Nash - Scientific Computing with PCs (523165), страница 32
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This is not always under our control. We havein the past resorted to making our own filters from rigid domestic forced air furnace filter material. Suchfilters were held in place by plastic U-channel (normally used as kitchen shelf edging), though Velcrowould do. We arranged that the cooling fan sucked air through the filter, but are aware that this is noteasy to do on all machines.92Copyright © 1984, 1994 J C & M M NashNash Information Services Inc., 1975 Bel Air Drive, Ottawa, ON K2C 0X1 CanadaSCIENTIFIC COMPUTING WITH PCsCopy for:Dr. Dobb’s JournalReduce clutterKeep wires off the floor and out of the way. Make sure the PC is on a steady surface, otherwise bangingor wobbling of the surface may cause disks to go out of alignment.Adjust ventilation or add fansThe cooling of PCs is often not given a very high priority.
Fans may be poorly positioned in the case.Floating-point hardware uses power to obtain the required speed. You can easily get a mild (thermal!)burn by touching a floating-point "chip" while it is processing. In a recent software demonstration, the PChad its case off and a desk fan blowing over a floating-point co-processor. The presenters complained thatwithout the fan, the unit was overheating, resulting in intermittent failure of the whole system. Theco-processor itself may not have been failing; the fault could be in nearby chips, or come from thermalstress on connectors or solder joints on the circuit board(s).Keep the PC room comfortableIf the PC room is hot or cold, dry or sticky, it is not only the user who suffers.
Overheating is a greaterdanger than cold, since it is rare that PCs live in rooms where the temperature is even approaching thefreezing point. Once the power is on, the PC will generate some heat. If the room is dry, static electricitymay be a problem. High humidity may give condensation on components and cause short circuits.Control staticStatic electric discharges from the user against the keyboard or other ungrounded parts of the equipmentcan have serious consequences by altering memory contents or burning out integrated circuits.
In our ownexperience, we have rarely needed to take special measures such as anti-static carpet. Some users installa grounded button or wire that they touch before touching any other part of the equipment. Such a buttonis not needed if a grounded conductor is available, such as the metal casing (unpainted) of the PC.However, it is important to verify that the casing is grounded and to remember to touch it before touchingthe keyboard. High voltage discharges to the casing may still cause troubles. Therefore, if one notices thatstatic electricity has reached the level of sparks, it is time to take other measures such as anti-static carpetsand humidification.Clean the PCEven with dust filters on PC air intakes, some dust will get inside.
Therefore, once a year or so, it is agood idea to check the interior of the equipment and clean if necessary. This implies some disassemblyof the PC and removal of circuit boards. We use a vacuum cleaner with a gentle brush nozzle to removedust from the circuit boards and the chassis. It is important to ensure that the PC can be reassembledcorrectly and that circuit boards are kept grounded during cleaning to avoid static electricity damage.Video display screens of CRT type attract dust and may need more frequent cleaning. Be careful if youhave a fabric anti-glare surface.
Keyboards get grimy from ink, sweat, and general hand-dirt, and theyhave many places to attract hair and dust. Vacuum gently and wipe with a damp cloth when the PC isturned off.11.2 Bad Habits — Smoke, Sticky Fingers, Games, PetsThe glossy advertisements for PCs show them everywhere — in the office, in the kitchen, in the familyroom, in the car. Unfortunately, many areas of human habitation are quite hostile to most PCs.Many work and home environments have tobacco smoke and ashes in the air. Disregarding the healtharguments, it is wise to keep any magnetic recording surface out of smoky air. Ashes can settle on the11: HARDWARE AND OPERATING PRACTICE93surfaces and scratch them, causing loss of data.
Worse, the smoke can dissolve the binders of the magneticrecording medium, resulting in data loss. Though there is some dispute as to the necessity of avoidingsmoke, we have personally observed a reduction in magnetic media data errors after smoke waseliminated from a machine room.
