What Pentium, PCI and Windows 95 Offer for Data Acquisition

Unless you insist on buying last year’s model, almost any IBM-compatible PC you purchase today will come with a Pentium processor, a minimum of 8-MB RAM, probably a 1-GB hard disk and Windows® 95 software preloaded. It will also feature the new 32-bit-wide Peripheral Component Interconnect (PCI) bus.

While PCs do not innately constitute the platform of choice for data acquisition, their high capability vs cost ratio has made them economically indispensable whenever computational and control operations must be performed. Neither Windows 3.x nor Windows 95 are well-suited for real-time data acquisition. However, they are mainstream and provide the operating system (OS) platform for many application programs used in conjunction with data acquisition programs.

But even if not ideal, do the features provided by this year’s PCs make them technologically better for data acquisition applications? The answer is yes— and no. It depends on the application.

For most low-speed data acquisition applications, it will make no difference whether the PC contains a Pentium instead of a 386 processor or includes other advancements. But the situation is quite different if there are extensive post-acquisition computational or display demands, high sampling-rate requirements, simultaneous multichannel sampling or long record length.

New Hardware Features

New or expanded features of today’s PCs can provide qualitative and cost advantages, primarily due to these factors:

Faster Processors

While analog/digital converter characteristics, rather than processor speed, generally determine the maximum achievable input rates, CPU capabilities greatly influence post-acquisition data-processing performance. For example, with faster CPUs, higher FFT update rates may be achieved and transforms performed with a greater number of points, which improves speed and precision. More data can also be sent to the display and better real-time graphics can be generated.

Cost savings may also be achieved, pointed out Leslie Brooks at Alligator Technologies. “The main processor’s speed is now almost up to the speed of DSP chips. So, instead of buying separate DSP boards, engineers can just multitask the main processor, reducing the cost of the entire system,” Ms. Brooks said.

More Memory

More RAM enables storage of more data points per test. This provides several advantages, for instance: “For data acquisition software with pretriggering capabilities, such as Snap-Master, the more data that is collected and stored prior to the trigger event, the greater the likelihood of quickly pinpointing the causes that led up to the failure event,” noted Fred Brown III, Product Manager at HEM Data.

More RAM also makes it possible to run more applications concurrently, or use the Windows Object Linking and Embedding (OLE) feature, with less concern about memory shortages or sluggish operation. Extra RAM and hard disk space also can lead to more cost-effective implementations.

“For example, IOtech’s WaveBook/512 serves as a digitizing and multiplexing front end to the PC’s processing and data storage,” explained Bob Walchli, Senior Software Design Engineer at IOtech. “Instead of duplicating features already provided by the PC, such as memory for data storage, the WaveBook/512 leverages off the PC’s capabilities.”

Today’s hard drives can also store larger data files; for example, a >1-GB hard drive is large enough to contain all data created during the crash test of an automobile. When used in conjunction with enough RAM and a fast (EISA or PCI) data transfer bus, a substantial amount of real-time data can be streamed to disk, even while the PC simultaneously generates corresponding graphic-intensive displays.

PCI Bus

Most Pentium-based PCs include several empty slots for PCI cards and a few for ISA- or EISA-compatible cards. The PCI bus is processor-independent and allows peripherals, or plug-in cards, to access system memory directly, without using the CPU.

The 32-bit-wide PCI bus facilitates asynchronous data transmission at rates up to 132 MB/s, which is equivalent to 66 MS/s. While actually achievable data rates are slower, depending on the characteristics of the peripherals, this is a vast improvement over the 1 to 3 MB/s possible with the 16-bit ISA bus or up to 32 MB/s over EISA.1

“By taking advantage of the Pentium power and the high bandwidth of the PCI bus, Data Translation’s PCI-EZ Series data acquisition boards provide gap-free simultaneous A/D, D/A and digital I/O operation at full rated throughput,” said Chad Stalker, Data Acquisition Product Marketing Manager of Data Translation. “The processor independence of the PCI bus makes it possible to simultaneously gather and analyze data.”

