Class One: Computer Basics
I. What Is A PC?
The abbreviation "PC" stands for Personal Computer, as opposed to the large mainframe computers which were used by businesses. But the actual usage is a little narrower.
Historically, the first commercially built personal computer - or home computer, as it was called then - was called the Altair, and it was built in 1974. Before that, there had been other kits to build little computers but they were basically just toys or science fair projects.
From 1974 to the end of the 70's there were a number of small computers built. There were few standards, each company's computers were different, and you used programs made by or for that company's machine. The most successful was the Apple II, built by Apple Computers, which was the first computer to come totally assembled and with a monitor. It ran at an amazingly fast 2 MHz. (I'll explain megahertz later on.)
In 1981, IBM, the giant of the mainframe computer industry, built a computer called the PC, which ran at 4.77 MHz. It followed that with the PC-XT, and then the PC-AT, which ran at 8 MHz.
Other manufacturers began making "clones", that is, they copied the IBM PC's, and their machines were called IBM-compatibles, or PC's. This meant that they could run the same software as the IBM machines, and use many of the same peripherals; in other words, there was a standard. Very quickly, all the other companies either changed over to making IBM-compatibles or went out of business - except for Apple. (Actually, Atari and Commodore continued for a while.)
Nearly all today's Personal Computers are descended from the PC-AT, with the exception of the Apple Macintosh, and (recently) a few Mac clones. So the term PC basically today means any small computer other than a Mac.
Another adjective which is sometimes used (often in a derogatory sense) for PC's running Windows is "Wintel" systems (from Windows + Intel, the largest maker of PC chips.) PC's are also occasionally referred to as Intel-compatibles, to distinguish them from both the Mac and from a few small computers which use processors like the DEC Alpha chip and others which were originally designed for mainframe and mini-computers, and require special software.
II. Inventory of Parts
The physical parts of a computer system are called the hardware. The most essential parts are input devices such as the keyboard and mouse, output devices such as the monitor or printer, and the computer itself. The components except for the computer itself are called peripherals. Some smaller computers, such as laptops, have these all together in one unit. Larger computers have them as separate components connected with cables. There are two basic styles, desktop models, which are horizontal and usually have the monitor placed on top of them, and tower or mini tower models which are vertical and usually placed to the side or underneath the desk.
The monitor is the screen you look at; it's not called the "TV". It is usually a CRT (cathode ray tube), except for laptops or notebooks which use a flat panel or LCD (liquid crystal display). Some desktop PC's now have LCD's, but they are still very expensive compared to CRT's.
The computer itself is contained in the case. Inside, you have a power supply and fan, a motherboard, drive bays, and controller or adapter cards, along with some ribbon cables. On the back, you have some ports, or outlets into which you can plug peripherals.
The power supply steps down voltage from 120 volts AC house current to five or twelve volts DC and sends the power to the other components. Many problems with computers are caused by power problems, such as spikes, surges and fluctuations in current. Any computer should be connected through a surge protector, which looks like an ordinary power strip and usually costs about ten dollars or less. This is a good investment, since a power surge which would not even be noticed by an electric appliance can corrupt your data, or even damage your computer. (A surge protector is not sufficient to protect your computer from a large surge such as would be caused by a lightning strike nearby. You should still unplug your computer during thunderstorms.) If you use your computer for crucial purposes such as running a business, or if you keep it running unattended for long periods, you should consider an uninterruptible power supply, or UPS, which, in addition to a higher degree of surge protection, also gives you power conditioning and a battery which will keep your system running long enough to save your data and shut it down properly in the event of a power outage. Some even shut the computer down automatically when the power goes out. The cost of a UPS can range from about fifty dollars to several hundred, depending on what you want to connect to it and how long you need it to run on batteries.
One question I have been asked at previous classes is whether it is better to turn the computer off when it's not being used, or to leave it on. The answer really depends on the computer and how you use it. If you only use a computer a couple hours a week, or if you have an old computer without energy-saving features, then you should turn it off. If you use it several hours every day, and it has the energy-saving features (such as turning off the monitor and other energy hungry devices after a certain period of idleness), then you might be better off leaving it on all the time; the reason is that the most stressful time for a computer, or any other electronic device, is when it is turned on cold and heats up. This is known as thermal stress. So leaving it on may increase the lifetime of the components. (For the same reason, if you have a computer which is really cold - for instance, a laptop which has been sitting in a car in the wintertime - you should let it warm up to room temperature before turning it on, to decrease the thermal stress.) This also makes it possible to use the computer as your telephone answering machine, or to receive faxes.
