hardwhere

hardwhere

1. in the CPU are

   • Memory Unit
     • The Memory Unit, often referred to as main memory, primary memory, central memory, core memory, is the location where quick and easily accessible information can be read from and written to by the Control Unit.
     • Access to and from main memory is very fast.
     • At any one time it will normally contain: 1) The Operating System (or part that is currently in use) 2) The software currently in use 3) The data which the software is using.
     • The memory is volatile, and when something held inside it is not being used it must be lost or written back to slower storage devices such as the hard drive.
   • Arithmetic Logic Unit (ALU)
     • Arithmetic operations
       • (addition, subtractions, multiplication, division)
     • Logical operations
       • (comparing one data item to another, is it smaller, greater, equal to)
     • Acts as a conduit through which all I/O to computer is done
       • (Gateway to the processor)
   • in the Control Unit this happends
     • FETCH
       • causes the next instruction to be fetched from main memory
     • DECODE
       • produces signals which control the other parts of the computer such as the ALU.
     • EXECUTE
       • causes the instruction to be executed.

2. ·

   • We already know that the CPU is made up of the ALU, Control Unit and the Memory Unit.
     • In addition, the CPU contains circuitry controlling the interpretation and execution instructions.
       • Special storage locations called registers are included in this circuitry to hold information temporarily.
         • Registers: An extremely fast piece of on-chip memory, usually 32 or 64 bits in size for temporary storage of a binary value.

3. some more rejsters

   • Program Counter
     • Holds the address of the next instruction to be executed. It is also known as the sequence control register (SCR) or the sequence register.
   • Memory Address Register
     • Holds the position / address in memory of the location containing either: The next piece of data to be read or The next instruction to be used
   • Memory Data Register
     • The contents of the address specified in the MAR are copied to the MDR. This may be either: An instruction / operation or The data to be used (with an instruction) or Data to be copied to an address Both the MDR and the MAR serve as ‘buffer’ registers to compensate for the difference in speed between the CPU and memory.
       • Communication Facility
         • For a big company spanning over different parts of the country the employees can save long distance phone calls and it overcomes the time lag in overseas communications. Computer conferencing is another use of WAN where users communicate with each other through their computer system.
       • Remote Data Entry
         • Remote data entry is possible in WAN. It means sitting at any location you can enter data, update data and query other information of any computer attached to the WAN but located in other cities. For example, suppose you are sitting at Madras and want to see some data of a computer located at Delhi, you can do it through a WAN.
       • Centralised Information
         • In modern computerised environment you will find that big organisations go for centralised data storage. This means if the organisation is spread over many cities, they keep their important business data in a single place. As the data are generated at different sites, WAN permits collection of this data from different sites and save at a single site.
       • For a computer to access a WAN e.g. the Internet we need certain specialised software: Browser, FTP clients, Protocols
         • Serial data transmission: sends the bits for a character, one after another, along the same data line.
           • Parallel data transmission: sends the bits for a character simultaneously along separate lines.
             • Baseband: Single stream of data using the whole bandwidth.
               • The number of bits that are transferred between devices in a specified amount of time.
             • Broadband: Several signals sent simultaneously where the bandwidth is shared.
               • These types of files / transmission are said to be “Time sensitive” because they lose their value in a particular time period.

4. some more rejisters

   • Current Instruction Register
     • Holds the instruction while it is being decoded/executed. The contents of the MDR are copied to the CIR if it is an instruction. Contains the operator and the operand of the current instruction. For example, a machine language instruction to load the contents of location 1000 into the accumulator might be written LDA 1000
   • Accumulator
     • The accumulator or “General Purpose Registers” as they are often called are used for performing arithmetic functions. Computers have between 1-16 of these, and they act as a working area.
   • Status Register
     • Contains “status” bits or flags that are set or cleared based on the result of an instruction. For example, one particular bit will be set If overflow occurs, and another bit set if the result of the last instruction was negative.
       • Repeaters, Switch & Hubs
         • The media of any network has limitations on the distance a signal will travel before it deteriorates to an undecipherable level.
           • Repeaters can be used to make the signal travel further by amplifying the signal. However, these devices also repeat noise on the line.
             • Topologies that include devices to regenerate rather than repeat the original signal avoid these problems. Network cards in ring networks do this, as do switches and routers.