Food and drink near PCs is also unwise, so forgo a PC recipe databaseon the kitchen counter.PCs also survive poorly in the company of unsupervised or ill-behaved children. If children are allowedto use the PC, they should be trained to operate it with due care and attention. Toddlers may copy oldersiblings — we know of one who was taught that only diskettes go in floppy disk drives after he fed ina grilled cheese sandwich. Learning fast, his next computer session involved feeding multiple diskettesat once in the same drive! The use of the PC for games encourages rough treatment of the keyboard inparticular, with excited players pounding keys. It is surprising PCs survive as well as they do, given theway they are made.
Joysticks and mice also get mistreated, but most can be replaced for only a fewdollars. Games are often traded, and are a main avenue for transmission of computer viruses. We havepurged most games from our machines.Some parents use access control mechanisms — locks, passwords, etc. — to limit how children may usethe PC.
For example, parental files may be in a separate disk partition hidden unless a password is given.Our own SnoopGuard has been used in this way (Nash J C and Nash M M, 1993).Pets often have hair and feathers to get in the works or on disks. Some pets also like marking theirterritory. We know of a tomcat who scored a hit on the inside of a floppy disk drive!11.3 Disks and Their CareIn this section we consider some practical ways of minimizing difficulties with disks of various types.•When disks have protective envelopes (5.25") or cases (CD-ROM), use them to reduce the chances ofcontaminating the surface.•Store disks in an orderly way, maintaining disk catalogs if large disk sets are used.
This reduces diskhandling and saves time as well.•For archival information, use disk write-protect features (notch or slider) to avoid deletion oroverwriting.•Handle disks gently.•Use reinforced mailers when shipping disks.•Drive doors or levers should be closed slowly so the user can note any resistance suggesting the diskis poorly positioned, which could cause read/write errors. About 5% of the time that we load 5.25"disks we feel sufficient resistance to stop, joggle the disk in the drive and try again.
Gentle handlingalso saves wear and tear on the drive, reducing the chance of misalignment. 3.5" disks and CD-ROMsare less problematic; the Macintosh does most of the work for us.•Keep disks away from wires, tools or other electromagnetic fields. A magnet of any sort can causetrouble with magnetic recording media. Paperclips, often stored in magnetic holders, are a commonhazard. There are magnetic coils inside most display screens.
Students we know have managed toerase whole boxes of disks by placing them next to the screen in the computer lab.•Do not leave disks lying around to be dropped, bent or otherwise mishandled. Use a disk box, asimple rack made by sawing slots in a block of wood or by folding and stapling paper (Figure 11.3.1).•If a diskette appears to be unreadable, it may help to try reading it on another machine.
If successful,copy data to another disk. Alignment of the heads on the writing and reading drives may not beexactly the same. Even if both drives are within specification, they may still be different enough tocause errors.94Copyright © 1984, 1994 J C & M M NashSCIENTIFIC COMPUTING WITH PCsNash Information Services Inc., 1975 Bel Air Drive, Ottawa, ON K2C 0X1 CanadaCopy for:Dr. Dobb’s Journal•Heavy-handed diskette insertion, vibration from keyboards or from impact printers may betransmitted to fixed disk read-write heads, causing mispositioning or else physical contact with thespinning disk.
We try to keep mechanical vibration isolated from disks, so our dot matrix printers liveon small separate tables made from sawhorses with a plywood top. Some commercial PC furniturehas poor design from the point of view of vibration and physical access to printers for paper andribbon adjustment or clearing jams.•The disk may not be initialized or formatted in the correct way. MS-DOS and Macintosh machinesuse very different formats for 3.5 inch disks. 3.5 inch High Density (1.44MB capacity) disks mayappear unreadable if formatted at 720K.
By covering the hole that distinguishes the formats, thesedisks may be made readable again.•5.25 inch diskettes on MS-DOS machines generally store either 360K or 1200K of data. The highercapacity is achieved by closer track-to- track spacing, which requires that the read-write head use anarrow magnetic track. Errors may occur when a diskette formatted on a 360K drive (with "wide"tracks) is overwritten on a 1.2 Megabyte drive.
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