feature sets will depend on a number of hardware and software factors.
Processing Power
The ability to offer interactive 3-D graphics and motion video while running other simultaneously launched applications in preemptive multitasking environments, like Windows NT, demands a lot of processing horsepower. Intel claims that its CPUs will be able to handle the majority of the load.
Expect an MMX-enabled P55C-200 Pentium to be the minimum requirement for a multimedia desktop CPU by the end of this year. With the help of MMX instruction extensions, the P55C can easily handle a 33.6-Kbps software modem, MPEG-1 decoding at 30 frames per second, or low-resolution videoconferencing by itself.
Of course, this assumes a system with sufficient cache and memory subsystems to provide enough bandwidth (528 MBps for 64 bits, a 66-MHz external cache, and a 264-MB minimum for 64-bit, 33-MHz extended data
out [EDO] DRAM). MPEG-2 decoding with Dolby AC-3 sound, a common DVD requirement, necessitates a graphics/multimedia accelerator on a 200-MHz P55C system if smooth 30-fps playback is desired.
But MMX alone cannot provide significant help for 3-D graphics. According to Vivian Lu, product manager for First International Computer (FIC), MMX increases 3-D performance by only about 20 percent. A 3-D chip is still necessary even with MMX, especially when an Intel P5-level chip set is used. Stepping up to the P6 chip level opens up more possibilities, however.
MPEG-2 Decoding
Klamath, Intel's MMX- and Accelerated Graphics Port (AGP)-enhanced Pentium Pro, is expected to easily provide enough horsepower to handle MPEG-2 decoding and sound for DVD playback. This is due not only to its 50 percent to 60 percent higher processing power (266 MHz with a 512-KB cache versus a P55C-200's 512-KB external synchronous burst cache) but also to its second-level cache, which is twice as fast as that
of the P55C. With a floating-point performance over twice that of the P55C (up to 266 MFLOPS at 266 MHz), Klamath also has the ability to handle more 3-D geometry setup tasks during rendering, achieving a software-rendering speed up to an estimated 400,000 shaded polygons per second.
Intel currently has no plans to support AGP at the Pentium level. Arthur Pai, director of desktop product management for Acer, says that "third-party core-logic vendors, such as VIA and Opti, will offer AGP-capable chip sets." This is potentially a very important development, particularly for home users. Pai adds that, with AGP, motherboard makers will be able to use simplified, inexpensive 3-D chips that, along with AGP, will provide good 3-D performance. "S3, ATI, and Cirrus Logic are all now working on chips that utilize AGP and hence will have simplified feature sets at a low price," he explains.
The key competing x86 processors, AMD's K6 and Cyrix's M2, also have MMX instruction extensions and AGP, as well as acc
elerated floating-point performance that's close to the Pentium Pro level while keeping the standard Pentium pin-out. The use of a K6 or an M2 chip along with third-party AGP core logic opens the possibility of a less-than-$1200 multimedia PC with 3-D video and audio.
System I/O Bus
Two years ago, it looked like the 32-bit, 33-MHz, 132-MB PCI bus would provide more than enough bandwidth for any use. But that was before 3-D graphics and motion video entered the mainstream -- not to mention faster disk interfaces, such as the new 80-MB Ultra2 wide SCSI and the 200-MB dual-port Fibre Channel-Arbitrated Loop (FC-AL).
To prevent another occurrence of I/O choking similar to what happened with ISA-bus-equipped 486 PCs, two complementary strategies have since been used to create more bandwidth. The first was to expand PCI to a 64-bit width (264-MBps peak bandwidth with 8-KB bursts at 33 MHz). The second strategy was to double the clock rate to 66 MHz, for a peak bandwidth of 528 MBps.
However, at 66 MHz, PCI can reliably support only three to four loads (and two slots at most) per bus compared to 10 loads (five slots, or four slots and a bus bridge) per bus for PCI at 33 MHz. It also requires an additional regular PCI bus in the system for less-demanding cards. Thus, having two PCI buses simultaneously and independently attached to the main memory bus is what effectively doubles the total I/O bandwidth.
Intel's AGP
The newest solution to the bandwidth problem is Intel's AGP. A separate graphics point-to-point connection based on a revision of the PCI 2.1 specification, AGP includes bidirectional bus traffic, read queuing, and DMA mastering, all operating in parallel with the system's main PCI bus. This 32-bit bus runs at 66 MHz, using dual-edge clock transfers to move data on both sides of the clock edge for an effective throughput of 133 MHz, producing a peak bandwidth of 528 MB.
This bandwidth is necessary if a 3-D graphics chip is accessing the textur
e data from main memory -- the main purpose of this bus. Uncompressed motion-video manipulation will also welcome that bandwidth. AGP will first be implemented in Intel's 440LX chip set for Klamath, which is expected to be announced this summer.
As the days of standard DRAM draw to a close with the advent of synchronous DRAM (SDRAM), Rambus DRAM, and other new memories, the solution for the main-memory speed problem might finally be here. What kind of memory bandwidth will new desktops need to satisfy 3-D and motion-video requirements?
Again, Pentium-class systems using a P55C, K6, or M2 will become the baseline. Using the new Intel 430TX (or the similar Opti, SiS, or VIA chip sets), these systems will have 64-bit SDRAM main memory, offering a peak burst bandwidth of 528 MB at 66 MHz (or 600 MBps on the 75-MHz bus of the 225-MHz Cyrix M2). Pentium Pro systems, including those based on the new Klamath, will have the same peak main-memory bandwidth as current Pentiums, but with a deeper bus pipelini
ng.
At the end of this year, the 300-MHz Deschutes, racing at 100 MHz to provide a peak bandwidth of 800 MB, will bring a faster system bus to the Pentium Pro world. Klamath, Deschutes, and other future Intel processors will have a key ad-vantage over the Pentium: an AGP graphics bus closely tied to the main memory bus.
The need for AGP as a way around the requirement of huge amounts of video memory is significant. FIC's Lu says that "without AGP, 3-D video must go to 128 bits. That means that even 4 MB of video memory will barely be sufficient. Instead, you need to go to 1 MB of Rambus DRAM, as Cirrus Logic has done." But even with AGP, future3-D graphics might require Rambus DRAM. In fact, Intel has said that Rambus DRAM is the memory of choice for late 1998 -- not only on the video end, but for system memory as well.
Even with the appearance of $1200 3-D multimedia PCs, there remains a marketing problem: a lack of software for the platform. When Intel released its MMX technology, it could
demonstrate only a handful of games that take advantage of the new instruction set.
FIC's Lu says that programmers' response to AGP is even more negative. If game-playing is what's driving consumers to 3-D, then the PC will remain at a distinct price disadvantage compared to game machines costing $200.
Next-Generation Multimedia Desktops
