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3. Buying the Basics

In this section, we cover things to look out for that are more or less independent of price-performance tradeoffs, part of your minimum system for running Unix.

Issues like your choice of disk, processor, and bus (where there is a strong tradeoff between price and capability) are covered in the section on performance tuning.

3.1. Getting Down to Cases

I used to say that cases are just bent metal, and that it doesn't much matter who makes those, as long as they're above an easy minimum quality (on some really cheap ones, cards fail to line up nicely with the slots, drive bays don't align with the access cutouts, or the motherboard is ill-supported and can ground out against the chassis).

Unfortunately, this isn't true any more. Processors run so hot these days that fans and airflow are a serious concern. They need to be well designed for proper airflow throughout.

If you're fussy about RFI (Radio-Frequency Interference), it's worth finding out whether the plastic parts of the case have conductive coating on the inside; that will cut down emissions significantly, but a few cheap cases omit it.

Look for the following quality features:

Should you buy a desktop or tower case? Our advice is go with tower unless you're building a no-expansions personal system and expect to be using the floppies a lot. Many vendors charge nothing extra for a tower case and the absolute maximum premium I've seen is $100. What you get for that is less desktop clutter, more and bigger bays for expansion, and often (perhaps most importantly) a beefed-up power-supply and fan. Putting the box and its fan under a table is good for maybe 5db off the effective noise level, too. Airflow is also an issue; if the peripheral bays are less cramped, you get better cooling. Be prepared to buy extension cables for your keyboard and monitor, though; vendors almost never include enough flex.

The airflow thing is a good argument for a full- or mid-tower rather than the `baby tower' cases some vendors offer. However, smaller towers are getting more attractive as boards and devices shrink and more functions migrate onto the motherboard. A state of the art system, with all 3" disks, 300W power supply, half-size motherboard, on-board IDE and 64meg of RAM sockets, and half-sized expansion cards, will fit into a baby or midized tower with ample room for expansion; and the whole thing will fit under a desk and make less noise than a classic tower.

For users with really heavy expansibility requirements, rackmount PC cases do exist (ask prospective vendors). Typically a rackmount case will have pretty much the same functionality as an ordinary PC case. But, you can then buy drive racks (complete with power supply), etc. to expand into. Also, you can buy passive backplanes with up to 20 or so slots. You can either put a CPU card in one of the slots, or connect it to an ordinary motherboard through one of the slots.

I've recently become a big fan of Antec cases. They're inexpensive, sturdy, and thoughtfully engineered.

3.2. Power Supplies and Fans

Power supplies can matter but quality is cheap; give preference to those with a Underwriter's Laboratories rating. There's some controversy over optimum wattage level. On the one hand, you want enough wattage for expansion. On the other, big supplies are noisier, and if you draw too little current for the rating the delivered voltage can become unstable. And the expected wattage load from peripherals is dropping steadily. On the other hand, processors and their cooling fans eat a lot more power than they used to.

The choice is generally between 200W and 300W. After some years of deprecating 300W-and-up supplies, I'm now persuaded it's time to go back to them; a modern processor can consume 50-75W by itself, and for the newer dual-processor board the power supply needs to be rated 450W or up.

Quality brands include PC Power and Cooling, Antec and Sparkle. A lot of no-name power supplies are out of spec; this is an area where buying a name brand is good tactics (the price premium won't be large).

About that annoying fan noise, ask if the power-supply fan on a target system has a variable speed motor with thermostatic control; this will cut down on noise tremendously. However, be aware that a thermostatic sensor basically measures the temperature at the sensor (typically within the power supply box) and makes sure there is enough airflow to keep the power supply from overheating. The sensor does not know a thing about the temperature in certain hot spots likely to develop in a PC case (CPU, between SIMMs, between drives mounted in vertically adjacent bays).

This can be a problem, because in garden variety tower cases there often isn't enough airflow to cool all components effectively even if a single fan is going at full speed. This is especially true if your computer has lots of add-on cards or hard disks (not much airflow between cards or between drives). Note that the fan in the power supply was basically designed to cool the power supply, not the components in the case. Not providing additional fans is a sign of cheapness. On tower PCs with "expensive" engineering (e.g. HP Vectra, Compaq) one will find one to two extra fans besides the one in the power supply.

