Embedded Files
How does a computer work?
How does a computer work?
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 term has been used in the computer industry 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.
2.1.1.pdf
The form, design and implementation of CPUs have changed over the course of their history, but their fundamental operation remains almost unchanged. Principal components of a CPU include the arithmetic logic unit (ALU) that performs arithmetic and logic operations, processor registers that supply operands to the ALU and store the results of ALU operations, and a control unit (CU) that fetches instructions from memory and "executes" them by directing the coordinated operations of the ALU, registers and other components.
Block diagram of a basic uniprocessor-CPU computer. Black lines indicate data flow, whereas red lines indicate control flow; arrows indicate flow directions.
Click here to check out the little man computer
Most modern CPUs are microprocessors, meaning they are contained on a single integrated circuit (IC) chip. An IC that contains a CPU may also contain memory, peripheral interfaces, and other components of a computer; such integrated devices are variously called microcontrollers or systems on a chip (SoC). Some computers employ a multi-core processor, which is a single chip containing two or more CPUs called "cores"; in that context, single chips are sometimes referred to as "sockets". Array processors or vector processors have multiple processors that operate in parallel, with no unit considered central.
Work through this website to learn more about the CPU and memory
Primary memory and cache
Primary memory and cache
Computer data storage, often called storage or memory, is a technology consisting of computer components and recording media used to retain digital data. It is a core function and fundamental component of computers.
The central processing unit (CPU) of a computer is what manipulates data by performing computations. In practice, almost all computers use a storage hierarchy, which puts fast but expensive and small storage options close to the CPU and slower but larger and cheaper options farther away. Often the fast volatile technologies (which lose data when powered off) are referred to as "memory", while slower persistent technologies are referred to as "storage"; however, "memory" is sometimes also used when referring to persistent storage.
In the Von Neumann architecture, the CPU consists of two main parts: control unit and arithmetic logic unit (ALU). The former controls the flow of data between the CPU and memory, while the latter performs arithmetic and logical operations on data.
Generally, the lower a storage is in the hierarchy, the lesser its bandwidth and the greater its access latency is from the CPU. This traditional division of storage to primary, secondary, tertiary and off-line storage is also guided by cost per bit.
A CPU cache is a cache used by the central processing unit (CPU) of a computer to reduce the average time to access data from the main memory. The cache is a smaller, faster memory 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 organised as a hierarchy of more cache levels (L1, L2, etc.).
2.1.2.pdf2.1.3.pdfExplain the machine instruction cycle
Explain the machine instruction cycle
An instruction cycle (sometimes called fetch-decode-execute cycle) is the basic operation cycle of a computer, taking place in a defined time period, during which one instruction is fetched from memory and executed. It typically consists of four stages: Fetch, Decode, Execute, and Store.
In simpler CPUs, the instruction cycle is executed sequentially: each instruction is completely processed before the next one is started. In most modern CPUs, the instruction cycle is instead executed concurrently in parallel, as an instruction pipeline: the next instruction starts being processed before the previous instruction is finished, which is possible because the cycle is broken up into separate steps.
Each computer's CPU can have different cycles based on different instruction sets, but will be similar to the following cycle:
Fetching the instruction: The next instruction is fetched from the memory address that is currently stored in the program counter (PC), and stored in the instruction register (IR). At the end of the fetch operation, the PC points to the next instruction that will be read at the next cycle.
Decode the instruction: During this cycle the encoded instruction present in the IR (instruction register) is interpreted by the decoder.
Read the effective address: In case of a memory instruction (direct or indirect) the execution phase will be in the next clock pulse. If the instruction has an indirect address, the effective address is read from main memory, and any required data is fetched from main memory to be processed and then placed into data registers (Clock Pulse: T3). If the instruction is direct, nothing is done at this clock pulse. If this is an I/O instruction or a Register instruction, the operation is performed (executed) at clock Pulse.
Execute the instruction: The control unit of the CPU passes the decoded information as a sequence of control signals to the relevant function units of the CPU to perform the actions required by the instruction such as reading values from registers, passing them to the ALU to perform mathematical or logic functions on them, and writing the result back to a register. If the ALU is unvolved, it sends a condition signal back to the CU. The result generated by the operation is stored in the main memory, or sent to an output device. Based on the condition of any feedback from the ALU, Program Counter may be updated to a different address from which the next instruction will be fetched.
The cycle is then repeated.
2.1.4.pdfThe need for persistent storage
The need for persistent storage
Persistent storage is when you save a file and it's still there when turn your computer back on
Primary memory contains a ROM and a RAM chips. A ROM chip can only store pre-programmed sets of instructions. A RAM chip is volatile and loses everything that is stored in it when the computer is turned off.
What happens when we want to store something long-term , such as photographs, movies and documents?
