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High-Tech Times Article 010

Choosing CPUs, Chipsets, and Memory

What's your PC strategy for the future?  Even as a computer reseller, it seems to me that the day a new PC arrives in-house, it's already outdated.  This is a problem whether you're buying one PC for your home, or setting up a few hundred for your company.  I'm going to try to unveil some of the major developments in chip sets, Central Processing Units (CPUs), memory, and data buses over the next 12 to 18 months to give you at least a fighting chance at avoiding obsolescence.


Buying a PC has, on one hand, become nearly as easy as buying a calculator, while on the other hand, is horribly complex.  Although there is little magic today in buying a basic computer system, PC technology is advancing at breakneck speed, and timing is everything.  The only thing that's worse than finding out the PC you just bought is now $300 cheaper is finding that it's $300 cheaper and has a bunch of new features that you can't add to the one you just bought!


Gone are the days when CPUs were straightforward, and megahertz speed was everything.  With MMX, Slots 1 and 2, Socket 7, and AGP, today's buyer must be well-educated on which features you don't need, which ones you can't live without, and where to spend your hard-earned money.  Although full coverage of today's features would take up all of this paper, I'm going to present a brief overview.  So let's start with the most basic part of the computer: the CPU.


Today, you can buy Pentium IIs ranging from 233 to 400 MHz, with 450-MHz on the near horizon.  Up to 333-MHz, these CPUs have a bus speed of 66 MHz (the bus speed is the fastest data transfer rate between CPU and all other parts of the computer), while the faster processors up the bus speed to 100 MHz.  The data bus is a critical component for those of us who use AutoCAD, PhotoShop, 3D Studio Max, and other data-intensive applications.


Did I mention that Intel hasn't been producing Pentium (or MMX) CPUs for several months?  The Pentium is a dead line, with Pentium IIs replacing them.  The high-end Pentium IIs are renamed as the "Xeon" (no, I have no idea how to pronounce this, and I got three different answers from three Intel reps), while the lower-end CPUs have become the "Celeron" line.  And you will never find a Pentium (with or without MMX) that supports the Accelerated Graphics Port (AGP), as Intel feels that the Xeon and Celeron are better suited.  It also means you'll have to cough up more bucks for the faster AGP graphics throughput....  Check out for a more detailed explanation (this is a big PDF file that takes a while to download).


What's beyond Xeon?  Well, the CPU code-named Merced is the first CPU to use the IA-64 instruction set, co-developed with HP, is roughly four times more powerful than the current Xeon, and is expected to show up in mid-1999.  Although it's a completely new architecture, Merced will run our existing X86 code through a hardware emulator.  But since Intel's other CPU, code-named Willamette, will run X86 code in native mode around 2000, we can expect few changes in basic software applications.  At least until the enhanced Xeon core, code-named Katmai, appears in late-1999, with enhanced 3D graphics floating-point instructions, and likely more cache memory, as well.


Cache memory comes in several flavors, and is another key speed factor.  The new Celeron chips running at 266 MHz are actually cacheless Pentium IIs, and tests show they may not be any faster than a standard (and less expensive) Pentium MMX.  Level-2 cache (L2) is located in the Pentium II module, and is the quickest way to increase data throughput, as it's physically connected to the CPU itself.  Level-3 cache (L3) is memory external to the CPU when L2 is integrated.  Don't worry if this confuses you - you're not alone!  Take a look at Table 1 to see a summary of Intel's cache configurations and speed.


A CPU is not an island.  It requires a chip set, which is "core logic" where most system features are kept, including various buses, types of memory, and disk controllers.  As Intel makes the majority of PC chip sets, I'm going to stick with theirs in this article.


The Intel 440LX motherboard is the current standard for Pentium II CPUs, and handles new features like AGP, Universal Serial Bus (USB), and processors up to 333 MHz.  But the newest 440BX motherboards will handle the new 350- and 400-MHz Pentium IIs, and has 100-MHz bus speed.  And you will soon be seeing entry-level machines with the 440EX (economy?) motherboards, Celeron CPUs, and AGP Level 2. 


Starting with Pentium IIs, Intel has moved to a new processor interface called Slot 1.  Rather than the flat CPU we're all used to, Slot 1 puts the CPU and L2 cache on a printed-circuit board with an edge-connector (like a very small add-in board).  This board is encased in a cartridge, which then is plugged into the slot.  Intel wants you to believe that Slot 1 is superior to the older Pentium socket (known as Socket 7), but these configurations are really quite alike.  Both are 64-bit-wide, 66-MHz interfaces with a maximum bandwidth of 528 MB/sec.  And both have sped up to 100-MHz, increasing bandwidth to 800 MB/sec.


