View Full Version : SYSTEM BUS ?'s
09-21-2001, 06:46 PM
I'm working on A+ right now, and have a question about "system bus".
My online training states that system bus consists of external and expansion. External includes address, data and control, whereas expansion includes ISA, EISA, PCI, AGP etc. But my book reading (SYBEX) states "the most common type of external bus- is the expansion bus." So one source tells me that external and expansion are different and one says they're the same. Then I look it up here at PC Guide, and it tells me that there is processor bus, local bus, FSB etc. Is there a common ground or standard as to how system bus is broken down? Maybe I'm missing something here. Any help would be greatly appreciated. Thank you.
09-22-2001, 01:25 AM
Here's a couple of sites for you to help clear this up-be warned they're pretty detailed!
CPU Buses (http://www.cit.ac.nz/smac/hf100/hf100m4.htm)
CPU structure and function (http://www.latech.edu/~choi/Bens/Teaching/Csc364/Slides/BzCH11_files/frame.htm)
Hmm, i far as i've always known, the address, data and control bus were internal while the expansion bus( which contains the I/O devices ) is the external bus-so it could be called either the external or expansion bus.
There is of course a bit more detail than that to the way a PC communicates among itself-it can be frustrating trying to explain this to someone especially with out visual aids.
not too mention kinda hard to grasp yourself sometimes! http://www.PCGuide.com/ubb/tongue.gif
The PC guide covers it quite well i always thought, and here is another site that offers some in depth explanantion and history on the different bus types, System Buses (http://www.csn.ul.ie/~stephen/buses.html).
"640K ought to be enough for anybody. - Bill Gates, 1981"
"Imagination is more important than knowledge. Knowledge is limited. Imagination encircles the world." --Albert Einstein (1879-1955)
[This message has been edited by iisbob (edited 09-22-2001).]
09-22-2001, 08:42 PM
Your question reminded me that I didn't really know what the SMBus (System Management Bus) is. No info in the "Guide", nor in the twelveth edition of "Upgrading...PCs", so I did a Google search.
From smbus.org (http://www.smbus.org/specs/index.html):
The System Management Bus (SMBus) is a two-wire interface through which various system component
chips can communicate with each other and with the rest of the system. It is based on the principles of
operation of I2C*.
SMBus provides a control bus for system and power management related tasks. A system may use SMBus
to pass messages to and from devices instead of tripping individual control lines. Removing the individual
control lines reduces pin count. Accepting messages ensures future expandability.
With System Management Bus, a device can provide manufacturer information, tell the system what its
model/part number is, save its state for a suspend event, report different types of errors, accept control
parameters, and return its status."
OK, so what is I2C? From Philips (http://www.semiconductors.philips.com/i2c/facts/):
"In modern electronic systems there are a number of peripheral ICs that have to communicate with each other and the outside world. To maximize hardware efficiency and simplify circuit design, Philips developed a simple bi-directional 2-wire, serial data (SDA) and serial clock (SCL) bus for inter-IC control."
I seem to remember the SMBus being in my first-generation Pentium Dell, but it doesn't seem to be used in PCs anymore.
[This message has been edited by kenja (edited 09-22-2001).]
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