Desperately need an A+ mentor

[annsolomon]

Hi folks. I'm absolutely awed by the number of smart people in this forum and have learned so much from y'all over the past months.

I'm really a database application person but my company wants me to get more involved with desktop support. They sent me to A+ training (hardware & OS) and it was really interesting. I learned a lot of really neat stuff but am still having problems grasping some very basic ideas.

For example: system bus, data bus, address bus, local bus, video bus. How many other buses are there for crying out loud? When I left the class I thought buses were the wires that ran along the motherboard between the CPU and various devices. Now I just read (in the A+ Certification Bible by Ed Tetz, etal) that the "Pentium processor had a 32-bit address bus, 32-bit registers, and a 64-bit data bus."

Does this mean there are buses on the motherboard AND in the CPU. It's too confusing.

Is there anyone out there who can help with these weird questions I have?

Thanks in advance.

Ann

 

[edfair]

Some of them. But it will require a digression back to 1975 and a simpler processor. It had a 16 bit address bus and an 8 bit data bus. To write the address was put on the address bus , the data on the data bus and write and data enable was put on the system bus. To read the address was put on the address bus and data enable was asserted and the data was read off the data bus. Next step of complexity was combining the address and data bus on the board. Everything worked on an 8 bit address and data bus with a 5 bit control bus split between 3 state lines and 2 data state lines. For the high order address that portion was put on the bus, state value was put on the state lines and the r/w and data enable was set to the right value. Those parts of the system requiring 16 bit access would latch the data for further use. Then the lower 8 bits were strobed onto the a/d lines with a different state address and latched if needed. Then the data was strobed out the same way. Coming back in used different state values. This covers the basic concepts of address, data, and control.
Registers are storage boxes within the processor, latching transistor circuits that can store the state of the connected lines. When reading from data, say, the data values on the data lines (0 or 1)(<.7 v or >2.4 v aprox) are captured by the register. This data can then be moved around within or outside the processor by the instruction set of the processor.
32 bit address bus of the description says the processor works by asserting any of 32 lines of addressing. The registers handle 32 bits or lines. 64 data lines indicate that the data registers can access 64 lines.
Address bus, data bus , control bus. Video bus to the AGP video chip or slot (or on 486s to the video local bus), PCI bus between the PCI controller and the PCI boards, ISA bus from the processor to the ISA slots.
Might try a copy of &quot;repairing and upfrading PCs&quot; by Scott Mueller for some good info. Into about the 15th edition by now but suspect that he has kept all the older info along with adding current.

Ed Fair
Any advice I give is my best judgement based on my interpretation of the facts you supply. Help increase my knowledge by providing some feedback, good or bad, on any advice I have given.

 

[annsolomon]

Ed, bless your heart for jumping in there with me but I think you're talking over my head.

&quot;Some of them.&quot; Does that mean some PCs have buses on the motherboard AND in the CPU but not all of them?

Do you have the patience to explain in simpler terms the read/write processes you outlined? I'm sure, if I had a better basic understanding, the explanation you gave would be very enlightening.

I understand the concept of on/off (binary) but are you saying that in order to be &quot;on&quot; a voltage of more than 2.4 (approximately) must be sent? Can you believe that my instructor didn't pass that on to us? WOW!

I'll definitely stop by the library tomorrow to look up Scott Mueller. Thanks for the reference; I'm always looking for good books.

I sure hope you'll come back to me. In the meantime, I'll reread your comments to try and get a better understanding.

Thanks again.

Ann

 

[mainegeek]

I would recommend that book as well. If you can get your hands on an older PC 286 or 386. a set of Dos and Win3.0 disks and a handful of legacy cards and build one it may help as well. I think I recall Dos 6.2 had a glossary explaining dos file names,commands, usage and syntax.
I don't know what the A+ exams consist of today. I took them years ago. Then it was 2 exams Dos/Windows + Core (hardware). Starting as far back as you can will probably give you a better understanding of todays technology. Especially the boom through the 90's.

 

[annsolomon]

Thanks mainegeek. I'm even more anxious now to get my hands on that book.

However, I'm still looking for an answer to the bus question. I pictured the data bus as the wires that run on the motherboard that helped the devices communicate with the CPU. What, exactly, are the &quot;wires&quot;? I don't really know how to ask that question. I guess I'm trying to find out what kind of material the wires are made of. From what Ed told me earlier, I understand they have to be made of something that voltage can flow through.

Is the data bus in one area of the motherboard and the system bus in another area and the address bus in another area or are they all intermingled? Should I be able to look at the motherboard and see where the different buses are? And, as asked in my original post, are there really buses also located in the CPU?

