Component 2 Flashcards
Hardware and communication
Advantages of QR codes over traditional barcodes
- Higher capacity / Require less space / the same data can be stored over a smaller surface area.
- Readable from any direction.
- Damage resistant when printed / built in error correction
- Allow for structured appending / data split over multiple codes
- Scanning software or application is supplied with smartphones
Uses of QR codes:
- Used to open a URL when scanned
- Calendar data. Including appointment details that may be saved directly ro a dgital diary.
- Location data. That cna be scanned and processed to give directions
- Email address. That can be used to open a blank email with pre-defined recipient and subject
Predictive analysis service
- The use of data, statistical algorithms / machine learning / modelling teachniques.
- To identify the likelihood of future outcomes / trends
- Based on historical data
- Provides an assessment of what will happen in the future
- Produce data visualisations
- Data cleansing and transformation
Sources of unstrucutred data that could be used to provide this service
- Publicly shared comments about travel / holidays on social media
- Sensors in smart devices, such as location sensors
- Online questionaries / hotel satisfaction surveys
Importance and use of TCP/IP protocols
- The internet protocol (IP) is the address system of the internet / has core function of delivering packets of information from a source device to a tareget device
- TCP is used in conuction with IP in order to maintain a connection between the sender and the target / to ensure packet order and for error checking.
Process of TCP connection (3-way handshake)
- Source sends SYN ‘intial request’ packet to the target server in order to start the dialogue
- Target server responds with a SYN-ACK packet to agree to the process.
- Source sends an ACK packet to the target to confirm the process
- The email message is broken down into packets, sent via the internet / traverses a seties of gateways before arriving at the target device where the group of packets are reassembled by the TCP.
why creating a text document by voice recognition may be preferred over keyboard entry
- dictating a letter, essay, coursework
- recording findings / events whilst carrying out manual process / procedure
- because of poor typing skills / lack of speed
- as required due to injury / impairment of disability
- to avoid repetitive strain or injury
- dictate notes whilst working on other tasks by hand such as during surgery an autopsy or whilst carrying out an experiment.
why controlling an electronic device by voice input may be preferred over keyboard entry
- giving commands to car enterainment / navigation system
- giving commands to home heating and lighting control system / home digital assistant
- can reset radio channels whilst driving without need to look away / take hands off the controls
- Convenience / Can operate home control system from a remore location / change TV station without moving
why managing a security system by voice print recognition may be preferred over keybaord entry
- voice operated door entry system
- voice authentication for online banking
- No need to remember password or entry code
- improved security provided by unique voice print
Why tasks cannot be carried out in parallel
- Task 3 cannot be carried out in parallel with task 2 because it rquires the result from task 2
Identify two hardware devices required to make a wireless connection to a network
- Network interface card
- Wireless access point / wireless router
State two protocols used for wireless digitial communication
- Bluetooth
- WiFi
- WAP
- WPA
- WEP
- 802.11
Describe one disadvantage for using a public wireless network
- laack of security
- arising from each of interception of transmitted data
Describe the role of three regiseters used in the Fetch-Decode-Execute cycle
- Program counter (PC) - an increasing counter that keeps track of the memory address of the next instruction to be executed
- Memory address register (MAR) - holds the address in memory of the next instruction to be executed or the address to which data will be sent and stored.
- Current instruction register (CIR) - is a temporary holding register for the instruction that has been fetchd from memory and is being executed.
- Memory data register (MDR) - this holds data that is being transferred to or from RAM
- Accumulators - short-term, intermediate storage of arithmetic and logic data
- Status register - contains information about the state of the processor and are used to test for various conditions in an operation such as “is the result negative”, “is the resilt zero”.
Decribe a switch/router/multiplexor
Switch
- a switch is used to connect computers in a local area network
- The switch is programmed / maintains a table with the IP addresses/machien addresses of connected devices, so can send data to the require devices, so can send data to the required device.
- when a packet of data is received by the switch, it is checked to determine the destination address.
