System Unit

Memory consists of electronic components that store
instructions waiting to be executed by the processor, data
needed by those instructions, and the results of processing
the data
Stores three basic categories
of items
The operating system and
other system software
Application programs
Data being processed and the
resulting information
Each location in memory has
an address
Memory size is measured in kilobytes (KB or
K), megabytes (MB), gigabytes (GB), or
terabytes (TB)
The system unit contains two
types of memory
Volatile memory
Loses its contents when
power is turned off
RAM chips usually reside on a memory
module and are inserted into memory
Three basic types of RAM
chips exist
Dynamic RAM (DRAM)
Static RAM (SRAM)
Magnetoresistive RAM (MRAM)
The amount of RAM necessary in a computer
often depends on the types of software you
plan to use
Nonvolatile memory
Does not lose contents when
power is removed
Flash memory can be erased
electronically and rewritten
CMOS technology provides high
speeds and consumes little
Readonly memory (ROM) refers to memory
chips storing permanent data and
Memory cache speeds the processes of the
computer because it stores frequently used
instructions and data
A PROM (programmable readonly memory)
chip is a blank ROM chip that can be written
to permanently
EEPROM can be erased
Access time is the amount of time it
takes the processor to read from
Measured in nanoseconds
Expansion Slots and Adapter Cards
An expansion slot is a socket on the
motherboard that can hold an adapter
An adapter card enhances functions of a
component of the system unit and/or
provides connections to peripherals
Sound card and video card
With Plug and Play, the computer
automatically can configure adapter cards
and other peripherals as you install them
Removable flash memory includes
Memory cards, USB flash drives,
and PC Cards/ExpressCard
Ports and Connectors
A port is the point at which a peripheral
attaches to or communicates with a system
unit (sometimes referred to as a jack)
A connector joins a cable to a port
A USB port can connect up to 127
different peripherals together with a single
You can attach multiple peripherals
using a single USB port with a USB hub
Other types of ports include
Firewire port
Bluetooth port
SCSI port
eSATA port
IrDA port
Serial port
MIDI port
A bus allows the various devices both inside
and attached to the system unit to
communicate with each other
Data bus
Address bus
Word size is the number of bits the
processor can interpret and execute at a
given time
Expansion slots connect to
expansion buses
Common types of expansion
buses include
PCI bus
PCI Express bus
Accelerated Graphics Port
USB and FireWire bus
PC Card bus
Putting It All Together
Intel Core 2 Duo or Intel Celeron Dual
Core or AMD Sempron
Minimum RAM: 2 GB
Small Office/ Home Office
Intel Core 2 Quad or Intel Core 2 Extreme
or AMD Athlon FX or AMD Athlon X2 DualCode
Minimum RAM: 4 GB
Intel Core 2 Extreme or AMD
Turion X2
Minimum RAM: 2 GB
Intel Itanium 2 or AMD Quad Core Opteron
or Intel Quad Core Xeon or Sun UltraSPARC
Minimum RAM: 8 GB
Intel Core 2 Quad or Intel Core 2 Extreme or
AMD Athlon FX or AMD Athlon X2 DualCore
Minimum RAM: 4 GB
The processor, also called the
central processing unit (CPU)
Multicore processor
Dualcore processor
Quadcore processor
The control unit is the component of the
processor that directs and coordinates most
of the operations in the computer
The arithmetic logic unit (ALU) performs
arithmetic, comparison, and other operations
The processor contains registers,
that temporarily hold data and
The system clock controls the
timing of all computer
A processor chip generates heat
that could cause the chip to burn up
Require additional cooling
Heat sinks
Liquid cooling technology