If you do decide to leave your machine on all the time, however, there are a couple of things to consider:
First, if you use Windows 95/98, you will need to restart it once or twice a day, in order to let it reclaim resources, delete temporary files, and do other housecleaning which the Operating System does when it shuts down. (I leave the Windows Resource Meter - which is located on the Start Menu under Programs, Accessories, System Tools - in my system tray, so that I can see when the Resources are getting low. These are two small (64K) areas in memory which hold information about the programs which are running at a given time; if they fall below a certain level, the system may crash. Theoretically, when a program shuts down, the resources it uses are released, but not all programs are properly written to do this, so you will see the resources decrease over time.)
Secondly, you should seriously consider buying a UPS in this case.
The fan cools the system and removes heat caused by the components. Some cases have more than one. The sound you hear when the computer is running is the fan. Be careful to keep it unobstructed, not right up against the wall, and clean from dust. You should also avoid using a computer when the temperature gets into the high nineties, unless you have air-conditioning. Overheating is a common cause of computer failures. Some new computers have temperature sensors built-in, which can give you a warning or even shut down the computer if it gets too hot inside. The danger point is about 110 degrees.
The motherboard is a circuit board into which other components are plugged. It contains the central processing unit or CPU, which is the part of the computer that does the computing. The CPU chip will have a primary or level one cache. The motherboard will generally (except on very old machines) have a secondary cache or level two. On some CPU's this is also built into the CPU chip. I'll explain a little later what caches are, and why they are important.
Another thing the motherboard will have is the RAM, which stands for random access memory. This is the working memory of the computer. All the programs and documents which you have open at a particular time are loaded into the RAM. This is volatile memory, which means it retains information only when the computer power is turned on. This is why you should save your work to disk frequently, in case the power goes out or your computer crashes and has to be restarted..
The motherboard also contains the Basic Input Output System or BIOS, which is a small program in a non-volatile (permanent) memory called ROM (Read Only Memory) which boots up the computer and takes care of the communication between the operating system and the hardware. (More about the BIOS later.) Since the BIOS is read-only, it must store the changeable information about how your hardware and especially the hard disk is configured in another chip called the CMOS, which contains a battery, a clock, and the configuration memory. This is a little bit of memory which is always on, running from the battery, and contains basic settings of the hardware configuration of the computer. A good idea when you get a new computer is to write down (or print out) the settings from your BIOS, in case the battery goes dead or you get a virus such as Chernobyl, which can erase the BIOS. To access your BIOS settings, on most computers you just hold down the delete key when the machine is starting up. (If this doesn't work, check your manual to see how to access the BIOS.) Be sure not to change any of the BIOS settings unless you are very sure what you are doing!
Finally, the motherboard will have various buses, or pathways connecting the different components, with expansion slots for plug-in controller or adapter cards, such as video cards, sound boards, internal modems and so forth.
Another type of component inside the case is the drive bays. The drive bays contain drives. Most important is the hard disk drive, usually shortened to hard drive. This is the main internal storage device. It is permanent storage as opposed to memory. Whatever you save, unless you put it on a floppy disk, goes somewhere on your hard drive. If there's only one it is usually called Drive C. This is the C drive that you see listed in your Windows Explorer or "My Computer".
Another type of disk drive is the floppy disk drive. The original floppy disks were 5 ½ inches flat and very flexible. These are now completely obsolete and new computers do not have 5 ½ in. Floppy drives. They were replaced by 3 1/4 in. disks enclosed in hard plastic shells. Most of those you see today will hold 1.44MB of data. (What MB are will be explained later.) These are still the most common way of transferring small amounts of data, but are becoming obsolete. The iMac and some other so-called legacy-free computers don't have floppy drives. There are two incompatible formats, IBM and Macintosh. The first floppy drive is always called drive A; a second floppy drive if present is called drive B.
Floppies - and hard disks - are magnetic media. You want to keep them well away from any magnet, including your PC's speakers, or they may become corrupted or erased.
