5.06 Basic computer structure.pdf

Basic Computer Structure (5.6.1) Learning Objectives 5.6.1.1 Describe computer-related terminology including bits, byte, software, hardware, CPU, IC, RAM, ROM and PROM (Level 2). 5.6.1.2 Describe the applications of computer based technology in aircraft systems (Level 2). 2023-03-...

Basic Computer Structure (5.6.1) Learning Objectives 5.6.1.1 Describe computer-related terminology including bits, byte, software, hardware, CPU, IC, RAM, ROM and PROM (Level 2). 5.6.1.2 Describe the applications of computer based technology in aircraft systems (Level 2). 2023-03-03 B1-05a Digital Techniques / Electronic Instrument Systems Page 145 of 285 CASA Part 66 - Training Materials Only  Computer Terminology Basic Computer Operation Computers work by manipulating 1s and 0s (binary data). A computer takes input data from input devices and translates it into output data for output devices. Complex computers, such as the modern desktop computer or the flight control computer, although required for different uses, are made up of the same combinations of components. Physically, computers are typically centred around a motherboard, containing a Central Processing Unit (CPU), Random Access Memory (RAM) slots, and several other integrated circuits (ICs) responsible for connecting to peripherals such as sound cards, graphics cards, speakers etc. The outputs of a computer is greatly varied and dependant on the software running on the computer. © Aviation Australia Computer hardware (high-level) 2023-03-03 B1-05a Digital Techniques / Electronic Instrument Systems Page 146 of 285 CASA Part 66 - Training Materials Only  Binary Digits Transistors At the lowest level an IC is made up of lots of transistors that switch between two states; ON and OFF. Transistors are switched on and off by applying a voltage to the base. Computers function using only two logic levels; ON and OFF or 1 and 0, respectively. This is why the binary numbering system is so important. A 1, or ON, or a HIGH, is typically about 5-V DC, and a 0, or OFF, or a LOW, is typically 0-V DC in electronic components. Aviation Australia Transistors switch between two states based on voltage applied to the base 2023-03-03 B1-05a Digital Techniques / Electronic Instrument Systems Page 147 of 285 CASA Part 66 - Training Materials Only  Bits A Binary Digit (Bit) of information is the 1 or 0 applied to the transistors, gates or integrated circuits of the computer system. All of a computer's processes are performed by processing bits of information. As described in the previous topics, the combination of electronic components can allow for bits of information to operate logic circuits. The following transistorised light circuit operates as a simple AND gate. To switch the light ON, you must apply a high, or 5-V DC, to both the transistors. In this way, logic can be used to perform a function; the light will only switch ON if both inputs are high. This is the foundation of all computer processing. Aviation Australia Transistor circuit operating as an AND gate In this case, you can imagine a physical switch at input A and a switch at input B. These inputs are connected to the 5-V DC power source. Initially, both switches are open and there is no current flow, therefore no voltage and thus both states are 0. Pressing the switch at input A and allowing current to flow through Transistor 1, makes input A the equivalent of a bit value of 1. However, this circuit configuration is an AND gate and requires both input A and input B to be high or 1s. Pressing the switch at input B allows 5-V DC to flow through Transistor 2. With input A and B high, both transistors are forward biased and the LED circuit can operate, turning the LED on. Logically, this circuit can be represented by the AND gate. 2023-03-03 B1-05a Digital Techniques / Electronic Instrument Systems Page 148 of 285 CASA Part 66 - Training Materials Only  © Aviation Australia AND gate (logic symbol) 2023-03-03 B1-05a Digital Techniques / Electronic Instrument Systems Page 149 of 285 CASA Part 66 - Training Materials Only  Bits, Nibbles and Bytes A bit is not a large enough vehicle to carry much information. With 1 bit, there are only two possible values: 0 and 1. As you increase bits, the total number of states the bits can represent increase exponentially. For example: With 2 bits to represent a value, there are four possible values: 00, 01, 10 and 11. With 3 bits, there are eight possible values: 000, 001, 010, 011, 100, 101, 110 and 111. With 4 bits there are 16 possible values. With 8 bits there are 256 possible values (and so on). © Aviation Australia 2-Bit combinations (4 total) Certain significant number of bits have been given distinct names: A Nibble is 4 bits of data (1111). A Byte is 8 bits of data (1111 1111). A byte of information can output 256 possible combinations of bits and far more useful in designing computer components and modules than a bit. A single character on a keyboard is represented internally as a series of 8 bits, or a byte. Computers typically store and manipulate bunches of 8 bits of data. These 8 bits make up a byte. American Standard Code for Information Interchange (ASCII) codes use 8 bits to represent a single character, such as the letter A or the number 7. Thus, the computer can store and manipulate an individual byte (a single character) or a group of bytes (several characters, a word) at a time. These individual bytes or groups of bytes form the basic unit of memory. 