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The Pentium III is dead; long live the Pentium 4.

Toronto Star Fast Forward column for November 2, 2000

Copyright ©, Myles White, 2000

Intel is poised to release the next generation of its Pentium line of computer processors - the Pentium 4 - within weeks or perhaps even days. This time around the company's marketing experts are dropping the Roman numeral, perhaps to avoid inevitable jokes about the processor needing an IV (possibly not).

Intel faces a problem: how to distinguish the Pentium 4 from its previous Pentium III processors. Unlike the evolution from Pentium to Pentium MMX and Pentium Pro to Pentium II, then III, there's no beefed up instruction set - such as the MultiMedia eXtensions or Streaming SIMD (single instruction multiple data) Internet instructions, additional tasks the processor can do - to set them apart.

That means Intel is going to have to invest heavily in educating consumers about parts of the computer that it and both the manufacturing and retail sectors have been downplaying: the processor chip set and that part of PC motherboards now called the Front Side Bus.

To put it in jargon terms, the new Pentium 4 is expected to debut at 1.4 GHz running on a blistering 400 MHz front side bus.

Say what? Regular readers of Computer Wares know all about the front side bus and its effect on processor performance. They've also read a lot about processor chip sets. Therefore, I'll beg their indulgence while I explain them again.

Front Side Bus

The front side bus is the data pathway that connects the processor to main system memory (the 32, 64, or 128 MB of memory you boast about your system having), BIOS (basic in/out system - a combined traffic map and traffic manager of on-board components and internal peripherals), the Accelerated Graphics Port bus, and the processor chip set (more about it below).

And yes, there is a back side bus or at least there was. It was the data pathway that connected the processor to level 2 cache memory when that memory was a separate component, external to the processor - either residing on the motherboard, or inside a cartridge such as in the Pentium II, classic Pentium III (formerly code-named Katmai), and first AMD Athlon processors.

All current Intel Pentium III (formerly code-named Coppermine), Intel Celeron, AMD Athlon (Thunderbird), and AMD Duron processors have level 2 cache memory inside the processor and it runs at the same speed as the processor, so you can forget the back side bus as a performance factor (but don't forget the level 2 cache - we'll talk about it more below).

Back to the front side bus. Current front side bus speeds are 66 MHz (Celeron), 100 and 133 MHz (Pentium III), 200 MHz (Athlon and Duron), and soon, 400 MHz (Pentium 4) and 266 MHz (AMD Athlon <italic>Mustang<italic>). Why the front side bus speed is important is that there is a direct relationship between its speed and the numbers you hear associated with processor speed.

If you see a reference to a 933 MHz Pentium III, for example, that figure of 933 MHz is the internal speed of the processor and is always a multiple of the front side bus speed. When data enters the processor, it moves among a number of internal components at that speed. But that "933 MHz" is derived from the front side bus speed of 133 MHz and the processor is said to use a multiplier of 7. An 866 MHz processor uses a multiplier of 6.5 and a 1 GHz processor (1,000 MHz) has a multiplier of 7.5. When Intel sets out to make a fast Pentium III, it doesn't target a specific MHz or GHz number, it tries to boost the multiplier as high as it can go.

The front-side bus speed, aside from determining the internal speed of the processor, also has an effect on overall system performance, because it's important to know how quickly data gets to the processor to be worked on, and how fast it moves somewhere else to carry out the processor's instructions. It's also why knowing how fast the processor is doesn't give you all the information you need to figure out how fast the system will be.

If I tell you that one computer has a 700 MHz Intel Celeron in it, that another has a 700 MHz Intel Pentium III, and a third has a 700 MHz AMD Athlon or Duron in it, you won't be able to figure out which is a better performer unless you also know their front side bus speeds (66 MHz, 133 MHz and 200 MHz respectively). And now you also know why manufacturers and retailers have been shy to share this information with you.

Level 2 Cache

I ran by the term "level 2 cache memory" quickly, as though it was of minor importance, but it's not, because it's another distinguishing factor. When you buy a computer that's advertised as having 32, 64, or 128 MB of memory in it, that's an important performance indicator (and also has a direct effect on its price). But that main system memory is slow compared to how fast the processor runs. Many times every second (933 million times, if you use the example of the 933 MHz Pentium III), the processor "ticks" over (why this speed is sometimes called its "clock speed"). Each time it ticks, something can happen. If it ticks and nothing happens, that wastes efficiency (and technically it's called a "wait state").

