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Describe the internal components of a computer system: processor, clock, main memory, cache memory, buses (address, data and control), I/O controllers, registers and ports;
Describe the fetch-execute cycle;
Evaluate the factors that can influence the speed of processing: processor type and clock speed;
Explain the need for secondary storage;
Describe secondary storage media: magnetic, optical and flash;
Evaluate the use of secondary storage media for common applications.
Architecture Lesson recording
Architecture Lesson recording
Secondary Storage Lesson Recording
Secondary Storage Lesson Recording
Image taken from BBC Bitesize Revision
Internal Components of a Computer system
Internal Components of a Computer system
(The Processor is the brain the computer you may be more familiar with it being referred to as the CPU at GCSE Level.)
processor
processor
The processor consists of the Control Unit (CU)
...a series of registers
...and the Arithmetic Logic Unit (ALU)
It includes main memory/IAS
It carries out mathematical/logical operations
...during the FE cycle
CCEA 2024 Q3 a
Control Unit
Control Unit
(As the word Control suggests - it controls/coordinates the movement of data.)
(HAS NOT BEEN ASKED BEFORE)
The control unit is a digital circuit that coordinates the movement of data, the sequencing of instructions and directs the operation of the other components of a computer system by providing control and timing signals.
Timing signals are provided by an internal clock which helps to synchronize the operation of the internal components and which helps determine how many computer instructions are carried out (executed) each second.
The CPU needs a certain number of clock ticks to carry out each instruction. Clock speed is expressed in megahertz (MHz) or gigahertz (GHz).
CCEA Fact File
Learn these points below, this is a common question in GCSE Computer Science.
The CU provides several functions:
it fetches, decodes and executes instructions
it issues control signals that control hardware
it moves data around the system
clock
clock
(Part of the the Control Unit)
Produces pulses/timing signals
… for the synchronisation
… of operations between HW components/internal components
... Expressed in GHz or MHz
CCEA 2021 Q4 a
Arithmetic Logic Unit (ALU)
Arithmetic Logic Unit (ALU)
(As the word Arithmetic suggests it deals with mathematical and logical operations)
(HAS NOT BEEN ASKED BEFORE)
The ALU is a digital circuit which forms part of the processor.
It carries out mathematical and logical operations on data associated with instructions being executed.
CCEA Fact File
Learn these points below, this is a common question in GCSE Computer Science.
The ALU has two main functions:
It performs arithmetic and logical operations (decisions). The ALU is where calculations are done and where decisions are made.
It acts as a gateway between primary memory and secondary storage . Data transferred between them passes through the ALU.
Main Memory
Main Memory
Part of internal memory.
Immediate access memory
Made up from Random Access Memory/volatile memory
CCEA 2018 Q3 a [2]
Main memory is referred to as Random Access Memory (RAM). Main memory is Volatile memory meaning it will be lost if power is removed.
Main Memory at any time stores a portion of the operating system, application software currently running and other data items the processing unit needs when carrying out operations.
CCEA Fact File
rom
rom
Contents fixed during manufacture
Holds boot up sequence/BIOS
(2 x [1])
CCEA 2022 Q3 a
Cache Memory
Cache Memory
Explain how cache memory is used by the processor. [3]
Cache memory stores copies of contents of most frequently/recently accessed memory locations/data/applications/programs/data files instructions
The processor first searches cache memory
... before searching main memory
CCEA 2022 Q3 b & 2018 Q3 b
Buses
Buses
Remember the CPU is the Processor.
Exam tip: Learn this diagram, as it is in the CCEA Fact File and you could be asked to fill in the blanks.
Operating in isolation, each of the internal components of a typical computer system has a very specific function.
Communication between each of these components is necessary during the execution of program instructions.
Communication systems known as buses are used to support the transfer of signal between the internal components of computer system (internal buses) and to allow for communication with the various input and output (I/O) devices used for communication with the outside world (external buses).
A bus is basically a set of physical connections in the form of set of physical cables or printed circuits used to connect the various hardware components used in the execution of a set of instructions.
(Exam tip: A definition of a bus has not been asked before, it is more likely to ask for the specific function of a bus as listed below. This may help you understand though what a bus is.)
CCEA Fact File
Data Bus
Data Bus
Transfers instructions and data
...between processor components/memory/registers
...during the FE cycle
CCCEA 2024 Q3a
Address Bus
Address Bus
Transfers/Stores the location in memory
...to be accessed for reading/writing data
(2 x [1])
CCEA 2022 Q 3 a
control Bus
control Bus
Transfers signals within the CPU
CCEA 2019 Q3 b
Table taken from CCEA Fact File
Registers
Registers
Registers are small amounts of high-speed memory contained within the CPU.