A newer type of disk drive is the CD ROM drive. The abbreviation stands for Compact Disk read-only memory. CD ROM disks are the main way of buying software today. A CD-ROM drive can also play music CD's. CD ROM drives are being replaced very slowly by DVD-ROM or digital video disk ROM. Today, many new computers have CD recordable or CD rewritable drives or even DVD rewritable drives. If you are buying a new computer, this is one "extra" you should consider, if only for making backups. Unlike hard disks and floppies, CD's and DVD's are optical media; the danger to them is not magnets but scratches. Be very careful not to lay the disks down on the shiny silver side, or put anything on top of them. A CD ROM or DVD-ROM drive is usually called Drive D, unless you have more than one hard disk drive.
Other types of storage you may see are Zip drives, Jaz drives, super floppies and tape drives. The most common is the hundred megabyte Zip drive. These types of drives are usually called drive E.
On the back of the computer, as I mentioned, are the ports. Usually you will have a monitor and a mouse port, which are their own types; one or two serial ports - the oldest and slowest type - called COM1 and COM2, which you would use for a serial-type mouse or an external modem; and a parallel port, which is also relatively slow, for your printer. Many older scanners, Zip drives, and other peripherals also connect via the parallel port, which is a problem, since there is only one on most machines, and you have to hook your printer up through your scanner or zip drive. This is called a pass-through connection, and it means that you will not be able to use both devices at the same time (for instance, to print directly from your scanner or scan to a file onto a zip drive.) To get around this limitation, most computers built in the last few years have at least two Universal Serial Bus (USB) ports, which look sort of like big, boxy phone jacks, and are much faster than the older types. USB peripherals can be hooked up to one another (chained) and they will all work at the same time. If you have a choice of parallel or USB for a printer or scanner, you should always choose USB. Again, the i-Macs and legacy-free computers no longer have parallel ports. Another type you may occasionally see is a SCSI port. (This stands for Small Computer Systems Interface, and is pronounced "scuzzy".) These are very fast, but also expensive and a little hard to install.
With a lot of peripherals, your computer may start to look like Spaghetti City. Fortunately, however, you will probably only have one of each type, except USB (where anything can plug into any port anyway), so you probably don't need to worry about plugging anything in to the wrong place. It's just a matter of finding the right-sized and shaped socket for each type of plug. Be sure that you don't plug in or unplug anything unless it's USB without turning the power off first, or you may damage the peripheral or the computer.
III. A little about how computers work
Essentially, a computer is just a complicated adding machine. Information, called data, and lists of instructions for dealing with it, called programs, or software, are put into the working memory, either from an input source such as the keyboard or mouse, or from a storage source such as the hard disk or a floppy, in the form of binary numbers, that is zeroes and ones. Each zero or one is called a bit. An eight bit number is called a byte. The central processing unit or CPU retrieves instructions and data from the memory and carries out arithmetic on these numbers, then sends the results back to the memory, or to an output device such as the monitor or printer.
Caching
The different components of the computer don't all work at the same speed. The CPU is the fastest component, and they're being improved faster than any of the others. The system bus, which connects the CPU to the main memory, is much slower than the CPU. Memory chips of different types have different speeds; the slower types are very cheap, but the fastest type is very expensive. Hard disk drives are slower than memory and floppy drives are slower than hard disk drives. And so on. The result could be that the system would only work at the speed of the slowest component, and the faster ones would be idle most of the time waiting for input. This is the reason for caching, which occurs at several levels.
Think of it as though you're writing a research paper. You could go to the library, look up some information, then go home and write a few sentences, go back to the library, look up some more information, go back home and write a few more sentences and so on. You would spend most of your time driving back and forth to and from the library. Alternatively, you could check out the books you need, take them home, copy the information you need into a notebook, and as you're writing you can look up the information first in your notebook, then in the books you checked out, and only if it's not in either of those do you need to go back to the library. This is the idea of caching.
First, the CPU has a primary cache on its own chip. This is a small amount of very fast and expensive static memory which runs at the speed of the CPU. The secondary cache or L-2 is a somewhat larger amount of fast memory. Information or data used by the CPU is stored in these caches and looked for there first before the CPU looks for them in the main memory. The main memory itself caches data from the hard drive, floppies, etc.; and data from a network or the Internet is cached on the hard drive.
