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Flashcards by Mr Wiggly Gamer A.C, updated more than 1 year ago
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Created by Mr Wiggly Gamer A.C
almost 3 years ago
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| Question | Answer |
| 2 situations where Harvard architecture is preferred | Embedded systems such as digital signal processing Microprocessors (<- Weaker) |
| 3 advantages of the Harvard architecture | Reduce bottleneck of single data/address bus(es) Avoids possibility of data being executed as code (which could be exploited) Instruction and data memory can have different word lengths (<- Weakest) |
| Name 3 special purpose registers which act in the fetch portion of the fetch decode execute cycle | Program counter Memory buffer register Current instruction register |
| Why can the program counter be incremented simultaneously to data being transmitted into memory buffer register | Order of execution is unimportant Carried out by different hardware |
| State name of only unidirectional bus | Address bus |
| How to calculate bytes of data which can be accessed by an address bus of x bits and y lines How many bits per line | 2^x x/y (Each line contains a certain number of bits) |
| What is meant by the term bus | A set of parallel lines/wires that are used to connect components inside the computer in order to pass signals between them. |
| What is the purpose of the control bus. 6 examples of control signals (sent through the control bus) | Transmit command, timing and specific status information between system components. Clock timing Interrupt requests I/O read and write Memory read and write |
| The data bus transfers … and … | The data bus transfers DATA and COMMANDS |
| Relate to bus (sends signals in/ out) Processor Main memory I/O Controller (r = receive from, s = send to ,b = both) | Processor: s address, b control & data Main memory: r address, b control & data Input device: r address, b control & data |
| Modern computers have 64-bit address buses. Explain what is meant by this | 2^64 memory locations are available (64 lines/ tracks) |
| Describe two difference between the way Harvard and Von Neuman architecture operates. (in cs, you are not required to compare, it is implied) (good practice to do it anyway) | In Harvard architecture: Instructions and data have separate buses and are stored in separate memories Instruction word size can be different to data word size Instructions and data can be fetched simultaneously |
| Explain the fetch portion of the fetch-decode-execute cycle | - Contents of Program Counter transferred to Memory Address Register - Address bus used to transfer this address to main memory - Transfer of main memory content uses the data bus - Contents of addressed memory location loaded into the Memory Buffer Register - Increment (contents of) Program Counter and fetch instruction simultaneously - Contents of MBR copied to Current Instruction Register |
| Explain the decode portion of the fetch-decode-execute cycle | - Decode instruction held by the Current Instruction Register - The control unit decodes the instruction - Instruction split into opcode and operand |
| Explain the execute portion of the fetch-decode-execute cycle | - If necessary, data is fetched - If necessary, data is stored in memory - The opcode identifies the type of operation to be performed - Result may be stored in register/ accumulator - The operation is performed by the processor - Status register updated - If jump / branch required Program Counter is updated |
| 1 situation where Von Neuman architecture is preferred | General purpose machines |
| What is meant by the term stored program concept? | Machine code instructions stored in main memory are fetched and executed serially by a processor that preforms arithmetic and logical operations Programs can be moved in and out of memory. |
| Name 4 system hardware decisions which will effect the processors performance | number of cores cache memory clock speed word length address bus width data bus width |
| How does number of cores effect performance of hardware | -Having 2 or more independent processing units means that tasks can potentially run in parallel -Individual tasks could be split up to make use of extra cores, which would increase speed of execution |
| What is cache memory and how effect performance of hardware | -Memory that can be accessed very quickly -Memory located on (A. close to) the processor -To store most frequently used instructions /data -More instructions/ data can be stored in the cache -This increases the probability that a particular data item/instruction is in the cache when fetched -Instructions/data stored in cache can be accessed more quickly than instructions/data in main memory |
| How clock speed effect performance of hardware | By increasing clock speed the processor will execute more instructions per unit time |
| How word length effect performance of hardware | Increasing the word length the processor (how many bits can the processor manipulate) >can handle more data per instruction >can access a larger amount of memory through direct addressing >can have a larger instruction set |
| Explain what happens when an interrupt occurs during the FDE cycle | Current processor state saved on stack Source of the interrupt is identified Interrupts of low priority are disabled Appropriate interrupt service routine called Processor state restored Interrupts are re-enabled |
| What is meant by opcode and operand? | opcode = instruction operand = data |
| (1) Explain the role and operation of ALU Control Unit | ALU: - performs arithmetic and logic operations (+, -, /, *, OR, XOR, etc) Control Unit: - To synchronise operation of processor - control operation of fetch-execute cycle - Controls fetching operations -To execute (some) instructions |
