These systems were the first type to be produced. It is an electronic machine capable of performing arithmetic functions on numbers which are represented by some physical quantities such as temperature, pressure, voltage, etc. Analog refers to circuits or numerical values that have a continuous range. The popular analog computer used in the 20th century was the slide rule.
Virtually all modern computers are digital. Digital refers to the processes in computers that manipulate binary numbers (0s or 1s), which represent switches that are turned on or off by the electrical current. A bit can
have the value 0 or the value 1, but nothing in between 0 and 1. A desk lamp can serve as an example of the difference between analog and digital.
If the lamp has a simple on/off switch, then the lamp system is digital, because the lamp either produces light at a given moment or it does not. If a dimmer replaces the on/off switch, then the lamp is digital, because the amount of light can vary continuously from on to off and all intensities in
between. Digital computers are more common in use and it will be our focus of discussion.
This is when a computer makes is of both analog and digital components and techniques. Such a computer requires analog to digital and digital to analog converter which will make analog and digital data palatable to it. The basic classification nowadays uses the following.
A computer is referred to as “desktop” when it is relatively small enough to be positioned on top of a table where a person is working. Such a computer can also be placed on the floor or somewhere under, or aside of, the table, in which case the monitor would be placed on top of the table. This is the most common type of computers used in the office or at home. A desktop
computer is made of different parts that are connected with cables.
A computer is called a laptop when it combines the CPU, the monitor, the keyboard, and the mouse in one unit to be so small that you can carry it on your laps when traveling or commuting.
A laptop is also called a notebook. Other parts, such as an external mouse, an external keyboard, or peripherals such as a printer or a projector, can be connected to the laptop. A laptop is only physically smaller than a desktop but, everything considered, it can do anything that a desktop can do
A server is a computer that holds information that other
computers, called workstations, can retrieve. Such workstations
are connected to the server using various means. This means that they could be connected using cable, wireless connection, etc.
Only computers that maintain a type of connection with the server can get the information that is stored in the server. Normally, although not particularly recommended, any computer, including a desktop or even a laptop can be used as a server, as long as it can do the job required.
A server is more defined by the program (called an operating system) that is installed in it, not how the machine looks. Any type of computer, including a desktop, a laptop, a CD or DVD machine, etc can be connected to a server. The person who sets up a server also defines the types of connections it is made for.
A mainframe is a computer, usually physically big, that does almost all the jobs for other types of computers that are connected to it. This is a broad definition but other aspects are involved. As a server, the program (operating system) that runs in the mainframe defines its role.