So the bottom line is, use thermostatic controls if you can to cut noise. But if you want high reliability, use two or more fans. Modern designs normally also have a small auxilliary fan mounted right over the chip.

The noise produced by a fan is not just a function of the speed with which it turns. It also depends on the nature of the airflow produced by the fan blades and the bearings of the rotor. If the blades causes lots of turbulent airflow, the fan produces lots of noise. One brand of fans that is much more silent than most others even if going at full throttle is Papst.

3.3. Motherboards

Provided you exercise a little prudence and stay out of the price basement, motherboards and BIOS chips don't vary much in quality. There are only six or so major brands of motherboard inside all those cases and they're pretty much interchangeable; brand premiums are low to nonexistent and cost is strictly tied to maximum speed and bus type. Unless you're buying from a "name" outfit like Compaq, Dell, or AST that rolls its own motherboards and BIOSes, there are only four major brands of BIOS chip (AMI, Phoenix, Mylex, Award) and not much to choose between 'em but the look of the self-test screens. One advantage Unix buyers have is that Unixes are built not to rely on the BIOS code (because it can't be used in protected mode without more pain than than it's worth). If your BIOS will boot properly, you're usually going to be OK.

The old ``AT'' and ``Baby AT'' motherboard form factors are obsolete. It's an ATX world now.

There are still a few potential gotchas to beware of, especially in the cheaper off-brand boards. One is ``shadow RAM'', a trick some boards use for speeding up DOS by copying the ROM contents into RAM at startup. It should be possible to disable this. Also, on a cacheing motherboard, you need to be able to disable cacheing in the memory areas used by expansion cards. Some cheap motherboards fail to pass bus-mastering tests and so are useless for use with a good SCSI interface; on others, the bus gets flaky when its turbo (high-speed) mode is on. Fortunately, these problems aren't common and are becoming less so.

You can avoid both dangerously fossilized hardware and these little gotchas by sticking with a system or motherboard design that's been tested with Unix.

Some other good features to look for in a motherboard include:

If you're changing a motherboard, see the Installing a Motherboard page first. This one even has a Linux note.

3.4. Memory

All current PC designs include a cacheing memory controller and some fast on-chip cache that combine to produce higher effective speeds. Judging the cache design used to be one of the trickiest parts of the motherboard, but that stuff is all baked into the processor itself now.

Current motherboards use PC100 or PC133 SDRAM, which comes packaged on 168 pin DIMM modules. SDRAM is a large step forward in memory speed, at 10ns. SDRAM does not need to be installed in pairs. The key words you want to see on the spec sheet are:

For current motherboards with 133MHz Memory Bus support, PC133 should be used instead of PC100; it gives 33% greater memory bandwidth at very little additional cost. DDR-SDRAM and RDRAM are faster memory types that retrieve data in chunks and give you faster throughput. So-called `PC266' memory is designed for motherboards that transfer at 133 but double the width of the front-side bus connecting processor and memory.

As the throughput of processor-to-memory buses rises, memory latency (bus cycles required for the first fetch in a chunk) is becoming a more important statistic. Lower numbers are better.

For more technical stuff on memory architectures, see The Ultimate Memory Guide maintained by Kingston Technologies.

3.5. Buying a Video Card

Video controllers translate byte values deposited in their video memory by your GUI (usually an X server under Linux) into an analog RGB signal which drives your monitor. The simplest kinds treat their video memory as one big frame buffer, requiring the CPU to do all dot-painting. More sophisticated ``accelerated'' cards offer operations such as BitBlt so your X server can hack the video memory algorithmically. These days almost all cards even at the low end actually have some acceleration features.

Cards are rated by the maximum number of analog signal changes they can produce per second (video bandwidth). Video bandwidth can be used to buy varying combinations of screen resolution and refresh speed, depending on your monitor's capabilities.

Another important variable of video cards is the size of their on-board video RAM. Increased memory lets you run more colors at higher resolutions. For instance, a 1MB card usually will only allow 256 colors at 1024x768 while a 2MB card usually allows at least 16-bit color (a palette of about 65,000 colors). You'll need 4MB of video memory to use 24-bit or ``true'' color (16 million colors) at 1024x768.

