Computer System Organization

A digital computer consists of an interconnected system of processors, memories, and input/output devices. Processors, memories, and input/output are key concepts and will be present at every level, so we will start to study computer architecture by looking at all three in turn.

PROCESSORS

The CPU (Central Processing Unit) is the ‘‘brain’’ of the computer.

A central processing unit (CPU) is the electronic circuitry within a computer that carries out the instructions  of a computer program by performing the basic arithmetic, logical, control and input/output (I/O) operations specified by the instructions. The computer industry has used the term “central processing unit” at least since the early 1960s.Traditionally, the term “CPU” refers to a processor, more specifically to its processing unit and control unit (CU), distinguishing these core elements of a computer from external components such as main memory and I/O circuitry.

The CPU is composed of several distinct parts. The control unit is responsible for fetching instructions from the main memory and determining their type. The arithmetic logic unit performs operations such as addition and Boolean AND needed to carry out the instructions.

The CPU also contains a small, high-speed memory used to store temporary results and certain control information. This memory is made up of a number of registers, each of which has a certain size and function. Usually, all the registers have the same size. Each register can hold one number, up to some maximum determined by the size of the register. Registers can be read and written at high speed since they are internal to the CPU. The most important register is the Program Counter (PC), which points to the next instruction to be fetched for execution. ( The name ‘‘program counter’’ is somewhat misleading because it has nothing to do with counting anything, but the term is universally used. Also important is the Instruction Register (IR), which holds the instruction currently being executed. ( Most computers have numerous other registers as well, some of the general-purpose as well as some for specific purposes.

What is the,,bus,,?

In computer architecture, a bus is a communication system that transfers data between components inside a computer, or between computers. This expression covers all related hardware components (wire, optical fiber, etc.) and software, including communication protocols.

Early computer buses were parallel electrical wires with multiple hardware connections, but the term is now used for any physical arrangement that provides the same logical function as a parallel electrical bus. Modern computer buses can use both parallel and bit-serial connections and can be wired in either a multi-drop(electrical parallel) or daisy chain topology, or connected by switched hubs, as in the case of USB.

CPU Organization

• A system bus is a link that connects every segment of a system to the central storage and carries out the data transfer in them.
• It is a pathway composed of cables and connectors which is used to carry data between a computer microprocessor and the main memory.
• It provides a communication path for the data and control signals moving between the major components of the computer system.

The types of system buses are

1. Data

• These are the pieces of information that are to be transferred.
• The data is transferred between peripherals, memory and the CPU. The data bus can be a very busy pathway.

2. Address

• It stores information about where the data is to be transferred.
• The components pass memory addresses to one another over the address bus.

3. Control

• These are the set of instructions regarding what to do with the data.
• It is used to send out signals to coordinate and manage the activities of the motherboard components.

Characteristics of a System Bus

1. Bus Width

• The size of a bus also known as its width.
• It determines how much data can be transferred at a time.
• This refers to the amount of information that can be transferred once.

2. Bus Speed

• This refers to the no. of bits or bytes the bus can send per unit time.
• It is also defined by its frequency. Frequency means that the number of data packets sent or received per second. Each time that data is sent or received is called a cycle.

The system bus combines the functions of the three main buses, namely Control Bus, Address Bus, Data Bus. The control bus carries the control, timing and coordination signals to manage the various functions across the system. The address bus is used to specify memory locations for the data being transferred.

The data bus, which is a bidirectional path. It carries the actual data between the processor (CPU), the memory and the peripherals (Input and Output). The system bus architecture varies from system to system and can be specific to a particular computer design. The other common characteristics of system buses are based on the primary role, connecting devices internally or externally, etc.

Internal Bus

• It is also known as an internal data bus, a memory bus, a system bus or Front-Side-Bus.
• It connects all the internal components of a computer, such as CPU and memory, to the motherboard.
• Internal data buses are also referred to as a local bus because they are intended to connect to local devices.
• This bus is quick and independent of the rest of the computer operations.

External Bus

• It is also known as an expansion bus.
• It is made up of the electronic pathways that connect the different external devices, such as a printer, etc.

