SYSTEM CLOCK:

Every computer has got a system clock. It‟s located in the microprocessor. The
clock is design by a piece of quartz crystal. The system clock keeps the computer
system coordinated. It‟s an electronic system which keeps oscillating at specified
times intervals, between 0 & 1. The speed at which this oscillation takes place is
called the cycle of the clock. The time taken to reach from „0‟ to „1‟ and back is
called clock cycle the speed of the system clock is measured in terms of Hz.

SYSTEM BUS:

Bus means the electronic path between various components Bus refers to
particular types of a cable. Each cable of a bus carries information of one bit.
Buses are of 3 types :

(1) Address Bus:It carries the address of memory location of required
instructions and data. The address Bus is unidirectional, i.e., data flows in
one direction from CPU to memory. The address bus data determines the
maximum number of memory addresses. This capacity is measured in
binary form. E.g. A 2 –bit address bus will provide 22 addresses.

(2) Data Bus: Data bus is an electronic path that connects CPU, memory &
other h/w devices. Data bus carries the data from CPU to memory or I/P–
O/P devices and vice versa. It‟s a directional bus because it can transmit
data in either direction. The processing speed of a computer increases if the
data bus is large as it takes more data at one time.

(3) Control Bus: Control Bus controls the memory and I/O devices. This bus
is bidirectional. The CPU sends signals on the control bus to enable the
O/P of the addressed memory devices.

EXPANSION SLOT:

The main function of the mother board is to enable connectivity between various
parts of a computer with processor & memory. Various hardware cards can be
fixed on the mother board to save different purposes. Mother boards have slots to
fix the various cards-like video card, modem, sound cards etc, expansion slots on
the motherboard can be used fro the following purposes:
(i) To connect the internal devices of a computer eg. Hard disk etc. to the
computer bus.
(ii) To connect the computer to the external devices like mouse, printer etc.
The above functions are carried out with the help of adapters.

VARIOUS CARDS:

(1) Sound Card: The sound card converts the
sound into computer language & vice versa. All sound cards are based on
MIDI (Musical Instrument Digital Interface) which represents the music in
electronic form. The main part of sound card is DSP (Digital signal
processor) which uses arithmetic logic to bring out sound effects.

(2) SCSI (Small Compute System Interface) :This technology is used in high
speed hard disk. It‟s often used in servers where high volume of data is
used. At present different versions of SCSI are used. The capacity of the
SCSI is determined by the bus width and speed of the interface. Through
SCSI the computers bus is extended by means of the cable. It‟s an extension
of the computer bus.

(3) Network Cards : N/W card is a versatile device because it performs a number of
tasks that contribute to the entire process of transmitting and receiving data between computers. It links a computer to another computer of the n/w through cable wires. A seven-layer model of OSI (Open System Interface) is used in the Internet for receiving and transmitting of data.