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Logical Block Diagram

System Unit

• System unit is created by inter-connecting lots of parts.

• All of the components of a computer system require power to perform.

• And also the system unit components needs protection from out-side entities. (dust, humidity, insects…..)

System unit cont……

• Therefore to provide,– Power– Protection– Outer AppearanceComponents of the system unit well organizedin side a ‘Protected Chassis’.

Chassis• The chassis consist of space for,– Motherboard– Power supply – Input/output connectors– Expansion cards– Expansion bays– Switches and wires – Indicator Light Emitting

Diodes (LEDs)

Chassis Types

• According to the outer appearance and the device organization inside, chassis are differs.

• Mainly there are two types of Chassis using.– Tower Chassis– Flat-bed Chassis

Tower Chassis

• The system unit components are screwed on to the right side panel of the chassis.

• The outer appearance looks like a ‘Tower’.• Input/output connectors attached from the rear.• More popular type in these days.• There are some sub-types of Tower Chassis as well.

Tower Chassis Types

Mini-TowerMid-TowerFull-Tower

Flatbed Chassis• The older version of chassis types.• Very rarely used in these days.• Branded computers still manufacturing these

types of chassis for office environments.• Flatbeds are more compact and saves occupying

space.• There are two types of Flatbed chassis.– Desktop– Slim Desktop

Desktop

Slim-Desktop

Power Supply

• Is the component that supplies power to a computer.

• More specifically, a power supply is typically designed to convert 100-120 V (North America and Japan) or 220-240 V (Europe, Africa, Asia and Australia)

• Provides 5V output by using 250Watt +

• Mainly Two types of Power Supplies are there,» AT» ATX

AT-Advanced Technology • Older version of Power supplies.• Power switch is not soft-switch one.• Computer is connected directly to the power supply

ATX-Advanced Technology Extended

• New version of Power supplies.• Power switch is soft-switch one.• Computer is connected to the power supply through

the motherboard.

Power supply connectors• Power supply have many connectors to provide

power to the system components.– Mini plug-provides power to the floppy drive– Molex power connector-provides power to hard drives,

CD/DVD drives– Motherboard power connector-provide power to the

motherboard– 12v ATX power connector-this is required to provide

additional power to the Pentium4 processor. This is plugged in to the motherboard.

– SATA (Serial Advanced Technology Attachment) power connector-provides power to the SATA devices)

Drive bays• Drive bays are a part of the chassis which is

used to attach drives such as the,– Hard disk– CD/DVD Drives– Floppy drives.

Buttons and Indicators

• The power button and reset buttons are located on the front panel of the chassis.

• With two LEDs for indicating the,– HDD usage (Red)– Power (Green)

Power

Reset

Components of the System Unit

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