The purpose of the level 2 cache memory is to act as a temporary parking lot for data on its way into the processor and on its way out. It's also a place the processor can store the results of temporary calculations. Without it, the processor has to use main system memory directly, which slows it down. With cache memory, particularly when it's part of the processor die and running at the same speed, the processor becomes more efficient. With lots of it, that efficiency goes up.

You don't get a choice of how much level 2 cache memory comes with your system any more, because it comes as part of the processor, but it helps to explain why one processor is faster than another when all other things are equal. For example, the current "Coppermine" Pentium III processors have 256 KB of Level 2 cache. Celerons have 128 KB. Athlons can have varying amounts, but 256 KB is typical for the "Thunderbird" version. Durons have only 64 KB, but the vast difference in front side bus speed (200 MHz compared to 66 MHz for Celerons) more than makes up the difference (Durons are being clocked at roughly 25 per cent faster than Celerons when both have the same internal speed).

AMD is planning a new Athlon, code-named Mustang, to compete with Pentium 4. While the company will increase the front side bus speed to only 266 MHz (compared to 400 MHz for Pentium 4), it also plans to increase the on-board level 2 cache memory to 1 MB. Can't wait to get my hands on both to test 'em.

Chip Sets and Memory

There's one more factor that it's becoming important to know about the system you're preparing to buy. Actually, understanding the details of the processor chip set that's in the system has been important for some time, but because it is now having an even greater effect on the type of memory you get with your computer, understanding the chip set is becoming crucial.

The chip set is the set of two to four components on the computer's motherboard that determines: - the front side bus speed, and therefore which processor(s) it can use - the type, speed and upper limit of the amount of memory it can use - the type and upper limit of data transfer rates of hard drives, CD- and DVD- drives - support for Universal Serial Bus and High Speed Serial Bus (FireWire), and which types of parallel port (Standard, bi-directional, EPP, ECP) - support for advanced remote management, advanced power management - support for wake on ring, wake on LAN - PCI (Peripheral Component Interconnect) bus speed and how the PCI slots communicated with the processor - support for Accelerated Graphics Port (AGP) and at what speed (1X, 2X, 4X)

For a couple of years now, the basic type of memory accompanying PCs has been the same: synchronous dynamic random access memory (SDRAM). As front side bus speeds have increased, so has SDRAM speed (e.g., PC66, PC100, and now PC133).

Beginning with Intel's i820 chip set, a new type of memory has appeared. Direct RAMbus DRAM (DRDRAM) is about twice as expensive as SDRAM and Intel swears we'll see some differences in performance one it releases 400 MHz and higher front side bus speeds. But so far, no one has been able to measure any overall performance differences (in my tests, for example, DRDRAM systems write slightly faster, but read slightly slower).

While Intel still supports SDRAM in its 815 series chip sets, it maintains the reliance on DRDRAM in its newer i840 chip set and in the i850 due to be released with the Pentium 4.

When you have a computer using DRDRAM, you can't go back to SDRAM and you can't mix the two types. Nor can you upgrade a SDRAM system to the newer DRDRAM (even if you were silly enough to want to do so).

Needless to say, with the increased price and unnoticeable performance difference, resistance to DRDRAM is significant not only among consumers, but also among manufacturers. And that brings us to another of Intel's nightmares: VIA.

Taiwanese chip set and processor manufacturer, VIA, is championing yet another type of memory: Double Data Rate DRAM (DDR DRAM). I noted above that current SDRAM variations include one (PC133) that runs at the same speed as the 133 MHz front side bus. DDR DRAM supports a front side bus speed of 266 MHz. Its performance is nearly double that of PC133 SDRAM and the cost differential is about 15 per cent. Guess which one is becoming more popular.

But this is one more case where not knowing what chip set is in your new computer will come back to haunt you. SDRAM, DDR SDRAM, and DRDRAM are physically different and don't fit the same slots. They also require explicit chip set support. You can't mix and match them, and if you ever want to add more, you'll have to know precisely what you have so you can get more of it.

Computers are getting faster. They're also getting more complicated. Aren't you glad (he said with a grin) that you're alive in these exciting times?

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