Operating System

• the software components consist of system software and application software. the application programs cannot directly interact with the hardware components and therefore needs a special system program called “Operating system” which can interact with the hardware components through a set of drivers. the operating system manages all application programs and system resourse.

• An operating system(OS) is system software that is designed to provide a user friendly interface between the computer system hardware and applications programs.

• Application praograms are user initiated program to perform different jobs on the computer system. A computer user interacts with the computer system through applications programs to get the various jobs done.

• An operating system is an interface between a computer user and computer hardware components connected to the system.

• the BIOS program initiates the booting sequence to search and load the operating system into the RAM. An operating system is a system software designed to control and manage computer system.

• the BIOS(Baisc input output system) is the set of program instruction used to boot a computer system. these routines(system software) provide basic drivers for peripherals such as the keyboard, monitor and mous. these drivers also provide the user with a way to edit or alter the configureations settings.

System Architecture and Operating Systems

• An operating system provides two basic services
  • Abstraction(抽象概念)
    • Abstraction hides the complexities and details of different hardward configuration. application need not be device specific for each device connected to the computer system.
  • Arbitration(仲裁)
    • Arbitration ensures that all the system resources and hardware devices are shared amongst different processes running simultaneously on the system without any conflict

• the application program cannot directly interact with the system hardware components and input/output peripheral devcies connected to the system. AN operating system(OS) performs as an interface between a user applications and computer hardware.

• the application program can communicates with the system hardware components only through operating system. the operating system in turn communicates with the hardware components through a system software called “device drivers.”

• An Operating system is an eseential component of the computer system. it is a system program which provides services, resources and runtime environment for application programs running on the computer system.

• An operating system architecture is a term that specifies the overall structure of the operating system, its logical components and the logical interrelationships of various components that constitute(构成) an operating system

• An operating system structure(OS design approach/architecture) can be classified based on the design approach and implementation by the operating system.

  • simple structure OS
  • layered approach OS
  • Monolithic Appoarch OS
  • Microkernel Approach OS

Computer system Bus

• the computer systems consist of number of components. there components are connected to each other with a network of wires running accross the computer. in computer architecture the connecting wire is referred as bus and the network is referred as “Bus system”

• Bus system
  • the performance of computer system depends upon number of factors such as CPU, RAM and the bus system is also one the important factor. the bus system is a network of individual Buses within a computer system.

Internal and External Buses

• A computer system consist of number of internal components which mainly include CPU, MotherBoard, Internal add on cards(Graphic card, sound card, network card), RAM and hard disk

• A system bus is a set of parallel wires which connects the two or more independent major internal components of a computer system. system bus transfer data, memory addresses and device control instruction.

• the CPU contains a control unit which controls the functioning of all other components. the control bus is used to transfer the control signals form one component to another component

• A control bus is a computer bus that is used by the CPU to communicate with devices that are connected to the computer system. these devices are connected with the help of cables and printed circuits board.

• the CPU transmits a variety of control signal to the system components and the devices also transmit control signal to the CPU using the control bus

• the control bus is bidirectional and assists the CPU in synchronizing control signals to the internal devices and external components. the control bus includes device interrup signal lines, byte enable lines, memory read/write signals and status lines.

• the CPU executes the program instructions by fetching the instructions from the main memory RAM

• in order to perform the memory read or write operation from the main memory RAM, the CPU sends either read or write control signal on the control bus and address of the memory location along the “address bus” from where the operation is to be performed. the address bus is a part of the “system bus”

• Number of devices are connected to the computer system and each of this device has unique memory address(address in RAM)

• the CPU identifies these devices with reference to the device address and communicates with the device for different operations to be performed. A device can requiest action through a hardware interrupt. A seperate line coming from the device will go to an interrupt controller which produces a signal to notify the CPU that a dvice needs attention.

• in computer architecture, the data bus is a wired connection dedicated for transmiting the data between the CPU and other components. the data bus is a part of the system bus in addition to address bus and control bus.

