Computer hardware

The hard disk drive (HDD) is the computer’s main permanent storage: it holds the operating system, programs and user files; data is written magnetically and the disk is divided into tracks and sectors. The first Winchester drive was made by IBM in 1973. Today SSDs are common: they are made of flash chips with no moving parts, so they are fast and shock-resistant. Portable media include USB flash drives, memory cards and optical discs (CD ≈ 700 MB, DVD ≈ 4.7 GB, Blu-ray ≈ 25 GB; read with a laser beam), while old floppy disks (1.44 MB) are no longer used. Output devices are the monitor (LCD/LED or OLED), printers (inkjet and laser) and plotters; input devices are the keyboard, mouse, scanner, webcam, microphone and touch screen. The screen image is made of pixels, and picture quality depends on the number of pixels (for example 1920×1080). Never open a computer or monitor case: dangerous voltages are inside, and repairs are for specialists.