compsci final

Random access memory

A random-access memory is one in which the access time of each memory cell is approximately constant. More specifically, random access stands in contrast with serial access where memory cells are accessed in turn until the desired cell has been located. Generally, semiconductor technology offers random access and mechanical (magnetic or optical) memory offers serial non‐random access.

Serial access

A serial access memory is arranged so that data elements are accessed sequentially. That is, several (or even very many) elements must be read before the desired element has been located. Therefore, the access time depends on the physical location of the data. Magnetic memory (disk) and optical memory (CD, DVD, and Blu‐ray) are examples of serial access memories.

Dynamic RAM

Dynamic memory, DRAM, is a form of semiconductor (chip) memory that is used to store the bulk of a computer’s data in immediate access memory. The most important aspect of DRAM is that it stores data using a single transistor and that the data gradually leaks away, requiring a recharge operation every few milliseconds. DRAM is currently the densest form of memory in terms of bits per transistor.

Static RAM

Static RAM is a form of semiconductor memory that stores data in a cross‐coupled flip‐flop. However, it uses more transistors per cell (4 or 6) than DRAM but it does not have to be refreshed. Static RAM is generally faster than DRAM but more expensive per bit.

Motherboard

The central interface for all the components of a PC. Everything connects to the mother-board via slots, wires, readouts and connectors.

Access time

The time taken to read a memory element. This is usually the time taken from the start of an access cycle to the time at which the data has been read or written. The access time of read and write accesses may be the same, but not all memories have equal read and write access times.

Non‐volatile memory

Non‐volatile memory retains its data when powered down. Typical examples are magnetic memory, optical memory and flash memory.

Cycle time

The cycle time of a memory is the period between consecutive accesses. Static RAM has equal read/write access times and cycle times. DRAM has a longer cycle time than an access time because it is necessary to perform internal operations between consecutive read and write accesses.

Data Bus

Carries the data between memory and the MBR

Address Bus

Carries the memory location of the instructions/data being received.

Control Bus

A bus with 2 states, set or enable, which govern if the data bus is reading or writing to memory.

Secondary Storage

Used to store programs and data. It can be partitioned to allow for dual-booting multiple operating systems.

Input Device

A device (piece of computer hardware equipment) that is used to provide data and control signals to an inform-ation processing system such as a computer or inform-ation appliance. Examples of input devices include keyboards, mouse, scanners, digital cameras, and joysticks.

Output Device

Any device used to send data from a computer to another device or user. Most computer data output that is meant for humans is in the form of audio or video. Examples include monitors, projec-tors, speakers, headphones and printers.

BIOS/UEFI

Basic Input Output System/Unified Extensible Firmware Interface. The BIOS performs the hardware initialization during the bootup, and provides runtime services between the OS and hardware. UEFI was designed to be the successor to the BIOS.

Virtual Memory

When the RAM is full, the OS uses some of the secondary storage as Virtual Memory. This means the computer can continue to run. Pages (blocks of data) are transferred to the virtual memory when not needed thus freeing up space, and returned to RAM when they are needed.

RAM

The “working” area of the computer. Programs and data currently in use is stored in the RAM. On startup the BIOS loads the OS into the RAM.

Characteristics:

• Random Access - allows data items to be read or written in almost the same amount of time irrespective of the physical location of data inside the memory.

• Volatile : content is emptied on power down.

ROM

A permanent area of storage. The contents cannot be altered by software. Contents of ROM is written at manufacture.

Characteristics:

• Read-Only Acces

• Non-Volatile: retains data at power down

• Mainly used to store firmware or applic-ation software in plug-in cartridges.

• ~4MB

• Examples of ROM: Bootloader (BIOS/-UEFI)

Kernel

The very core of the OS that provides the interface between the user and the hardware. Applications use the kernel to send/receive data from hardware.

Memory Management

An OS must manage the computer’s memory including adding/removing programs and data from RAM, allowing multiple programs to be run at the same time. The OS also reallo-cates memory when it is no-longer in use (i.e. when a program is closed).

Buffer

A buffer is a sequence of memory locations, its size depends on the I/O device, it is used to hold data temporarily until it is processed by the CPU.

Status register

It is a sequence of bits, its size depends on the I/O device, it is used to report the status of the I/O to the CPU.

Input/Output

I/O is the communication between an information processing system, such as a computer, with the outside world, possibly a human or another system. Inputs are signals or data received by the system, and outputs are signals or data sent by it.

Interrupt

An interrupt is a signal emitted to the processor by software or hardware, to indicate that there is an event (which is temporary) that requires immediate attention.

I/O Interrupt

A status of a channel has changed, Occurs when an IO operation is complete or a device is ready.

Process Management

Involves the scheduling and switching of programs and threads. Modern PCs have “multi- tasking” but it is just clever scheduling.

Throughput

Throughput refers to the number of processes completed per unit time. It is a measure of the efficiency and productivity of a system or process. It indicates the rate at which work is being done and the ability of the system to handle and process tasks effectively.

