P7
Polling
Polling is
when a CPU checks the printer to see if it’s ready to receive another printing
it does this by using ‘’busy flag’’ if the ‘’busy flag’’ is ON then the printer
is not ready to receive another print. Polling it’s a really good thing so you
don’t overload the printer and confuse it. When the busy flag is OFF the
computer will send the data to the printer the ‘’busy flag’’ will show the
digit 1 to the CPU this makes the computer aware that its ready to receive data
however when the ‘’busy flag’’ shows the 0 it will make the CPU ready to receive
data for printing and it’s not busy. The disadvantage of using this system is
that the CPU is keep checking to see if the printer is ready and doing all this
it wastes a lot of resources trying to find information out.
Polling is
the main priority in the CPU this means is the first task that the CPU will attempt
if the printer is in use by another computer and the CPU is still checking if
the printer is in use may use a lot of valuable resources and slow down the
computer.
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CPU
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PRINTER
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Tries to send information busy flag is on
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CPU
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PRINTER
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The CPU will keep sending the data until the busy flag
is OFF
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Computer sends data but the ‘’busy flag’’ is OFF so it’s
able to print the data
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The CPU will
keep trying to check if the printer is ready and because as a priority its
wasting a lot resources until the printer is no longer busy. They are is another
way the computer to find out whether the CPU is ready to print and do not waste
a lot of resources this is called interrupt this works on how the CPU send the
data to the printer buffer and if the buffer if full the CPU remove data will
poke the CPU interrupt this is the form of acknowledging the computer that is
ready to print this saves a lot of system resources because the computer is no
longer checking all the time to see whether the ‘’busy flag’’ is ON and is no
longer a high priority.
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CPU
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PRINTER
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Sends data to the printer
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CPU
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PRINTER
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Buffer is empty printer interrupts CPU
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CPU
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PRINTER
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Printer buffer is FULL
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The best one
to use would be interrupts as the CPU will be able to focus on other tasks
rather than wasting resources to find out whether the printer is in use or not.
P8
CISC:
Pronounced sisk, and stands for complex instruction set
computer. Most personal computers use a CISC architecture, in which the CPU
supports as many as two hundred instructions. The traditional architecture of a
computer which uses microcode to execute instructions. Instructions may be
variable in length and use all addressing modes, requiring complex circuitry to
decode them.
RISC:
It’s a type of microprocessor that recognizes a relative
limited number of instructions. One advantage is that they can execute their
instructions very fast because the instructions are so simple. Another
important advantage is that the RISC chips requires transistors which makes
them cheaper to design and produce.
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karbosguide.com
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The RISC machine executes instructions faster because it
does not have to go through a microcode conversion layer. The RISC compiler
generates more instructions than the CISC compiler for the same processing.
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Comparison
between RISC and CISC
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CISC
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RISC
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Emphasis
on hardware
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Emphasis
on software
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Includes
multi-clock complex instructions
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Single-clock,
reduced instruction only
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Memory-to-memory:
"LOAD"
and "STORE" incorporated in
Instructions
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Register
to register:
"LOAD"
and "STORE" are
independent
instructions
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Small
code sizes, high cycles per second
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Low
cycles per second, large code
Sizes
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Transistors
used for storing complex
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Spends
more transistors on memory registers
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CISC (complex instruction set computer) and RISC (reduces
instruction set computer) CISC is a type of processes within the CPU it uses
complex instructions and it takes time. RISC is a type of processes which uses
small types of instructions in order to get the job done the fastest way
The advantages of using RISC would be that it will be able to
work on small programs faster you should mainly use RISC for non-important
programs this is because it gets the job done really fast and is a lot more effective to smaller
programs this is because it only uses simple processes if it was working on a
larger program then it wouldn’t be as accurate for the large programs because
it works so fast it might miss parts. It has faster processing’s so its able to
do tasks faster e.g. less important tasks. Simpler hardware. Because the instruction set
of a RISC processor is so simple, it uses up much less chip space, extra
functions, such as memory management units or floating point arithmetic units,
can also be placed on the same chip. The disadvantages of RISC is that it
doesn’t work with larger programs right due to the simple instructions it uses
and how fast it works.
Advantages of CISC It’s more effective for larger programs
because of its complex instructions it doesn’t work well with smaller programs because
they don’t need so many complex instructions, and CISC may be a lot slower to
process it than RISC.
More energy effective because it works with the code instead
of just doing loads of simple ones.
The disadvantage of CISC that it does instructions a lot
slower because of its complex instructions.
So that as many instructions as possible could be stored in
memory could be of almost any length this means that different instructions
will take different amounts of clock time to execute, slowing down the overall
performance of the machine
P9
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20
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201
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20
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200
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Memory
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NA
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N/A
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120
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IR
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ACC
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PC
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CPU
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20
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201
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20
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200
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Memory
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Get 200
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20
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121
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IR
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ACC
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PC
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CPU
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The second instruction is executed
and stores a copy of the contents in the accumulator and stores it in to the
memory location 201.
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20
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201
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20
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200
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Memory
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Store 200
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20
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122
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IR
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ACC
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PC
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CPU
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20
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201
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20
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200
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Memory
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STOP
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20
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123
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IR
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ACC
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PC
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CPU
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http://yoram.info
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Memory Data
Register (MDR)
Instruction
Register (IR)
Program Counter
(PC)
Accumulator
Each register is designed for a special purpose and the
volume of each varies. This special purpose could be to contain the address of
instructions or data being accessed in main memory its called Memory Address
Register (MAR). The register, which contains the actual instruction or data,
fetched or to be stored in the main memory, is called the Memory Data Register
(MDR). The Instruction Register (IR) holds the current instruction to be
executed. A register that holds the address of the next instruction to be
executed and when this instruction is fetched by (IR) it increases
automatically to point (hold) the next address of the instruction to be
executed and is referred to as the Program Counter (PC). The Accumulator
collects intermediate results from the ALU in order to store and manipulate
these intermediate results to obtain the final desired result.
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