GCSE
COMPUTER
SCIENCE
Everything You Need to Know
,Topic 1 -
What is a Computer system? A collection of HARDWARE and SOFTWARE working
together to create a CODED SOLUTION.
It involves a set of inputs being processed to present a set of outputs.
Basic Computer System model Memory
|
Input---CPU----Output
|
Secondary Storage
,Basic Computer (Storage) Must have Memory (Primary storage)
Holds data which is currently being used and instructions which are currently being executed
Must have Secondary Storage
Data that does not need to be used frequently
Von Neumann Architecture A processor where data and instructions are stored in the same
memory and accessed via buses. Programs were generally input from setting switches. Data
and programs would be held in the memory
CPU components CPU- hardware that executes programs and manages the rest of the
hardware. "Brain"
Cache- Fast memory, close to the CPU, holds data temporarily which is likely to be used
again in the same program
Main memory- Holds data which is currently being used and instructions which are currently
being executed.
Fetch-Execute Cycle the basic process performed by the CPU. On each cycle the CPU
fetches the instruction from main memory, decodes the instruction and executes the
instruction.
CPU components F-D-E cycle CU CU (Control unit)- Coordinates all activities in CPU
-controls execution of instruction in correct sequence
-decodes instructions
-controls processor timing using pulse on system clock
-sends and receives control signals from other devices
CPU components F-D-E cycle ALU Logical operations- And, Or, Not
Shift operations- bits in word can be shifted left or right
Arithmetic operations- + - * /
Special Purpose Registers very fast memory location used in the execution of instructions
CPU components (Registers) MAR- memory adress register
MDR memory data register
PC- program counter
ACC- accumulator
MAR memory address register- holds the adress of the instruction where it should be stored
or fetched
MDR memory data register- holds the data of the instruction when stored or fetched.
PC program counter- holds the memory address of the next instruction
ACC Accumulator- operations processed in ALU are stored in the ACC
, Factors that affect CPU performance Clock speed- Speed at which a processor operates
measured in Hz
Cache size- Data frequently used by processor can be accessed quicker
Number of cores- two or four instructions can be processed simultaneously. Parallel
processing
Embedded system small computer built in to a piece of equipment which has a purpose of
carrying out a specific function
Characteristics of an Embedded system reliability
Minimal recourses such as a timer, ROM, sensors
RAM Random access memory- main memory, act as temporary storage for programs and
data while program is being executed.
Virtual memory virtual memory- part of hard drive can act as main memory. Slower
than RAM. Holds programs which are currently being run but not programs which are
currently being executed- this happens in main memory and VM only ACTS as main
memory.
Volatility volatile- when you turn of power, data is lost
non volatile- data can still be kept and stored even without a power source
Secondary Storage Non volatile, Holds more data than main memory
Examples-Magnetic disks, Solid state drive (SSD), Optical device
Memory vs Storage memory- Volatile, small amount of storage capacity, Accessed directly
by the CPU
storage- Non volatile, Large amount of storage capacity, not directly accessed by CPU
Solid State Drive (SSD) Holds data using electronic switches
no moving parts
more reliable
lighter
lower power consumption
Magnetic disks Read with a moving disk inside the disk drive
susceptible to damage
vulnerable to magnetic fields
read from/ write to slower
minute magnetic particles to store data
Optical device CD, DVD, Blue Ray
Lasers write data on disc by burn lines and is read
Slow transfer speeds
moving parts
COMPUTER
SCIENCE
Everything You Need to Know
,Topic 1 -
What is a Computer system? A collection of HARDWARE and SOFTWARE working
together to create a CODED SOLUTION.
It involves a set of inputs being processed to present a set of outputs.
Basic Computer System model Memory
|
Input---CPU----Output
|
Secondary Storage
,Basic Computer (Storage) Must have Memory (Primary storage)
Holds data which is currently being used and instructions which are currently being executed
Must have Secondary Storage
Data that does not need to be used frequently
Von Neumann Architecture A processor where data and instructions are stored in the same
memory and accessed via buses. Programs were generally input from setting switches. Data
and programs would be held in the memory
CPU components CPU- hardware that executes programs and manages the rest of the
hardware. "Brain"
Cache- Fast memory, close to the CPU, holds data temporarily which is likely to be used
again in the same program
Main memory- Holds data which is currently being used and instructions which are currently
being executed.
Fetch-Execute Cycle the basic process performed by the CPU. On each cycle the CPU
fetches the instruction from main memory, decodes the instruction and executes the
instruction.
CPU components F-D-E cycle CU CU (Control unit)- Coordinates all activities in CPU
-controls execution of instruction in correct sequence
-decodes instructions
-controls processor timing using pulse on system clock
-sends and receives control signals from other devices
CPU components F-D-E cycle ALU Logical operations- And, Or, Not
Shift operations- bits in word can be shifted left or right
Arithmetic operations- + - * /
Special Purpose Registers very fast memory location used in the execution of instructions
CPU components (Registers) MAR- memory adress register
MDR memory data register
PC- program counter
ACC- accumulator
MAR memory address register- holds the adress of the instruction where it should be stored
or fetched
MDR memory data register- holds the data of the instruction when stored or fetched.
PC program counter- holds the memory address of the next instruction
ACC Accumulator- operations processed in ALU are stored in the ACC
, Factors that affect CPU performance Clock speed- Speed at which a processor operates
measured in Hz
Cache size- Data frequently used by processor can be accessed quicker
Number of cores- two or four instructions can be processed simultaneously. Parallel
processing
Embedded system small computer built in to a piece of equipment which has a purpose of
carrying out a specific function
Characteristics of an Embedded system reliability
Minimal recourses such as a timer, ROM, sensors
RAM Random access memory- main memory, act as temporary storage for programs and
data while program is being executed.
Virtual memory virtual memory- part of hard drive can act as main memory. Slower
than RAM. Holds programs which are currently being run but not programs which are
currently being executed- this happens in main memory and VM only ACTS as main
memory.
Volatility volatile- when you turn of power, data is lost
non volatile- data can still be kept and stored even without a power source
Secondary Storage Non volatile, Holds more data than main memory
Examples-Magnetic disks, Solid state drive (SSD), Optical device
Memory vs Storage memory- Volatile, small amount of storage capacity, Accessed directly
by the CPU
storage- Non volatile, Large amount of storage capacity, not directly accessed by CPU
Solid State Drive (SSD) Holds data using electronic switches
no moving parts
more reliable
lighter
lower power consumption
Magnetic disks Read with a moving disk inside the disk drive
susceptible to damage
vulnerable to magnetic fields
read from/ write to slower
minute magnetic particles to store data
Optical device CD, DVD, Blue Ray
Lasers write data on disc by burn lines and is read
Slow transfer speeds
moving parts