What happens when you turn the computer on (boot up)
The BIOS detects that the computer has been turned on. It checks the memory, then sees what hardware is attached, and initializes (sets up) the hardware. It then looks for instructions on how to boot up. The first place that it looks by default is drive A.
Important: never turn on the computer with a floppy in drive A unless you intend to boot from it, because:
A. If it has a virus, the virus will load before you have booted up, and therefore before your antivirus program has loaded, and is free to trash your computer.
B. If it is a bootable floppy, one which has boot up instructions, the computer will follow those instructions rather than the ones on your hard drive, and you may find it doesn't work the way you expect it to.
C. If it is not a bootable disk, the computer will stop and ask you to remove it before it continues to boot up.
If there is no floppy in drive A, the BIOS next looks on the hard drive. It gets information about your hard disk's organization from the beginning of the disk: the Master Boot Record and (assuming you're running DOS/Windows) the DOS Boot Record. Once it knows where to find information on the hard disk, it turns to the Operating System. The files it's looking for in Windows 95/98 are two hidden files called IO.SYS and MSDOS.SYS and the command shell, named command.com. These files must normally be in the root directory, that is they must be listed as files in the main directory of drive C, not in one of the folders. If these files are accidentally deleted, moved, renamed, or corrupted in any way, the computer will have to be booted from a floppy and the files restored. There can be other problems as well which will keep the computer from completing the boot-up process. This is one reason why you should make an emergency boot disk on a floppy as soon as you start using a new computer. You can do this from the Windows 95/98 startup program (go to Start, Control Panel, Add New Programs, Start Disk, and follow the directions) or from most antivirus or diagnostic utility programs.
The machine will then finish loading the operating system, or the most important parts of it, into memory. The operating system is a large program which controls the computer, manipulates files, and lets you run other programs, called applications, to do specific tasks. DOS, Windows 3.x, Windows 95, Windows 98, Windows NT, OS/2, and Linux are examples of operating systems. We will cover operating systems in the next lesson.
Then the operating system will take over, and in the case of Windows will load your startup group.
IV. Understanding Computer Specs
CPU's
The CPU is the heart of the computer. The main way they are described is in terms of their speed, how many instructions they can carry out per second. The unit for this is the Hertz. One instruction per second would be one Hz, ten instructions per second would be ten Hz, etc. this is compounded with the standard metric prefixes, kilo meaning 1,000, mega meaning 1,000,000, giga meaning 1,000,000,000, and so forth. Thus, 500 Megahertz (MHz), for example, would mean 500 million instructions per second.
In the early days of IBM compatible computers, CPU's were given numbers ending in 86, such as 8086, 80186, 80286, 80386, 80486... These are usually referred to without the 80 as 386, 486 etc. The next chip should have been the 586, and some companies used that name for their next chip. But Intel, which is the main chip manufacturer, decided that since numbers can't be trademarked, they would call their 586 the "Pentium". Pentiums are referred to by their speed in MHz, so a Pentium 60 operates at 60MHz, or 60 million instructions per second, a Pentium 200 at 200MHz, and so on. Intel's competitors use other terms, such as AMD's K6 and Athlon chips, but they all give speeds in MHz. Intel is now up to the Pentium IV; it also makes economy Celeron and high end Xeon chips.
Most new computers today have CPU speeds of a gigaherz (one billion instructions per second) or more. Top speeds tend to double about every two years, or a little less.
Besides the actual processor speed, another key difference between CPU chips is how much primary and secondary cache the system has, and whether it runs at the processor speed or half speed, etc. This can have a huge effect on the performance of the system. The amount and speed of the caches is the main difference between chips like the Pentium and Athlon and economy chips like the Celeron or the AMD Duron.
System Bus
The system bus is the pathway between the main memory and the CPU. Computers using Intel chips slower than the Pentium II 350 used 66MHz buses, while the Pentium II 350 or higher used a hundred megahertz bus, the Pentium III uses 133MHz and the AMD Athlon uses a two hundred megahertz bus. You should keep this in mind in comparing speed and price. The speed jump from a 300 to a 350 was more than from a 350 to a 400 because of the faster system bus. This is not really an independent item, since when you choose a CPU you thereby choose whatever bus it supports.