Cache Function

A CPU cache is a hardware cache used by the central processing unit (CPU) of a computer to reduce the average cost (time or energy) to access data from the main memory. A cache is a smaller, faster memory, closer to a processor core, which stores copies of the data from frequently used main memory locations. Most CPUs have different independent caches, including instruction and data caches, where the data cache is usually organized as a hierarchy of more cache levels (L1, L2, etc.).

All modern (fast) CPUs (with few specialized exceptions) have multiple levels of CPU caches. The first CPUs that used a cache had only one level of cache; unlike later level 1 caches, it was not split into L1d (for data) and L1i (for instructions). Almost all current CPUs with caches have a split L1 cache. They also have L2 caches and, for larger processors, L3 caches as well. The L2 cache is usually not split and acts as a common repository for the already split L1 cache. Every core of a multi-core processor has a dedicated L2 cache and is usually not shared between the cores. The L3 cache, and higher-level caches, are shared between the cores and are not split. An L4 cache is currently uncommon and is generally on dynamic random access memory (DRAM), rather than on static random access memory (SRAM), on a separate die or chip. That was also the case historically with L1, while bigger chips have allowed integration of it and generally all cache levels, with the possible exception of the last level. Each extra level of cache tends to be bigger and be optimized differently.

Other types of caches exist (that are not counted towards the “cache size” of the most important caches mentioned above), such as the translation look aside buffer (TLB) that is part of the memory management unit (MMU) that most CPUs have.

Caches are generally sized in powers of two: 4, 8, 16 etc. KiB or MiB(for larger non-L1) sizes, although the IBM z13has a 96 KiB L1 instruction cache.

Instruction Execution Cycle

• This is a process of getting the instruction from the memory, decoding it to the machine language and executing it. So, three basic steps of the cycle are:

Fetch the instruction.
Decode it.
Execute.

• The whole process of fetching the instructions from the memory, decoding it to the machine language and executing it, is termed as an instruction cycle.

PRIMARY MEMORY

The memory is that part of the computer where programs and data are stored. Some computer scientists (especially British ones) use the term store or storage rather than memory, although more and more, the term ‘‘storage’’ is used to refer to disk storage. Without a memory from which the processors can read and write information, there would be no stored-program digital computers.

Bits

The basic unit of memory is the binary digit, called a bit. A bit may contain a 0 or a 1. It is the simplest possible unit. (A device capable of storing only zeros could hardly form the basis of a memory system; at least two values are needed.) People often say that computers use binary arithmetic because it is ‘‘efficient.’’ What they mean (although they rarely realize it) is that digital information can be stored by distinguishing between different values of some continuous physical quantity, such as voltage or current. The more values that must be distinguished, the less separation between adjacent values, and the less reliable the memory. The binary number system requires only two values to be distinguished. Consequently, it is the most reliable method for encoding digital information.

Memory Addresses

In computing, a memory address is a reference to a specific memory location used at various levels by software and hardware. Memory addresses are fixed-length sequences of digits conventionally displayed and manipulated as unsigned integers.Such numerical semantic bases itself upon features of CPU (such as the instruction pointer and incremental address registers), as well upon the use of the memory like an array endorsed by various programming languages.

 

 

Microprocessor

The microprocessor is the central unit of a computer system that performs arithmetic and logic operations, which generally include adding, subtracting, transferring numbers from one area to another, and comparing two numbers. It's often known simply as a processor, a central processing unit, or as a logic chip. It's essentially the engine or the brain of the computer that goes into motion when the computer is switched on. It's a programmable, multipurpose device that incorporates the functions of a CPU (central processing unit) on a single IC (integrated circuit).

Working

A microprocessor accepts binary data as input, processes that data, and then provides output based on the instructions stored in the memory. The data is processed using the microprocessor's ALU (arithmetical and logical unit), control unit, and a register array. The register array processes the data via a number of registers that act as temporary fast access memory locations. The flow of instructions and data through the system is managed by the control unit.

Benefits of a Microprocessor

But computer systems aren't the only devices that use microprocessors. Everything from smartphones to household appliances to cars use microprocessors these days. Here are a few reasons why microprocessors are so widely used:

• They don't cost a lot - Due to their use of IC technology, microprocessors don't cost much to produce. This means that the use of microprocessors can greatly reduce the cost of the system it's used in.
  
  
• They are fast - The technology used to produce modern microprocessors has allowed them to operate at incredibly high speeds--today's microprocessors can execute millions of instructions per second.
  