• A data bus has many different features, but one of the most important feature is its width. the width of a data bus refers to the number of bits(electrical wires) that the bus is consist of. the common data bus widths includ 8 bit, 16 bit, 32 bit and 64 bit. wider the bus width, faster would be the data flow on the bus.

What is a Expansion Bus?

• the performance features and functionality of a computer system can be extended by adding an additional cards such as graphics card or sound card

• the expansion slots are the ports located on the motherboard of a computer system in which an expansion cards can be installed. the user can used these slots to insert additional expansion cards as per the functional requirements.

• An expansion bus is a group of wire OR PCB used to connect with the expansion slots on the motherboard used for installing expansion cards.

• An expansion bus provides an input / output pathway for transferring information between internal hardware components such as RAM or the CPU and expansion cards such as a graphics card or sound cards.

What is a Front side & Backside Bust

• FSB- Front Side bus:

  • the FSB is bus which physically connects the processor with the NorthBridge chipset and the main memory RAM, hard drives and PCI on the motherboard.

  • the FSB is also referred as system bus, memory bus, processor bus which is a part of the motherboard and conncets the processor to the main memory(RAM)

• Backside bus is a computer bus that connects CPU to Level2 cache memory. backside bus is a bus that is present inside the processor chip, which specifically link ALU and internal L2 cache, so that the flow of data from L2 cache can take place at a very high speed.

• the data flow through the backside bus is fater than the front side bus. backside bus(BSB) is a part of central processing unit now but the speed of this bus totally depends upon the speed of the processor.

Bus types and FUnctions.

Motherboard BUS

• all these components are connected to the system with a network of wires and these wires are known as computer buses.

• A bus is a common communication pathway through which information flows from one computer component to another.

• the computer bus system is a network of thses buses which physically connect all the components with wires(actual bus wires OR circuit wires on the motherboard). the bus system consist of different types of buses based on the component being connected and function assigned to the bus.

• A bus can consist of set of wires grouped together as connection wire or a printed circuit boards which carry the data and other commands(instructions) from the CPU to the memory and to various other components connected to the system. the bus performance is an important parameter to access the system performance.

• All the internal components of a computer system are connected with each other with a network of group of cables. the various system components communicate with each other through this network of group of cables called bus system.

• the bus consist of group of cables and each of these cable can carry 1Bit(0 or 1) at a time. therefore a bus consist of a group cables so that a group of bits can be sent through the bus.

• A CPU is connected to internal components such as RAM and external peripheral device by using device controller circuits all put on only two controller chips called chipset. the chipset consist of NorthBridge and Southbridge placed on the motherboard

• the memory controller NorthBridge and input/out controller Southbridge circuits on the MotherBoard are connected to the main memory RAM and other peripheral devices by uisng system bus wires which carres three type of information

  • Memory addresses
  • Control Instruction
  • Data

• A bus is a information highway over which information flows and wider the bus, the more information can flow over channel. therefore, a compatible bus width and bus speed is important for the optimal CPU and RAM performance.

• this is similar to a multi lane wider highway that can carry more cars due to more number of lanes available for traffic. whereas, a single lane road can carry less number of cars are compared to a multi lane road.

• the computer system buses essentially carries three different types of information
  1. Address Bus - Carries memory location addresses
  2. Conrtol Bus - Device control instructions from CPU
  3. Data Bust - Carries data from and to the CPU
• the computer bus consist of group of wires and each wire carry one bit of data(0 or 1). the bus width is the total number of wires present in the bus which indicates total number of bits that the bus can transfer at a time.

• the size of a bus is known as its bus width, is important because it determines how much data(in bits) can be transmitted at one time. the Larger system bus width significantly improves the processor performance.

• For example

  • A 64 bit bus has 64 cables thus can transmit 64 bits of data at a time

• the bus speed is another important measure of the bus performance. the bus speed is defined by its frequency expressed in Hz. the bus frequency is the number of data packets sent or received per second. Each time that data is sent or recieved, it is called as one cycle.

