3.3.2. Organization of a Computer System

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Organizations exchange data between different devices digital computer system (DCS) is based on the parallel data transfer, so each bit by its 'wire' in a set of power lines to transmit a signal called BUS, according to the scheme in the following Figure.

 Block-scheme of Computer
Figure 3.3.5 Organization of 8 bit computer system.

The principle of operation is as follows: Microprocessor based on an order from the keyboard is loaded from disk (external unit) over the data bus required program, i.e. over control (controller) plugged into one of the slots (u1 - u4) is connected to the bus, by order dedicated disk controller via the control bus. The program is loaded from disk byte by byte. When it comes to the first byte of the data bus, he is present at the entrance to all of the devices 'hooked' on the bus.

Over the microprocessor address bus determines the place to be in working memory write each byte of the program. Via control bus gives order to facilitate the passage of the working memory and the data bus with data transfer into the working memory. Upon enrollment data microprocessor disables access to working memory. Then gives the order to the disk (or from cache memory disk) took second byte and repeats the process with the other data and be sure that no other information is stored at the previous location, and so on until all the data is not transferred into the working memory.

During operation, the microprocessor monitors that are in your memory free to accept new data. By the same principle to accept data from the keyboard or from another device via the I / O channel or device connected through the 'slot'. Of course, the data from ROM are always available microprocessor that part of the memory can not be written.

The whole process of transferring bytes takes place at high speed toward the microprocessor clock which receives the clock generator. Each clock (pulse from the generator) is a warrant for the execution of the following actions. Clearly, the faster the clock speed, or if the microprocessor clock pulses received more in one second sequences quickly. The number of pulses from the clock generator in one second (unit of measurement called Hertz - Hz) is the operating frequency of the computer. Multiplying and dividing the result is the same operating frequency at which work CORE microprocessor, cache memory, working memory, buses, and other assemblies. Usually today under operating frequency involves working computer microprocessor core frequency, which joins the description FSB (Front Side Bus) that describes the operating frequency of the external bus microprocessors.

Operating frequency is dependent on the quality of the microprocessor, RAM, and other components of the computer connected to the bus, and their ability to quickly receive the information and can not be greater than the speed of the slowest component in the system. Typically ranges from 4 MHz to 1000 MHz and higher. 4'000'000 simplistic to 1000'000'000 tasks in one second. Generation process since 2006th year of computational tasks performed with operating frequencies up to 4 GHz. Memory systems still can not keep such a high speed and work with multiple smaller working frequencies.

All three form a bus system bus. What is the number of bus conductor greater the greater the speed of the system, since it simultaneously transmit multiple bits. Intel's 8086 processor works with the data bus of eight bits (as in Figure 3.3.5), with 80386 data bus of 32 bits, a Pentium with a data bus of 64 bits.

New versions of PCs have two bus systems, one with fewer lines for the slower and simpler devices like a printer, mouse, etc., and the other with multiple lines for direct connection of processors with memory, video card, disk controller and devices that require fast communications. So, tact of slow and fast bus is not the same. Newer processors for internal tasks using multiple clock faster than the bus clock.

Thus, the components in the computer are working on at least three different operating frequencies, depending on which type of bus is associated. How motherboards can support multiple types of microprocessors, the jumper is determined tact individual components so that they match each other in terms of speed work, or in modern motherboards described relations adjust the settings in the BIOS, or the BIOS automatically adjusts all by combining with program support.

Example II

In the PC world, we often encounter the buses called:

      ISA (Industry Standard Architecture) - 16 bit bus.
      EISA (Enhanced Industry Standard Architecture) - 32 bit bus
      MCA (Micro Channel Architecture) - versions of 16 and 32 bit bus.
      VLB (VESA Local Bus) - versions of 32 bit bus.
      PCI (Peripheral Component Interconnection) - 32 bit bus.
      AGP (Accelerated Graphics Port 1x-8x) - 32 or bit bus.
      PCI-X (faster and improved PCI standard) - 32 or 64 bit bus.
      PCI-Express (x1-x32) - bus 'width' 8 bits of x-'lane'.

ISA bus is often referred to as the AT-bus to the computer name in which it was first implemented, the IBM AT - Advanced Technology PC conceived the family microprocessor INTEL 80286th Number of bits bus refers to the data bus. Data transfer rate (bandwidth) is not the same for all of these and the usual bus bandwidth for each of the list is 8 MB/s, 32 MB/s, 64 MB/s, 132 MB/s and 524 MB/s and up to PCI-X PCI-Express.

Previously known concepts, conceived on a special bus for graphics memory, until recently the standard in the PC world - AGP port. These have a connection with the processor clocked at more than the PCI bus in the case of its lack of graphics memory controller can serve resource 'classic' memory. In this way, considerably accelerating graphics applications written specifically for this type of computer. AGP port and PCI bus are promoted several times but not compatible, so you can find AGP 2x, AGP 4x and more. In essence, the AGP is not a bus, only serving a graphics card, hence the name 'port'.

Significantly improved PCI bus is a PCI-Express bus that is designed to transfer data over high speed serial channels (lanes) which are combined in a group of up to 32 channels (lanes), this means that the physical size of the slots for different devices. Standard allows devices to be designed for the x1 slot can be inserted in the x32 slot. No need for the AGP port, which served only to support graphics, and as the PCI-Express bus can essentially support multiple graphics devices. In addition to the above rate at one corridor was significantly increased compared to the standard PCI bus. Inside lane transmission is standard with significantly improved system synchronization and management and hence higher speed data transfer with fewer physical lines per corridor. When the PCI-Express (PCI-E) bus lane is used more for data transfer is performed parallel transfer data sets, as in the classic bus, which means that data has elements parallel and serial communications. All of the newer types of buses, not only in computers but also for network devices using this mechanism for transferring data.


As newer microprocessors operate at several times higher frequencies of the options bus computer system, a special controller for the bus as part of chipset, takes care of the data transfer between external microprocessor bus (FSB) and other devices to computers connected to the bus system. It is therefore necessary that the faster processors in addition to its junction with 'cache', auxiliary fast memory, for internal use, and during one clock bus system performs several internal actions microprocessors. What is a 'cache' greater processor efficiency is higher because more things can be prepared. The basic purpose is to reduce the average access time in RAM. According to the site in a system with three different types of 'cache' by:

Different types of bus is used to communicate to the working memory, hard disk and optical devices as well as to the processor. The traffic through the entire system and synchronizing speed rail cares a special group of several electronic circuits ICs - Chipset. About the effectiveness of a computer trying to basically achieve the operating frequency RAM as close to the FSB frequency. As the demands on the issue of liability chipset is growing steadily, and these components 'progressed' to the fact that consumers have become quite large and quite heated, and often have a passive radiator on the chassis. But more about that in the description of a PC (Chapter 3.5).


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