5. buses

   • • communicates the physical addresses of computer memory elements/locations that the requesting device wants to access (read/write).
     • The width of an address bus determines how much memory can be accessed. For example, a 16-bit wide address bus reaches across 216 = 65,536 (64k) memory locations, whereas a 32-bit address can address 232 = 4,294,967,296 (4Gb) locations.
   • Local Area Networks (LAN)
     • a method of connecting computers together in a small geographical area, for example confined to one building or site.
     • Computers and peripheral devices are linked via a direct physical connection (cabal) or a wireless connection. A LAN can be connected to other LANs, or to a WAN.
     • To communicate on a network a computer needs a network NIC. The card converts data from the computer into a form that can be transmitted over the network and converts data received from the network into a form for the computer.
     • Actions which are taken by the O.S without the user being aware of them. If the network is transparent then the user is unaware of being on a network terminal believing it to be a P.C.
     • WAN: connects geographically remote computers or networks, for example computers in different sites, towns or continents.

6. Device Connectivity

   • Device can be connected to a computer either by physical wiring “hard wire” (physical) or by some kind of remote connection “wireless” (non-physical).
     • Can be measured in the rate at which data can be transmitted along the medium: the bits per second or baud rate.
     • Data rate can be increased by using higher quality cable with less attenuation or sending more than one signal at a time or increasing the frequency at which data is sent.
     • Copper has a low bandwidth, wireless higher bandwidth and fibre very high bandwidth. High frequencies attenuate more quickly which reduces the number of frequencies that can be used with copper.
     • Each signal can be sent on a different frequency or wavelength. The number of frequencies that can be used before they interfere with each other is known as the bandwidth.
       • more about hardwhere
         • Judgements have to be made whether a device should be hard wired or wirelessly connected. Factors for consideration include : Cost, distance, response speed, space availability, accessibility Arrange the following methods of connection into the appropriate category.
         • Random Access Memory (RAM)
           • Ordinary kind of memory, used for storing programs which are currently running and data which is currently being processed. This type of memory is volatile
         • Read Only Memory (ROM)
           • Non-volatile memory, its contents are permanently etched into the memory chip at the manufacturing stage.
         • Magnetic
           • Data recorded onto magnetic disks. Mechanical parts move over the disks surface to read and write data.
         • Optical
           • Data is recorded onto optical disks. Lasers read and write data. Highly portable.
         • Solid State
           • Data is recorded onto solid state memory chips. Very durable and fast, no mechanical moving parts needed.
         • Transfer of data
           • The process is slightly more complex however, two further areas to understand in the transfer of data include Interrupts and Buffers.
         • Interrupt
           • a signal from some device or source seeking the attention of the processor.
         • Buffers
           • Buffers are extensively used in computer systems to help match the speeds of many devices.
           • Buffers or “cache” are often used between the high processing speeds of the CPU (processor) and the much slower speeds of main memory, of the even slower speeds of devices such as the hard disk.
           • In this way a block of data can be written to a buffer as though it were being written to main memory or disk. The high speed processor can then carry on with the next operation while the main memory or disk data is read from the buffer at a much slower rate.
         • Data transfer between RAM and other devices (Buffers)
           • Data needs to be transferred from the hard disk to the memory so it can be used by the processor.
           • Data needs to be transferred from the memory to the hard disk so it is not lost when the power is turned off.
           • The problem is that the devices operate at very different speeds. The hard drive cannot write data to the disk as quickly as the memory can send it.
           • The solution is to use a buffer. A small piece of memory that can be filled with data from the main memory. The hard drive can then take data from the buffer when it is ready.
           • When the buffer is nearly empty the hard disk controller sends an interrupt on the control bus to tell the processor to fill the buffer up again.
           • You don’t want the hard disk to have to stop writing data because it is a very slow component. Buffers allow all devices to work at their maximum speed.

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