• the bus speed is generally referred to the FSB-Front Side Bus speed which connects the CPU to the memory controller chip NorthBridge.

• most buses tranmit one bit of data per line, per clock cycle, although newer high-performance buses like AGP may actually move two bits of data per clock cycle, doubling performance. similary older Buses like the ISA bus may take two clock cycles to move on bit which is a significant reduction in the performance

• the bus bandwidth which is also called as throughput, refers to the total amount of data that can theoretically be transferred on the bus in a given unit of time

• using the highway analogy, if the bus width is the number of lanes, and the bus speed is how fast the cars are driving, then the bandwidth is the product of these two and reflects the amount of traffic that the channel can concy per second.

• the Buses are limited by their width in bits. they are usually 8, 16, 32 or 64-bits wide. the bit size of the bus tells us how many bits can be sent by the bus at any one time. Example: A 32-bit bus can send 32bits at once.

• the system bus that connects the CPU to the memory is called the Front-side bus(FSB). CPU cores share level 2 and level 3 cache memory across the FSB. they will usually connect to Level2 cache through the back-side bus(BSB). the BSB is much faster than the FSB

Motherboard

• the motherboard is a largest PCB(printed CIrcuit board) in a computer system where some of most imporatant components(such as Processor and RAM modules) are connected with each other. motherboard also acts as junction(汇合处) for all other components.

• the list of the number of components on the motherboard is pretty long and also depends upon the motherboard architecture. however, some components are vital(必不可少的) to the functioning of the system and will be present on all the motherboard

1. Clock generator
   • the instructions(Fetch->decode->execute->store:machine cycle) executed by the CPU are carried out in a given number of clock cycles and therefore the overall processing speed of the CPU(i.e the speed with which it can execute programs) will be directly related to the number of clock cycles per second. in other words, all other factors being equal, the faster the clock speed, the faster the CPU will operate. this also results considerable amount of heat and thus CPU needs an efficient cooling system.
2. CPU socket
   • A CPU socket or CPU slot is mechanical component that provide mechanical and electrical connections between a microprocessor and a printed circuit board(PCB). this allows the CPU to be replaced without soldering.
   • the CPU sockets have retention(保持) clips that apply a constant force and retain the CPU firmly inside the socket. for Processor with a large number of pins, either zero insertion force(ZIP) sockets or lang grid array(LGA) sockets are used instead
   • the Processor sockets use a pin grid array(PGA) where pins on the underside of the processor chip connect to holes in the processor socket.
3. RAM - Memory Sockets
   • RAM is considered to be the main memory for a computer system and each program must be first loaded into the RAM for CPU to initiate its execution.
   • the RAM memory is available in modules of standard sizes(500MB, 1GB) and these modules are fitted on the motherboard of a system in slots which has a locking mechanism.
   • RAM module must be supported by the motherboard. the maximum RAM supported also depends upon the CPU(32bit OR 64 bit) and the type of the operating system installed on the computer system.
4. ROM BIOS

• BIOS stands for Basic Input Output System which is a system software and it is the first start-up program executed by the CPU when computer system is switch on

• the main purpose of the BIOS program is to provide the bare minimum essential resources(hardware check, initial set of drivers) to the CPU during computer system booting(starting) process till the main operating system is loaded and the system is ready for other Application to run.

1. CMOS RAM & Battery

• the CMOS(Complementary Metal-Oxide Semiconductor) is a RAM chip on the MotherBoard which is a Battery powered Semiconductor chip inside computer that stores system information and user preferences.
• the CMOS chip is used to retain the user settings when system is turned off. this information range from the system time and data to system hardware settings preferred by the user.

• A CMOS/Real-time CLock(RTC) is a computer clock(most often in the form of an integrated circuit) that keeps track of the current time and date

• Although the term RTC often refers to the devices in personal computers, severs and embedded system. RTC are present in almost any electronic device which needs to keep accurate time.