  
• They consume little power - Power consumption is much lower than other types of processors since microprocessors are manufactured using metal oxide semiconductor technology. This makes devices equipped with microprocessors much more energy efficient.
  
  
• They are portable - Due to how small microprocessors are and that they don't consume a lot of power, devices using microprocessors can be designed to be portable (like smartphones).
  
  
• They are reliable - Because semiconductor technology is used in the production of microprocessors, their failure rate is extremely low.
  
  
• They are versatile - The same microprocessor chip can be used for numerous applications as long as the programming is changed, making it incredibly versatile.

Categories of Microprocessors

Microprocessors can be classified in different categories, as follows:.

Based on Word Length

Microprocessors can be based on the number of bits the processor's internal data bus or the number of bits that it can process at a time (which is known as the word length). Based on its word length, a microprocessor can be classified as 8-bit, 16-bit, 32-bit, and 64-bit.

 

Reduced Instruction Set Computer (RISC)

RISC microprocessors are more general use than those that have a more specific set of instructions. The execution of instructions in a processor requires a special circuit to load and process data. Because RISC microprocessors have fewer instructions, they have simpler circuits, which means they operate faster. Additionally, RISC microprocessors have more registers, use more RAM, and use a fixed number of clock cycles to execute one instruction.

 

Complex Instruction Set Computer

CISC microprocessors are the opposite of RISC microprocessors. Their purpose is to reduce the number of instructions for each program. The number of cycles per instruction is ignored. Because complex instructions are made directly into the hardware, CISC microprocessors are more complex and slower. CISC microprocessors use little RAM, have more transistors, have fewer registers, have numerous clock cycles for each instruction, and have a variety of addressing modes.

 

Special Purpose Processors

Some microprocessors are built to perform specific functions. For example, coprocessors are used in combination with a main processor, while a transputer is a transistor computer: a microprocessor that has its own local memory.

Evolution of Microprocessors

We can categorize the microprocessor according to the generations or according to the size of the microprocessor:

First Generation (4 - bit Microprocessors)

The first generation microprocessors were introduced in the year 1971-1972 by Intel Corporation. It was named Intel 4004 since it was a 4-bit processor.

It was a processor on a single chip. It could perform simple arithmetic and logical operations such as addition, subtraction, Boolean OR and Boolean AND.

I had a control unit capable of performing control functions like fetching an instruction from storage memory, decoding it, and then generating control pulses to execute it.

Second Generation (8 - bit Microprocessor)

The second generation microprocessors were introduced in 1973 again by Intel. It was a first 8 - bit microprocessor which could perform arithmetic and logic operations on 8-bit words. It was Intel 8008, and another improved version was Intel 8088.

Third Generation (16 - bit Microprocessor)

The third generation microprocessors, introduced in 1978 were represented by Intel's 8086, Zilog Z800 and 80286, which were 16 - bit processors with a performance like minicomputers.

Fourth Generation (32 - bit Microprocessors)

Several different companies introduced the 32-bit microprocessors, but the most popular one is the Intel 80386.

Fifth Generation (64 - bit Microprocessors)

From 1995 to now we are in the fifth generation. After 80856, Intel came out with a new processor namely Pentium processor followed by Pentium Pro CPU, which allows multiple CPUs in a single system to achieve multiprocessing.

Other improved 64-bit processors are Celeron, Dual, Quad, Octa Core processors.

Ports

It the connection point acts as interface between the computer and the external devices like: printer, modem, etc.

There are two types of ports :

1. Internal Port –

It connects the system’s motherboard to internal devices like hard-disk, CD drive, internal Bluetooth etc.

2. External Port –

It connects the system’s motherboard to internal devices like mouse, printer, USB etc.

Some important types of ports are as per follows :

1. Serial Port :  

• Used for external modems and older computer mouse
• Two versions-9pin,25pin
• Data travels at 115 kilobits per second

2. Parallel Port :          

• Used for scanners and printers
• 25 pin model

3. Universal Serial Bus (USB) Port :

• It can connect all kinds of external USB devices such as external hard disk, printer, scanner, mouse, keyboard, etc.
• Data travels at 12 megabits per seconds.