Secondary storage
Secondary storage
Secondary storage is a form of memory that we can change and is not volatile. It is an additional storage facility that is added to a computer to store data and programs when the power is turned off.
Secondary storage (also known as external memory or auxiliary storage), differs from primary storage in that it is not directly accessible by the CPU. The computer usually uses its input/output channels to access secondary storage and transfers the desired data using intermediate area in primary storage. Secondary storage does not lose the data when the device is powered down—it is non-volatile. Per unit, it is typically also two orders of magnitude less expensive than primary storage. Modern computer systems typically have two orders of magnitude more secondary storage than primary storage and data are kept for a longer time there.
2.1.5.pdfIn modern computers, hard disk drives are usually used as secondary storage. The time taken to access a given byte of information stored on a hard disk is typically a few thousandths of a second, or milliseconds. By contrast, the time taken to access a given byte of information stored in random-access memory is measured in billionths of a second, or nanoseconds. This illustrates the significant access-time difference which distinguishes solid-state memory from rotating magnetic storage devices: hard disks are typically about a million times slower than memory. Rotating optical storage devices, such as CD and DVD drives, have even longer access times. With disk drives, once the disk read/write head reaches the proper placement and the data of interest rotates under it, subsequent data on the track are very fast to access. To reduce the seek time and rotational latency, data are transferred to and from disks in large contiguous blocks.
Some other examples of secondary storage technologies are flash memory (e.g. USB flash drives or keys), floppy disks, magnetic tape, paper tape, punched cards, standalone RAM disks, and Iomega Zip drives.
The secondary storage is often formatted according to a file system format, which provides the abstraction necessary to organise data into files and directories, providing also additional information (called metadata) describing the owner of a certain file, the access time, the access permissions, and other information.
Most computer operating systems use the concept of virtual memory, allowing utilisation of more primary storage capacity than is physically available in the system. As the primary memory fills up, the system moves the least-used chunks (pages) to secondary storage devices (to a swap file or page file), retrieving them later when they are needed. As more of these retrievals from slower secondary storage are necessary, the more the overall system performance is degraded.
Tertiary storage
Tertiary storage
Tertiary storage or tertiary memory provides a third level of storage. Typically, it involves a robotic mechanism which will mount (insert) and dismount removable mass storage media into a storage device according to the system's demands; this data is often copied to secondary storage before use. It is primarily used for archiving rarely accessed information since it is much slower than secondary storage (e.g. 5–60 seconds vs. 1–10 milliseconds). This is primarily useful for extraordinarily large data stores, accessed without human operators. Typical examples include tape libraries and optical jukeboxes.
When a computer needs to read information from the tertiary storage, it will first consult a catalog database to determine which tape or disc contains the information. Next, the computer will instruct a robotic arm to fetch the medium and place it in a drive. When the computer has finished reading the information, the robotic arm will return the medium to its place in the library.
Tertiary storage is also known as nearline storage because it is "near to online". The formal distinction between online, nearline, and offline storage is:
Online storage is immediately available for I/O.
Nearline storage is not immediately available, but can be made online quickly without human intervention.
Offline storage is not immediately available, and requires some human intervention to become online.
For example, always-on spinning hard disk drives are online storage, while spinning drives that spin down automatically, such as in massive arrays of idle disks (MAID), are nearline storage. Removable media such as tape cartridges that can be automatically loaded, as in tape libraries, are nearline storage, while tape cartridges that must be manually loaded are offline storage.
Cloud storage is a model of data storage in which the digital data is stored in logical pools, the physical storage spans multiple servers (and often locations), and the physical environment is typically owned and managed by a hosting company. These cloud storage providers are responsible for keeping the data available and accessible, and the physical environment protected and running. People and organisations buy or lease storage capacity from the providers to store user, organisation, or application data.
Cloud storage services may be accessed through a co-located cloud computer service, a web service application programming interface (API) or by applications that utilize the API, such as cloud desktop storage, a cloud storage gateway or Web-based content management systems.
A large tape library, with tape cartridges placed on shelves in the front, and a robotic arm moving in the back. Visible height of the library is about 180 cm.
Off-line storage
Off-line storage
Off-line storage is a computer data storage on a medium or a device that is not under the control of a processing unit. The medium is recorded, usually in a secondary or tertiary storage device, and then physically removed or disconnected. It must be inserted or connected by a human operator before a computer can access it again. Unlike tertiary storage, it cannot be accessed without human interaction.
Off-line storage is used to transfer information, since the detached medium can be easily physically transported. Additionally, in case a disaster, for example a fire, destroys the original data, a medium in a remote location will probably be unaffected, enabling disaster recovery. Off-line storage increases general information security, since it is physically inaccessible from a computer, and data confidentiality or integrity cannot be affected by computer-based attack techniques. Also, if the information stored for archival purposes is rarely accessed, off-line storage is less expensive than tertiary storage.
