• How Computers Represent Data
• How Computers Process Data
• Factors Afecting Processing Speed
• Extending the Procesor’s Power to
How Computers Represent Data
• Binary Numbers
• The Binary Number System
• Bits and Bytes
• Text Codes
How Computers Represent Data – Binary Numbers
•Computer procesing is performed by transistors,
which are switches with only two posible states: on
•Al computer data is converted to a series of binary
numbers– 1 and 0. For example, you see a sentence as
a colection of leters, but the computer sees each
leter as a colection of 1s and 0s.
•If a transistor is assigned a value of 1, it is on. If it has
a value of 0, it is of. A computer’s transistors can be
switched on and of milions of times each second.
The Binary Number System
• To convert data into strings of numbers, computers use the binary 210
• Humans use the decimal system (“deci” stands for “ten”).
• The binary number system works the same way as
the decimal system, but has only two available symbols (0 and 1)
rather than ten (0, 1, 2, 3, 4, 5, 6, 7, 8 , and 9)
How Computers Represent Data – Bits and Bytes
•A single unit of data is caled a bit, having a value of 1
•Computers work with colections of bits, grouping
them to represent larger pieces of data, such as leters
of the alphabet.
•Eight bits make up one byte. A byte is the amount of
memory needed to store one alphanumeric character.
•With one byte, the computer can represent one of 256
diferent symbols or characters.
How Computers Represent Data – Text Codes
•A text code is a system that uses binary numbers (1s and
0s) to represent characters understood by humans
(leters and numerals).
•An early text code system, caled Extended binary coded
decimal interchange code (EBCDIC) uses eight-bit codes,
but is used primarily in older mainframe systems.
•In the most common text-code set, American Standard
Code for InformationInterchange (ASCII), each
character consists of eight bits (one byte) of data. ASCII
is used in nearly al personal computers.
•In the Unicode text-code set, each character consists of 16
bits (two bytes) of data.
How Computers Process Data
Where Processing Occurs:
•The Control Unit
•The Arithmetic Logic Unit
•The Role of Memory in Processing
•Types of RAM
How Computers Process Data –Where Processing Occurs
•Processing takes place in the PC’s central processing
•The system’s memory also plays a crucial role in
•Both the CPU and memory are atached to the
system’s motherboard, which connects al the
computer’s devices together, enabling them to
How Computers Process Data –The Control Unit
The two main parts of a CPU are the control unit and the
arithmetic logic unit (ALU)
• The control unit directs the flow of data through the
CPU, and to and from other devices.
• The control unit stores the CPU’s microcode,which
contains the instructions for al the tasks the CPU can
• It obtains the instruction from the program stored in
the main memory, interprets the instruction, and
issues signals that cause other units of the system to
How Computers Process Data –The Control Unit
• Instruction & Program Control registers of control unit
Hold the current instruction and the next instruction
to be executed. They help in selecting the instruction.
• Decoder : It has necessary circuitry to decode and
interpret the meaning of each and every instruction
supported by CPU. Each Instruction is supported by
microcode – which directs CPU to execute the
• Instruction Sets : Every CPU has the built-in ability
to execute a particular set of machineinstructions
caled its instruction set.
How Computers Process Data –registers
• Registers : Computer uses number of special memory in
its CPU caled registers. These registers are used to hold
information on a temporary basis.
• Memory Address Registers : Holds the addres of active
• Memory Bufer Registers : Holds the information on its
way to and from memory
• Program Control : Holds the addres of next instruction
to be executed
• Accumulator : Accumulates results and datato be
• Instruction : Holds an instruction while it is being
• Input/Output : Communicates with I/O devices.
Factors Affecting Processing Speed
•The System Clock
How Computers Process Data –The Arithmetic Logic Unit
• The actual manipulation of data takes place in the
• The ALU can perform arithmetic and logic
• The ALU is connected to a set of registers—smal
memory areas in the CPU, which hold data and
program instructions while they are being processed.
How Computers Process Data –Machine Cycles
•The CPU folows a set of steps-caled a machine cycle-
for each instruction it carries out.
•By using a technique caled pipelining, many CPUs can
process more than one instruction at a time.
•The machine cycle includes two smaler cycles:
üDuring the instruction cycle, the CPU “fetches” a
command or data from memory and “decodes” it for
üDuring the execution cycle, the CPU carries out the
instruction, and may store the instruction’s result in
How Computers Process Data –The Role of Memory
•RAM stores data and program code needed by the
CPU. The contents of RAM change rapidly and often.
•Read-only memory (ROM) is nonvolatile (or
permanent). It holds instructions that run the
computer when the power is first turned on.
•The CPU accesses each location in memory by using a
unique number, caled the memory addres.
