DIGITAL SIGNAL

DIGITAL SIGNAL

A digital signal is a physical signal that is a representation of a sequence of discrete values (a quantified discrete-time signal), for example of arbitrary bit stream, or of a digitized (sampled and analog-to-digital converted) analog signal. The term digital signal can refer to a continuous-time waveform signal used in any form of digital communication or a pulse train signal that switches between a discrete number of voltage levels or levels of light intensity, also known as a a coded signal, for example a signal found in digital electronics or in serial communications using digital baseband transmission in, or a pulse code modulation (PCM) representation of a digitized analog signal.

Waveforms In Digital Systems

A digital signal waveform: (1) low level, (2) high level, (3) rising edge, and (4) falling edge.

In computer architecture and other digital systems, a waveform that switches between two voltage levels representing the two states of a Boolean value (0 and 1) is referred to as a digital signal, even though it is an analog voltage waveform, since it is interpreted in terms of only two levels.

The clock signal is a special digital signal that is used to synchronize digital circuits. The image shown can be considered the waveform of a clock signal. Logic changes are triggered either by the rising edge or the falling edge.

SECONDARY STORAGE

FLOPPY DISK

3 size of floppy disk

A floppy disk is a data storage medium that is composed of a disk of thin, flexible ("floppy")magnetic storage medium sealed in a square or rectangular plastic carrier lined with fabric that removes dust particles.

Floppy disks are read and written by a floppy disk drive or FDD. Invented by the American information technology company IBM, floppy disks in 8-inch, 5¼-inch and 3½-inch forms enjoyed three decades as a popular and ubiquitous form of data storage and exchange, from the mid-1970s well into the 2000s.  While floppy disk drives still have some limited uses, especially with legacy industrial computer equipment, they have now been superseded by USB flash drives, external hard disk drives, optical discs, memory cards and computer networks.

USAGE   

The flexible magnetic disk, commonly called floppy disk, ^[4] revolutionized computer disk storage for small systems and became ubiquitous in the 1980s and 1990s in their use with personal computers and home computers to distribute software, transfer data, and create backups.

Before hard disks became affordable, floppy disks were often also used to store a computer's operating system (OS), in addition to application software and data. Most home computers had a primary OS (and often BASIC) stored permanently in on-board ROM, with the option of loading a more advanced disk operating system from a floppy, whether it be a proprietary system, CP/M, or later, DOS.

DISK FORMAT

Floppy physical sizes are often referred to by the nominal size in inches, even in countries where metric is the standard, and even though the size is defined in metric. For example, the ANSI specification is entitled in part "90-mm (3.5-in)", even though 90 mm is more nearly 3.54 inches.^[7]Formatted capacities are generally set in terms of kilobytes (1024 bytes), written as "kB".