True-Color Graphics Accelerators

An in-depth inspection of 35 PCI and five Macintosh NuBus cards for ultrafast graphics and deep colors

Jim Kane, Siva Kumar, and John Mcdonough

Last February, we tested four types of graphics adapters: those with VL-Bus, ISA-bus, EISA-bus, and Macintosh NuBus architectures. At that time, we could round up only three PCI-based (Peripheral Component Interconnect) adapters. But as PCI has become the standard local-bus interface, the former trickle of PCI cards has turned into a flood. There has even been speculation that Apple will replace Mac NuBus slots with PCI slots in a few years.

This Lab Report describes our evaluation of 35 PCI-based graphics adapters and five high-end NuBus Mac adapters. At $399, the average price of the PCI cards h ere is $70 less than the average price of the VL-Bus cards we tested last February. The average price for the Mac NuBus adapters has dropped by $790.

This test set includes both DRAM- and VRAM-based accelerators, in configurations ranging from 1 to 4 MB of video memory. In general, a graphics accelerator with 1 or 2 MB of DRAM will suffice for everyday business applications. But for instantaneous, photo-realistic color, you'd be wise to purchase a more expensive VRAM-based board. And while the fastest boards we evaluated use VRAM, our tests show that the performance edge these boards have over DRAM-based accelerators is sometimes inconsequential.

The PCI adapters we tested represent a variety of graphics accelerator chip sets; the majority were from S3. This is a major change from last year, when Tseng Labs was the most popular chip provider.

Reviews tend to catch manufacturers at various stages of leapfrogging each other with better technology. Every six months or so, manufacturers upgra de their components; whichever one has upgraded most recently often reaps the better review.

But there are specific price/performance trade-offs inherent in particular components, such as VRAM versus DRAM. Because DRAM chips must both update and display through just one port--whereas VRAM is dual-ported--at high resolutions and color depths there comes a point where VRAM is more efficient to use. This is especially true when you're working with full-motion video. Cards that have separate video accelerators offer the best performance for full-motion video playback. RAMDAC chips are also evolving rapidly. Some now include processes, such as hardware scaling and cursor control, that have traditionally been completed by the accelerator controller. Another innovative RAMDAC technology lets you display RGB and YUV windows on a screen simultaneously. Chip performance also varies by application, memory configuration, and vendor implementation. It helps to do some last-minute research when you're ready to make a purchase.

How to use this guide

To find the best graphics accelerator for your needs, follow the main headings until you come to the appropriate bus architecture and then look for the subcategory that's most relevant to your work.

We grouped PCI adapters into best-overall (a weighted combination of performance, features, and quality scores), high-performance, and low-cost subcategories. We grouped the Mac adapters into best-overall and high-resolution groups.

Prices shown are for the adapters as they were configured for our tests. Typically, the cost varies according to the amount, type, and speed of the installed RAM.

Performance results are given in transactions per second: The higher the number, the more transactions an adapter was able to complete. The tests employ a collection of screens from popular Windows and Macintosh applications. Except for the motion video tests, higher numbers indicate better performance.

Boards rated as excellent came with i nstallation software and the clearest manuals; a good rating identifies boards that can be installed without checking the documentation; fair-rated boards required a check of the user's manual; and boards that received a poor rating needed to have jumpers or IRQs reset.

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The Gadgetry of Graphics

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MONITOR INTERFACE
Most graphics adapters provide a single video connection based on the standard D-shell, 15-pin VGA connector. Some high-end boards offer RGB (i.e., BNC) connectors. Some boards have multiple active video connectors, allowing multiple monitor attachments.

GRAPHICS ACCELERATOR
Provides low-level graphics operations. A 64-bit chip can transfer data in and out of its internal frame buffer 64 bits at a time. DRAM, VRAM, and the local bus accept only 32 bits of data at a time. A 32-bit interleaved arch itecture prepares one bank of memory while transferring to a second bank, reducing the transfer to a single clock cycle. Look for 64- or 32-bit interleaved architectures.

VIDEO MEMORY
VRAM-based boards have the reputation of being dramatically faster than DRAM-based boards, but DRAM designs have improved to the point where they're not much slower. Choose DRAM for economy if you mainly operate in 1024- by 768-pixel resolution with 256 colors. VRAM is a must for refresh rates that provide clear images at higher resolutions and color levels.

BUS INTERFACE
We tested only PCI and NuBus adapters in this review. PCI's throughput is better than that of ISA and EISA; in addition, with its flexibility and ease of use, it's becoming the local-bus standard. For Macintosh systems, NuBus is the current accepted standard; it has been self-configuring for years.

VIDEO BIOS
At start-up, your system looks to the video BIOS (i.e., RO M) for the start-up code that identifies the graphics card and its software interrupt (which is almost always INT 10h) to control video actions. Sometimes the video BIOS is shadowed to system RAM for improved performance.