2023-03-03 B1-05a Digital Techniques / Electronic Instrument Systems Page 150 of 285 CASA Part 66 - Training Materials Only  A binary byte of data Primary storage capacities are usually specified in number of bytes. In modern computing memory is often referred to in kilobytes (KB), megabytes (MB), gigabyte (GB) and terabytes (TB). The symbol K (kilo) is equal to 1024 bytes. Therefore, if a computer has 512K bytes (not bits) of primary storage, then it can hold 512 × 1024, or 524 288, characters (bytes) of data in its memory. A MB of data is 1024 KB, a GB is 1024 MB and a TB is 1024 GB. 1 terabyte = 1e12 bytes or 1 000 000 000 000 bytes. 1 TB and 2 TB USB flash drives store data on a device the size of a thumb. © Aviation Australia Binary representations of bits and their terms 2023-03-03 B1-05a Digital Techniques / Electronic Instrument Systems Page 151 of 285 CASA Part 66 - Training Materials Only  Integrated Circuits An integrated circuit (IC) also known as a microchip, is an assembly of electronic components, fabricated as a single unit. As computer logic complexity grows, the number of logic gates and circuits required to represents data also grows. An IC allows for miniaturised active devices (e.g., transistors and diodes) and passive devices (e.g., capacitors and resistors) to be preconstructed and allow more complex logic actions to take place. The following circuit shows several discrete (full size) components on a printed circuit board (PCB) with a microchip. Circuit board containing discrete components and a integrated circuit If all of the internal components of an integrated circuit were the size of the traditional circuit components, a modern computer CPU would fill entire rooms. This was precisely the case during the early stages of computer development. Integrated circuits use miniaturised circuitry. In the early stages of miniaturising circuit components, resistors, capacitors and inductors were all much larger than transistors. As development progressed these components shrunk into the form of silicon wafers or chips. The process quickly required printed circuit boards where miniaturised components could be packed and stacked into circuits. When several miniature circuits are combined, the result is a small monolithic “chip,” which is often only a few square centimetres or square millimetres in size. The individual circuit components are generally microscopic in size. 2023-03-03 B1-05a Digital Techniques / Electronic Instrument Systems Page 152 of 285 CASA Part 66 - Training Materials Only  Inside an integrated circuit (Silicon Wafer) at 35x zoom ICs have almost entirely eliminated the use of individual electronic components in modern commercial applications. An integrated circuit contains thousands of transistors, resistors, capacitors, to perform a multitude of complex tasks such as multistage amplification, logic circuits, computer processor. Aviation Australia Surface mounted integrated circuits on a PCB 2023-03-03 B1-05a Digital Techniques / Electronic Instrument Systems Page 153 of 285 CASA Part 66 - Training Materials Only  The evolution of integrated circuits and miniaturised components has enabled the modern computing that is used across every industry today, including Aviation. Advantages of ICs Some advantages of integrated circuits are: Drastically reduced size and weight Increased reliability Lower cost Improved performance The packaging of ICs are designed to provide distinct inputs and outputs to the rest of the circuit as well as to dissipate the heat generated within. Disadvantages of ICs The main disadvantage of integrated circuits is the move to repair by replacement. ICs are difficult to repair and typically it is much cheaper to simply replace the component altogether. IC replacement 2023-03-03 B1-05a Digital Techniques / Electronic Instrument Systems Page 154 of 285 CASA Part 66 - Training Materials Only  Summary Transistors circuits are used to construct logic gates. Logic gates are used to construct integrated circuits and integrated circuits are used to construct computer processors. Logic gates in integrated circuit (IC) chips 2023-03-03 B1-05a Digital Techniques / Electronic Instrument Systems Page 155 of 285 CASA Part 66 - Training Materials Only  Computer Hardware Computer hardware refers to the physical components of a computer including the: Case Motherboard Central Processing Unit (CPU) Memory - RAM, ROM Graphics card Sound card Input devices - mouse, keyboard Output devices - monitor, speakers. It includes all the physical components and their makeup including circuit components such as resistors, transistors, capacitors etc. Computer hardware 2023-03-03 B1-05a Digital Techniques / Electronic Instrument Systems Page 156 of 285 CASA Part 66 - Training Materials