4. Firewire Port :

• Transfers large amount of data at very fast speed.
• Connects camcorders and video equipment to the computer.
• Data travels at 400 to 800 megabits per seconds.

5. Ethernet Port :

• Connects to a network and high speed Internet.
• Data travels at 10 megabits to 1000 megabits per seconds depending upon the network bandwidth.

Domain Specific Tools

Depending upon of its usages, the software may be classified as generic or specific. Generic software is a software that can perform multiple tasks in a different environment without being modified like a word processor software that can be used by anyone to make different types of documents as a report, whitepaper, training material, etc. Specific software is software for a particular application, like railway reservation system, weather forecasting, etc.

Some Domain Specific Tools :

1. School Management System : School management system handles various activities and processes of a school to facilitate campus management like examination, attendance, admission, student’s fees, timetable, teacher’s training, etc. It provides a healthy interaction among teachers, students, parents.

2. Inventory Management : Managing multiple tasks like purchase, sales, order, delivery, stock maintenance, etc. associated with raw or processed goods in any business is called inventory management. The inventory management software ensures that stocks are never below specified limits and purchase/deliveries are done in time. Inventory management system is very useful for forecasting, utilizing economies of scale and timing.

3. Payroll Management System : Payroll management system deals with the financial aspects of the employee’s salary, taking care of leaves, bonus, loans, etc. Some advantages of using this kind of management system are managed employee information efficiently, generate pay-slip at the convenience of a mouse click, manages its own security. Payroll software is generally a component of HR (Human Resource) management software in big organizations.

4. Financial Accounting : Financial management software keeps an electronic record of all financial transactions of the organization. Objectives of financial accounting

   • Record financial transactions as and when they occur so that the data can be analyzed for preparing a financial statement.

   • Calculate profit or loss, to enable management to take course-correction strategies if required.

   • Ascertain the financial strength of the company by determining its assets and liabilities.

   • Communicate the information to stakeholders through statements and reports, so that these stakeholders can take appropriate decisions on their investments in the business.

5. Hotel Management :Hotel management software helps hotel managers to keep track of inventory levels, daily orders, customer management, employee scheduling, table booking, etc.

6. Reservation System :A reservation system is a software that handles multiple modules like train routes, train management, seat booking, meal booking, train maintenance, train status, travel package, etc.

7. Weather Forecasting System : Weather forecasting system is a real-time software that predicts the weather of a place by collecting live data about atmospheric temperature, humidity, wind level, etc. It is used to predict major disasters like earthquakes, hurricanes, tsunamis, etc.

Secondary Memory

All secondary storage devices which are capable of storing high volume data is referred to secondary memory. It's slower than primary memory. However, it can save a substantial amount of data, in the range of gigabytes to terabytes. This memory is also called backup storage or mass storage media.

Types of Secondary memory

Mass storage devices:

The magnetic disk provides cheap storage and is used for both small and large computer systems.

Two types of magnetic disks are:

• Floppy disks
• Hard disks

Flash/SSD

Solid State Drive provides a persistent flash memory. It's very fast compared to Hard Drives. Frequently found in Mobile phones, its rapidly being adopted in PC/Laptop/Mac.

Optical drives:

This secondary storage device is from which data is read and written with the help of lasers. Optical disks can hold data up to 185TB.

Examples

• CD
• DVD
• Blue Ray

USB drives:

It is one of the most popular types of secondary storage device available in the market. USB drives are removable, rewritable and are physically very small. The capacity of USB drives is also increasing significantly as today 1TB pen drive is also available in the market.

Magnetic tape:

It is a serial access storage device which allows us to store a very high volume of data. Usually used for backups.

Characteristic Secondary Memory

• These are magnetic and optical memories
• Secondary memory is known as a backup memory
• It is a non-volatile type of memory
• Data is stored permanently even when the power of the computer is switched off
• It helps store data in a computer
• The machine can run without secondary memory
• Slower than primary memory

Primary Memory

Primary memory is computer memory that is accessed directly by the CPU.RAM, or random access memory, consists of one or more memory modules that temporarily store data while a computer is running.

Primary memory is also known as Main memory or Internal memory.

RAM is volatile memory, meaning it is erased when the power is turned off.

Characteristic of Primary Memory

• The computer can't run without primary memory
• It is known as the main memory.
• You can lose data in case power is switched off
• It is also known as volatile memory
• It is a working memory of the computer.
• Primary memory is faster compares to secondary memory.

