; hard disk = cheap SS drive = expensive NAS enclosure = expensive what is the use, capacity, speed, portability, durability, reliability and cost for cloud storage? stores documents and media files; unlimited capacity if you pay; depends on bandwidth/network speeds; isn't physical; durable and reliable if payments are made and company looks after deives; can be issues with data protection laws; expensive depending on the service but is usually free for a few GB