Only  Computer Software Software plays a major role in computer data processing. The software is the means in which instructions are translated from a human to computer. The hardware components including the electric circuits, logic and processing all exist with the primary goal of running software. Through the various input devices, a computer is instructed via software to perform a task. The operating system then receives the instruction and processes the job information to allocate memory and run processes accordingly. Computer software In the aircraft industry, Automatic Test Equipment (ATE) is commonly used to fault-isolate avionics components and circuitry. The cost of purchasing the ATE is far outweighed by the cost of purchasing the software to perform the fault isolation. Aircraft systems are loaded with software. From flight management system computers, flight control computers, and navigation computer systems are all loaded with software. The software versions are periodically updated to overcome problems, improve performance or to run using more accurate and contemporary data. 2023-03-03 B1-05a Digital Techniques / Electronic Instrument Systems Page 157 of 285 CASA Part 66 - Training Materials Only  Motherboard In PCs, the CPU is typically connected to a motherboard. Additionally, motherboards contain all the interconnecting circuitry and plug-in points for all of the internal electronic circuitry required to operate a modern computer: Memory - RAM and ROM Solid state drives Graphics cards Sound cards Memory cards Hard disc and CD drives. Motherboards Also typically housed within the computer case is a power supply module and one or more cooling fans. Cooling is a major part in modern computer systems, and several different technologies exist for keeping electronic components inside a computer cool, such as liquid and water cooling systems and multiple cooling fan setups. 2023-03-03 B1-05a Digital Techniques / Electronic Instrument Systems Page 158 of 285 CASA Part 66 - Training Materials Only  Microcomputers A microcomputer is an electronic device with a microprocessor as its central processing unit (CPU). The term microcomputer was formerly a common term for personal computers, particularly any of a class of small digital computers whose CPU is contained on a single integrated semiconductor chip. However, it is rare in the modern age of computing for computers to be referred to as microcomputers - the 'micro' has become redundant. Almost all modern devices all fall under the category of microcomputer; modern desktop PCs, video game consoles, laptops, tablets, smart phones, smart watches, pocket calculators and industrial embedded systems. Each of these computers are made up of the same patterns of technology, where size, performance and memory are maximised based on their physical size and power constraints. Modern computing devices Computer Architecture The way in which computers are built stays relatively consistent in all modern devices. At the highest level, a computer takes an input, processes it and provides a desired output. When the term Desktop PC is mentioned, the computer is considered everything inside the computer case. However, the computer can be broken into key components that allow for complex processing. 2023-03-03 B1-05a Digital Techniques / Electronic Instrument Systems Page 159 of 285 CASA Part 66 - Training Materials Only  A computer is made up of: The Motherboard which contains a bus system (internal and external) and houses all the components required to enable the computer to operate. The bus system (internal and external) serves as the communication highway of the motherboard. The internal bus links the different parts of the computer to the CPU and the main memory. Its primary task is to send data and instructions to the different areas within the motherboard, including the external bus. The external bus, also known as the expansion bus, serves as the interface for peripheral devices like hard discs, CD-ROM drives, and flash drives to connect to the CPU. The Central Processing Unit (CPU), which performs basic arithmetic, logic, controlling, and input/output (I/O) operations specified by the instructions in the program. The CPU typically contains several distinct sections which focus of different types of calculations. This will be elaborated further in the following section. The Main Memory, (known more commonly as RAM) which stores the programs and data when the central processor is actively using them. The I/O Circuitry, which are the computer peripherals enabling the input and output devices to actively communicate with the computer. There are a number of other external systems such as the Graphics Processing Unit (GPU) that are commonly used alongside computers, but are less tied to the avionics knowledge requirements and will not be expanded further. The following diagram maps the major components of a modern microcomputer into a high level flowchart. As demonstrated Flight Control Computers (FCC) follow a much similar structure despite quite different use cases. A major difference between an FCC and a personal computer is the strict requirements placed on the components used, their accuracy and the level of redundancies required within the system. 