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Control Unit (CU)
Control Unit coordinates and directs the operation of the hardware devices. It also coordinates the ow and
execution of the data and instructions that are fed into the computer’s memory. CU functions in an FDES
(Fetch-Decode-Execute-Store) cycle. It fetches the instruction and data from the memory unit & decodes
them and passes them to the ALU for further processing. It also directs the ALU to execute the instruction and
perform the required operations on the data.
Memory Unit (MU)
Memory Unit or main storage stores the data, instructions, intermediate results and final results that are ready
for the output. All instructions or data are stored in the memory unit before being used by the ALU or the CU.
The main storage is divided into a number of storage locations that can be accessed by a unique number or
address known as the memory address. Within the CPU there are high-speed, special-purpose memory units
called registers.
The Control Unit and the internal storage are linked together by sets of parallel electrical conducting lines
called buses. The buses that carry data are called ‘Data Buses’. To retrieve data from the memory, it is necessary
to identify the address of data in the main memory. The address is identified by Address Buses . The buses
that carry control signals are called ‘Control Buses’.
Output Devices
Output is the information obtained after processing the data. The user receives the result through output
devices. Output can be in the form of soft copy or hard copy. Soft copy refers to the digital copy which lies
in the storage device whereas hard copy refers to the printed contents on a paper or film. Some common
output devices are:
Printer Plotter
Speaker Monitor
Printer
Printer is a common output device that is used for the purpose of printing
documents. Printer generates a hard copy of data or information.
Printers are of different types depending upon:
Quality of Printing: The quality of output produced by the printer can be measured in units of dpi (dots
per inch) which is also termed resolution.
Speed: The speed of different types of printers varies widely. The speed of a printer is measured in cps
(characters per second), ppm (pages per minute) or lpm (lines per minute).
Printing Mechanism: There are different types of mechanisms that are applied in different types of
printers. Some printers print by striking the printer head on the paper, some print by forming images on
the paper, some print by spraying ink, etc.
Based on the mechanism, printers can be broadly classified into two categories:
Impact Printer Non-Impact Printer
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