1. Black panel connectors.
2. Chipset(North & South Bridge)

• the Northbridge is an IC(Intergrated Circuit) placed near CPU on the motherboard. the Northbridge is responsible ofr communications between the CPU interface, AGP slot and the main memory(RAM slots)

• when the CPU needs data from RAM, a request is sent to the Northbridge(memory controller). After the request has been recieved, it responds with how long the processor need to wait to fread the memory over the fornt side bus(FSB)
• the CPU can process the instructions at very high rate which is known as CPU speed. However the various internal and extenrnal hardwar components cannot match the CPU speed and therefore we need an intermediate device controller which acts as an interface between the CPU and the varius hardware components.

• the CPU communicates with different hardware components through the device controller chips installed on the motherboard.

• the southbridge is one of the chipset present on the motherboard which is connected to the processor through NorthBridge. the Southbridge mainly handles the communication ports on the motherboard which are used to connect peripheral devices. therefore, the Southbridge is also commonly referred as Input-Output COntroller. the Southbridge is connected to the Northbridge through a high speed bus and the Northbridge is connected to CPU through FSB - Front side bus.

1. Motherboard Buses

• the “buses” are group wires on the motherboard that connect the CPU to other components. there are many buses on the motherboard. A bus move instructions, data and the control signals around the system.

• the speed of a bus is measured in Mhz, the faster the bus, the faster data is communicated the speed of the mother board in defined by the bus speed.

1. Expansion slots.
   • the expansion card has an edge connectors on the lower edge of the card that precisely fits into the expansion slot on the motherboard. each expansion card has row of electrical contacts on the lower edge that is designed to establish an electrical connection between the motherboard and the electronic on the card which consist of mostly intergrate circuits(IC) chips.

• there are three types of expansion slots found in modern computers
  • PCI(peripheral(周边的) component interconnect)
    • PCle stands for PCI expresss. PCI express is a new technology that is slowly replacing AGP. PCI express x16 slots can transfer data at 4GBs per seconds, which is about twise faster than AGP 8x slot
    • PCI Express slots come in five different sizes and speeds
      • PCIe x1,PCIe x2, PCIe x4,PCIe x8,PCIe x16.
    • PCIe x16 slots are used for graphics card.
  • AGP(Accelerated Graphics Port)
    • the AGP stands for Accelerated Graphics Port.
    • AGP is an advanced port designed for video cards and 3D accelerators. Designed by intel and introudced in August of 1997. today, AGP slots has been replaced by PCI express slots.
  • ISA(Industry Standard architecture)
• they differ primarily in how fast they transfer information between the microprocessor and the expansion board.

Motherboard

CPU - CLOCK

• all computer contain an internal clock that regulates the rate at which instrucions are executed by the CPU and synchronizes all the various computer components

• Every microprocessor requires a clock for its functioning. the CPU requires a fixed number of clock ticks/ pulse (called as clock cycle/clock speed) to execute each instruction.

• A clock signal is a particular types of signal that oscillates between high and low state and these two states are utilized to coordinate operation of the various components within a computer system.

• A clock signal is produced by a clock generator (Quartz Oscillating Cristal). the Most common clock signal is in the form of a square wave.

• An executable program contains number of program instructions in the binary code which a CPU interpret as per instruction set and execute one by one

• An instruction is a command given to a computer processor by a computer program. at the lowest level, each instruction is a sequance of 0s and 1s that describes a physical operation to be performed by the CPU (such as “add” OR “Multiply”)

• for every tick (one digital pulse) of the clock, the CPU is able to process one piece of data or execute one instruction OR only part of the instruction for large instruction.

• some processors execute only one instruction per clock pulse. more advanced processors can perfrom more than on instruction per clock puls. the procssing speed of such processors will be more as CPU can execute more instructions per clock cycle.

• there are some other factors in addition to clock speed which affect the CPU processing speed such bit size of the “BUS” and size of the main memory RAM.

• A computer with a 32-bit bus will work faster at a given clock speed than a computer with a 16-bit bus. for these reasons, there is no simplistic, universal relation amongst clock speed, bus speed and millions of instructions per second(MIPS) executed by the CPU.