They are used by the processor to store small amounts of data that are needed during processing, such as:
the address of the next instruction to be executed
the current instruction being decoded
the results of calculations
Different processors have different numbers of registers for different purposes, but most have some, or all, of the following:
program counter
memory address register (MAR)
memory data register (MDR)
current instruction register (CIR)
accumulator (ACC)
Notes taken from BBC Bitesize Revision
Fetch-Execute Cycle
Fetch-Execute Cycle
Explain what happens during the fetch-execute cycle. [3]
The control unit
...gets each instruction in sequence (FECTCH)
It decodes the instruction (DECODE)
and then carries it out by sending control signals to other parts of the computer. (EXECUTE)
Specimen Q3 b
Steps in the Fetch-Execute Cycle
Steps in the Fetch-Execute Cycle
Load address into PC (Program Counter)
Copy PC (Program Counter) to MAR (Memory Address Register)
Increment PC (Program Counter)
Load Data into MDR (Memory Data Register)
Transfer Data to CIR (Current Instruction Register)
Execute instruction in CIR (Current Instruction Register)
CCEA 2021 Q4 e
Exam tip: This diagram is taken from CCEA Fact File and a previous question (2021 Q4) has displayed some of the boxes empty and pupils were asked to fill in the missing boxes. Learn this diagram.
Load address into PC (Program Counter) - The address of the first instruction to be read is loaded into the Program Counter (PC).
Copy PC (Program Counter) to MAR (Memory Address Register) - Before data/instructions can be accessed from main memory the contents of the Program Counter (PC) are placed in the Memory Address Register. (The Memory Address Register (MAR) will use the ADDRESS BUS to access the location where the instruction is stored).
Increment PC (Program Counter) - The Program Counter is immediately updated to point to the location of the next instruction to be executed.
Load Data into MDR (Memory Data Register) - A read signal will be sent via the control bus to memory and the instruction is transferred from memory to the Memory Data Register (MDR) via the DATA BUS.
Transfer Data to CIR (Current Instruction Register) - The instruction is then copied into the Current Instruction Register (CIR) where it is ready to be executed.
Execute instruction in CIR (Current Instruction Register) - The instruction/data held in the CIR is decoded and then executed.
Explain the purpose of Increment PC in the fetch-execute cycle. [3]
To prepare for the next FE cycle
The PC points to the address of the next instruction
...to be fetches/executed
CCEA 2021 Q4 f
Explain the role of the following registers during the fetch-execute cycle. Program Counter and Memory Data Register [4]
Program Counter
Holds the address/location of the next instruction
It is incremented during the fetch phase
(2x[1])
Memory Data Register
Stores the data/instruction being transferred to/from IAS
A data item will be copied to the MDR (for use at the next clock pulse)
(2x[1])
CCEA 2022 Q3 c
Describe the role of the Current Instruction Register during the fetch-execute cycle. [2]
Holds a copy
...of the instruction being executed.
(2x[1])
CCEA 2019 Q3 a
Ports
Ports
Port
Port
A physcial channel/socket/connection (acts as a connection point)
...where peripherals/devices can be connected
...to enable data transfer between devices and the processor
CCCEA 2024 Q3a & CCEA 2022 Q3 a
Exam tip: While this is the only question ever been asked about Ports before, it is worthwhile learning serial, parallel and USB ports as outline the in the CCEA Fact File content below incase it would come up.
CCEA Fact File
Factors that affect the speed of processing
Factors that affect the speed of processing
clock speed
clock speed
One of the factors which can affect the speed of processing is the clock speed of the processor. Explain how the clock speed can affect the speed of processing. [3]
The faster the clock
...the more instructions the processor can execute
...in a given time.
CCEA 2023 Q4 a i
Processor Type
Processor Type
Name and describe one other factor which can affect the speed of processing. [4]
The processor type.
RISC (Reduced Instruction Set Computing) processors has a smaller set
...a number of instructions may be needed for a basic operation
...which slows down the overall processing speeds
CISC (Complex Instruction Set Computing) processors has a larger instruction set
...one instruction can perform a basic operation
...which speeds up overall processing speeds
In dual-core/quad-core processors
...the workload can be shared between the cores
...enabling multitasking/multithreading
(3 x[1])
CCEA 2023 Q4 a ii
cache
cache
Cache size
Provides high speed access
...due to its close proximity to the processor
...to most frequently used instructions
...to most frequently used data
The greater the cache size the greater the number of instructions/data that can be accessed at high speed
...of data/software
...to transfer data between devices
(3x[1])
CCEA Q4 b (Mark scheme not correct for the question asked)
Describe two ways in which the processing speed of a PC can be improved. [4]
Upgrade the processor type
Example: dual/triple/quad/32bit/64bit/parallel processing.
(2x[1])
Upgrade the clock
...to one with a faster clock rate/so that more instructions are executed per second
(2x[1])
Increase the internal memory
...to ensure faster retrieval times/to reducing swapping in and out of memory.
Example: Ram / cache.
(2x[1])
CCEA 2017 Q4 a iii
Secondary Storage
Secondary Storage
Explain the difference between internal memory and secondary storage. [4]
Internal memory is part of the CPU.