CPU scheduling

CPU scheduling performs at the ready queue. It is done by short-term/CPU scheduler. It is responsible to minimize average waiting time.

CPU utilization

CPU utilization is defined as an average fraction of time for which the CPU is busy (0-100%). It can also be defined as the maximum use of CPU to keep it busy in process execution. The performance of the computer system will be increased with the increase in CPU utilization.

Arrival time (AT)

The time when the process has arrived into ready state (not in new state) is called the arrival time of the process.

Burst time (BT)

The time required for the process to complete its execution is called burst time.

Completion time (CT)

The time when the process completes its execution is called the completion time of the process.

Turnaround time (TAT)

Interval between the submission of the process and its completion is called Turnaround time. The time difference between the completion time and arrival time is called the turnaround time of the process. Or we can say, time spends by a process in main memory (RAM).

Waiting time (WT)

The time difference between turnaround time and burst time is called waiting time. It is the duration where the job is not executing. WT = TAT – BT

Response time

The time difference between the first response and arrival time is called response time of the process.

USB (Universal Serial Bus)

USB is an industry standard that creates specifications for connectors, cables and protocols for connection; power supply (interfacing) and communication among computers, computer peripherals as well as other desktops. There are a great many USB hardware including several different connectors, of which USB-C is the latest kind.

CPU slot

A CPU slot, also called a CPU socket or Processor socket, contains one or more mechanical components that provide mechanical and electrical connections between the PCB and a microprocessor (CPU). Therefore, you can install a CPU on a motherboard without soldering.

PCI (Peripheral Component Interconnect) slot

Peripheral Component Interconnect is a local computer bus for connecting hardware to a computer. It supports all the functions of a processor bus. PCI is usually been called Conventional PCI to distinguish it from its successor PCI Express (PCIe, PCI-e or PCI-E). PCI Express is a high-speed serial computer expansion bus standard designed to replace the older PCI, PCI-X and AGP bus standard. It is a general-use motherboard interface for the graphics card, SSDs, hard drives, Wi-Fi as well as Ethernet hardware connections.

AGP (Accelerated Graphics Port) slot

AGP was designed as a high-speed point-to-point channel for connecting a video card (graphics card) to a computer system. Primarily, it was used to assist in the acceleration of 3D computer graphics. AGP is originally designed to be a descendant of the PCI series of connections for video cards. Yet, it was replaced by the PCIe slots.

ISA (Industry Standard Architecture) slot

ISA is the 16-bit internal bus of IMB PC/AT and similar computers that are based on Intel 80286 and its immediate successors during the 1980s. It was backward compatible with the 8- bit bus of the 8088-based IBM PC largely.

There once was an attempt to extend ISA into a 32-bit bus, called Extended Industry Standard Architecture (EISA). The attempt wasn’t very successful, and the EISA was largely replaced by the later VESA Local Bus and the PCI bus.

Parallel port

A parallel port is a kind of interface for attaching peripherals on desktops. The name of this kind of port is derived from the way the data is sent. That is, the parallel ports send multiple bits of data at the same time. Serial interfaces, on the contrary, send bits one data at once. To achieve parallel data transfer, there are multiple data lines in the parallel port cables. The parallel port cable is larger than the cable of a contemporary serial port, which only has one data line within.

FDC (Floppy Disk Controller)

FDC is a special-purpose chip and associated disk controller circuitry. It controls and directs reading from and writing to a computer’s floppy disk drive (FDD).

IDE (Integrated Drive Electronics) controller

The devices used for connecting IDE, Ethernet, FireWire, USB and other systems can be called host adapter. So, the IDE controller refers to the host adapter. A host adapter, also called a host controller or a host bus adapter (HBA), connects a computer (acting as the host system) to other network and storage devices. Tip: Host adapter is usually used to indicate devices connecting SCSI, Fibre Channel and SATA devices.

CMOS (Complementary Metal-oxide-semiconductor) battery

CMOS battery, also called memory battery, clock battery or real-time clock (RTC), is generally a CR2032 lithium coin cell. The lifespan of the CMOS battery is estimated to be three years when the power supply unit (PSU) is unplugged or switch off.

Power supply connector

A power supply provides the necessary electrical power to let the computer to work. It takes standard 110-Volt AC (Alternative Current) power to DC (Direct Current) power of 12 Volt, 5 Volt, 3.3 Volt, etc.

Mouse and keyboard ports

All computers have a keyboard port connected directly to the motherboard. There are two types of connectors. The oldest one is a special DIN (Deutsches Institut für Normung) connector while the newest one is the mini DIN PS/2-style connector. Many PCs use the PS/2-style connectors for both keyboard and mouse; and the connectors are marked clearly for different usage.

DIP (Dual In- line Package) switch

A DIP switch is a manual electric switch packaged with others in a standard dual in-line package. The term may refer to an individual switch or the whole unit. The DIP switch is designed to be used on a printed circuit board (motherboard) together with other electronic motherboard components. It is usually used to customize the behavior of an electronic device for specific situations.

