CS UNIT 3

• This note discusses computer hardware, including memory, storage, and input/output devices

Hardware

• Primary storage/memory devices will be discussed
• Secondary storage, including removable devices, will be discussed
• Will discuss the benefits and drawbacks of embedded systems
• Hardware devices used for input, output, and storage will be covered
• Differences between RAM, ROM, SRAM, DRAM, PROM, and EPROM will be clarified
• The use of RAM, ROM, SRAM, and DRAM in various devices will be explained
• Monitoring and control systems will be touched on
• Logic gates (NOT, AND, OR, NAND, NOR, and XOR) will be explained
• The construction and use of truth tables will be presented
• Construction of logic circuits, truth tables, and logic expressions will be shown

Key Terms

• Memory cache: High-speed memory external to the processor for frequently needed data
• Random Access Memory (RAM): Primary memory that can be read from and written to
• Read Only Memory (ROM): Primary memory that can only be read from, not written to
• Dynamic RAM (DRAM): A type of RAM that needs constant refreshing
• Static RAM (SRAM): A type of RAM that doesn’t need refreshing, using flip-flops
• Refreshed: Requirement to recharge a component to retain its electronic state
• Programmable ROM (PROM): ROM that can be programmed once
• Erasable PROM (EPROM): ROM that can be reprogrammed using UV light
• Hard Disk Drive (HDD): Magnetic storage device using spinning disks
• Latency: Delay in system, like time to find track on hard disk
• Fragmented: Storing data in non-contiguous sectors
• Removable Hard Disk Drive: External HDD connected via USB
• Solid State Drive (SSD): Storage using electron movement, no moving parts
• Electronically Erasable PROM (EEPROM): ROM that can be modified by pulsed voltages and repeatedly erased/written
• Flash Memory: EEPROM type used in SSDs, memory cards etc.
• Optical Storage: CDs, DVDs, Blu-ray using laser light.
• Dual Layering: Used in DVDs with two recording layers.
• Birefringence: Reading problem in DVDs from refraction of laser light.
• Binder 3D Printing: Printing with dry powder and a binding agent.
• Direct 3D Printing: Printing by moving the print head in x, y, z directions.
• Digital to Analogue Converter (DAC): Converts digital data to analogue signals for devices like motors.
• Analogue to Digital Converter (ADC): Converts analogue data to digital for computer processing.
• Organic LED (OLED): Uses electron movement between cathode and anode, generating its own light without backlighting.
• Screen Resolution: Number of pixels horizontally and vertically on a screen.
• Touch Screen: Screen allowing selection by touch, using capacitive or resistive technology.
• Capacitive Touch Screen: Using glass layers forming a capacitor; touch changes the electric field.
• Resistive Touch Screen: Plastic layer touches glass layer on touch, completing a circuit and causing current flow.
• Virtual Reality Headset: Headset providing immersive virtual experience.
• Sensor: Input device reading physical data from surroundings.

Types of Memory and Storage

• Computers need memory and storage
• Memory: Internal devices that the computer can directly access, a workspace for temporary data or critical data for running the computer
• Storage Devices: Allow users to store applications, data and files and is persistent
• Storage is usually larger than memory
• Removable Storage: Allows for portable file storage between computers
• Internal memory includes registers (part of the processor)
• The memory cache is outside the processor, storing data that the processor will likely need again

Primary Memory

• Primary Memory: Memory that the CPU can directly access
• Contains RAM and ROM chips
• Allows processor to access applications and services temporarily
• Structure of primary memory includes SRAM, DRAM, ROM, PROM, EPROM, and EEPROM

RAM

• RAM provides fast data access compared to secondary storage
• RAM can be written to and read from
• RAM can store data, files, applications, or the operating system currently in use
• RAM is volatile, losing its contents when power is off
• Larger RAM generally improves computer speed
• If RAM is full, the processor accesses secondary storage, slowing down the computer

DRAM vs SRAM

• DRAM is made of transistors and capacitors
• DRAM needs constant refreshing to retain data as capacitors lose charge rapidly
• DRAM is less expensive to manufacture than SRAM
• DRAM consumes less power than SRAM
• DRAM has higher memory capacity than SRAM
• SRAM uses flip-flops to hold each bit of memory
• SRAM doesn’t need constant refreshing
• SRAM is faster than DRAM in data access
• DRAM is typical RAM for computers, while SRAM is useful in memory caches when speed is essential

ROM

• ROM shares random access properties with RAM
• ROM cannot be written to or changed
• ROM is non-volatile, retaining data without power
• ROM stores data needed when powering up

PROM and EPROM

• PROM is programmable ROM that can be altered once via a PROM writer that uses electrical current to burn fuses in a matrix
• PROM can only be written to once
• PROM are often used in mobile phones and RFID tags
• EPROM uses floating gate transistors and capacitors, and can be reprogrammed with ultraviolet light through a quartz window
• EPROM is used in applications under development, like the programming of new games consoles

Embedded Systems

• Embedded systems involve installing microprocessors into devices to enable operations to be controlled more efficiently
• Devices can be activated by web-enabled devices
• Central heating systems' on/off times and temperature can be set by mobile phone apps
• Embedded systems can be small and easy to fit into devices
• Embedded systems relatively low cost to make
• Embedded systems usually dedicated to one task, make for simple interfaces, and often no operating system needed
• Embedded systems consume little power and have fast reaction to changing input and mass production leads to reliability
• Embedded systems are difficult to upgrade for new technology, troubleshooting faults requires specialists, and they can be confusing to use
• Troubleshooting requires specialists and they can be open to hackers and viruses and are often just thrown away rather than being repaired