RAM
This is the working memory of the computer. It is measured in megabytes (millions of eight digit binary numbers). All the programs and data you're working on at any particular time have been loaded into RAM. If there isn't enough RAM available, Windows will use part of your hard disk as virtual memory. This is called a swap file. This prevents you from running out of memory, provided you have sufficient free space on your hard disk, but the more often you have to go to the swap file, the slower the computer will work, since the hard drive is much much slower than memory. Adding memory is usually the least expensive way of increasing your computer's speed, at least up to a certain point. If you're running Windows 95 or 98, you want from 32 to 64MB. If you run Windows 2000 or XP, or use photo editing programs like Photoshop with full page color photos, you want at least 128MB, and 256MB would be preferable.
There are many types of memory today, but again this is not really an independent choice, because the type you need for a given computer is determined by the speed and type of your CPU and system bus, so I won't go into the differences.
Hard disk
This is the internal storage of your computer; it is also measured in megabytes or gigabytes. There are two ways of figuring this. Traditionally, in computing, because information is in binary numbers, one kilobyte equaled 1,024 (210) bytes and 1MB equaled 1,024KB. Today most hard disk manufacturers use the standard metric definitions so that 1KB = 1,000 bytes and 1MB = 1,000KB. This can sometimes cause confusion. Windows Explorer uses the traditional computer language; this is why your total disk space as listed by Explorer will probably be slightly less than the size you expect. (The same thing is true, for instance, of ZIP disks; Windows will show them as having 95.7 MB capacity rather than 100MB.)
Hard disks on new systems today begin at about twenty gigabytes. The maximum now is about 80GB, but this is increasing steadily, and there are new technologies in the labs which may allow for massive drives in the near future. There are two types of hard disks used on modern systems. The standard is EIDE. A faster type is SCSI, but it is also more expensive. Unless you do video editing, or need a very large hard drive, you probably don't need a SCSI hard drive.
Monitor
Limiting the discussion to CRT monitors, the most obvious difference is size. For a long time, the standard size for monitors was 15 inches diagonal. Today, 17 inch is pretty standard and 19 inch is affordable if somewhat pricey. Remember that the monitor sizes are measured by the size of the CRT tube, which is partially covered up by the frame. Most ads today give a second measurement, for example, 17 inches, 15.7 visible. The second measurement is the one that tells you how big the monitor really is for practical purposes. I would not recommend less than a 17 inch monitor for anyone to use at home unless they are really cramped for space; the 15 inchers are too hard to read and you'll be scrolling all the time on the Internet.
Other important specifications are the refresh rate (how many times it redraws the screen per second - if it's less than 72, the flicker will give you a headache, and some people can detect flicker even at 80), the maximum resolution and number of colors supported (you don't need to worry about these on new monitors, they all have high enough resolution and plenty of colors) and the pitch (the higher the better.)
What Should You Look for in a Computer?
It depends on what you need the computer for. Some general considerations are as follows:
It used to be that most people just looked at the speed of the CPU when buying a computer. This was never really a good idea, but it even less important today. The slowest computer you could buy new today will have more speed than you need, unless you want to play the newest games or are really heavily into multimedia (video editing and so forth.) It might be a good idea to get a little higher than the minimum, as a hedge against future software requirements, but remember that the other components will likely become obsolete before you really need more CPU speed. If you're looking at used machines, remember that a Pentium 90 is about the slowest that will run Windows 95/98 adequately, much modern software specifies 166 or 200MHz, and multimedia or voice-recognition need 350MHz or better.
Memory is important, and has more to do with the actual speed you'll notice than the CPU speed does. To repeat what I said before, if you are running Windows 98 you will want at least 32MB, and 64MB would be even better; Windows 2000 or XP, or photo-editing, at least 128MB. Fortunately, RAM is one of the least expensive parts of the computer.
If you're going to be playing games, or playing a lot of video, the video card will be one of the most important considerations; if you're going to be playing music on it, you'll want the greatest sound card and a good set of speakers. For word-processing and surfing the Internet, on the other hand, you can get by with whatever is least expensive on these. One area where you don't want to skimp is the monitor; get at least a 17 inch.
Be sure your machine has USB ports and a few empty slots to add new peripherals. You want a modem (56K V90), at least a CD-ROM drive, preferably a CD rewritable drive, and if you don't get CD-RW, then some sort of removable storage beyond the standard floppy (at least a 100MB Zip drive, for example.)