Graphic-intensive and control applications are especially likely to benefit from the high bandwidth capability of the PCI bus. “Many of our applications have such extensive graphics that with older PCs it would literally take several seconds for the screen to redraw,” said Robert Gaurie of Sheldon Instruments. “In one case, this hampered the operator’s ability to respond to a critical shutdown situation involving hydroelectric motors. When we switched to a Pentium and the PCI bus, the system could shut down before any damage could occur.”

And What Can Windows 95 Offer?


MS Windows OS has two advantages over DOS: more memory-accessing and multitasking capabilities. Under Windows, several tasks seemingly run at the same time, using one rapidly switched CPU. Actually, each program runs by itself for some time, then returns control to Windows which, in turn, allows the next program to run.

With Windows 3.1x, it was not possible to know how long a program might tie up the system. Also, Windows 3.1x could not accommodate priority interrupts. As a result, the system was undeterministic, an undesirable attribute for many data acquisition applications. When one program hung up, it usually interrupted the operation of the whole system.

Windows 95 is a 32-bit OS (instead of 16-bit for Windows 3.1x) with improvements as well as new features. It permits pre-emptive multitasking, accommodates longer file names, supports plug-and-play implementations and addresses shortcomings in Windows 3.1x, including providing greater robustness. While all the improvements are welcome, only some of the features provide direct benefits for data acquisition applications at this time.

32-Bit Architecture

Although existing 16-bit applications can be run on Windows 95, they do not run faster; in fact, some even run slower. However, new data acquisition applications written for a 32-bit OS can benefit, especially for graphics- and computation-intensive tasks.

“Windows 95 will increase effective performance of graphics-intensive applications by as much as 30%,” said Mr. Gaurie. “For example, we can pass down two concatenated 16-bit words to main memory as opposed to taking a full cycle for each 16-bit data point. We have also noticed an increase in speed by moving over to 32-bit DLLs for doing accesses to our DSP boards.”

Making use of the full 32-bit capability of the OS may even obviate the need for speed-enhancing hardware. “Some computation-intensive tasks, such as those performed by the Windows 95 version of our Prime Factor FFT analysis software, may be accomplished almost as fast as if a DSP chip were used,” commented Ms. Brooks.

Pre-emptive Multitasking


If a 32-bit application is designed for it, the user can set the application’s priority level within certain restrictions. “However, the highest priority levels are reserved by the operating system,” warned Ray Huey, Software Product Manager at Keithley MetraByte. “Unexpected latencies can still occur, but they can be greatly reduced from Windows 3.1x.”

Robustness

Several basic architectural changes were made to improve robustness, such as assigning each native (32-bit) application its own virtual memory space. Theoretically, this means that if one native application crashes, it does not take the entire system with it.

“Also, there is additional layering of service calls between the application software, the operating system and the hardware to provide better error trapping and handling,” noted Mr. Huey. “While Windows 95 is much more robust than Windows 3.1x, there are still ways for everything to hang up.”

But many developers and users are quite impressed with the improvements in robustness. “Isolation between 32-bit applications is a major advantage of Windows 95,” said Dave Cunningham, Product Marketing Engineer at Hewlett-Packard. “When something went wrong in Windows 3.x, you were in trouble. That’s less likely in Windows 95. I have personally found Windows 95 to be much more stable than Windows 3.1x.”

Plug and Play

The plug-and-play feature automatically assigns resources when peripherals (plug-in cards) are being installed, obviating the need to set switches or jumpers. Of course, the hardware must be plug-and-play compatible to let the software perform this feat.

“But data acquisition users will most likely be left out in the cold,” predicted Mr. Brown. “A/D cards don’t have the market share of video cards, so don’t expect the data acquisition card manufacturers to suddenly support a feature that does nothing for raw performance but lets the cards automatically configure themselves.”