| (2) Clock General-Purpose Registers | Clock: - generates a timing signal which changes at a regular frequency - used by control unit to sequence its operations General-Purpose Registers: - Registers are small storage locations used to hold data temporarily. They have high read and write speeds. (located inside the processor) |
| (3) Status Register | This register stores single bit condition codes each of which indicates the outcome of an arithmetic and logical operations carried out by the ALU (e.g., positive/ negative/ zero value, overflow, equal) The status register also has single bits to control the operation of the control unit. |
| Define processor instruction set | Group of instructions that it can carry out. Each type of processor has its own instruction set, so instructions for one processor may not be compatible with other processors. Instructions are usually stored in machine code and consist of two primary parts: opcode and one or more operands. |
| Define immediate and direct addressing | Immediate addressing: the operand is the datum Direct addressing: the operand is the address in memory of where the datum can be found. Address to be interpreted as meaning either main memory or register. |
| NOT A REAL FLASH CARD FLIP IT | MAKE SURE TO PRACTICE WHRITING IN ASSEMBLY LANGUAGE |
| Describe the interrupt service routines (ISRs) | The operating system will have interrupt service routines (ISRs) designed to process each interrupt. An ISR is a mini program that has been designed to respond to an interrupt’s request. ISRs can be built into an operating system or provided via device drivers. |
| Describe the role of interrupts | Allows the currently executing process to be suspended So that a device/source that needs the immediate attention of the processor can be serviced |
| Why may an interrupt occur | A hardware device has signalled that it has data to process A hardware device has completed a task that it was asked to do A software process needs a service to be provided or OS function to be performed An allotted amount of time has expired and an action needs to be performed A hardware failure has occurred and needs to be addressed |
| When is the fetch-execute cycle interrupted | Between each execute stage and fetch stage of the cycle, the content of the status register is checked for changes that could signify the occurrence of an interrupt. |
| Once the ISR has finished executing... | Once the ISR has finished executing, the OS must return to the instruction that it was executing before it received the interrupt and continue from where it left off. (explains the need to save the volatile environment) |
| How does address and data bus width effect the performance of a processor | Address: Increasing the width of the address bus increases the range of addresses that it can specify, hence increasing the amount of addressable memory. Adding a single wire doubles the number of addressable memory locations. Data: Increasing the width of the data bus increases the volume of data that can be transferred over the bus at any one time, reducing the number of cycles required to fetch large volumes of data. |
| What are the main characteristics of a barcode | Barcodes are printed diagrams that consist of light and dark portions. They contain information which can be read by a computer using a barcode reader. There are 2 types, 1D (traditional) and 2D (QR). 2D barcodes can contain more information in the same amount of space as a 1D barcode but require more processing in order for the information to be extracted. |
| Describe how barcodes operate via reflected light method | -A light source / laser is directed at bar code -Moving mirror / prism moves light beam across bar code -Light reflected back -Black / white bands reflect different amounts of light -Photodiode measures amount of reflected light -Light reflected converted into an electrical signal (& encoded as binary) |
| Describe how barcodes operate via camera method | -Grid of pixel sensors // CMOS/CCD sensor -Each sensor measures light intensity of a point -Sensor outputs a voltage dependent upon light intensity -Voltages turned into binary data using a ADC -Image processing software analyses image -This identifies black / white bands in barcode which are turned into numbers |
| Describe how a digital camera operates | Light is focussed by the lens on to an array of sensors on the sensor chip - Each sensor produces an electrical current/signal - The signal represents a pixel - An ADC converts measurement of light intensity into binary (encodes data as binary) - Colour filter is applied to generate separate data values for red, green and blue colour components - The pixels are recorded as a group / array (A Bayer filter is a special colour filter used in digital cameras that has the same number of green filters as red and blue combined. Using a Bayer filter produces an image that is a closer approximation of what the human eye, which is most sensitive to green light, sees). |
| Describe how a laser printer operates | • Bitmap of image built in memory from page description. • Negative charge applied to photosensitive drum. • Laser beam directed at drum. • Mirror is used to direct laser beam. • Where laser strikes drum charge is neutralised. • Negative charge applied to toner. • Toner sticks to drum based on charge. • Paper passed over drum and toner transfers to it. • Positively charged transfer roller assists transfer of toner from drum to paper. • Heater fuses toner onto paper. • For colour printing four different colour toners // four drums are required. |