2023-03-03 B1-05a Digital Techniques / Electronic Instrument Systems Page 160 of 285 CASA Part 66 - Training Materials Only  © Aviation Australia Computer hardware (high-level) Computer Processors A computer processor is a huge collection of circuits similar to the adders described, designed to produce a particular output for certain inputs. A calculator is one of the simplest processors; its equivalent of a CPU is designed to deal only with numbers and to just perform mathematical calculations. Calculator components including simple processor 2023-03-03 B1-05a Digital Techniques / Electronic Instrument Systems Page 161 of 285 CASA Part 66 - Training Materials Only  A modern computer CPU performs much more complex calculations but is still nothing more than a collection of logic circuits configured to produce a desired outcome. The CPU is the brain of the computer. Operating System An operating system is a collection of many programs used by the computer to manage its own resources and operations. These programs control the execution of other programs. They schedule, assign resources, monitor and control the work of the computer. Not all computers have operating systems. The computer that controls a microwave oven does not need an operating system. It has one set of relatively simple tasks to perform, very simple input and output methods (a keypad and a Liquid Crystal Display [LCD] screen) and simple, never-changing hardware to control. A simple computer might not have an operating system Aircraft systems and components like Flight Management Computers (FMCs) and Multifunction Control Display Units (MCDUs) use very customised operating systems to manage the many functions they perform. 2023-03-03 B1-05a Digital Techniques / Electronic Instrument Systems Page 162 of 285 CASA Part 66 - Training Materials Only  The operating system of a Multi-function Control Display Unit performs many functions At the simplest level, an operating system does two things: it manages the hardware and software resources of the computer system. These resources include such things as the processor, memory, discs space and so on. The operating system provides a stable, consistent way for applications to deal with the hardware without having to know all the details of the hardware. 2023-03-03 B1-05a Digital Techniques / Electronic Instrument Systems Page 163 of 285 CASA Part 66 - Training Materials Only  Memory Technologies Memory Storage Technologies For the CPU to control and coordinate all processing activity, it must be able to locate each instruction and data item in storage. Consider the storage as nothing more than a collection of letterboxes. Each letterbox has a unique address and represents a location in memory. Like the mail in your letterbox, the contents of a storage location can change, but the number on your letterbox or memory address always remains the same. In this manner, a particular program instruction or data item that is held in storage can be located by knowing its address. Some computers can address each character of data in memory directly. Others address computer words, which contain a group of characters at a single address. Some types of data storage technologies include: Magnetic core storage Semiconductor Dynamic Random-Access Memory (DRAM) NAND Solid State Drives (SSDs) Magnetic tape storage Magnetic Disc Hard Drives (HDDs). 2023-03-03 B1-05a Digital Techniques / Electronic Instrument Systems Page 164 of 285 CASA Part 66 - Training Materials Only  Magnetic Core Storage Although magnetic core storage is no longer as popular as it once was, its concepts are easily understood and apply generally to the more integrated semiconductor and bubble-type memories. Magnetic core storage is made up of tiny doughnut-shaped rings made of ferrite (iron) that are strung on a grid of very thin wires. Since data in computers is stored in binary form, a two-state device is needed to represent the two binary digits (bits): 0 for OFF and 1 for ON. In core storage, each ferrite ring can represent a 0 or 1 bit, depending on its magnetic state. If magnetised in one direction, it represents a 1 bit, and if magnetised in the opposite direction, it represents a 0 bit. These cores are magnetised by sending an electric current through the wires on which the core is strung. It is this direction of current that determines the state of each core. Magnetic core storage Core storage is non-volatile – data is retained even if there is a power failure or breakdown since the cores store data in the form of magnetic charges rather than electric current. 