The card's video RAM size has no effect on its speed. What does affect speed is the type of memory on board. VRAM (Video Random Access Memory) is fast but more expensive; it features a dual-ported design allowing two devices (the CRT controller and the CPU) to access the memory at the same time. DRAM (Dynamic Random Access Memory) is is similar to the RAM used in main memories. It is cheaper, more common, and slower (because the CRT controller and the CPU must take turns accessing the video buffer).

A quick review of monitor standards:

Table 1. Monitor standards

NameResolutionColorsHorizontal FrequencyVertical FrequencyNotes
MDA720x350 18.43 KHz50 HzObsolete
CGA640x200215.85 KHz60 HzObsolete
EGA640x3501621.80 KHz60 HzObsolete
VGA640x4801631.50 KHz60 Hz 
VESA VGA640x4801638.86 KHz72 Hz 
VESA SVGA800x6001648.01 KHz72 Hz 
8514/A1024x7681635.20 KHz43.5 HzObsolete
VESA 1024x7681024x76825656.48 KHz70 Hz 

The Horizontal and Vertical Frequency columns refer to the monitor scan frequencies.

The vertical frequency is the upper limit of the monitor's flicker rate; 60Hz is minimal for ergonomic comfort, 72Hz is VESA-recommended, and 80Hz is cutting-edge. At resolutions above VGA, horizontal scans take long enough that the monitor may never reach anywhere near the vertical-frequency maximum; how close it gets is a function of the horizontal-scan frequency (higher is better).

For more information on how to avoid the evil screen flicker, see the XFree86 Video Timings HOWTO, a tutorial written by your humble editor and included with the XFree86 distribution.

It's no longer possible to find MDA video boards and monitors out there. Anyway, prices for SVGA have collapsed so totally that it's wouldn't be worth bothering.

XGA is an IBM-proprietary included for completeness, but is vanishingly rare in the clone market. 8514/A is another IBM standard supported by a few graphics accelerator cards. It is interlaced, and thus has a tendency to flicker. The VESA 1024x768 standard makes XGA and 8514/A obsolete.

SVGA or `Super VGA' strictly refers only to 800x600 resolution, but is widely used for 1024x768 and even 1280x1024 resolutions. Standards above 1024x768 are weak and somewhat confused.

These days, most vendors bundle a 15" or 17" monitor and super-VGA card with 1024x768 resolution in with their systems. Details to watch are the amount of RAM included (which will affect how much of that maximum resolution and how many colors you actually get), and whether the memory is dual-ported VRAM (slightly more expensive but much faster).

More information on video standards is available at the Video Display Standards page of the PC Guide site.

3.6. Selecting a Monitor

3.6.1. What To Look For On The Spec Sheet.

  • Dot pitch of 0.28 or smaller on a 12"-15" monitor; 0.30 is acceptable on larger ones, especially 19" to 21" screens (but look extra hard at 0.25 21-inchers like the Viewsonic 21PS or Nokia 445X). Dot pitch is the physical resolution of the screen's phosphor mask. Larger dot pitches mean that small fonts and graphic details will be fuzzy.

  • 72Hz or better vertical scan frequency, to cut flicker.

  • Non-interlaced display. Interlacing cuts the required scan frequency for a given resolution in half, but makes flicker twice as bad. As a result, interlaced monitors are rapidly disappearing; don't get stuck with one.

  • Does it have a tilt-and-swivel base? Adequate controls, including both horizontal and vertical size and horizontal and vertical centering? A linearity control, a trapezoidal control, and a color-temperature control are all pluses; the last is particularly important if you compose graphics on screen for hardcopy from a printer.

  • For X use, a 14", .28mm dot pit, non-interlaced 72Mhz monitor at 640x480 resolution is the bare minimum for comfortable use, and that resolution leaves you rather squeezed for screen real estate. 1024x768 is much better. If your budget will stand it at all, a 17" or 20" monitor is a good investment. A 17" monitor is minimum if you're going to go with 1280x1024 of 1600x1200 resolution.

If you can, buy your monitor from someplace that will let you see the same monitor (the very unit you will walk out the door with, not a different or `demo' unit of the same model) that will be on your system. There's a lot of quality variation (even in "premium" monitor brands) even among monitors of the same make and model.

Another good reason to see before you buy, and carry it home yourself, is that a lot of monitors are vulnerable to bumps. The yoke can get twisted, producing a disconcerting tilt in the screen image.

