Intel CPU Bus widths

trick000

I'm kind of digging up some old stuff that people have said about pentium bus widths. Oldgearhead had a post where he disagreed that pentiums have 64 bit bus widths. I think he is partially correct. Also the technotes wasn't very specific about which bus width they were talking about.

- CPU's have have two kinds of buses: Data Bus and address bus

- the first Pentium had a 32 bit Data Bus width and a 64 bit Address Bus width

- All pentiums after that (II, III, Xeon, Celeron) both have 64 bit data and address bus widths

I got this information from a book that I paid $49.99 for and I hope the authors did extensive research on this. If I am wrong then the book is wrong. Would anybody care to clarify?

Wyldstar

The Pentium Pro, II, and III all have 36 bit address busses (access up to 64 GB of RAM). I'm not terribly sure about P IVs and Xeons, but I believe they also only have a 36 bit address bus. All Pentiums have a 64 bit data bus and 32 bit internal registers. The newer processors (Opteron, Itanium, etc) with 64 bit registers have 64 bit address busses that support up to 250+ TB of RAM. I think that's right, anyway .

- WS

trick000

Wyldstar wrote:

The Pentium Pro, II, and III all have 36 bit address busses (access up to 64 GB of RAM). I'm not terribly sure about P IVs and Xeons, but I believe they also only have a 36 bit address bus. All Pentiums have a 64 bit data bus and 32 bit internal registers. The newer processors (Opteron, Itanium, etc) with 64 bit registers have 64 bit address busses that support up to 250+ TB of RAM. I think that's right, anyway .

- WS

Thanks for the input. Where did you get that info from?

Wyldstar

Osbourne Certification Press, A+ Certification Study guide 4th ed. pp. 192-195.

Or here's a quick online reference.

http://www.pcguide.com/ref/cpu/arch/extAddressSize-c.html

Note that for most computers (especially desktops) the address bus size is fairly irrelevant. Most motherboards don't support beyond 4GB worth of ram, so that is the limiting factor much more often than the size of the address bus.

- WS

trick000

Wyldstar wrote:

Osbourne Certification Press, A+ Certification Study guide 4th ed. pp. 192-195.

Or here's a quick online reference.

http://www.pcguide.com/ref/cpu/arch/extAddressSize-c.html

Note that for most computers (especially desktops) the address bus size is fairly irrelevant. Most motherboards don't support beyond 4GB worth of ram, so that is the limiting factor much more often than the size of the address bus.

- WS

sigh... I guess my book is wrong. Well that just makes me feel less confident about the other stuff they're carelessly writing about...

well I checked that webpage you gave me and they're saying pentiums and up have 64 bit DATA bus widths...

btw, the book is A+ complete study guide by sybex.

Wyldstar

Right. All fifth generation and later processors (Pentium and up) have a 64 bit data bus. They also all have 32 bit internal registers, which classifies them as a 32 bit processor.

The address bus width is 32 bits for the original pentiums, and 36 bits for all 6th generation and later processors (Pentium Pro onward). 64 bit address busses are the norm on all the newest processors with 64 bit internal registers (Merced, Opteron, etc). But they will DEFINENTLY not be covered on the A+ exam.

I'm surprised the Sybex book doesnt cover this very well. Sybex has a very good reputation for their study materials, although I personally used Mike Meyer's book for reference for this exam, and don't own that particular Sybex book.

Anyway, you probably won't see a lot of detailed stuff on the A+ exam about address bus widths of particular processors. Of course, it's good to know everything you can for any exam .

- WS

Webmaster

I've been working some time on a link directory for every exam. I started out with the A+ Core exam, and although I'm not quite ready coding the directory and adjusting it to our needs, I did add some links for the A+ Core including five about CPUs:
www.techexams.net/phplinks/index.php?PID=88