2023-03-03 B1-05a Digital Techniques / Electronic Instrument Systems Page 165 of 285 CASA Part 66 - Training Materials Only  Dynamic Random-Access Memory DRAM is a type of semiconductor memory that stores data in a memory cell (a tiny capacitor / transistor circuit) based on metal-oxide-semiconductor (MOS) technology. The capacitor is either charged or discharged to represent the 0 and 1 data states. The electric charge on the capacitors can slowly discharge, so without intervention the data on the chip would be lost. To prevent this, DRAM requires an external memory refresh circuit which periodically rewrites the data in the capacitors, restoring them to their original state. DRAM is volatile memory in that it loses its data on loss of power. DRAM typically takes the form of an integrated circuit with up to billions of DRAM memory cells. DRAM chips are low-cost and high-capacity computer memory. Die photograph of 128kB DRAM IC NAND Solid State Drive NAND SSD performance is related to the number of parallel NAND flash ICs used in the device. A single NAND chip is relatively slow in processing terms however when multiple NAND devices operate in parallel inside an SSD, the data throughput or bandwidth scales or increases accordingly. NAND SSDs have the ability to retain data without a constant power supply so data is retained or persists through sudden power outages. NAND SSDs are not suitable for long term (archive) data storage due to their slow leakage rate. 2023-03-03 B1-05a Digital Techniques / Electronic Instrument Systems Page 166 of 285 CASA Part 66 - Training Materials Only  Magnetic Tape Storage Another type of storage device is magnetic tape, which is like the tape used with commercial tape recorders. It is used mainly for secondary storage. It differs from commercial tape in that it is usually wider (ranging from 0.5 in. to 1 in.) and is manufactured to more rigid quality specifications. It is made of a Mylar base coated with a magnetic oxide that can be magnetised to store data. Magnetic tape comes in a variety of lengths (from 600 to 3000 ft), and is packaged in one of three ways: open reel, cartridge or cassette. Large computers use standard open reels, 0.5-in. wide tape that is 2400 ft in length. Magnetic tape On magnetic tape, 1s and 0s are recorded as strings of data (serial access memory). For data to be retrieved, tape must be cycled through to the appropriate position for the read/write head to extract data. Spools, cartridges and cassette 2023-03-03 B1-05a Digital Techniques / Electronic Instrument Systems Page 167 of 285 CASA Part 66 - Training Materials Only  Magnetic Disc Storage The popularity of disc storage devices is largely because of their direct-access capabilities. Magnetic discs resemble phonograph records coated with a magnetisable recording material (iron oxide), but their similarities end there. Magnetic discs come in many different sizes and storage capacities. They range from 3 in. to 4 ft in diameter and can store multi-millions of bytes. They can be portable (removable) or permanently mounted as hard drives. They can be rigid metal (hard discs) or flexible plastic (floppy discs or diskettes). Magnetic disc storage Data is written as tiny magnetic bits (or spots) on the disc surface using 8-bit codes. Each code represents a different number, letter or special character. When data is read from the disc, the data on the disc remains unchanged. When data is written on the disc, it replaces any data previously stored on the same area of the disc. Characters are stored on a single track as strings of magnetised bits (0s and 1s). The 1 bits indicate magnetised spots, or ON bits. The 0 bits represent unmagnetised portions of the track, or OFF bits. Although tracks get smaller as they near the centre of the disc, each track can hold the same amount of data because data density is greater on tracks near the centre. 5 MB, 10 MB and 6 TB hard discs 2023-03-03 B1-05a Digital Techniques / Electronic Instrument Systems Page 168 of 285 CASA Part 66 - Training Materials Only  8 in, 5.25 in and 3.25 in floppy discs Semiconductor Storage (Silicon Chip) Semiconductor memory consists of millions of tiny electronic circuits etched on a silicon chip. Each of these electronic circuits is called a bit cell and can represent a 0 or 1 bit, depending on whether or not current is flowing in that cell. Some of the advantages of semiconductor storage are: Fast internal processing speeds High reliability Low power consumption High density (many circuits) Low cost. Silicon memory is volatile – data is lost when power is removed. If the power on your computer fails and you have no backup power supply, all the stored data will be lost. Silicon memory is volatile 2023-03-03 B1-05a Digital Techniques / Electronic Instrument Systems Page 169 of 285 CASA Part 66 - Training Materials Only  Memory Storage Devices Computer Memory In computing, memory is a device or system that is used to store information for immediate use in a computer or related electronic system. The term memory is commonly used with with the term primary storage or main memory. All memory sections must contain facilities to store computer data or instructions (that are intelligible to the computer) until they are needed in the performance of the computer calculations. Before the stored-program computer can begin to process input data, it must store in its memory a sequence of instructions, tables of constants and other data it will use in its computations. The process by which these instructions and data are read into