The Caveat Emptor guide has a good section on evaluating monitor specifications. And there's a database of monitor specs at The Big Old Monitor List.

3.6.2. Eric Buys A Big Monitor: Smart Shopping Tips

In early 1996 the good folks at O'Reilly Associates dropped several $1000 checks on me in relatively quick succession (payment for fast-turnaround technical reviews). I decided to use the money to treat myself to a really good monitor.

This page tells you how I did it. Specific specs and pricing information will date quickly, but the method should still be good years from now.

My existing monitor wasn't bad -- a 17-inch Swan 617 that I could drive at a bit above 1024x768. Still, I yearned for more real estate -- especially vertical real estate, so I could view full PostScript pages using a legible font.

This brings us to our first prescription: be clear about what you want. It's easy, and very expensive, to buy more monitor than you'll really use.

I knew I wanted something in the 19-to-21-inch range, with 1280x1024 or higher resolution. I knew this would probably cost me about $2000, and could afford it. I knew I didn't need one of the monster projection monitors further upmarket, with screen sizes 24" and up. These will typically cost you $4K or so and are too big for desktop use anyway.

I also knew I didn't need one of the special true-color monitors designed for photo composition, making print separations, and so forth. These creatures (always Trinitrons) have better, denser color than conventional tubes but at a hefty price premium (and usually at some cost in available resolution). If all you're going to do most of the time is 16 or 256-color X screens, you don't need this capability.

Once you've settled on what you need, gather comparative data. It was 1996, so I started out by making phone calls to manufacturer 800 numbers. Then I discovered that almost all the manufacturers had Web sites, with technical specs for their monitors on them. Today, you'd go to the Web first.

(This space used to include detailed technical data on what I found " model numbers, resolutions, reviews of manufacturer websites, etc." but I've removed it because it's all five years out of data now.)

This wasn't at all a hard call. The ViewSonic 21PS and Nokia 445X stood out from the pack immediately; their combination of high bandwidth with a 21-inch screen size and ultra-fine .25 dot pitch promised better performance than the general run of .28-pitch monitors.

Nor was the choice between the two very hard. ViewSonic's 21PS is $600 less expensive than Nokia's 445X for very similar performance. And, other things being equal, I'd rather buy a monitor from a specialist monitor manufacturer than a general consumer electronics outfit best known for its cellular phones.

So I determined to order a ViewSonic 21PS.

This left me with a second problem. My ATI Mach 32 can't drive a monitor at higher than 1280x1024 resolution and 94MHz bandwidth. So it wouldn't be able to drive the 21PS at 1600x1200. I wound up buying a Mach 64.

The combination worked wonderfully (two years later I discovered that VA Linux Systems bought the same monitor for its high-end systems). The only problem I have with it is that monitor is way bright even dialed down to its dimmest setting. You'll need a strong light in the room where you install it. Also, be aware that the only really convenient way to move one of these monster monitors is with a forklift!

3.7. Keyboards

It's important to get a high quality keyboard with good key feel. See the typing-injury FAQ from to see what happens if you don't. Carpal tunnel syndrome is no fun for anyone, but it hits hackers particularly hard. Don't be a victim!

Hal Snyder of Mark Williams, Co sent us the following caveat: "We find that about 10% of cheap no-name keyboards do not work in scan code set 3. We are interested in scan code set 3 because only there can you reprogram the keyboard on a per-key basis as to whether keys are make-only, make-break, or autorepeat. It is a big win for international support and for X."

He continues: "Keytronic, Cherry, and Honeywell keyboards, as well as a large number of imports, work fine. My advice is to either buy a respected brand of keyboard, or deal with a vendor who will allow you to return an incompatible keyboard without charge."

Allen Heim <> writes: I'm sold on NMB keyboards (, available from Global Computer (, or at (800) 8-GLOBAL. Their line of mechanical-switch keyboards now have a lifetime warranty, and I've just ordered my second RT-8200 unit. I don't see it listed on their website currently, but I do see their "Windows 95-enhanced" model, the RT-8200W. It's the same thing, but with extra keys (which may be programmable; think of the Emacs "meta" key--could be useful).