In modern personal computers, most secondary and tertiary storage media are also used for off-line storage. Optical discs and flash memory devices are most popular, and to much lesser extent removable hard disk drives. In enterprise uses, magnetic tape is predominant. Older examples are floppy disks, Zip disks, or punched cards.
Practice question:
Practice question:
State some differences between primary and secondary memory
The functions of an operating system
The functions of an operating system
2.1.6.pdfAn operating system is a group of computer programs that coordinates all the activities among computer hardware devices. It is the first program loaded into the computer by a boot program and remains in memory at all times.
Functions of an operating system
The basic functions of an operating system are:
Booting the computer
Performs basic computer tasks eg managing the various peripheral devices eg mouse, keyboard
Provides a user interface, e.g. command line, graphical user interface (GUI)
Handles system resources such as computer's memory and sharing of the central processing unit (CPU) time by various applications or peripheral devices
Provides file management which refers to the way that the operating system manipulates, stores, retrieves and saves data.
Booting the computer
The process of starting or restarting the computer is known as booting. A cold boot is when you turn on a computer that has been turned off completely. A warm boot is the process of using the operating system to restart the computer.
Performs basic computer tasks
The operating system performs basic computer tasks, such as managing the various peripheral devices such as the mouse, keyboard and printers. For example, most operating systems now are plug and play which means a device such as a printer will automatically be detected and configured without any user intervention.
Provides a user interface
A user interacts with software through the user interface. The two main types of user interfaces are: command line and a graphical user interface (GUI).
With a command line interface, the user interacts with the operating system by typing commands to perform specific tasks. An example of a command line interface is DOS (disk operating system).
The operating system is responsible for providing a consistent application program interface (API) which is important as it allows a software developer to write an application on one computer and know that it will run on another computer of the same type even if the amount of memory or amount of storage is different on the two machines.
Handles system resources
The operating system also handles system resources such as the computer's memory and sharing of the central processing unit (CPU) time by various applications or peripheral devices. Programs and input methods are constantly competing for the attention of the CPU and demand memory, storage and input/output bandwidth. The operating system ensures that each application gets the necessary resources it needs in order to maximise the functionality of the overall system.
Provides file management
The operating system also handles the organisation and tracking of files and directories (folders) saved or retrieved from a computer disk. The file management system allows the user to perform such tasks as creating files and directories, renaming files, coping and moving files, and deleting files. The operating system keeps track of where files are located on the hard drive through the type of file system.
Click here for some more information about operating systems
Practice question:
Practice question:
Outline how the operating system ensures that files are only accessed by the users allowed.
Software applications
Software applications
Applications come in several different types:
Utility programs - examples include virus scanners, disk defragmenters and backup utilities.
Generic - general purpose software that is not written for any particular type of business. Examples of this include word processors and spreadsheets.
Integrated - a collection of software that has a common set of commands/icons. Usually they include word processors, spreadsheets and graphics software, but they can contain databases as well. They tend to be cheaper than purchasing each application separately.
Specific - software written for a defined purpose. Accountancy software is a good example of this that can be bought by anyone.
Bespoke - bespoke software is written when a company requires a piece of software to perform a very specific task or function and there's no existing software that does what they need. It can be very expensive.
2.1.7.pdfPractice question:
Practice question:
State some differences between a Spreadsheet software application and a Database Management System
Common features of applications
Common features of applications
2.1.8.pdfCommon features of applications are:
Toolbars - a toolbar is a GUI widget containing icons, menus, buttons and/or text. Toolbars are seen in many types of software such as browsers and graphic manipulation software.
Menu - a menu is essentially a list of options presented to a computer user. The choices presented may be selected in a number of ways such as rolling over a mouse cursor, clicking a mouse button, pressing on a touch screen etc.
Dialogue boxes - in a GUI the dialogue box is a window that allows the user to interact. It may be in the form of an alert, to provide information or to request the user to make a choice.
GUI components - "GUIs use a consistent visual language to represent information in computers.". This is generally conveyed by the acronym WIMP: windows, icons, menus and pointing devices.
Binary and Hexadecimal representation of data
Binary and Hexadecimal representation of data
2.1.9.pdfFor some additional information about this topic click on this link
Two's complement - representing negative numbers
Two's complement - representing negative numbers
It's possible to represent negative numbers in binary using the two's compliment method. Check out the video below for an explanation of how this works:
Now try out these two games to test your skill! Binary Game, Hexadecimal Game
Can you write a python program to convert from denary to binary?
Think about the steps involved:
Input a number
as long as it is greater than 1 divide it by 2
print the remainder
We could use the following python operators to do this:
// - whole number division and % - remainder division
Now try to create your own recursive program to convert denary numbers to binary
Data representation
Data representation
Data representation.pptxSimple logic gates
Simple logic gates
2.1.12.pdfPage updated
Report abuse