Modem

A contraction of "Modulator - demodulator", a modem allows a computer to communicate over an analogue medium (most commonly a telephone line). The modem encodes digital signals from the computer as analogue signals suitable for transmission (modulation) and decodes digital data from a modulated analogue signal (demodulation). Using modems two computers may communicate over a telephone line, with the data passed between them being represented as sound.

Modems are usually involved with dial-up internet services. As broadband catches on, they are falling into disuse. However, the devices used to connect to broadband connections are also called modems, specifically DSL Modems or Cable Modems.

Printer

A printer makes marks on paper. It can print images and text.

The most common types of printers today are

• Laser printer: Prints very crisp text, but cheaper models can only print in black and white. Good for places like offices where high printing speed is needed.
• Color inkjet printer: Prints photos and other images in color (using 4 colors of ink -- cyan, magenta, yellow, and black), but the text they print is often not as crisp as a laser printer.
• 
  

The average printer of the early 1990s would connect to a computer through its parallel port. To connect it to the computer via parallel port, one would have to screw it into the port. Today many printers are connected through USB. This is because it is easier to connect and remove through a simple plug and play system. It also allows for faster transfer speeds than parallel.

USB Flash drive

Memory sticks or Flash drives are solid-state NAND flash chips packaged to provide additional memory storage. 

These drives are quickly replacing floppy disks as a means of transferring data from one PC to another in the absence of a network.

Flash memory

Some common types of Flash memory cards are CompactFlash, Secure Digital (SD), and xD. There are other formats which are falling into disuse, such as Smartmedia (SM) and MultiMediaCard (MMC).

Flash memory is faster than magnetic media and much more rugged. The main reason Flash hasn't yet replaced hard drives is that Flash memory is much more expensive per gigabyte than hard drives.

DVD-RW drive

DVD's hold about 4.7 gigabytes and dual-layer disks hold 8.4 gigabytes (dual layer equipment and disks are now becoming more affordable)

DVD-ROM drive

Digital Video/Versatile Disk Read Only Memory (DVD-ROM)

This optical drive works on a similar principle to the CD-ROM, with a laser being used to read data stored in pits on the surface of a reflective disk. DVDs are read using a shorter wavelength of light (a red laser, rather than an infra-red one). In addition to having a greater data-density, DVDs may be double sided and may be "dual layer".

cd-rw drive speeds

Compact disc Read/Write drives support the creation of CD-R and CD-RW discs, and also function as CD-ROM drives. These drives use low-powered lasers to 'burn' data into the active layer of the disc.

CD-R (Compact disc recordable) discs are 'write once' - once they have been written to, the data cannot be erased or changed. However, multisessions can be created and more data can be added.

CD-RW (Compact disc rewritable) discs can be rewritten or erased multiple times. This is a two-pass process so they typically take twice as long as CD-R discs to produce.

CD-RW drives will typically have three speed ratings - one for reading discs, one for writing CD-R discs and another for writing CD-RW discs. Speed ratings vary from 1x to 52x, where 1x means that a CD is written/read in 'real time' - a 52 minute audio CD would take about 52 minutes to create at 1x speed, and about 1 minute at 52x speed.

The data can be written to the disc in a variety of formats to create an audio CD, a data CD, a video CD or a photo CD. The audio CDs should play on most standard audio CD equipment and the video and photo CDs will play on many consumer DVD players.

Many CD writers (also known as 'burners') are now combination drives which also function as DVD-ROM drives.

Most DVD-RW drives also have CD-RW capabilities.

[edit]

read-head of a computer cd-rom drive

Compact Disc Read Only Memory (CD-ROM) is a standard format for storing a variety of data. A CD-ROM holds about 700 MB of data. The media resembles a small, somewhat flexible plastic disc. Any scratch or abrasion on the data side of the disc can lead to it being unreadable.

Cleaning CD's: Dust can be removed from a CD's surface using compressed air or by very lightly wiping the information side with a very soft cloth (such as an eyeglass cleaning cloth) from the center of the disc in an outward direction. Wiping the information surface of any type of CD in a circular motion around the center, 

however, has been known to create scratches in the same direction as the information and potentially cause data loss. Fingerprints or stubborn dust can be removed from the information surface by wiping it with a cloth dampened with diluted dish detergent (then rinsing) or alcohol (methylated spirits or isopropyl alcohol) and again wiping from the center outwards, with a very soft cloth (non-linting : polyester, nylon, etc.). It is harmful, however, to use acetone, nail polish remover, kerosene, petrol/gasoline, or any other type of petroleum-based solvent to clean a CD-R; the use of petroleum based solvents will damage the polycarbonate surface and the CD-R will become unreadable.

hard drive disk

A hard drive consists of one or more magnetic platters or disks and a read arm with two electromagnetic coils for each disk. Each hard disk is divided into many sectors,

 each containing a certain amount of data. As of now, it is the cheapest and most common way to store a lot of data in a small space.

Floppy Disk drives

8" Floppy Disk: In the late 1960s IBM invented the 8-inch floppy disk. This was the first floppy disk design. Used in the 1970s and as a read-only disk it had storage-write restrictions to the people it was distributed to. However, later on a read-write format came about. In today's modern society it is rare to find a computer that uses the 8-inch floppy disk.

