總線(xiàn)介紹 part1

System Bus Types, Functions, and FeaturesThe heart of any motherboard is the various signal pathways or buses that carry signals between the components. A [url=mkMSITStore:G:\emule下載書(shū)_1\E-Book_OK\Upgrading%20and%20Repairing%20Computers\Upgrading%20and%20Repairing%20Laptop%20Computers.chm::/0789728001_app02.html#app02gloss01entry198]bus[/url] is a common pathway across which data can travel within a computer. This pathway is used for communication and can be established between two or more computer elements.
The PC has a hierarchy of different buses. Most modern PCs have at least three main buses; some have four or more. They are hierarchical because each slower bus is connected to the faster one above it. Each device in the system is connected to one of the buses, and some devices (primarily the chipset) act as bridges between the various buses.
The main buses in a modern system are as follows:

• Processor bus. Also called the front-side bus (FSB), this is the highest-speed bus in the system and is at the core of the chipset and motherboard. This bus is used primarily by the processor to pass information to and from cache or main memory and the North Bridge of the chipset. The processor bus in a modern system runs at 66, 100, 133, 200, 266, 400, 533, or 800MHz and is normally 64 bits (8 bytes) wide.
• AGP bus. This is a high-speed 32-bit bus specifically for a video card. It runs at 66MHz (AGP 1x), 133MHz (AGP 2x), 266MHz (AGP 4x), or 533MHz (AGP 8x), which allows for a bandwidth of up to 2,133MBps. In laptop systems, the AGP interface is onboard, meaning that there is no slot; instead, it is a direct connection between the North Bridge or memory controller hub of the chipset and the video chipset.
• PCI bus. This bus, as it originally appeared in newer 486 and all Pentium class systems, is usually a 33MHz 32-bit bus. This bus is generated by either the chipset North Bridge in North/South Bridge chipsets or the I/O controller hub in chipsets using hub architecture. Although this bus is manifested in a desktop system as a collection of 32-bit slots, normally white and numbering from four to six on most motherboards, laptops normally have a single Mini PCI slot. This Mini PCI slot is the same as the standard PCI, except for a different connector and smaller physical form factor. Additionally, the CardBus slots in most laptops are a specialized variation of PCI, which can accept credit card–size adapters. High-speed peripherals, such as SCSI adapters, network cards, video cards, and more, can be plugged into laptop Mini PCI or CardBus slots.
• LPC bus. The low-pin-count bus is a 33MHz 4-bit bus that has a maximum bandwidth of 16.67MBps; it was designed as an economical onboard replacement for the obsolete ISA bus. In systems that use LPC, it typically is used to connect Super I/O chip or motherboard ROM BIOS components to the main chipset. LPC is faster than ISA and yet uses far fewer pins and enables ISA to be eliminated from the board entirely.
  

Some newer laptop motherboards feature a special MDC (mobile daughter card) connector, which provides an interface for modem, audio, and networking solutions based upon the AC'97 (audio coder/decoder) interface. Some laptop manufacturers refer to MDC cards and sockets as communications daughter card (CDC) cards and sockets, although they are the same thing. The MDC connector provides a low-cost, small form factor module suitable for mobile systems. This is a dedicated connector for cards that are specific to the system or motherboard design to offer communications and networking options. They are not designed to be general-purpose bus interfaces, and cards for these connectors are not sold on the open market. Usually, they're offered only as a preinstalled option with a given system. They are designed so that a system manufacturer can easily offer configurations with and without various communications options, without having to reserve space on the motherboard for optional chips.
For example, I recently purchased a laptop in which I wanted to integrate every type of wireless networking possible, including tri-mode 802.11a/b/g as well as Bluetooth. Unfortunately, the manufacturer did not offer a system that incorporated all of these devices, although various models included one or the other. Rather than add external CardBus devices, which would be unwieldy and use up all of the available slots, I purchased an internal 802.11a/b/g Mini PCI card and a combination Modem/Bluetooth Mobile Daughter Card (MDC) and installed them myself. Because such cards are not normally sold retail, I merely ordered them as if they were repair parts for the various models that incorporated them and installed them myself. The particular laptop in question (an IBM R40) already had integrated WiFi antennas, so all I needed for the ultimate WiFi solution was the $99 Mini PCI 802.11a/b/g card. My particular system did not include an internal Bluetooth antenna, although one could be ordered and installed as a repair part. So, I ordered a Modem/Bluetooth MDC module for $37 and an internal Bluetooth antenna for $8, and installed them in a matter of minutes. Because of the standardization available with Mini PCI and MDC, it's possible to upgrade many other laptops in a similar manner. Now I have all of these communications devices internally mounted, and the CardBus socket remains free for other uses.
For the most part, modem, sound, and Bluetooth cards are implemented via MDC modules, while higher-speed WiFi wireless networking options are normally installed via Mini PCI cards. Mini PCI cards are available that support the 802.11a, 802.11b, or 802.11g standards individually, or in combo cards supporting 802.11a/b/g all in one.
The system chipset is the conductor that controls the orchestra of system components, enabling each to have its turn on its respective buses. [url=mkMSITStore:G:\emule下載書(shū)_1\E-Book_OK\Upgrading%20and%20Repairing%20Computers\Upgrading%20and%20Repairing%20Laptop%20Computers.chm::/0789728001_ch05lev1sec2.html#ch05table01]Table 5.1[/url] shows the widths, speeds, data cycles, and overall bandwidth of virtually all PC buses.

搞笑呢
英文的怎么 看的懂

誰(shuí)看得懂
告訴一聲