Following the wave of mid-1990s publicity about repetitive-strain injuries, ergonomic keyboards have become increasingly common. One that looks promising to your editor (though I haven't yet used it) is the Marquardt MiniErgo MF2, from Marquardt Switches, Inc.; 2711 Route 20 East, Cazanovia NY 13035, phone (315)-655-8050; suggested list price $170, AT-compatible interface). Michael Scott Shappe <> sent me a rave review of the Marquardt after having used it about six months.

The MF2 features a conventional QWERTY layout, but with the right and left halves split apart and rotated about 30 degrees towards each other in a shallow V shape. The theory is that being able to angle your arms inward and your elbows out produces a less stressful typing position.

The MF2 has no keypad, but it does have the standard 12 function keys across the top and arrow keys at the point of the V (meant to be thumb-operated).

I have seen and used a device called the Maltron ergonomic keyboard. This keyboard splits the keys into two main groups, each arranged in a dished hollow. Each hand also has easy access to separate thumb pads of nine keys each; there is one numeric and arrow-key pad in the center of the unit, between the right and left-hand groups. Also, the keys in each group do *not* have the alternate-row staggering of the conventional (Scholes) keyboard; this subtle change reduces torsional stress on the fingers and wrists tremendously.

I found the Maltron easy to use, and regretted having to give it back.

For more details on many ergonomic keyboards and typing-injury issues in general, see Dan Wallach's FAQ on repetitive strain injuries and ergonomic input devices, published monthly in news.answers

3.8. Floppy Drives

There's not much to be said about floppy drives. They're cheap, they're generic, and the rise of CD-ROM drives as a cheap distribution medium has made them much less important than formerly. You only ever see the 3.5-inch `hard-shell' floppies with 1.44MB capacity anymore.

You'll probably never use floppies for anything but first boot of a new operating system. Bootable CD-ROMs, standard of most PCs these days, eliminate even that use. So go ahead and settle for cheap Mitsumi and Teac floppy drives. There are no `premium' floppy drives anymore. Nobody bothers.

3.9. Printers

There's one huge gotcha about printers: Don't Get a `GDI' printer!

3.9.1. GDI printers: avoid!

Low-end printer manufacturers have been increasingly moving towards `GDI' or `Windows' printers for their laser or LED models. These have the unfortunate characteristic of being, at worst, unusable from Unix; and at best, useable only with reduced resolution (e.g., 300 dpi from a 600 dpi printer).

The problem is that the design of laser printers inherently requires that data move onto the imaging drum at a precisely-controlled rate, and so laser (and LED) printers have traditionally included a CPU of moderate speed and enough RAM to image an entire page, either as a complete bitmap or as ASCII, using a quick font rasterizer to form images on-the-fly. GDI printers, however, offload this responsibility to the computer, and therefore require very specialized drivers that (a) are not available for any Unix, AFAIK; and (b) slow down the computer a lot when printing is underway.

Most GDI printers DO support HP's PCL in a lower resolution, so they can often be used from Unix via Ghostscript, but only in 300 dpi and/or missing some features. They may also be slower in this mode than in their native GDI modes. In order to print at 600 dpi with Ghostscript, a PCL printer must support HP's PCL at level 5e or better, so printer purchasers should look for that in any non-PostScript model, at least at the moment. (Naturally, all of this could change if/when support is added to Ghostscript for more esoteric models; but AFAIK, this is the current set of limitations.)

Finally, I've seen one extra twist on this already-twisted marketplace: The Brother HL-720 is advertised as supporting `PCL 5e for DOS' (or words to that effect). What this means is that it's a GDI model with a DOS driver that takes PCL 5e input and translates it to the printer's native GDI mode. Needless to say, this is useless for Unix.

GDI printers are a bad design even for the DOS lemmings, because they slow the machine down significantly while printing is going on. Like `WinModems', they're a sleazy way for manufacturers to save a few bucks. Our advice is, buy a printer with native Postscript and avoid all this crap.

3.9.2. Non-GDI printers

There really isn't all that much to be said about printers; the market is thoroughly commoditized and printer capabilities pretty much independent of the rest of your hardware. The PC-clone magazines will tell you what you need to know about print quality, speed, features, etc. The business users they feed on are obsessed with all these things.