Secondary Storage

• Secondary storage consists of devices not directly accessible by the CPU
• Secondary storage is non-volatile, retaining data as long as required
• Secondary storage has a larger capacity compared to primary memory
• Secondary storage has a slower data access time than RAM and ROM
• Applications, operating systems, device drivers, and general files are stored on secondary storage
• Magnetic, solid state, and optical are types of secondary storage

Hard Disk Drives

• HDDs store data digitally on magnetic disk surfaces
• HDDs contain platters that spin at high speeds with read-write heads to access the surfaces
• Data is stored in sectors and tracks on the magnetic surfaces
• HDDs have slow data access when compared to RAM
• HDD applications require the read-write heads to constantly seek the correct data blocks
• HDD latency is the time it takes of a block of data on the track to rotate to the read-write head
• HDD head movements cause latency
• HDDs undergo deletions and editing leading to data fragmentation, slowing data access
• Direct access device; however, data sequentially within a sector

Removable Hard Disk Drives

• Removable HDDs : External HDDs connected to the computer using USB ports
• Removable HDDs are a backup and a way of transferring files between computers

Solid State Drives

• SSDs reduce latency
• SSDs retrieve data faster than HDDs
• SSDs have no moving parts
• They control the movement of electrons within NAND chips
• Memory are non-volatile and rewritable
• Some SSDs use EEPROM (NOR chips)
• Most SSD storage devices use NAND technology (flash memory)
• EEPROM is more expensive, faster, allows data to be read byte at a time
• NAND only allows blocks to be read/erased
• Flash memory main benefits are reliability, lighter, lower power consumption, less heat, very thin, and faster access speeds
• The main drawback of SSD is longevity
• Conservatively rated at only 20 GB write operations per day over a three year period
• Flash memory devices cannot overwrite existing data; it must be erased first before writing new data

Memory Sticks/Flash Memories

• Also known as pen drives
• Connect to the computer through the USB port
• Has the advantage of being small and lightweight, making them suitable for transferring files between computers
• Can also be used as small back-up devices for music or photo files, for example
• Complex or expensive software, such as an expert system, will often use a memory stick as a dongle to prevent illegal or unauthorized use of the software or copying the software

Optical Media

• CDs and DVDs are optical storage devices that uses laser light to read data from, and write data onto, the surface of a disk
• Uses a thin layer of metal alloy or light-sensitive organic dye
• CD/DVD uses a single, spiral track which runs from the centre of the disk to the edge
• CD/DVDs is divided into sectors allowing direct access of data
• Standard single layer DVDs have more storage because the 'pit' size and track width are smaller and DVDs use lasers with a wavelength of 650 nanometers

Blu-Ray

• Using blue laser light means that the 'pits' and 'bumps' can be much smaller, consequently, a Blu-ray can store up to five times more data than a DVD
• Blu-ray uses a single 1.1 mm thick polycarbonate disk while DVDs use a sandwich of two 0.6 mm thick disks
• Blu-ray has secure encryption system to help to prevent piracy and copyright infringement
• Optical storage media is used as back-up systems to transfer files between computers or manufacturers supply software

Laser Printers

• Use dry powder ink rather than liquid ink
• Static electricity aids in the creation of a laser printer page
• Laser printers print the whole page simultaneously
• Colour laser printers utilizes blue, cyan, magenta, and black
• The general steps in the operation are; Data received, printer driver, check if printer is available, data is sent to printer and stored, drum becomes positively charged, drum is coated in toner, negatively charged paper is rolled on drum and toner sticks, paper is transported to fuser and charge is removed before the next page

Inkjet Printers

• Made up of print head, ink cartridge, stepper motor and paper feed
• The print head contains rows of nozzles that spray droplets of ink onto the paper to form characters
• The droplets are produced using of thermal bubble or piezoelectric process
• Thermal bubble - tiny resistors create heat makes the ink vaporize and ink ejection from the head occurs

Speakers

• speakers convert a digitised sound file stored on machine into sounds; The process involves DAC -> Amplifier -> Speaker
• The rate at which the DAC can translate the digital output into analogue voltages is known as the sampling rate

Microphones

• Microphones are used to convert sounds waves into an electrical signal
• Microphones are either internal or use USB or wireless connectivity
• when sound is created the air vibrates and vibrates the microphone diaphragm
• coil around the diaphragm induces electrical current

Screens

• Screens use either LCD, LEDs, or newer OLED tech
• OLEDs allows for very thin screens, not needing back lighting and use pixel technology to form an image
• Touch screens use either capacitive or resistive tech
• Capacitive touchscreens are medium cost and durable but only works with bare fingers and resistives are cheaper, doesn't work well in sunlight or permit multi-touch

Virtual headset

• Virtual headsets give the wearer the experience of a virtual environment using a video display, lenses, headphones and motion tracking using sensors

Sensors

• Sensors read/measure physical properties such as temperature, pressure, acidity, etc.
• ADC are used to convert this anlogue data to digital data to be processed by computer
• DAC convert digital data to analogue to control external devices
• Sensors are used for both monitoring and control activities of external computer controlled tools