| Describe the principles of operation of a passive RFID | -RFID tag contains transmission circuitry and antenna -Memory on tag stores data -RFID reader transmits / sends signal -Signal induces current in RFID tag -RFID tag transmits data by radio wave -RFID reader converts radio wave back into binary data -RFID tag is a passive device -RFID transmits over very short range |
| Difference between active & passive RFID tags | Active RFID tags can continuously broadcast their own signal (which is useful when the real time movement of an object needs to be tracked) Active: bulkier, larger range, more expensive |
| principles of operation of a hard disk | Magnetic medium. Binary digits represented by magnetising spots on disk. Disk made up of platters. Disk divided into tracks and sectors. Tracks are concentric circles. Drive head can move in/out. Disk continuously spinning while in operation. Disk spins at high speed (5400 to 10000 revolutions per minute). Data read/written as correct sector passes under read/write head. Medium and drive/device in sealed enclosure (<- not that good). Hard disk drive is a random-access device. |
| principles of operation of a optical disk | Reading mechanism -Low power beam of light is shone at disk -Light is focussed on spot on track -Some light is reflected back from disk -Amount of light reflected back is measured -Disc spins at constant linear velocity How data is represented -Data is stored on one/spiral track -Continuation of land/pit reflects light whereas transition between land and pit scatters light -Transition between land and pit indicates a 1 and continuation of land/pit represents 0 (bit number could be flipped) |
| principles of operation of a SSD | • Data is stored electronically (there are no moving parts) • Data is stored in floating gate transistors (transistors that do not lose their charge when power is no longer applied) • Presence of trapped electrons / charge or absence indicates 0 / 1 • NAND/ flash memory • Data is organised into pages / blocks • A whole block of data must be written • A block must be erased before it can be overwritten • Controller manages the organisation of the data, reading and writing of data |
| Explain why the volatile environment (the contents of registers) must be saved before an interrupt is serviced. | So that the currently running process/task/program can be returned to As the code that deals with the interrupt (ISR) will overwrite register values |
| Why laser printers are suitable | Low cost per printed page (toner is cheaper per page than ink) Prints many pages per minute (high print speed) Options to install a greater variety of paper trays Toner will not dry out |
| Barcode vs RFID | -In RFID, many tags can be read simultaneously. Which is not an issue if scans are time stamped. Barcodes however cannot uniquely identify an item (=> can be scanned multiple times) -RFID can be read through barriers (especially active). Barcodes must be visible -Barcodes easily damaged. |
| Explain the need for secondary storage within a computer system | -To store data / programs whilst the computer is turned off as the contents of RAM are lost when the computer is turned off -To transfer data / programs between computers -Allows the storage of data sets / files that could not fit in RAM (<- worst point) |
| Compare SSD, hard disk and optical disk |
Image:
A (binary/octet-stream)
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| Suitability of SSD, hard disk and optical disk |
Image:
A (binary/octet-stream)
|
| What is the role of the address bus | The address bus is used to select a specific memory location containing a word of data or an instruction. It does this by carrying the address of the desired location on its bus. |
| What is the role of the data bus | The data bus provides a bidirectional path for moving data and instructions between system components |
| What is the role of an I/O controller Why are peripherals not directly connected to the processor | An I/O controller is a board of electronics that enables the processor to control and communicate with peripheral through an I/O port Each peripheral operates differently => the invention of a new type of peripheral will require the processor to be redesigned |
| How is main memory organised | Memory consists of a contiguous block of read/write, randomly accessible storage locations constructed from semiconductor technology. It is a store for addressable words, one word per location, each word contains the same number of bits. Each location is - Capable of remembering what was written to it - able to change it's contents to another bit pattern - assigned a unique integer address by which it can be located - capable of providing a copy of it's contents |
| What is meant by volatile memory (in context of main memory) What is meant by random access in the context of memory | Contents in each storage location is lost when power is removed Time taken to access any location is the same Storage locations can be selected one after another, non-contiguous, starting from any memory address. |
| Processor | Manages fetch decode execute cycle Executes instructions |
| Difference between CMOS and CCD | CMOS has smaller pixels (worse in low light conditions + less sensitive to light) CCD sensors typically have less noise CCD sensors are more expensive and consume more power (meaning CMOS is more suitable for portable devices such as smartphones) |
| Compare SSD's and Hard disks | Magnetic disk drives are useful where large capacity is needed without the cost of very large SSDs Solid state disk drives have faster access speeds and lower latency than magnetic disk drives which is useful for loading frequently used software |
| Explain why it is faster to access data from solid state storage than from an optical disk. | No movable parts, so no need for the read/write heads to move to the correct position Purely electronic so minimal latency |
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