Hardware and software

OR )> AND |) NOT |>º NOR )>º NAND |)º XOR ) )>

Truth tables are compiled in numerical order OR: A OFF , B OFF = 0 A OFF , B ON = 1 A ON , B OFF = 1 A ON , B ON = 1 AND: A OFF , B OFF = 0 A OFF , B ON = 0 A ON , B OFF = 0 A ON , B ON = 1 NOT: A OFF = 1 A ON = 0 NOR: A OFF , B OFF = 1 A OFF , B ON = 0 A ON , B OFF = 0 A ON , B ON = 0 NAND: A OFF , B OFF = 1 A OFF , B ON = 1 A ON , B OFF = 1 A ON , B ON = 0 XOR: A OFF , B OFF = 0 A OFF , B ON = 1 A ON , B OFF = 1 A ON , B ON = 0

Writing a logic statement, steps: • X (or other) = • final logic gate in the middle • brackets on either side of gate in the middle • logic gate in middle of either bracket for both sides and continue working backwards

From information or logic statement, work from middle gate and place last and continue working from middle till done.

Stored program concept (Von Neumann Architecture) • single processor in computer system • processor uses sequential fetch-execute cycle • data (files) and instructions (software) both stored in same memory (RAM) Prior to this if a computer wanted to carry out another task it would have to be physically rewired

Main stages of the processor’s cycle • Fetch - the instruction • Decode - the instruction • Execute - the instruction

Memory Unit: • temporary storage areas for data and instructions • inside the processor (not within RAM) Arithmetic-Logic Unit (ALU): • carries out mathematical equations on data • evaluates relational comparisons • inside the ALU is a general-purpose register called the accumulator (data needs to be placed in the accumulator for calculations to be carried out by the ALU) Control unit: • co-ordinates what and where data goes when it enters or leaves the processor • it also controls the interactions between the different parts of the processor (e.g. the registers) IAS/Immediate Access Memory (Cache memory): A processor also has built-in cache memory. This is super-fast memory (much faster than RAM) that is stored within the processor.

Refer to IG Computer Science OneNote for answer OneNote > Content Library > Unit 3 > Parts of a Processor

A temporary memory location within the processor. Registers store data and instructions whilst they are being processed. Registers are also used to move data and instructions into and around the different parts of the CPU.

MAR - memory address register Contains the location in RAM of the current instruction being processed MDR - memory data register Contains the contents (values, instruction) returned from RAM CIR - current instruction register Contains a copy of the contents of the MDR Responsible for decoding the instruction PC - program counter The location (memory address) in RAM of the next instruction to be fetched

ACC (accumulator) - stored in ALU Keeps track of data that needs to be accessed over a period of time during processing

Buses are wires used to transmit data within the processor and on the motherboard. Three types of buses: Address bus - used by PC and MAR to transmit locations in RAM (i.e. addresses) Control bus - used by the PC and the MDR to send instructions Data Bus - used to carry data between RAM and the MDR, and between the MDR and the CIR

Fetch execute cycle steps • PC has address of next instruction • PC copied to the MAR • Lookup MAR and get contents. Copy contents into the MDR • Copy MDR contents into the CIR • PC is then incremented by 1 • The instruction is decoded and then executed • Repeat

An input device digitised by a scanning device such as flatbed or barcode scanner. How a 2D scanner works: • Scanner shines a light beam onto document. • Scanner detects level of reflected light from positions on the document. • Light intensity is converted by software for each pixel position into a combination of 0s and 1s by sensing different intensities of light and dark from the document. How a flatbed works: • Place document - raise cover, put document on panel and close • Very bright light - (xenon lamp) • Scan head - moves across the document and image is created and sent to a lens using mirrors • Charge Couple Device - focused image falls on CDD, IC’s etched into silicon and software produces digital image OCR Optical character recognition: OCR alongside 2D scanner used in airport for passport to face identification eg. Distance between the eyes Width of the nose Shape of the cheek bones Length of the jaw line Shape of the eyebrows

Linear Barcodes are 1D and the most commonly used Steps: • Infra-red laser light shines onto linear barcode. • Light reflected back into the moving mirrors/prism • The barcode reader’s charge-coupled device (CCD) measures the amount of reflected light input. • Light measurement is converted into an electrical charge (1 or 0). • Data from the bar code is sent to the computer’s processor in binary form.

Quick response codes are faster to read and have a greater storage capacity than UPC linear barcodes. Scanned digitally by phone’s image sensor then interpreted by microprocessor.

Keyboard works using plungers at the bottom of each key which when pressed pushes 2 electrical contains completing a circuit (key matrix). Key matrix (circuits) stored in ROM

Trackerball Mouse: - Similar to the concept of the original mouse but upside down. The movement of the ball in the socket contains sensors. The data from the sensors processed by a software determines the movement of the pointer. Optical Mouse: - A red LED bounces light off the surface onto a CMOS sensor which sends each image to the DSP for processing. The DSP detects if the mouse has moved, at what distance and at what speed.

All microphones need to input a varying pressure wave and then convert this to an electrical reading. • Sound vibration hits a diaphragm. • Movement of the diaphragm causes a coil to move. • Movement of the coil induces a current through the electromagnetic effect. • The electrical current is digitised (ADC - analogue-digital converter) • The digital content is played back using software.

Light: Light Sensors are photoelectric devices that convert light energy (photons) into an electrical (electrons) signal eg. barcode scanner, automatic lights as it gets dark Temperature: A temperature sensor is a device, typically, a thermocouple or RTD, that provides for temperature measurement through an electrical signal. eg. thermometer Pressure: A Pressure sensor measures the amount of force exerted. eg. old-style electric doors, pressure inside gas canisters

All computers must use Primary storage and it is directly accessible by the processor because it is connected directly to the motherboard. - RAM random access memory RAM is volatile and directly connected to the CPU.

RAM stores data and instructions that are currently open and running. If a file or program is not open, it will not be in RAM. RAM contains parts of the operating system that are currently in use. Contents stored in RAM are directly accessible to the processor. When you load a stored file it is first loaded into RAM before any changes made to the file are processed by the CPU. RAM is volatile so when power to the computer system is lost so are the contents of RAM. Storage capacity is in GB and has read and write ability. Its contents change every time we use a computer.

ROM stores your computer system’s BIOS and bootstrap loader. Basic Input Output System (BIOS) Most do not need to access the BIOS on a regular basis, if at all. The BIOS allows us to change things like the bootable drive. Bootstrap loader When you first turn on (‘boot’) your computer, the operating system has not yet loaded. Your computer performs a self check of its hardware. It makes sure that it recognises it has RAM and a bootable drive of some sort. ROM is non-volatile memory between 4-8 MB storage

Magnetic/Solid state/ off-line A laptop or desk top computer either has an (HDD) or an (SSD) as its main secondary memory/storage device. Secondary storage devices are not directly accessed via the processor. Their contents are first be loaded into RAM before being transferred to the CPU for processing.