Computer Science Flashcards
Registers
A fast access storage location found in the CPU where data or control information is temporarily stored.
Program counter (PC)
A counter that keeps track of the memory address of which instruction is to be executed next.
Memory address register (MAR)
Holds the address in the main memory that is to be read to or written from.
Current instruction register (CIR)
A temporary holding area for the instruction that has just been fetched from memory and is being decoded and executed.
VN Architecture Characteristics
Binary format, fetched from main memory,, fetched one at a time, one instruction is decoded before another is fetched (as and when required).
Von Neumann Architecture def
The design on which general purpose computers are based. Von Neumann architecture provides a simple explanation of the construction of the CPU and its relationship with other components of the computer.
Control Unit def
Control Unit – directs the flow of instructions and / or data and coordinates the other parts of the CPU. It generates clock ticks (controls the clock).
Arithmetic Logic Unit def
Arithmetic Logic Unit – the ALU performs all the calculations and logical operations in the CPU.
Memory def
Memory – used for temporary storage of currently running programs and data.
Address bus def
Address bus - when data is saved or loaded from memory, the address at which it is to be stored or loaded from must be sent. The storage address of data always travels in one direction along an address bus.
Data bus def
Data bus - data will then need to be moved between several parts of a computer. The path along which data travels is called a data bus.
Control bus def
Control bus - the controller uses the control bus to send control signals to different parts of the computer.
Bus def
Buses allow data to be transferred to different parts of the computer
Fetch def
The fetch cycle takes the instruction from the main memory using the address, and stores it in the current instruction register, and moves the program counter on one so that it points at the next instruction.
Execute def
The control unit authenticates the instruction in the current instruction register. The instruction is decoded to determine the action that needs to be carried out.
Decode def
The actual actions that happen during the execution cycle depend on the instruction itself.
Cache def
Cache – incredibly fast, but very expensive volatile memory used in the CPU. The cache temporarily holds data and instructions that are used frequently. It consists of a small number of store locations that can be accessed very quickly by the CPU; it is quicker than RAM.
Cache affecting performance
More cache memory improves performance as it can provide instructions and data to the CPU at a much faster rate than other system memory such as RAM. In addition, more cache memory will allow more instructions that are repeatedly used by the CPU to be stored in cache and therefore increase the hit rate, improving the performance of the processor as a result.
Clock speed def
Clock speed – the number of fetch-decode-execute cycles that the CPU can carry out per second. This is usually measured in Hertz.
Clock speed affecting performance
The faster the clock speed, the faster the computer can run the fetch-decode-execute cycle and therefore process more instructions in any given period. However, the faster the clock speed, the more power is generally required, which creates greater requirements for heat dissipation and can place more strain on battery life.
Cores def
Cores – some processors have multiple processors (known as cores) which can run in parallel, sequentially or can multitask.
Cores affecting performance
In a single-core CPU each instruction is processed one after the other, whereas in a dual-core CPU, two instructions may be processed at the same time. In theory, a dual-core CPU should mean that the computer can process instructions twice as fast as a single-core CPU. Performance may be affected where one core is waiting on the result of another and therefore cannot carry out any more instructions, leading to the performance being no better than a single-core processor.
RISC def
RISC processors can process a limited number of relatively simple instructions. To carry out more complex commands, the problem is broken down into a longer list of simpler instructions. The advantage of this is that a RISC processor can process these simpler instructions quickly. Processing simpler instructions also requires less circuitry to decode and execute these instructions, which in turn means less power consumption and therefore less heat being generated.
CISC def
CISC processors can process a large number of complex instructions. This allows the processor to understand and carry out complex tasks with only a few instructions. The advantage of this is that a CISC processor can process complex instructions, without having to break them down into many simpler instructions. Processing complex instructions, however, requires more circuitry to decode and execute these instructions, which in turn means more power consumption and therefore more heat being generated. Because of this, CISC CPUs will usually come with a heat sink or fan embedded.
