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Linux Tutorial - The Computer Itself - Cases
  Uninterruptable Power Supplies ---- The Right Hardware  


Cases

A computer case is more that just something that protects the inside of you're your computer from spilled coffee and other dangers associated with the typical computer user. It also protects you from the inside of your computer. The 110 volts flowing through the power supply (220 in Europe and other places) is not something you want to meet up with unexpectedly.

In addition, the computer case is both the skin and skeleton for your computer. It holds everything together and hold them in the proper location. You motherboard is attached to the case, so the expansion slots need to be in the proper position when you insert a card, the connectors on the end of the card are sticking out of the computer and not pointing in.

Fortunately, there is a standard in both motherboard and case design that helps keep things from pointing in the wrong direction. However, idiots are getting smarter ever day, so this system will never be idiot proof.

One of the first things to look at is the physical construction of the case. Cases come in many, many, many different sizes and shapes. PCs cases are normally though of in terms of desktop, mini-tower, tower and maxi-tower, or something similar. As its name implies, a desktop case is one that is intended to sit on your desktop. The smaller the better. In fact, a new term "small footprint" case is used to refer to cases that are even smaller than traditional desktop cases (XT, AT, and Mini-AT).

These cases lay flat on your desk and often have a set of four compartments (or bays) arranged in a 2x2 square to hold hard disks, floppy drives and CD-ROM drives. The obvious limitation is expansion. The motherboard is often smaller and therefore there is less room for expansion cards. Plus, there is not much extra room in the case if you wanted to add too much more.

Tower cases stand vertically, with the bays one on top of the other. With mini-towers, the case is small enough that it might fit on your desk as this is generally just a re-arrangement of the desktop case. That is, you have room for four devices. Big towers are just that. There are usually at least six bays for devices which could have some access slot at the front (i.e. floppy-drive, CD-ROM, tape drive, etc.). However, this space could also be used for hard disk, as the cases are usually provided with some kind of plate covering the front. In addition, there is room for a couple more hard disk.

However, this is a classic case of not judging a book by its cover. I have seen large cases before that had some really goofy construction. The result was few bays and a lot of wasted space.

In the last couple of years, server cases have made it to the market, which are a lot larger than tower cases. This are normally the same height, but can be several times wider. There is room for a dozen or more hard disk and many are designed explicitly with the goal of have a large number of disks that you set up in some kind of redundant array (RAID). However, in every case I have seen, these were delivered with a pre-built system.

There are a couple of key aspects to consider when looking for a case. First, the case and the motherboard need to fit together. There are a number of motherboard types and for the most part, the holes in the motherboard match those for the case. There are usually more hole than you need and some combination is likely to fit.

However, what you need to consider it that the motherboard should not lay completely flat against the motherboard. It needs to be spaced above the case so that none of the metal on the case can touch the motherboard. This ensures that no short circuit is possible. Along with all of the motherboards I have purchased in recent years have been nylon spacers, which keep the motherboard away from the metal frame of the case.

The next aspect is the placement of the bays for the hard disks. I have met my share of cases, where you almost need to take the case apart in order to get to the bays. If this is the case, you can end up spending a lot of time replacing the drives and a lot of money on band-aides for your scraped knuckles.

If you have a tower case and can use one of the front-loading bays, it makes it much easy to get the drives into the bays. However, it may make getting the cables onto the drives is another problem. Both of these issues become mute (for you) if you have someone else doing the maintenance. If, however, you are the ones building the machines or replacing defect drives, how hard it is to get access to the bays is an important consideration. DEC did it right for a few years until something caused them to change their minds. Drives were inserted into the case sideways and not front to back. Although they still laid flat, there was no problem getting the drives in and out. There were typically enough slots for four to six drives and several pairs brackets were provided that screwed onto the hard disk. With the brackets in place, the drives slide in, locked into place, with the plug end sticking out. It was also a simple matter to remove the drives when you need. Unfortunately, just prior to being purchased by Compaq, DEC changed the construction of their cases and getting at the drives was almost impossible. In fact, I have yet to see worse placement than I saw on some of the cases.

Also consider how easy it is to open and close the case. There should be no "trick" to opening closing the case. I have had some where you had to apply just the right amount of pressure on the top and bottom of the side panels that slid into the case from the back. First, this meant having to move the case far enough away from the wall so you had room to pull the sides off. Plus "just the right amount of pressure" was harder than it sounds.

The next important issue is cooling. Unless you are running an old 486, you probably have at least the fan on your CPU (as well as the one for the power supply). However, that may not be enough. All electronic devices generate heat and it can build up pretty fast in the enclosed space of your computer case.

The most common way for the computer cases to get cooled is simply letting the hot air escape out the holes in the case. However, I have seen places were the computer is hidden under a desk, with almost no circulation at it overheated. Even if the computer is in the open, you may still not have enough circulation inside the computer, particularly if you have a lot of peripherals in your machine. If this is the case, you might want to consider getting a fan card. As its name implies, it is a fan that sits in one of your expansion slots and helps circulate air.

You should also consider the design of the case. I have seen many where an extra fan was built into the case that blew directly onto the hard disks. In other cases, an additional fan would blow onto the CPU.

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Copyright 2002-2009 by James Mohr. Licensed under modified GNU Free Documentation License (Portions of this material originally published by Prentice Hall, Pearson Education, Inc). See here for details. All rights reserved.
  




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