There are four main types of retail computers: the Mac®, short for Macintosh® and made by Apple® Computer, the PC, short for Personal Computer and originally made by IBM®, and mobile tablets and cell-phones from many sources.
The PC was so successful that numerous companies have since cloned this technology. This is hardware - mechanical stuff that you can physically handle and weigh.
For the hardware to do useful work, its various components are controlled by a machine level system ("firmware") - originally the Basic Input Output System ("BIOS"), superceded by the Unified Extensible Firmware Interface ("UEFI") - which provides an interface between the hardware and a large suite of software called the Operating System ("OS").
By contrast, software is not something you can handle and weigh. It is nothing more than a complex series of patterns - "machine language" - that is stored and read electrically, magnetically, and/or optically (and, once upon a time, physically from "punch cards").
We mainly deal with PCs which are running Microsoft® Windows® operating systems including Windows 10, 8.1, 8, 7, Vista, and XP. We started with Windows 95, 98, ME, and 2000, but these OSes are so old and creaky that they're not worth the effort. Microsoft no longer supports XP, so it's now just a click away from lurking malware. Using Apple's support website, we've solved some problems with Macs (and so can you).
Bytes, Bits, and Strange Numbers
A "byte" is a character, such as A, B, C, 1, 2, 3, etc. A byte (represented by an upper case "B") is made of smaller units called "bits" (represented by a lower case "b").
A bit is basically a single switch that means "On,Off", "Yes,No", or "1,0". Counting with only ones and zeros makes up the "binary" number system, which uses powers of 2 (21="10", 22="100", 23="1000", etc) for numbers greater than 1. Counting in binary looks like this:
The number of bits in a byte depends on the computer hardware. Obsolete computers used 8- and 16-bit characters. Modern ones use 32- and 64-bit characters.
While computers use strange number systems, such as binary and hexadecimal, humans still do best with the "decimal" number system, which uses powers of 10 (101=10, 102=100, 103=1,000, etc) for numbers greater than 9.
One result is a sightly confusing mixture of decimal and binary, when expressing quantities of bytes:
A "kilobyte" (KB) is roughly a thousand bytes - actually 1,024, or 210 bytes.
A "megabyte" (MB) is roughly a million bytes - actually 1,048,576, or 1,0242, or 220 bytes.
A "gigabyte" (GB) is roughly a billion bytes - actually 1,073,741,824, or 1,0243, or 230 bytes.
A "terabyte" (TB) is roughly a trillion bytes - actually 1,099,511,627,776, or "a terribly large number".
Why do you need to know this?
Let's say your Internet service offers a connection speed of "1Mb/s". The advertising says so in big bold type. You're thinking "megabytes per second", but the lower case "b" actually makes it "megabits per second". So on a 32-bit system, your connection speed would only be 32 kilobytes per second maximum (about 3% of what you thought).
If you're buying a new computer, it should have a bare minimum 250GB hard drive, and 2GB of RAM (but you really should get 3-4 times these amounts).
A Basic PC
That glowy thing on your desk usually has:
A monitor, so you can see the most important results, the tip of the iceberg really, of what the computer is doing. Normally, you would not want to know the rest of what it's actually doing to get those results.
Human interface devices, so you can tell the computer what you want it to do. These devices commonly include:
A device to input individual characters or specific commands, such as a keyboard, so you can spell things out in detail, and write a letter or a program.
A pointing device, such as a mouse, touch pad, or touch screen, which controls a graphical pointer on the monitor, so you can start various actions by selecting elements displayed on the monitor.
Other more exotic devices are available to perform similar functions for people with special needs. For example, reknowned physicist Dr. Stephen Hawking has written extensively, both technically and for the general public, from a physical state of near immobility using highly specialized human interface devices. And you thought you had it rough.
A CPU (Central Processing Unit): the main "brain" which controls and performs most of the computer's work.
A "mother board" which connects and coordinates all other components.
Temporary (volatile) storage, known as "RAM" (Random Access Memory), which remembers just what is currently being worked on, only for as long as it's needed. Its advantage is that it operates at much higher speed than non-volatile storage. The bare minimum of RAM that you should even consider is 1GB (1,024MB). Our advice: get at least 3GB. To understand why, read our page about memory.
Permanent (non-volatile) storage, typically an internal hard drive, which holds all of your files and the operating system even when it's turned off. It's permanent only in the sense that, if the contents are left alone, they will stay as they are indefinitely. If the computer will be your primary workstation, the hard drive should be at least 200GB. Our advice: get at least 500GB with a minimum 16MB cache. Tip: when buying a hard drive, you should not pay more than $0.15 per gigabyte.
Cooling equipment, including fans, deflectors, heat sinks, and even liquid cooled refrigerators.
Other permanent storage drives and cards:
An optical drive, such as a CD or DVD drive. Either get one CD drive and one DVD drive, or get a "combo drive" which handles both. Make sure the drive(s) can do all three kinds of operations: "read" (unlimited), "write" (once), and "rewrite" (unlimited, or until the disk wears out). There are many types of optical media (disks), such as CD-R, CD-RW, DVD-R, DVD+R, DVD-RW, and DVD+RW. All of them are "read unlimited". In addition, a single "R" means the disk can only be written once, whereas "RW" means the disk can be rewritten multiple times.
Other types of internal or external drives which use removable media, such as:
a card reader combo drive - often built into the chasis, reads and writes to various camera cards;
a zip drive - low capacity, expensive, error-prone;
a floppy drive - only 1.44MB capacity and unfashionable, but cheap and occasionally useful;
a tape drive (rare) - uses small to large capacity magnetic tape cartridges.
Other removable drives (not part of the basic computer) - usually plugged into the computer's FireWire or USB ports:
flash drives, also called "thumb drives", and cards, range from 16MB to 32GB.
Hardware ports for plugging in various external hardware ("peripheral devices"), such as Audio Input, Audio Output, Ethernet, FireWire, Microphone Input, Monitor, Telephone Input and Output, PS/2 (keyboard and/or mouse), Serial, type "S" video, and USB ports (the more, the better).
More stuff we'll explain as time allows: fax, hub, Internet service, LAN, modem, printer, router, scanner, surge protector, UPS, WAN, etc.