Most popular printers are supported by GhostScript, and so it's easy to make them do PostScript. If you're buying any letter-quality printer (laser or ink-jet), check to see if it's on GhostScript's supported device list -- otherwise you'll have to pay a premium for Postscript capability! Postscript is still high-end in the MS-DOS market, but it's ubiquitous in the Unix world.

Warning, however: if you're using ghostscript on a non-Postscript printer, printspeed will be slow, especially with a serial printer. A bitmapped 600 dpi page has a lot of pixels on it. Further, if you're doing much printing, ghostscript will create enormous spool files. (megabytes/page). At today's prices, paying the $750 or so for Postscript capability makes sense.

If you're buying a printer for home, an inkjet is a good choice because it doesn't use gobs of power and you won't have the toner/ozone/noise/etc mess that you do with a laser. If all you want is plain-ASCII, dot-matrix is cheaper to buy and run.

Inkjets are great in that they're cheap, many of them do color, and there are many kinds which aren't PCL but are understood by Ghostscript anyway. If you print very infrequently (less than weekly, say), you should be careful to buy a printer whose print head gets replaced with every ink cartrige: infrequent use can lead to the drying of the ink, both in the ink cartrige and in the print head. The print heads you don't replace with the cartrige tend to cost nearly as much as the printer (~$200 for an Epson Stylus 800) once the warranty runs out (the third such repair, just after the warranty expired, totalled one informant's Stylus 800). Be careful, check print head replacement costs ahead of time, and run at least a cleaning cycle if you don't actually print anything in a given week. (Conversely, toner starts out dry, and ribbon ink won't evaporate for years...if you truly print only rarely, but neither a dot matrix nor a laser makes sense, consider buying no printer and taking your PostScript files to a copy shop...)

A parallel interface is a cheap way to make your printer print a lot faster than a serial line, and everyone's got a parallel port in their PC.

A few printers for the MS-DOS market require a special controller card and proprietary cable to do PostScript. These require MS-DOS software and typically won't run under Unix at all.

Meanwhile, there are several true 600 dpi lasers that grok PCL 5e, yet cost less than $500 retail. Currently (December 1997) these include the Lexmark Optra E (and E+), the HP 5L (and 5L with suffix, and probably 6L), and the Brother 760. As you can't easily buy a new hard drive smaller than 2 gigabytes, tens of megabytes of spare space in /var/spool should be the accepted norm, rather than a problem, for new systems; I've also noticed that PCL 5e seems to include some amount of compression (probably RLE or font encoding) which works rather well for text, further reducing the spool requirements.

One of our spies says good things about the Canon BJC-240 and 250. He reports they preint well with Ghostscript and are more reliable than Deskjets.

I personally have a LaserJet 6MP, and like it.

3.10. Power Protection

3.10.1. Overview

Finally, I strongly recommend that you buy a power conditioner to protect your hardware. MOV-filtered power bars make nice fuses (they're cheap to replace), but they're not enough.

The technical info in the remainder of this section is edited from material supplied by David E. Wexelblat ><.

There are several levels of power protection available to the home computer user. I break this down into 4 levels; others may have different ways of classifying things. The levels are:

  1. Surge Suppressor

  2. Line Conditioners

  3. Standby Power Supplies

  4. Uninterruptible Power Supplies

And here's what they mean:

3.10.2. Surge suppressors

These are basically a fancy fuse between the source and your hardware; they clamp down spikes, but can't fill in a low voltage level or dropout.

This is a bare minimum level of protection that any piece of expensive electronics should have. Note that this applies to more than just AC power; surge suppressors are available for (and should be used on) phone lines, and RS-232 and parallel connections (for use on long lines; generally not needed if the devices is colocated with the computer and all devices are protected from outside sources). Note also that all devices connected to your computer need to be protected; if you put a surge suppressor on your computer but not your printer, then a zap on the printer may take out the computer, too.

An important fact about surge suppressors is that they need to be replaced if they absorb a large surge. Besides fuses, most suppressors rely on on components called Metal-Oxide Varistors (or MOVs) for spike suppression, which degrade when they take a voltage hit. The problem with cheap suppressors is that they don't tell you when the MOV is cooked, so you can end up with no spike protection and a false sense of security. Better ones have an indicator.

You can buy surge suppressors at any Radio Shack; for better prices, go mail-order through Computer Shopper or some similar magazine. All of these are low-cost devices ($10-50).