I hope I'm not trying your patience too much. I'm really not stupid but I'm sure having a hard time with this issue.

Ann

 

[edfair]

Some of them referring to answers to your questions.
You don't even want to get into the busses inside the processor chip. With 15 million transistors in 1/2 square inch the interconnects get hairy.
When the processor is described as 32 bit bus, it means that the signals to the outside world are to a 32 bit bus (32 pins on the chip connect to 32 different traces that are the address bus).
I need to confuse you now. There may be more than 1 pin per address. To simplify interconnects the manufacturer might put a duplicate set on another side of the chip. And all address lines don't neccessarily need to connect to an address bus. Small specialized systems can do work in less than the full memory map. (memory or I/O addressed by the maximum address lines available to the processor).

Assume the 16/8 chip from 1975. On power up, after the clock has operated 64 cycles the microcode in the processor activates the address lines FFFEh and FFFFh and reads in the jump vector for power up reset. FFFEh=1111111111111110. This address is placed on the address lines and a logic glue chip interprets part of the high order address lines to select a partitular chip on the board. The rest of the lines go to address lines on the chip which enable E0h to show up on the data line which in turn is readinto a register on the processor. Then FFFFh is put on the address line and the chip puts 00h on the data line and it is read into the processor. Since this was power up the microcode reads these two bytes of data into the address register, high order first. The next processor cycle writes the contents of the address register onto the address bus and gets the instructions back that it is to process for the first step of the power up reset.

You don't really need the detail. I got it because I built and debugged small systems at the bit level when the little systems hit. Don't guess I've looked at a address or data line for real information in years.

Ed Fair
Any advice I give is my best judgement based on my interpretation of the facts you supply. Help increase my knowledge by providing some feedback, good or bad, on any advice I have given.

 

[annsolomon]

Ed, I truly appreciate your information and beg your patience. I'm not ready for the level of knowledge you're trying to impart. I just want to know:

1. How many buses are there? (data, system, address, what else)

2. Are there really buses on the motherboard AND in the CPU? Are there buses in other places?

3. What material are the wires on the motherboard made of?

Ann

 

[edfair]

Yeah, there are busses in the processor. You don't need to know what they are or how they work. They are used to transfer stuff in, out, or internally.
Address lines are activated out of the processor via pins that are connected to the address lines on the address bus on the motherboard.
Data lines are activated out of or into the processor via pins that connect to the data bus.
Control lines, ditto. Address and data can use the same bus(multiplexed).
Bus names as in my first post except I left out EISA, which was a specialized I/O bus. to recap:
address, data, control, I/O (several different types)

On the board the bus is traces of copper that lead to and from chips or interconnects. Board started as a sheet of fibre with a sheet of copper laminated to it. Then all except the traces and the interconnects were etched off of it. And several boards with different circuits can then be stacked together to get a complete set of interconnects if it is complex. And generally , after the etching, insulation is printed over the top of the traces.


Ed Fair
Any advice I give is my best judgement based on my interpretation of the facts you supply. Help increase my knowledge by providing some feedback, good or bad, on any advice I have given.

 

[mainegeek]

The wires that you are asking about are refered to as a circut. I believe the material of the circut is copper.
These circuts make up the different buses. Think of it as a road map. The buses are used as a pathway for data to travel. This gives 2 or more computer components the ability to communicate with one another. Most PC's have at least 3 buses and the newer ones have more. Along with I/O buses like USB, FireWire,PC-Card and so on. These buses 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. The chipset act as bridges
between the various buses. The main buses are The Processor (cpu) Bus, The video (AGP) Bus, The Pci Bus and
The ISA Bus.

 

[annsolomon]

Thanks Ed & maingeek. You guys are wonderful. I sure hope you'll be around for more of my questions. I really want to do well on the A+ exam but, more importantly, I really want to understand this stuff so I can help the folks at work more efficiently.

Ann

 

[dppnwspec]

I would also advise pointing your browser to

http://www.examnotes.net

and then become a member.

Once you become a member, then you can post questions, like the ones you've been asking, on the A+ forum that is dedicated to persons like yourself that are seeking the coveted A+ Certification. I have found Examnotes to be a very informative when I have a question myself or am looking to learn new things.

 

[annsolomon]

Thanks dppnwspec. I'm always looking for new sites like that.

Ann

 

[dppnwspec]

One of the members of Examnotes also runs a forum of his own. You can find it at:

http://www.mcsefreak.com/forum.htm

Give his site a look at too.

jim.