5.25" Floppy Disk: This disk was introduced some time later, and was used extensively in the 1980s.

3.5" Floppy Disk: This storage medium is the most common of those listed in this section, still in somewhat wide use today. Floppy disks hold from 400 KB up to 1.44 MB. The most common types found are 720 KB (low-density) and 1.44 MB (high-density). Floppy disks have largely been superseded as a transfer medium, first by rewritable CD-ROM (CD-RW) drives and now by flash drives, but are still used as backup storage for small amounts of data. A fair proportion also survive as original installation media for older software applications.

Several other floppy types and sizes have been introduced, such as 2", 2.5" and several competing 3" and 3.25" formats as well as the ~120 MB SuperDrive which was compatible with standard 3.5" disks, but none of these were ever very popular and all are quite rare now. Recently, it has become increasingly common for computers to be manufactured without floppy disk drives, and even some motherboards lack standard floppy disk connection headers, so it is expected that the floppy disk will soon fade completely from general use.

[edit]

Class 2 Components: Storage

Class 2 components are storage media for non-volatile data.

Do not put magnetic media (including floppy disks, hard drives, video cassette tape) through airport X-ray machines. The X-rays themselves are not the problem -- it's the magnetic fields from the conveyor-belt motors that all too often erase magnetic media.

Optical media -- Compact Disks (CDs) and the similar-looking DVDs -- are completely immune to magnetic fields. They can be run through airport X-ray machines without any problems.

Flash memory is also immune to magnetic fields.

Sometimes one can distinguish between "fixed media" (the hard drive) that is more or less permanently mounted inside the computer case, and "removable media" (just about every other kind of media) that is easy to pull from one computer and put into another computer.

AGP Cards

Most graphic cards produced from about 1998-2004 were AGP (Accelerated Graphics Port) cards. They are placed in a certain slot on the mainboard with an extra high data transfer rate. The interface was invented to keep the graphics card away from the PCI bus, which was starting to become too constrained for modern graphics cards.

Every graphic card carries a graphic chip (GPU) and very fast DDR RAM for textures and 3D data. Their data buses have 1X, 2X, 4X, and 8X speeds. The bus is 32-bit, much like PCI.

AGP slots are slightly shorter than PCI slots and often brown in color. A similar type of slot called AGP Pro is longer and has extra power leads to accommodate modern video cards. It didn't really catch on in the mainstream market, and graphics card makers preferred to add an extra power connector to supply the power they needed.

RAM

Random Access Memory (RAM) is a memory that the microprocessor uses to store data during processing. This memory is volatile (loses its contents at power-down). When a software application is launched, the executable program is loaded from hard drive to the RAM. The microprocessor supplies address into the RAM to read instructions and data from it. RAM is needed because hard drives are too slow to operate with the speed of a microprocessor.

Some of the types of RAM are SDRAM, DDR RAM, Rambus RAM, SIMM, DIMM.

Motherboard

The Motherboard (also called Mainboard) is a large, thin, flat, rectangular fiberglass board (typically green) attached to the case. The Motherboard carries the CPU, the RAM, the chipset and the expansion slots (PCI, AGP - for graphics -, ISA, etc.).

The Motherboard also holds things like the BIOS (Basic Input Output System) and the CMOS Battery (a coin cell that keeps an embbeded RAM in the motherboard -often NVRAM- powered to keep various settings in effect).

Most modern motherboards have onboard sound and LAN controller, some of them even have on-board graphics. These are adequate for standard office work and system sounds. But dedicated sound and graphics cards plugged into the expansion slots offer much better quality and performance

Class 1 Components

The CPU (Central Processing Unit) is the 'brain' of the computer.

It's typically a square ceramic package plugged into the motherboard, with a large heat sink on top (and often a fan on top of that heat sink).

All instructions the computer will process are processed by the CPU. There are many "CPU architectures", each of which has its own characteristics and trade-offs. The dominant CPU architectures used in personal computing are x86 and PowerPC. x86 is easily the most popular processor for this class of machine (the dominant manufacturers of x86 CPUs are Intel and AMD). The other architectures are used, for istance, in workstations, servers or embedded systems CPUs contain a small amount of static RAM (SRAM) called acache. Some processors have two or three levels of cache, containing as much as several megabytes of memory.The CPU (Central Processing Unit) is the 'brain' of the computer.

It's typically a square ceramic package plugged into the motherboard, with a large heat sink on top (and often a fan on top of that heat sink).

All instructions the computer will process are processed by the CPU. There are many "CPU architectures", each of which has its own characteristics and trade-offs. The dominant CPU architectures used in personal computing are x86 and PowerPC. x86 is easily the most popular processor for this class of machine (the dominant manufacturers of x86 CPUs are Intel and AMD). The other architectures are used, for istance, in workstations, servers or embedded systems CPUs contain a small amount of static RAM (SRAM) called acache. Some processors have two or three levels of cache, containing as much as several megabytes of memory.

Computer hardware

• The Motherboard and things directly attached to it.
• Computer chassis and screen, preferly with standard sizes (i.e. ISO A4 for notebook chassis).
• Storage media

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