Jumper

A jumper is a short length of conductor that is used to close, open or bypass part of an electronic circuit. Typically, jumpers are used to set up or configure printed circuit boards like the motherboard.

Heat sink/heatsink (cooling system)

A heat sink is a passive heat exchanger that transfers the heat generated by parts of motherboard into a fluid medium like liquid or air. The fluid medium will dissipate away from the device. Thus, the temperature of the device is kept within a tolerable range. On the motherboard, the heatsink is usually used to cool CPU, GPU (graphics processing unit), chipsets and RAM modules.

Clock generator

A clock generator is an electronic oscillator (circuit) that produces a clock signal for usage in synchronizing a circuit’s operation. The clock signal ranges between high and low frequencies, thus creating a metronome for the coordination of actions.

Virtual memory

Virtual memory is an illusion of extremely large main memory. It is a technique used by operating systems to provide the illusion of having more physical memory (RAM) than is actually available. It allows programs to use more memory than what is physically installed by temporarily storing data that is not currently in use on the hard disk. When the data is needed, it is swapped back into the main memory. This allows for efficient memory management and enables programs to run smoothly even when the physical memory is limited.

Paging vs Segmentation & Virtual Memory

• Segmentation. Memory is split into variable sized blocks, and programs are segmented, with each segment being a logical divider. A segment table then maps segments onto memory blocks. Generally slower than paging due to the placement algorithm.

• Paging. RAM is split into fixed sized blocks - frames. Programs are split into same-sized blocks - pages. Any page can be placed in any frame, easy to allocate as all equal size.

• If the RAM is full. Pages are transferred to the secondary storage acting as memory - Virtual Memory. Pages are moved in/out as needed.

• Thrashing is when pages are being constantly swapped between RAM and Virtual Memory. It can cause speed issues as the secondary storage’s speed << RAM's speed.

What are the components of I/O devices?

There are 2 main components of I/O Device: Hardware Interface and Internal Structure.

What is hardware structure?

Hardware Structure is the device interface. it represents the interface used by the system to control the device, and every device has an interface and a protocol for typical interaction.

How many registers are used in the hardware of an I/O device?

There are 3 registers in use: Status Register, used to get the status of the device, Command Register, used to tell the device to perform a certain task, and Data Register, used to pass data to the device, or get data from the device.

What is the internal structure of an I/O device?

Internal Structure is the device abstract implementation, it is device specific (meaning it depends on the device itself). Simple devices need one or few hardware chips to implement their functionality, while more complex devices need a simple CPU(also called a micro- controller), a general purpose memory¬(either DRAM, SRAM or both), and device specific chips to get their jobs done.

Why are I/O slow?

They are slow for 3 reasons:

1. They are the main way of interaction between the user and the computer, so they can be as fast as the user.

2. Their signal is analog and need to be converted to digital.

3. They depend on mechanical movements which is slow compared to digital signals.

What 2 components does each I/O device need?

Each I/O device must have: a buffer and a status register.

• Hardware Interface: This acts like a handshake spot, allowing the device to communicate with the rest of the computer system. It defines how data is formatted, transmitted, and received by the device.

• Internal Structure: This is the inner workings of the device itself. It includes the mechanics, electronics, or other components that perform the specific function of the device, like capturing input (keyboard) or displaying output (monitor).

What is the protocol of programmed I/O technique?

The protocol has 4 steps:

1. Poll the device to see if it is ready to receive a command (this is done by repeatedly reading the status register).

2. The OS sends data to the data register.

3. The OS writes a command to the command register, this also implicitly tells the device that the data is present in the data register and that it should begin working on the command.

4. The OS waits for the device to finish by again polling it in a loop to see if it has finished (it may then get an error indicating a success or a failure).

When do we call something PIO (programmed I/O)?

We call something Programmed I/O (PIO) when the CPU directly controls the data transfer between itself and an I/O device. In PIO, the CPU uses software instructions to:

• Initiate the transfer: The CPU sends a signal to the device indicating it wants to read or write data.

• Manage the transfer: The CPU uses specific instructions to read data from or write data to special device registers or memory locations.

• Check for completion: The CPU typically has to loop and keep checking the device status until the transfer is complete

What are the disadvantages of PIO?

This technique wastes a great deal of CPU time just waiting for the potentially slow I/O device to complete its activity.

How does the processor respond to an interrupt?

It responds by suspending its current activities, saving its state, and executing a special function called interrupt handler or Interrupt service routine.

What do we mean by interrupt service routine?

Interrupt Service Routine (ISR): is a special function that is called when there is an interrupt, this function is called by the processor and not the programmer.

What values do we need to save when an interrupt happens?

The typical values include condition code flags (flag registers) and contents of any register used by both the interrupted program and ISR.

What values does the processor save?

The processor only saves the Program Counter (PC) which is also called Instruction Pointer (IP) and the values of Processor status register. Other values must be saved by the programmer.

Operating systems

Common components of operating systems include: (1) process management, (2) memory management, (3) file management, (4) I/O system management, (5) secondary-storage management, (6) networking, (7) protection, (8) interpreter system.