Others are more optimistic. “Many of the support calls we receive for HP BenchLink products, for instance, involve the connection between the instrument and the PC, rather than problems with software,” said Mr. Cunningham. “Plug and play isn’t perfect; but since it eases the difficulty of installing hardware, it is worthwhile.”

Long File Names

Under DOS and Windows 3.1x, file names could be no longer than 8.3 characters. This has changed under Windows 95, and files can be designated with much longer, and usually more meaningful, names. This works well for all new 32-bit applications, but not if a mix of 32- and 16-bit applications are to be run.

“Each long file name automatically generates an alias name in the older format—a truncated version that 16-bit programs will recognize when accessing the file,” explained Kerry Newcom, President of Capital Equipment. “This can create several problems.

“For instance, when using long file names on network drives and sharing files with Windows 3.x, clients may tend to delete the long names. Or when backing up a Windows 95 hard disk to tape and then restoring, the tape can wipe out longer file names, leaving eight-character aliases, such as FILENA^1.TXT. In a mixed environment of Windows 95 and Windows 3.1x programs, it may be far better to stick with the old 8.3 file-naming convention,” Mr. Newcom suggested.



Conclusions

 

The increased processor speed, memory and bus transfer rates furnished by today’s PCs can certainly benefit many, but not all, data acquisition systems. Applications that tend to gain the most are those that require high-speed acquisition, data streaming to disk, or extensive post-processing. Better human interfaces can also be achieved since the PCs support better graphics without penalizing performance.

 

However, some of the increased hardware performance may not aid the application at all, but merely support the increased demands made by new software. “In fact, a Pentium with 8 MB of DRAM and running Windows 95 is not much faster than a 486 machine running Windows 3.1x,” observed Mr. Gaurie.


As for software, many applications will continue to be adequately served by DOS with its low overhead, and some will still require a real-time deterministic OS. But for all others, there is a question of whether, or when, to upgrade from Windows 3.1x to Windows 95.

“For the majority of PC-based data acquisition applications, Windows 3.1x already provides enough performance,” said Mr. Brown. “Windows 95 does improve on Windows 3.1x, but we are not talking orders of magnitude here. Some of the more annoying limitations of Windows 3.1x have been revamped in Windows 95. As a result, the whole system runs much smoother, but most users will not need to move immediately to Windows 95 to attain significant real-world performance.”

However, moving is probably only a matter of time, since much of the software used in conjunction with data acquisition will be upgraded and only supported as Windows 95 versions. Existing and future 16-bit data acquisition applications can certainly run under Windows 95, which may be looked upon as a 32-/16-bit OS, but functionality can be improved if they are native 32-bit applications.

Many applications that require more performance or greater robustness than either Windows 3.1x or 95 can provide will be written for Windows NT, the true 32-bit environment. A smooth migration from Windows 3.1x to Windows 95 may provide PC-based data acquisition system developers with the opportunity to prepare for the future and gain performance advantages.

References

1. Stalker, J. C., “ISA vs PCI in Data Acquisition,” EE-Evaluation Engineering, March 1996, pp. 14-18.

2. Copeland, L., “Performance Considerations for High-End PC I/O Boards,” Datel Application Note AN-9, 1995.

3. Boriero, P., “Windows NT vs Windows 95,” EE-Evaluation Engineering, November 1995, pp. 30-35.

These companies provided information for this feature:

Alligator Technologies (714) 850-9984

Capital Equipment (617) 273-1818

Data Translation (800) 525-8528

Datel (508) 339-3000

HEM Data (800) 436-4330

Hewlett-Packard (800) 452-4844

Intelligent Instrumentation (800) 685-9911

IOtech (216) 439-4091

Keithley MetraByte (800) 348-0033

National Instruments (512) 794-0100

Sheldon Instruments (800) SHELDON

Copyright 1996 Nelson Publishing Inc.

May 1996




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