Two Types of Primary Memory are:

• RAM
• ROM

RAM

The full form of RAM is Random Access Memory. The information stored in this type of memory is lost when the power supply to the PC or laptop is switched off. The information stored in RAM can be checked with the help of BIOS. It is generally known as the main memory or temporary memory or cache memory or volatile memory of the computer system.

Two main types of RAM are:

• Static RAM
• Dynamic RAM

Static RAM

Static RAM is the full form of SRAM. In this type of RAM, data is stored using the state of a six transistor memory cell. Static RAM is mostly used as a cache memory for the processor (CPU).

Dynamic RAM

DRAM stands for Dynamic Random Access Memory. It is a type of RAM which allows you to stores each bit of data in a separate capacitor within a specific integrated circuit. Dynamic RAM is a standard computer memory of the many modern desktop computers.

This type of RAM is a volatile memory that needs to be refreshed with voltage regularly. Else it loses the information stored on it.

Uses of RAM

Here, are important uses of RAM:

• RAM is utilized in the computer as a scratchpad, buffer, and main memory.
• It offers a fast operating speed.
• It is also popular for its compatibility
• It offers low power dissipation

ROM

ROM (read only memory) is a flash memory chip that contains a small amount of non-volatile memory. Non-volatile means that its contents cannot be changed and it retains its memory after the computer is turned off.

Types of ROM

PROM: Programmable ROM, or PROM, is essentially a blank version of ROM that you can purchase and program once with the help of a special tool called a programmer. A blank PROM chip allows current to run through all possible pathways; the programmer chooses a pathway for the current by sending a high voltage through the unwanted fuses to “burn” them out. Static electricity can create the same effect by accident, so PROMs are more vulnerable to damage than conventional ROMs.

EPROM: Erasable Programmable ROM chips allow you to write and rewrite them many times. These chips feature a quartz window through which a specialized EPROM programmer emits a specific frequency of ultraviolet light. This light burns out all the tiny charges in the EPROM to reopen its circuits. This exposure effectively renders the chip blank again, after which you can reprogram it according to the same process as a PROM. EPROM chips will eventually wear out, but they frequently have lifetimes of over 1000 erasures.

EEPROM: To modify an Electrically Erasable Programmable ROM chip, apply localized electrical fields to erase and rewrite the data. EEPROMs have several advantages over other types of ROM. Unlike the earlier forms, you can rewrite EEPROM without dedicated equipment, without removing it from the hardware, and in specifically designated increments. You don’t have to erase and rewrite everything to make a single edit.

Cache Memory

Cache memory is an extremely fast memory type that acts as a buffer between RAM and the CPU. It holds frequently requested data and instructions so that they are immediately available to the CPU when needed. Cache memory is used to reduce the average time to access data from the Main memory.

Register

A processor register is a quickly accessible location available to a computer's processor. Registers usually consist of a small amount of fast storage, although some registers have specific hardware functions, and may be read-only or write-only.

 

 

 

 

 

 

Software Concepts

A Computer is an electronic device that can perform various operations of computation at a greater speed than what an ordinary machine or human mind can do. It is driven by many entities including the physical and tangible components that we can touch or feel, called the Hardware and programs and commands that drive the hardware, called the Software.
The Software refers to the set of instructions fed in form of programs to govern the computer system and process the hardware components. For example:

• The antivirus that we use to protect our computer system is a type of Software.
• The media players that we use to play multimedia files such as movies, music etc. are Software.
• The Microsoft Office we use to edit the documents is a Software.

Depending on its use and area of implementation, Softwares can be divided into 3 major types:

1. System Software
2. Application Software
3. Utility Software

System Software

These are the software that directly allows the user to interact with the hardware components of a computer system. As the humans and machines follow different languages, there has to be an interface that will allow the users to interact with the core system, this interface is provided by the software. The system software can be called the main or the alpha software of a computer system as it handles the major portion of running a hardware. This System Software can be further divided into four major types:

1. The Operating System – It is the main program that governs and maintains the inter-cooperation of the components of a computer system. For eg., Microsoft Windows, Linux, Mac OS etc.
2. The Language Processor – The hardware components present in the computer system does not understand human language. There are three types of languages involved in the world of human-machine interaction:
   