3.10.3. Line Conditioners

These devices filter noise out of AC lines. Noise can degrade your power supply and cause it to fail prematurely. They also protect against short voltage dropouts and include surge suppression.

My Tripp-Lite 1200 was typical of the better class of line conditioners; a box with a good big soft-iron transformer and a couple of moby capacitors in it and no conductive path between the in and out sides. With one of these, you can laugh at brownouts and electrical storms. You can get for $139 or so by mail order. A fringe benefit of this little beauty is that if you accidentally pull your plug out of the wall you may find you actually have time to re-connect it before the machine notices (I did this once). But a true SPS or UPS is better.

Netter Trey McLendon has good things to say about Zero Surge conditioners. He says: "Our systems at work [...] have been protected for 2.5 years now through many a violent strike knocked [out] the MOV-type suppressors on a Mac dealer's training setup across the street from us. The Zero Surge just sort of buzzed when the surge came in, with no interruption whatsoever. The basic principle is this: ZS units slow down the surge with a network of passive elements and then sends it back out the neutral line, which is tied to ground _outside at the box_ by code. MOV units shunt the surge to ground _at the computer_, where it leaps across serial ports, network connections, etc. doing its deadly work."

Price vary widely, from $40-400, depending on the power rating and capabilities of the device. Mail-order from a reputable supply house is your best bet. Line conditioners typically don't need to be replaced after a surge; check to see if yours includes MOVs.

3.10.4. Standby power supplies (SPSs)

These devices are battery-based emergency power supplies that provide power for your system via an inverter if the power fails. An SPS will generally have all the capabilities of a line conditioner as well.

Note: these devices do not come on line until after the power fails, and have a certain amount of delay (typically some milliseconds) before they come on line. If the capacitors in your power supply are not large enough, the SPS may not cut in soon enough to prevent your computer from seeing the power failure.

Note also that many SPSs are marketed as Uninterruptable Power Supplies (see below). This is incorrect. Any device with a non-zero cutover time cannot be a true UPS. If the ad mentions a cutover time, it's an SPS, and not a UPS.

The price range for these devices (increasing with increasing peak load capacity and with decreasing cutover time) is $200-2000. An SPS will not need to be replaced after absorbing a large surge.

3.10.5. Uninterruptable power supplies (UPSs)

These devices provide full-time isolation from the incoming AC line through a transformer of some sort. These devices are on-line at all times, and if the AC line fails, the batteries will cut in. Your devices will see no interruption of their incoming AC. UPSs cost more, and provide more features. They are the ultimate in power protection. Many UPSs have an intelligent interface that will notify a connected device of a power failure, allowing it to shut down cleanly. UPSs also provide the capabilities of a line conditioner. The price range (for devices in the size range for a home computer) are $200-$1500. An UPS will not need to be replaced after absorbing a large surge.

Now, given this information, how does one decide what to get? For a system that runs unattended, like most Unix systems, it is best to have a device that provides both power holdover and a power failure signal. Hence, for a Unix system, a UPS or SPS with Unix monitoring software is the best choice.

If the vendor isn't secretive about interface specs, it's fairly simple to write your own daemon to monitor a serial port, and send init a SIGPWR signal when it sees a powerdown notification on the port. Freeware power-monitor demons are available for Linux.

Many UPS/SPS signal ports work by asserting a pin, so that one could use a modem-control serial port on the PC and wire this pin to "Carrier Detect" in order to monitor it. Some, like the APC "SmartUPS" series, actually conduct an ASCII dialog with the host through a serial line in order to accomplish the monitor functions.

Our recommendation for a production Unix environment is a configuration like the following:

  1. An on-line UPS or SPS for the computer system. An intelligent interface is mandatory, along with appropriate software for ordered shutdown.

  2. Surge suppression on all phone lines, and also on serial/parallel lines that leave the room.

  3. Line conditioners on any devices not connected to the UPS. If you do take a power hit, it's cheaper to replace a $50 line conditioner than a $1500 laser printer.

If this is too expensive for you, then downgrade the UPS/SPS to a line conditioner like the TrippLite. But don't go without at least that. Running unprotected is false economy, because you will lose equipment to electrical storms — and, Murphy's Law being what it is, you will always get hit at the worst possible time.

