Computers are not much use without peripherals. The nature of these peripherals is changing rapidly.

Peripherals usually attach to a host computer, but are not a necessary or core part of the computing facility. Many formerly separate peripherals are built in these days. Peripherals typically more or less depend upon the host computer to be of use. Examples are disk drives, video monitors, keyboards, mice, printers, microphones, MIDI music keyboards, loud speakers, web cameras, image scanners. Whether a peripheral is built in, or separate, depends on both technology and fashion.

In 1967, IBM invent the (eight inch) floppy disk drive, as a storage media to start up their mainframes. Subsequent floppy disks came in 5 inch and Sony's 3.5 inch sizes. They never held more than a few megabytes. Essential during the 1970's and 1980's.

Apple dropped floppy disks in 1998, providing a USB 1.1 port instead. The outcry at the time was very loud. Now everyone has dropped floppy disks. The last manufacturer, Sony, stops producing them in March 2011.

In 1982, Sony and Philips released the specifications for digital compact discs (CD), an optical disc originally intended for sound recordings. Over 600 megabyte storage. The DVD appeared in 1995, and can store seven times as much as a CD. DVD is mainly used to distribute movies. An even newer format from 2003 is Blu-Ray, which stores multiple gigabytes. Optical drives became essential during the 1990's for distributing programs, music and video.

Downloading video is overtaking optical disks for distributing video. For example, YouTube started in 2005 with a few thousand videos. It made it easy for users to put video on the web. Google bought YouTube in 2006 for US$1.65 billion. Users now upload millions of videos a day. Users download over a billion videos a day.

Apple started dropping optical discs from their computers in 2008. For example, the operating system for a MacBook Air comes on a USB card. You can also update over the internet, or via another computer.

Hard disk drives were once giant separate devices, like the IBM RAMAC of 1956. This RAMAC had 50 disks, each two feet in diameter. The whole thing could store 5 MB. It cost US$3200 a month to lease.

The first hard drives specifically for personal computers were the Shugart ST506 models of 1980. They could store around the same 5 MB as the IBM RAMAC above.

Hard drives now tend to be built in to every computer. One terabyte drives cost less than A$100. That is 200,000 times the capacity of a 5MB drive. The largest capacity available today is three terabyte.

Apple started optionally dropping hard disk drives from their computers in 2008. Apple offer much faster solid state Flash memory. Apple's latest two very portable (under 1.5 kg) computers do not even have a hard drive available, although you could connect one via a USB port.

External displays and monitors are getting larger and have greater resolution. Size and resolution are different. For example, a projector shows video on a large screen. However the resolution is low. In fact, it is so low I am having trouble using it.

The largest LCD displays normally seen are 24, 27 and 30 inches, unless you connect your computer to a large screen television.

Displays now tend to be built in, as notebook computers increasingly replace desktop computers.

Typical computer resolutions in the past were 1024 x 768 (76% of users have higher). However most notebook computers can display 1920 x 1080 (1080p high definition TV) on an external display.

The next step up could be as much as 4096 x 3072 pixels, which exceeds any commonly available display. Cinemas will get these resolutions first.

All current Apple notebook computers are capable 2560 x 1600 pixels to an external display.

Webcams are cameras that display on the web. The first known use was 1991, where one was used at Cambridge University to monitor the state of the coffee pot in the common room. The coffee cam is now in Germany.

Many notebook computers now have a built in webcam. All Apple notebook computers have webcams. Top of the line music players have webcams. Mobile phones have webcams.

Modern mobile phones may include an accelerometer, a compass, a gyroscope, and access to the global positioning system.

The Apple iPhone has a number of sensors, mostly from ST Microelectronics The microelectromechanical system (MEMS) based LIS302DL model accelerometer used in the iPhone and iPod Touch gives a maximum displacement reading of about +/- 2.3G with a resolution of about 0.018 g.

There is an STMicroelectronics gyroscope similar to a L3G4200D with a GK10A MEMS die providing finer yaw, pitch and roll readings of angular displacement (how fast is it spinning) than the accelerometer.

A digital compass is included. The iPhone 3GS and iPad uses the AK8973 chip. The iPhone 4 uses the AK8975 chip.