It consists of RAM/ROM/Cache memory.
Secondary storage is external to the CPU.
Example: magnetic/optical/flash media
CCEA 2017 Q4 a ii
Optical and flash are types of secondary storage media. Explain why secondary storage is needed. [3]
Main memory is volatile (temporary).
This is why permanent storage is needed.
Secondary storage is non-volatile (permanent).
Secondary memory has more capacity than main memory.
This is needed to hold all software/data needed by a computer.
Enables data to be transferred to another computer system.
(3x[1])
CCEA 2018 Q3 c
A science class uses a smartphone to record a video for an experiment. Explain why the smartphone needs secondary storage [2]
Main memory is volatile
Secondary storage is non-volatile.
(2x[1])
CCEA 2022 Q3 d
Magnetic secondary storage
Magnetic secondary storage
Magnetic media refers to devices which use different patterns of magnetisation to store data. Magnetic storage devices provide a non-volatile storage medium.
Hard discs represents one example of magnetic storage media.
Information can be read from and written to the disc using read/write heads which operate very closely to the surface of the disc.
A magnetic material, such as iron oxide or chromium oxide, is embedded in the disk. To record data, a recording head moves past the disk while electric currents passing through it produce a magnetic field.
The magnetic surface of the hard disc drive is contains tiny magnetic regions known as domains and each domain can be magnetised on one of two polarities to represent 1 or 0.
Domains are invisible to the human eye.
CCEA Fact File
Diagram taken from CCEA Fact File
The data is stored in a very orderly pattern on the disc surface. Bits of data are arranged in concentric, circular paths called tracks. Each track is broken up into smaller areas called sectors; forming a block of data. When the contents of the disc are being updated data is transferred between the processor and the disc in sectors. Each sector can be accessed randomly using read/write heads which move backwards and forwards across the disc. The disc rotates underneath the read/write heads.
CCEA Fact File
Diagram taken from CCEA Fact File
The hard drive inside your computer will have an assembly of hard disc surfaces (called platters). Most hard discs will have more than one platter to increase the storage capacity of the device. The drive shown here has two platters and four read/write heads so data can be read from and written to all surfaces in the disc pack.
CCEA Fact File
The read/write heads are on a fixed assembly unit which means all of the read/write heads move in and out at the same time. Before data can be stored on the surface of a disc it is processed first using a complex mathematical formula to determine the location for storage. All of the read/write heads will move into place and the read/write operation can then take place.
CCEA Fact File
Diagram taken from CCEA Fact File
During the write process as one track on a disc surface fills up the corresponding track on the surface underneath will be used to record the rest of the data associated with that file; building up what is known as a cylinder of data or a seek area.
CCEA Fact File
optical secondary storage
optical secondary storage
Describe how data is written to a DVD. [3]
The surface of the disk is coated in aluminium/is reflective.
A red laser is used
...to create pits
...and lands
...which represent 0s and 1s/binary
(3x[1])
CCEA 2018 Q3 d
Flash secondary storage
Flash secondary storage
Evaluate the suitability of using a USB memory stick for storing data and transferring data between devices. [6]
Features of USB memory stick
Uses flash memory/solid state technology. It is non-volatile.
It has no moving parts.
Its contents can be electronically erased and reprogrammed multiple times. It is random access storage medium.
It has relatively high-speed access.
It requires relatively little power.
Evaluation for storing and transferring data between devices.
It is very compact/portable/robust so is a very convenient method of storing and transferring data.
Memory sticks can have a large capacity and are suitable for transferring and storing large amounts of data.
The contents can be erased /re-written. A memory stick can be used many times.
A USB port is available on most devices enabling data transfer between them.
Smart phones use flash storage. Evaluate the use of flash storage in this case. [6]
Features of flash
Flash memory uses solid state technology
...with no moving parts
It has relatively high-speed access
...requiring relatively little power
Evaluation for use in a smart phone
It is very compact/portable/robust making it suitable for use in a device carried around
It requires relatively little power and can be powered by a battery
Its content can be erased/re-written so suitable for storing user data
CCEA 2022 Q3 a
A computer can use an internal hard disk or a flash memory pen. Compare the use of these devices for storage. [6]
Internal hard drive
The primary storage device fixed inside the computer/an integral part of the computer/not portable/magnetic medium/moving parts.
Storage
The operating system/application software/data files.
Higher capacity measured in terabytes.
Flash memory pen
Portable device/plug and play device/no moving parts/solid state.
Storage
File transfer/Backup/Archive
Lower capacity measured in gigabytes
CCEA 2019 Q3 d
Evaluate the suitability of using a USB memory stick for backing up data. [5]
A memory sick is non-volatile (permanent memory) - it can be used to store data permanently.
A memory stick is portable - it can be removed and the backup stored safely away from the live system.
A memory stick is rewriteable - it can be used for backups.
CCEA 2018 3 e
AS2 Architecture.pptxPast Paper Questions
Past Paper Questions
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