    
   
   
   • Machine-Level Language: The machines only understand the digital signals or the binary codes or the binary language which consist of strings of 0’s and 1’s. These are totally machine dependent language.
   • Assembly-Level Language: These are the Low-Level Language(LLL), that forms a correspondence between machine level instruction and general assembly level statements. Assembly language uses a mnemonics to represent each low-level machine instruction or operation-code also called the op-codes. For eg., ADD instruction is used to add two entities, the HALT instruction is used to stop a process etc. It is a machine dependent language and varies from processor to processor.
   • High-Level Language: These are the simple English statements, that humans use to program and code as it is easy to read and understand to the human world. For eg., Java, C, C++, Python etc.

   The machine level language is very complex to understand and code, therefore the users prefer the High-Level Language or the HLL for coding. These codes need to be converted into the machine language so that the computer can easily understand and work accordingly. This operation is performed by the Language Processor which is made up of further three components:

   • Assembler: This language processor is used to convert the assembly language into machine level language.
   • Compiler: This language processor is used to convert High-Level Language into machine level language in one go, thus execution time is fast. The error detection is difficult in a compiler. Programming Languages like C, C++ and Scala use compiler.
   • Interpreter: This language processor is also used to convert High-Level Language into machine level language line-by-line, thus execution time is slow. Error-detection is easier in an interpreter as it reports as soon as a bug is caught and restarts the process. This consumes unnecessary memory. Programming Languages like Python, Ruby and Java uses an interpreter.
3. The Device Drivers – The device drivers and the device programs or the system software that acts as an interface between the various Input-Output device and the users or the operating system. For eg., the Printers, Web cameras come with a driver disk that is needed to be installed into the system to make the device run in the system.
4. The BIOS – It stands for Basic Input Output System and is a small firmware, that controls the peripheral or the input-output devices attached to the system. This software is also responsible for starting the OS or initiating the booting process.

Application Software

These are the basic software used to run to accomplish a particular action and task. These are the dedicated software, dedicated to performing simple and single tasks. For eg., a single software cannot serve to both the reservation system and banking system. These are divided into two types:

1. The General Purpose Application Software: These are the types of application software that comes in-built and ready to use, manufactured by some company or someone. For eg.,
   • Microsoft Excel – Used to prepare excel sheets.
   • VLC Media Player – Used to play audio/video files.
   • Adobe Photoshop – Used for designing and animation and many more.
2. The Specific Purpose Application Software: These are the type of software that is customizable and mostly used in real-time or business environment. For eg.,
   • Ticket Reservation System
   • Healthcare Management System
   • Hotel Management System
   • Payroll Management System

Utility Software

These are the most basic type of software which provides high utility to the user and the system. These perform the basic but daily need tasks. For eg.,

• Antivirus Softwares: These provide protection to the computer system from unwanted malware and viruses. For eg., QuickHeal, McAfee etc.
• Disk Defragmenter Tools: These help the users to analyse the bad sectors of the disk and rearrange the files in a proper order.
• Text-editors: These help the users to take regular notes and create basic text files. For eg., Notepad, Gedit etc.

Device Drivers

A device driver is a small piece of software that tells the operating system and other software how to communicate with a piece of hardware.

For example, printer drivers tell the operating system, and by extension whatever program you have the thing you want to print open in, exactly how to print information on the page

sound card drivers are necessary so your operating system knows exactly how to translate the 1s and 0s that comprise that MP3 File  into audio signals that the sound card can output to your headphones or speakers. 

The same general idea applies to video cards, keyboards, monitors, mice, disc drivers, etc.

Keep reading for more on why drivers are important, including some more examples, as well as information on how to keep your drivers updated and what to do if they're not working properly.

Working of Device Driver:
Device Drivers depend upon the Operating System’s instruction to access the device and performing any particular action. After the action they also shows their reactions by delivering output or status/message from hardware device to the Operating system.For Example a printer driver tells the printer in which format to print after getting instruction from OS, similarly A sound card driver is there due to which 1’s and 0’s data of MP3 file is converted to audio signals and you enjoy the music. Card reader, controller, modem, network card, sound card, printer, video card, USB devices, RAM, Speakers etc need Device Drivers to operate.