Front Side Bus (FSB) - what does it mean & why is it important

[NewJeffCT]

A few months ago, when I started browsing around for new computers, I asked a friend of in the I/T field for some ideas regarding a new computer and she sent a link to me about some special deals and had the comment on one that said, "and it has 800 FSB!!" like I knew what that meant.

So, what does it mean?

[tyedyeto]

1. Delete - wrong info...sorry

[Clintmax]

2. Are you sure...

Front Side Bus has something to do with the computers memory. I'm not exactly sure what.

[Tallison]

4. Actually, I think it has to do with the CPUs efficiency in

communicating with RAM and other components of the motherboard (like AGP sockets and so forth), measured in data width and speed (MHz). It ultimately dictates the speed with which you can run programs of varying complexity.

I've always found good user-friendly explanations of FSB and other such stuff at:
http://computer.howstuffworks.com/

(Edited for grammar)

[billyskank]

6. Wrong

The front side bus is the channel by which data is moved to the CPU from the computer's memory and other peripherals (video card, sound card, USB ports, etc) and vice versa. Think of it as like a pipe that carries data.

The front side bus is described in terms of its width and its speed. The width is the number of bits it can carry at once; for a Pentium this will be 32 bits, which means it can transfer a number between 0 and 4,294,967,296. A number bigger than that would have to be split up and transferred in two goes.

The speed of the front side bus is the rate at which it can transfer chunks of data. An 800Mhz FSB can carry 800 million chunks a second. For this reason, as CPUs get faster, the FSB must also be cranked up faster, otherwise the speed of the CPU is wasted because it is waiting for data to be carried out to or received from the rest of the computer.

[Deja Q]

3. FSB - it's the data bus going from the CPU to the RAM. But it's bollocks,

at least when you consider how little work the Pentium 4 does per clock cycle.

Now if the P4 did as much work per clock cycle as the AMD Athlon, then the 800MHz FSB would cremate the Athlon.

Instead it's a virtual tie; the Intel doing slightly better at some things; the Athlon better at others. And as the Athlon costs a lot less...

[Clintmax]

5. Yep! This is it! Thanks, Hypno. n/t

[Deja Q]

7. Forgot to add; the Athlon's FSB (depending on the model) runs at

266, 333, or 400MHz.

(I need to look up the specs of the Athlon 64 but I think it's 400 but using DDR2 so it's effectively 800... The P4, as I recall, uses DDR2 as Intel just wasn't able to force Rambus down peoples' throats.)

[jmowreader]

8. I shall try

A bus in a computer is a group of wires. They call it that because the computer bus carries information like a city bus carries passengers. (Well, they hadda call it something.)

There are two kinds of buses inside your computer--address buses and data buses. The address bus is used to tell the computer to look at a particular spot in the computer's high-speed memory--RAM and ROM. It's important to the user mainly because it sets an upper limit on the amount of RAM you can have. (When the Macintosh 128k was released, we knew that the processor could address a for-that-time stupendous 16MB RAM because it had a 24-bit address bus. No one had any idea what you would ever need 16MB RAM for, although we were plenty pissed that the design of the Mac limited it to 4MB RAM. We didn't know what you'd ever want with that much RAM either. Before you start chortling, remember that neither DOS nor the Macintosh operating system would run more than one program at a time. And before you start laughing about how limited the Mac's measly memory capability was, remember that the 8088 processor in the IBM PC and PC-XT had a 20-bit address bus and would only address 1MB RAM.)

Which brings us to the data bus, the subject of this discussion.

Modern processors have two: the front-side bus and the back-side bus. The back-side bus is where your cache memory lives. Cache is a very small amount of very fast memory--just a couple of megabytes. I can explain what it does later if you'd like. It's on a separate bus because if the CPU was making cache requests along the same bus as it was making main-memory requests, it would slow the cache down so much that having it would be pointless. It's as small as it is because (1) it's expensive as hell, (2) it generates a lot of heat, and (3) nowadays, they put a lot of it in the processor itself and they don't want the processor to be the size of a Buick.

The front-side bus is where your main memory lives. (This is also the bus the computer uses to talk to the video card, hard drive, modem and all the other things your computer is running, but that's not important now.) You know when you look at a computer ad, it says "This computer has 512MB RAM!" That's main memory. It's sitting on the front-side bus. And the faster that bus runs (it hasn't run at processor speed in decades) the faster your memory calls run and the faster your computer goes. Fast is good. The bus is rated in megahertz, same as your computer used to be before they started selling GHz PCs, and 800MHz is a very fast one.

Short answer: this computer is nice and fast.

[NewJeffCT]

9. thanks

I'm actually starting to see PCs with more than 800FSB now, too.