The main advantage of Slot 1 is that the CPU and L2 reside in the cartridge rather than on the motherboard, giving the cache a dedicated, non-shared high-speed path to the processor.  For Xeon, L2 runs at half the CPU speed (i.e., 200 MHz in a 400-MHz CPU).  So L2 runs faster than if it were limited to the motherboard speed (now 100 MHz), and doesn't share bandwidth with other PC subsystems as in Socket 7.  Another Slot 1 advantage is that it can process multiple simultaneous transactions, which Socket 7 cannot.  This makes Slot 1 a superior choice for multiprocessing (dual processor) systems, as long as you don't need more than two CPUs (Slot 1's current limitation).



Data buses in the PC are also advancing rapidly. Please look at Table 2 for a summary.  AGP derives from the older Peripheral Components Interconnect (PCI) bus, but is dedicated to graphics, and other subsystems can't share it.  Version 1 of AGP runs at 66 MHz, and debuted with Intel's 440FX chip set.  These first-generation video boards support peak bandwidth of 264 MB/sec.  AGP 2X mode can transfer two chunks of data per clock-cycle, thus doubling bandwidth to 528 MB/sec.  Just off the assembly line is AGP Version 2, which introduces the 4X mode, which again doubles bandwidth to a mind-numbing 1 GB/sec!  Intel has included a new Universal Connector to allow new systems to accept both old and new AGP boards, so your "old" AGP board at least has a bit more life in it.


I've covered USB in earlier articles, and so I'll pass it by, and simply refer you to for more current information on this 12 Mb/sec data bus.  You'll see a lot more support for USB devices when (if?) Windows 98 ships.


The last bus I'll discuss is called "FireWire" or 1394 (referring to its international standard).  1394 is similar in many ways to USB, but provides much higher bandwidth.  Standards are in place for 100-, 200-, and 400-Mb/sec, with 800 Mb/sec on the horizon.  To give you an idea how fast this is, 400 Mb/sec equals 50 MB/sec, which is faster than Ultra-SCSI-3's 40 MB/sec.  And the forthcoming 800 Mb/sec is as fast as today's newest motherboards at 100 MB/sec!


This makes 1394 ideal for everything from high-resolution scanners to video digitizing, and may even make a dent some day in SCSI hard-drives.  Unfortunately for us, vendors are slow to adopt 1394, which was finalized in 1995.  But with direct 1394 support in the Intel 440BX motherboards, Windows 98, and NT 5.0, I think we'll see the 1394 standard come up quickly by 1999.


Last, but certainly not least, is Random-Access Memory (RAM).  With all the advances in CPUs and data buses, don't forget that RAM may be the most important system component.  But RAM technologies haven't advanced as fast as CPUs.  Since the advent of the original PC, we've had six families of CPU: 8086, 80286, 80386, 80486, P5 (Pentium), and P6 (Pentium Pro and II).  But the RAM family tree is less branched: Fast-Page, Extended Data Out (EDO), and Synchronous DRAM (SDRAM).


To compensate for RAM speeds that don't keep up with the CPU, Intel has used cache memory on the CPU itself, and every CPU since the 80486 has a small installed Level-1 cache.  But as cache RAM is expensive, eventually system RAM must get faster.  Most of today's computers use SDRAM, whose main difference from its forebears is that it is synchronized with the system clock (now 100 MHz).


If you're buying a computer that uses the 440BX chipset, be very careful that the manufacturer includes 100-MHz SDRAM!  The older RAM chips look alike, but will not function on the new motherboards.  Future RAM upgrades may be much harder, in fact.  During the transitions from Fast-Page to EDO to SDRAM, many motherboards gave you capabilities to use pretty much whatever RAM chips you had laying around.  But that flexibility is coming to an end.  You have to pay closer attention to what RAM you buy, as you'll live with it for many years.


One recent RAM improvement is the Dual In-Line Memory Module (DIMM). DIMM differs from the older SIMM in that SIMM chips are 32-bit, and thus require pairs to interface with the 64-bit Pentium II, while DIMMs are 64-bit and are added one at a time.  The move to 100-MHz SDRAM is likely to be short-lived; they can transfer only about 100 MB/sec, and just don't provide enough bandwidth for the data-hungry new CPUs.  But choosing your new RAM probably won't be easy.


One new RAM architecture is the SDRAM-DDR, or double data-rate.  This RAM consortium is competing with a second group that plans to quadruple bandwidth to 400 MB/sec using a RAM design called SyncLink.  But those of us who watch Intel closely are looking at a separate company called Rambus that is proposing the RDRAM chip as the new standard; Intel and Rambus have been working closely for several years, and unless the Federal government challenges Intel's dominance as a chip set and motherboard standard, Rambus is a shoo-in.


Practically speaking, Intel's support isn't as important as the fact that Direct-RDRAM is really the only architecture that can provide enough bandwidth for Merced and other new CPUs.  DRDRAM uses two 800-MHz data channels, for a stellar 1.6 GB/sec throughput, and more channels can theoretically be added.  That's enough headroom for at least two more generations of CPUs.


So here you are with even more to think about than you expected.  I hope  that this brief overview helped.  See you next month.


                [Check out Hightech‑010.p65 for the final copy]