the computer is called loading. Memory (internal storage) 2023-03-03 B1-05a Digital Techniques / Electronic Instrument Systems Page 170 of 285 CASA Part 66 - Training Materials Only  Storage Device Classification Memory in computers is categorised into short-term data storage and long-term data storage. Computer memory typically refers to the short-term data, whereas computer storage refers to the long-term data. The speed and performance of a system depends on the amount of memory that is installed. An analogy is the difference between a desk and a filing cabinet. The desk represents the memory of your computer. Items that are required for immediate use are kept on the desk for easy access. However, not much can be stored on a desk due to its size limitations. The filing cabinet represents the storage of the computer. It holds items that need to be saved and stored but are not necessarily needed for immediate access. The size of the filing cabinet means that it can hold a large number of things. Technically, both are means of storage. For that reason, the more technical name for the two types are; primary storage devices and secondary storage devices. Primary Storage Primary storage is located on the motherboard (often called internal storage). As a result, data can be read from and written to primary storage extremely quickly. This gives the processor fast access to the data and instructions that the primary storage holds. The different kinds of memory used within the CPU are: Random-Access Memory (RAM) Read-Only Memory (ROM) Programmable Read-Only Memory (PROM) Erasable Programmable Read-Only Memory (EPROM). The two main types of primary storage are ROM, which is non-volatile, and RAM, which is volatile. Non-volatile memory keeps its contents even when the computer is switched off. Volatile memory loses its contents when power is lost. Primary storage is comparatively limited in size, especially when compared with secondary storage. In a modern personal computer, primary storage is often either 4 GB, 8 GB or 16 GB in size. Primary storage mechanisms 2023-03-03 B1-05a Digital Techniques / Electronic Instrument Systems Page 171 of 285 CASA Part 66 - Training Materials Only  Random-Access Memory Random-Access Memory (RAM) is one of the most important components in determining a computer's performance. RAM is where applications store and access data on a short-term basis. It stores the information your computer is actively using so that it can be accessed quickly. RAM is volatile, similar to a blackboard on which you can scribble down notes, read them and wipe them away when you are finished with them. In the computer, RAM is the working memory. Data can be read (retrieved) from or written (stored) in RAM just by giving the computer the address where the data is stored or is to be stored. When the data is no longer needed, you can simply write over it. This allows you to use the storage again for something else. PC RAM ICs allow data to be retrieved rapidly and overwritten when no longer required RAM is where all the calculating is done by the processor, storing data which it can then randomly access quickly. In contrast, a CPU would run very slowly by reading and writing all calculations directly to and from secondary storage such as a hard drive. RAM is the best-known form of computer memory and is considered ‘random access’ because you can access any memory cell directly if you know the row and column that intersect at that cell (address). 2023-03-03 B1-05a Digital Techniques / Electronic Instrument Systems Page 172 of 285 CASA Part 66 - Training Materials Only  Read-Only Memory In silicon memory devices, usually data is lost when power is removed. Silicon-based ROM differs from silicon-based RAM. The term ROM is associated with solid-state memory devices. Only the computer manufacturer can provide these programs in ROM, and once they are done, they cannot be changed. Consequently, you cannot put any of your own data or programs in ROM. Read-Only Memory (ROM) In most computers, it is useful to have often-used instructions, such as those used to bootstrap (initial system load) the computer or other specialised programs, permanently stored inside the computer. Memory that enables us to do this without the programs and data being lost (even when the computer is powered down) is called read-only memory. 2023-03-03 B1-05a Digital Techniques / Electronic Instrument Systems Page 173 of 285 CASA Part 66 - Training Materials Only  Programmable Read-Only Memory An alternative to ROM is Programmable Read-Only Memory (PROM) that can be purchased already programmed by the manufacturer or in a blank state. By using a blank PROM, you can enter any program into the memory. However, once the PROM has been written into, it can never be altered or changed. The main disadvantage of PROM is that if a mistake is made and entered into PROM, it cannot be corrected or erased. Also, a special device is needed to ‘burn’ the program into PROM. Unknown / Xelteksuperpro, CC BY-SA 3.0, via Wikimedia Commons Programmable Read-Only Memory (PROM) and PROM Programmer PROM is a way of allowing a user to tailor a microcode program using a special machine called a PROM programmer. This machine supplies an electrical current to specific cells in the ROM that effectively blows a fuse in them. The process is known as ‘burning the PROM’. This means once it has been programmed, the memory will act as ROM, will not be corrupted or inadvertently erased, and will not erase with loss of power. 