Unit 3 Computer Architecture & Storage Flashcards
What does the CPU do?
The CPU processes instructions
When you run a program, it is the
CPU which processes the
instructions and data that are input
The results are then output
What are the 2 major components of the CPU?
Arithmetic logic unit(ALU) and Control unit (CU)
What is a register?
A register is a very fast
memory location in the
CPU itself
Name all CPU registers and state their purpose.
Program Counter (PC)
holds the address of the next instruction to be executed
Memory Address Register (MAR)
Holds the memory address of where data or instructions are to be fetched
Memory Data Register (MDR)
Stores the data or instruction which has been fetched from memory
Current Instruction Register (CIR)
holds the instruction currently being executed or decoded
Accumulator (ACC)
holds the result of an instruction before it is transferred
to memory
What is the purpose of the control unit?
The control unit coordinates and controls
all of the activities taking place within
the CPU
It decodes instructions and executes them
It receives signals from the system clock
What does the ALU do?
The ALU or Arithmetic Logic Unit is where the actual
arithmetic operations are done
It also carries out logical operations such as those including
AND, OR and NOT
How does the fetch-decode-execute cycle work?
The CPU operates by repeating
three operations:
FETCH – causes the next
instruction and any data
involved to be fetched from
main memory
DECODE – decodes the
instruction
EXECUTE – the instruction
is executed
This process is then repeated…
What does the program counter do?
The Program Counter holds
the address of the next
instruction to be executed
What does the accumulator do?
Accumulator
The accumulator (ACC) is
where arithmetic and logic
results are temporarily stored,
much like the M+ function on
a calculator
What do the MAR and MDR do?
The MAR holds the memory address of where instructions are to be fetched from memory
The MDR holds the actual instruction, and the data that has been fetched.
What does the CIR do?
The current instruction register holds the instruction that is being executed or decoded at the moment
What affects CPU performance?
Clock speed
Processor cores
Cache
What is clock speed?
Everything in a computer happens on the pulse of
the internal clock
Therefore, the faster the clock speed, the faster the
instructions are processed
How do multi-core processors work?
A dual-core processor has two processors in the
same integrated circuit, linked together
A dual-core processor has the potential to perform two
instructions at the same time
This allows twice as many instructions to be executed,
however, it doesn’t always perform at this rate as software
may not be able to take full advantage of both cores
WHy can multi core be faster than single core?
A quad-core processor working on many different
tasks simultaneously, under ideal conditions can be
up to four times faster than a single-core processor
How does cache memory work?
Cache is a small amount of very
fast, expensive memory in the CPU
It can be accessed faster than
regular main memory (RAM)
What are the levels of cache mamory?
Level 1 cache is extremely fast but small (between 2-256KB),
located on the CPU. Each core will have its own
Level 1 cache
Level 2 cache is usually also given to each core. It is very
fast, but a little slower than Level 1 cache. The typical size is
256KB-8MB
Level 3 cache is the slowest type of cache, but still faster
than RAM. It is usually located on the CPU and stores
4MB-50MB. The cache is shared between all the cores on
the processor
What are the benefits of cache?
The data used most often by the CPU is held in
Level 1 cache so is available extremely quickly
In most systems, Level 1 cache is used about 50% of the time,
with Level 2 cache being accessed about 90% of the time
This greatly reduces the time that the CPU has to wait for data
from main memory
The size of the Level 2 cache is a major factor in
determining the performance of the CPU
What are buses?
A bus is a set of parallel wires connecting two or
more components of the computer
What are the 3 buses that make up the system bus?
Address Bus: stores the address of the memory or device
controller to be read from or written to
Data Bus: carries data throughout the computer system
Control Bus: uses control signals to control all activities
within the CPU
What are external buses?
The CPU is also
connected to the external
Input-output device
controllers by means of
the system bus
What are instruction sets?
Instruction sets are all the possible instructions that
are able to be decoded and executed by a CPU
What are operands and operators?
An operator performs an operation (calculation) on the
operand(s)
The operands are the values used
What are opcodes and operands?
When programming a processor a special language
called assembly code is used
The program is then assembled into a binary form known as
machine code – this is what is run by the processor
The assembly code (and machine code) make use of
opcodes and operands
The opcode is the instruction and the operands are the values
that the instruction works on