An important question is "How do I know how big a UPS/SPS to get?" The watt rating of the UPS/SPS should be at least the sum of the peak ratings off all equipment connected to it (don't forget the console monitor). Power-supply marketroids tend to quote you capacities and formulas like "sum of VA ratings + 20%" which (surprise!) push you towards costlier hardware. Ignore them. If a watt rating is not given, watts = 0.75*VAmax.

One other consideration is that you typically shouldn't put a laser printer on a UPS — toner heaters draw enough current to overload a UPS and cause a shutdown within seconds. The other thing is that you can't even put the laser printer on the same circuit with a UPS — the heater kicks on every 20-30 seconds, and most UPSs will see the current draw as a brownout. So buy a separate line conditioner for the laser printer.

Finally, read the UPS's installation manual carefully if you're going to use it with other power-protection devices. Some UPSs don't like having surge suppressors between them and the equipment.

David personally recommends surge suppressors and line conditioners from Tripp-Lite (available both mail-order and retail), and UPSs from Best Power Technologies (Necedah, WI - 1-(800)-356-5737). I can enthusiastically second the TrippLite recommendation, but haven't dealt with Best Power at all.

Tripp-Lite has a whole range of products, from a $10 phone-line surge-suppressor, to line conditioners and SPSs with prces in the hundreds of dollars. They have a line of $50-80 line conditioners that are good for most peripherals (including your home stereo :->).

Best Power Technologies sells two lines of UPSs in the range for home systems. The older and more expensive FERRUPS line (which is what David has) has a smart interface, and very good filtering and surge-suppression capabilities. He says "I have a 1.15kVA FERRUPS for my home system, which is overkill with my current hardware (although it rode out a 45 minute power failure with nary a whisper - no reboot). In 1990, I paid ~$1600 for this device, and that has since gone up. They also sell a newer line of Fortress UPSs. These are better suited in price for home systems. I don't know much about them, as they were not available when I bought my UPS. I expect that this is what most people will want to consider, though. In addition, Best sells Check-UPS, a software package (in source form) for monitoring the UPS and shutting it down. I have found Best to be a good company to deal with, with competent, knowledgeable sales people (who will be able to help you pick the right device), and helpful, courteous, and responsive technical support."

Other things to know:

A UPS should be wired directly to (or plugged directly into) the AC supply (i.e. a surge suppressor is neither required nor suggested between the wall and the UPS). In addition, a surge suppressor between the UPS and the equipment connected to it is redundant.

3.11. Radio Frequency Interference

(Thanks to Robert Corbett <Robert.Corbett@Eng.Sun.COM> for contributing much of this section)

Radio Frequency Interference (RFI) is a growing problem with PC-class machines. Today's processor speeds (above 33MHz) are such that the electromagnetic noise generated by a PC's circuitry in normal operation can degrade or jam radio and TV reception in the neighborhood. Such noise is called Radio Frequency Interference (RFI). Computers, as transmitting devices, are regulated by the Federal Communications Commission (FCC).

FCC regulations recognize two classes of computer:

If a PC is to be used in a home or apartment, it must be certified to be FCC class B. If it is not, neighbors have a legal right to prevent its use. FCC class A equipment is allowed in industrial environments.

Many systems are not FCC class B. Some manufacturers build boxes that are class B and then ship them with class A monitors or external disk drives. Even the cables can be a source of RFI.

It pays to be cautious. For example, the Mag MX17F is FCC class B. There are less expensive versions of the MX17 that are not. The Mag MX17 is a great monitor (I wish I had one). It would be painful to own one and not be allowed to use it.

An upgradeable system poses special problems. A system that is FCC class B with a 33 MHz CPU might not be when the CPU is upgraded to a 50 or 66 MHz CPU. Some upgrades require knockouts in the case to be removed. If a knockout is larger than whatever replaces it, RFI can leak out through the gap. Grounded metal shims can eliminate the leaks.

Even Class B systems don't mix well with wireless phonesets (not cellular phones, but the kind with a base station and antennaed headset). You'll often find a wireless phone hard to use withing 20 feet of a Class B machine.

To cut down on RFI, get a good metal case with tight joints, or at least make sure any plastic one you buy has a conductive lining. You can also strip the painted metal-to-metal contacting parts of paint so that there's good conductive metal contact. Paint's a poor conductor in most cases, so you can get some benefit from this.

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