MCA-402
Computer Organization
Q1. Explain the term Logic Gate . Discuss any 3 logic gates.
A1.
Logic gates are the basic building blocks of any digital system. It is an electronic
circuit having one or more than one input and only one output. The relationship
between the input and the output is based on a certain logic. Based on this, logic
gates are named as AND gate, OR gate, NOT gate etc.
AND Gate
A circuit which performs an AND operation is shown in figure. It has n input (n >= 2)
and one output.
Logic diagram
Truth Table
OR Gate
A circuit which performs an OR operation is shown in figure. It has n input (n >= 2)
and one output.
Logic diagram
Truth Table
NOT Gate
NOT gate is also known as Inverter. It has one input A and one output Y.
Logic diagram
Truth Table
Q2. Differentiate between Half Adder and Full Adder.
A2.
Definition of Half Adder
An arithmetic circuit that carries out summation of 2 inputs of one-bit is
known as a ​half adder​.
Everyone is familiar with basic addition technique in which when two bits
are required to be added then, the addition begins with the rightmost
column. As there is always a possibility of carry term to exists. The same
rule is utilized in the operation of half adders.
The figure below represents the logic symbol for half adder:
The figure clearly shows 2 applied inputs and 2 outputs for half adder. Out
of the two, one output shows the summation while other shows carrry
generated.
Definition of Full Adder
Full adders are the arithmetic circuits that generate a summation of 3 inputs
of one- bit.
The figure below represents the logic symbol of a full adder:
This figure clearly shows the 3 inputs applied to the full adder and the 2
outputs. Here, also the one output shows the summation result and the
other shows the carry bit generated.
Q3. What is the difference between RISC and CISC . Explain
A3.
Reduced Instruction Set Computer (RISC) is a type or category of the processor, or
Instruction Set Architecture (ISA). Speaking broadly, an ISA is a medium whereby a
processor communicates with the human programmer (although there are several
other formally identified layers in between the processor and the programmer). An
instruction is a command given to the processor to perform an action.
What are the differences between RISC and CISC?
The short answer is that RISC is perceived by many as an improvement over CISC.
There is no best architecture since different architectures can simply be better in
some scenarios but less ideal in others. RISC-based machines execute one
instruction per clock cycle. CISC machines can have special instructions as well as
instructions that take more than one cycle to execute. This means that the same
instruction executed on a CISC architecture might take several instructions to
execute on a RISC machine. The RISC architecture will need more working (RAM)
memory than CISC to hold values as it loads each instruction, acts upon it, then
loads the next one.
​The CISC architecture can execute one, albeit more complex instruction, that does
the same operations, all at once, directly upon memory. Thus, RISC architecture
requires more RAM but always executes one instruction per clock cycle for
predictable processing, which is good for pipelining. One of the major differences
between RISC and CISC is that RISC emphasizes efficiency in cycles per instruction
and CISC emphasizes efficiency in instructions per program. A fast processor is
dependent upon how much time it takes to execute each clock cycle, how many
cycles it takes to execute instructions, and the number of instructions there are in
each program. RISC has an emphasis on larger program code sizes (due to a
smaller instruction set, so multiple steps done in succession may equate to one step
in CISC).
Q4. Explain the Cache Memory and Virtual Memory
A4.
Cache Memory
In memory hierarchy, there is an additional level of memory which is Cache. It
is high-speed storage and much faster than the main storage. It is much
expensive as compared to main storage. So, a relatively small amount of
cache is used.
Programs and data need to be in main storage to be executed. Program or
data not needed immediately may be kept on secondary storage until needed
and then brought into main memory for reference.
Cache storage imposes this level of shuttling on the system. Programs in the
main memory shuttled to the cache before being executed. In the cache, they
may be executed much faster than in the main storage.
There is a cache hit when the cache has a copy of the required data and there
is a cache miss if the cache does not have a copy of that data item.
The overhead involved in shuttling programs back and forth will be reduced so
the performance increase obtained by the faster execution possible in the
cache.
Cache memory is a faster memory type that acts as a buffer between main
memory and the processor.
Virtual Memory
It is a memory management scheme that permits the execution of various
processes which may not be entirely in RAM. It is possible that user programs
can be larger than physical memory.
A 'swap file' is created in this area which is used to sustain data which the
processor does not need in a frequent amount of time.
It makes the programming much simpler because the programmer doesn't
have to take care of the size of the physical memory available.
By this CPU utilization and throughput increases as the user utilizes less
physical memory. So more users can keep their programs in memory.
Q5. What is ab IO processors ? How does it works ? Discuss its Organization.
A5.
Introduction of Input-Output Processor
Last Updated: 22-08-2019
The D
​ MA mode​ of data transfer reduces CPU’s overhead in handling I/O operations.
It also allows parallelism in CPU and I/O operations. Such parallelism is necessary to
avoid wastage of valuable CPU time while handling I/O devices whose speeds are
much slower as compared to CPU. The concept of DMA operation can be extended
to relieve the CPU further from getting involved with the execution of I/O operations.
This gives rises to the development of special purpose processor called
Input-Output Processor (IOP) or IO channel​.
The Input Output Processor (IOP) is just like a CPU that handles the details of I/O
operations. It is more equipped with facilities than those are available in typical DMA
controller. The IOP can fetch and execute its own instructions that are specifically
designed to characterize I/O transfers. In addition to the I/O – related tasks, it can
perform other processing tasks like arithmetic, logic, branching and code translation.
The main memory unit takes the pivotal role. It communicates with processor by the
means of DMA.
The block diagram –
The Input Output Processor is a specialized processor which loads and stores data
into memory along with the execution of I/O instructions. It acts as an interface
between system and devices. It involves a sequence of events to executing I/O
operations and then store the results into the memory.