RISC and CISC advantages and disadvantages
In order to handle complex instructions CISC CPUs are physically larger to accommodate more complex circuitry. RISC CPUs are designed to use less power and run cooler, meaning that they can be used in smartphones that do not have dedicated cooling systems such as fans.
RISC CPUs tend to be cheaper to mass produce. RISC CPUs run at lower clock speeds than CISC CPUs. They can perform simple tasks more quickly than CISC CPUs but are generally not used to carry out complex instructions.
Input device def
An input device allows data, such as text, images, video, or sound, to be entered into a computer system.
Keyboard
Computer keyboards are used to input data and commands into the computer by pressing the keys. Computer keyboards are common in the workplace and are usually used together with a mouse.
Graphics tablet
A graphics tablet is an input device that converts hand drawn artwork into a digital image. A graphics tablet is a flat touch sensitive surface. The user draws using a stylus as if they were drawing on a piece of paper. The image is transferred to the computer screen and can be stored, edited, and printed.
Mouse
A mouse is an input device that allows the user to control the co-ordinates and movements of a cursor on the computer screen. The left button is used to select items and the right button is used to access menus (these can be changed around in settings). Most mice now use a laser to track location on a smooth surface and mice can be wired or wireless.
Touchpad
A touchpad is a flat control surface used to move the cursor and perform other functions on a computer. Touchpads are commonly found on laptops and replace the functionality of a mouse. A touchpad is designed to be controlled with your finger.
Scanner
Scanners convert documents and images into digital files. Scanners can be run with additional software such as an optical mark reader (OMR) or optical character recognition (OCR). One example would be using OCR software in the computer to read handwriting and convert it into digital text.
Digital Camera
A digital camera is an input device that captures images (and sometimes videos) digitally. A digital camera uses an image sensor and a chip to capture an image, as opposed to the film used in traditional cameras.
Microphone
A microphone is an input device that receives analogue sound waves and converts them into electrical signals understood by the computer. Microphones play an important role in speech recognition.
Interactive whiteboard
An interactive whiteboard is usually used in classrooms. This device was developed long before touch screens. It is cheaper than touch screens and differs from normal screens as it can be used in plenty of ways when paired with a projector. It can be used for navigation systems or to write/design with your fingers or a stylus.
QR code scanner
QR code scanners, as seen on smartphones, can scan QR codes by taking a picture of them. The QR codes normally hold more data than barcodes, e.g., web addresses, contact details, calendar registrations and details of goods in factories and warehouses.
Barcode scanner
A barcode is a code that can be read by a machine. The code is represented by a series of black and white lines. These lines represent numbers from 0 to 9. The use of barcode scanners speeds up the process of data input into a system, e.g., scanning items at a check out desk in a supermarket.
Output device def
An output device is a piece of hardware that receives data from the computer to display either as an image, video, text, or sound.
Monitor
A monitor is an electronic visual computer display. It includes a screen and the case in which all circuitry is enclosed. Most monitors used with devices such as laptops, PDAs and desktop PCs are made using LCD screens as they are lighter and more energy efficient.
Speaker
Speakers are used to produce audio output that can be heard by the listener. When they receive audio input from a device, the electromagnetic waves are converted into sound waves. This input may be in either analogue or digital form. Analog speakers simply amplify the analogue electromagnetic waves into sound waves. Digital speakers must first convert the digital input into an analogue signal, then generate the sound waves.
Printer
A printer is an output device that prints paper documents. This includes text documents, images, or a combination of both. The two most common types of printers are inkjet and laser printers. Inkjet printers are commonly used by consumers, while laser printers are a typical choice for businesses.
Projector
A projector is an output device that projects an image onto a large surface, such as a white screen or a wall. It may be used as an alternative to a monitor or a television when showing video or images to a large group of people.
Touch screen
A touch screen is a digital visual display that also works as an input device that responds to the user’s touch. It allows users to make selections by touching the screen. A touch screen can be categorised as both an input and an output.