2023-03-03 B1-05a Digital Techniques / Electronic Instrument Systems Page 174 of 285 CASA Part 66 - Training Materials Only  Erasable Programmable Read-Only Memory Erasable Programmable Read-Only Memory (EPROM) was developed to overcome the drawback of PROM. PROMs can also be purchased blank from the manufacturer and programmed. Again, this requires special equipment. The big difference with EPROM is that it can be erased if and when the need arises. Data and programs can be retrieved over and over again without destroying the contents of the EPROM. They will stay there quite safely until you want to reprogram it by first erasing the EPROM with a burst of ultraviolet light. This is to your advantage because if a mistake is made while programming the EPROM, it is not considered fatal. The EPROM can be erased and corrected. Also, it allows you the flexibility to change programs to include improvements or modifications in the future. Erasable Programmable Read-Only Memory (EPROM) 2023-03-03 B1-05a Digital Techniques / Electronic Instrument Systems Page 175 of 285 CASA Part 66 - Training Materials Only  Software Storage Mediums Software storage mediums include reel-to-reel; 8-in., 5 1/4-in. and 3 1/2-in. floppy discs; cassette tapes; CDs and DVDs; portable hard drives; and flash drives. Flash memory cards are tiny and have no moving parts. Often, they are used in digital cameras and mobile devices. Reel to Reel; floppy disc and BIOS chip Secondary storage – These forms of memory storage are called secondary storage or auxiliary storage (compared to Random-Access Memory (RAM), Read-Only Memory (ROM), hard drives and so on. This is memory outside the main body of the computer (CPU) where we store programs and data for future use. In secondary storage, data and programs do not disappear when the power is turned off. Secondary storage is non-volatile. This means information is lost only if you, the user, intentionally erase it. Common magnetic storage methods are magnetic disc, tape and drum. 2023-03-03 B1-05a Digital Techniques / Electronic Instrument Systems Page 176 of 285 CASA Part 66 - Training Materials Only  Applications of Computer Based Technology in Aircraft Systems Digital Aircraft Systems The aircraft industry has adopted computer technology to provide improvements to aircraft safety, a reduction in pilot workload, operational economies, sophisticated In-Flight Entertainment (IFE) and centralised control of numerous cabin functions, e.g. passenger reading lights. Ever-increasing integration of computer technology is continuously improving a very wide range of aircraft applications and interfaces. In-Flight Entertainment and improvements in navigation and communication software are among the systems that are strongly enhanced by digital computer technology, e.g. by radar technology that displays storm activity and terrain. The data from the radar antenna is processed digitally by a processing unit and is then presented to the pilots as a display on a screen. This allows the pilots to adjust the flight path to avoid hazards. Digital screen on modern airliner Integration of computer systems has improved pilots’ ability to monitor and control aircraft systems. A digital processor achieves this by automatically collecting and storing data from aircraft systems and performing calculations to provide flight information to the pilot. This is much more efficient than older analogue methods which required a flight engineer to manually perform these tasks. Computer systems can also monitor systems independently and display a warning to the pilot if a defect is detected. 2023-03-03 B1-05a Digital Techniques / Electronic Instrument Systems Page 177 of 285 CASA Part 66 - Training Materials Only  Capabilities of Digital Computer Technology Enhanced pilot monitoring and control of aircraft systems Ability to store, recall and manipulate large volumes of information from aircraft systems Ability to monitor aircraft systems and alert the crew when required Software updates to an avionics system in an entire fleet of aircraft within minutes or hours – comparable updates to analogue systems would usually require replacement of hardware Improved estimations for navigation and flight time information Integration of display functions – multiple dials may be condensed into a single display Enhanced electronically controlled actuation of flight control surfaces, improving reliability and requiring less maintenance than mechanical linkages Considerably more accessible data for the flight crew, to the extent that a flight engineer is no longer required. Modern aircraft flight deck 2023-03-03 B1-05a Digital Techniques / Electronic Instrument Systems Page 178 of 285 CASA Part 66 - Training Materials Only