How Computers Process Data -Types of RAM
There are two basic types of RAM: static and dynamic
•Dynamic RAM (DRAM) chips must be recharged
with electricity very frequently, or they wil lose their
•Static RAM (SRAM) does not need to be recharged
as often as DRAM, and can hold its contents longer.
Another type of RAM, caled flashmemory, can store its
contents after power is turned of. Flash memory is used
in digital cameras to store pictures.
DRAM(Dynamic Random Acces Memory)and its evolution
DRAM chips are whatmake up RAM bars.They areatached
to aprintedcircuitboard whichistheninsertedinto the
coresponding slot. DRAM chiptechnology thenmoved on to:
10%to 20% fasterthan DRAM.
Roughly25%faster thanEDO RAM.
DDRor SDRAMI (DoubleData RateSDRAM)
Twice asfastas SDRAM.
Developed by Rambus,Inc.Roughly ten timesfaster than
SLDRAMisthe major competing technologyto RDRAM.
SIMM (Single In-line Memory Module)
72-pinSIMMs were usedin386sthroughPentiums.386sand
486s usedSIMMs individualy whereasPentiums required
SIMMs toworkinpairs. Therewerealso 30-pin SIMMsbut
these are too oldtobeworth anyatention. 72-pin SIMM
capacity canrangefrom 4MB to128MB.
DIMM (DualIn-line MemoryModule)
DIMMmemory is what isused nowadays. There aretwo types
ofDIMM: SO (SmalOutline) DIMM and 168-pinDIMM.SO
DIMMisusedinlaptops and notebooksforitison the whole, a
reducedversionofthe 72-pinSIMM. 168-pinDIMMcapacity
can rangefrom8MBto 512MB.
Factors Afecting Processing Speed – Registers
•The CPU contains a number of smal memory areas,
caled registers, which store data and instructions
while the CPU processes them.
•The size of the registers (also caled word size)
determines the amount of data with which the
computer can work at a one time.
•Today, most PCs have 32-bit registers, mean the CPU
can process four bytes of data at one time. Register
sizes are rapidly growing to 64 bits.
Factors Affecting Processing Speed – RAM
• The amount of RAM in a PC has a direct afect on
the system’s speed.
• The more RAM a PC has, the more program
instructions and data can be held in memory, which
is faster than storage on disk.
• If a PC does not have enough memory to run a
program, it must move data between RAM and the
hard disk frequently. This proces, caled swapping,
can greatly slow a PC’s performance.
Factors Afecting Processing Speed –The System Clock
•The computer’s system clock sets the pace for the CPU
by using a vibrating quartz crystal.
•A single “tick” of the clock is the time required to turn
a transistor of and back on. This is caled a clock
•Clock cycles are measured in Hertz (Hz), a measure of
cycles per second. If a computer has a clock speed of
300 MHz, then its system clock “ticks” 300 milion
times every second.
•The faster a PC’s clock runs, the more instructions the
PC can execute each second.
Factors Affecting Processing Speed –The Bus
•A bus is a path between the components of a
computer. Data and instructions travel along these
•The data bus’ width determines howmany bits can be
transmited between the CPU and other devices.
•The address bus runs only between the CPU and
RAM, and carries nothing but memory addreses for
the CPU to use.
•Peripheral devices are connected to the CPU by an
Factors Afecting Processing Speed –Cache Memory
• Cache memory is high-speed memory that holds the
most recent data and instructions that have been
loaded by the CPU.
• Cache is located directly on the CPU or between the
CPU and RAM, making it faster than normal RAM.
• CPU-resident cache is caled Level-1 (L1) cache.
External cache is caled Level-2 (L2) cache.
• The amount of cache memory has a tremendous
impact on the computer’s speed.
Extending the Processor’s Power to Other Devices
•Expansion Slots and Boards
Extending the Processor’s Power to Other Devices – Ports
•External devices—such as those used for input and
output—are connected to the system by ports on the
back of the computer.
•PCs feature a number of built-in ports, which are
ready to accept devices such as a printer, mouse,
keyboard, phone line, microphone and speakers,
•Most computers come with a serial port and a
paralel port. A serial port transmits one bit of data
at a time; a paralel port transmits data one byte at
Adding Other Devices –Expansion Slots and Boards
•If the PC does not have a port for an external device,
you can instal an expansion board into one of the
empty expansion slots.
•A board provides the correct port for the new device,
and connects the device to the CPU by way of the
computer’s expansion bus.
•Newer bus technologies such as Universal Serial Bus
(USB) and IEEE 1394 enable many devices to be
connected to one port.
•Smal Computer System Interface (SCSI) is an older
standard for extending the bus to multiple devices
through a single port.