Router
- A router is used to forward data packets between networks
- Routers control traffic on wide area networks such as the internet
- The router determines the destination of a data packet from the IP address in the packet protocol, then selects an appropriate route for onwards transmission
- Routers may hold information about current transmission speeds to adjacent nodes, so that the fastest path for onward transmission can be selected.
Multiplexor
- A multiplexor allows multiple messages to be combined, so that they can be sent over a data link simultaneously, then separated again at the end of the link
- Time divsion multiplexing allocates small time slices alternately for data from eahc of the input message streams
- Frequency division multiplexing sends the different messages simultaneously, but using different transmission frequencies.
- On a mainfram (multi-user_ computer a multiplexor allows input to the system from different terminals, then routes system output to correct terminal.
- on a wide area netwrok (internet) multiplexing may be used to combine messages for transmission over the very fast high-cpacity backbone of the netwok.
Data Transmission
Multiplexing - combines multiple signals into one so that multiple messages can be transmitted along the same channel at the same time
Parallel Transmission - sending each bit of a byte at the same time along separate channels. Examples include communication between components on the motherboard or video streaming (HDMI)
Faster data transmission than serial.
Serial Transmission - sending series of bits on after another along a single channel. Examples include network communications. Operates reliably over long distances
Requires only two wires. Can travel longer distances. Simpler interface
Data Collision:
- Bus networks are bi-directional.
- Messages might be transmitted simultaneously from two computers and
come into collision.
- Computers will detect that a collision has occurred due to the interference pattern
produced.
- All computers stop transmitting, then wait for a random time interval before attempting
to retransmit.
Ring Network Collisions:
- Ring networks operate in a single direction.
- Token ring networks carry a single circulating token, to which a message must
be attached for transmission. Only one message can be transmitted at a time.
- Larger ring networks are divided into sectors, separated by nodes. Only one
message may be present in each sector. Messages will not be transmitted onwards
until the next sector is clear.
Switch:
A switch is used to connect computers in a local area network.
- The switch is programmed / maintains a table with the IP addresses/machine addresses of connected
devices, so can send data to the required device.
- When a packet of data is received by the switch, it is checked to determine the destination address.
WAP (Wireless Access Point)
- Transmits and receives radio waves to/from devices’ wireless network interface cards.
- Might be connected to a router, but in a large building, several of these might connect to a switch, which would in turn be connected to a router.
Router:
- A router is used to forward data packets between networks.
- Routers control traffic on wide area networks such as the Internet.
- The router determines the destination of a data packet from the IP address in the packet protocol,
then selects an appropriate route for onwards
transmission.
- Routers may hold information about current transmission speeds to adjacent nodes, so that the
fastest path for onward transmission can be selected.
Multiplexor:
- A multiplexor allows multiple messages to be combined, so that they can be sent over a data
link simultaneously, then separated again at the end of the link.
- Time division multiplexing allocates small time slices alternately for data from each of the input
message streams.
- Frequency division multiplexing sends the different messages simultaneously, but using
different transmission frequencies.
- On a mainframe (multi-user) computer, a multiplexor allows input to the system from
different terminals, then routes system output to the correct terminal.
- On a wide area network (e.g. Internet), multiplexing may be used to combine messages
for transmission over the very fast high-capacity backbone of the network.
Half Duplex - Data can be sent in either direction, but only in one direction at a time.
Full Duplex - Data can be sent in either direction at the same time
Network Protocol - Necessary to specify data formats to enable devices to communicate with each other such as
connecting printer to computer or using http or other protocols to transfer data between devices
- Agreed apron set of rules which allows two devices to communicate and transfer data
Parallel Processing - Simultaneous use of several cores or processors to perform a single
task. Used when extremely large and complex calculation is being carried out
Circuit Switching:
- Path is set up between sender and receiver
- All data follows same paths in order
- Path cannot be used by any other data
Packet Switching:
- Data is split into packets
- Each packet has a destination address
- Packets are analysed by each node
- Packets are sent down the most appropriate path
- Each node maintains a routing table
- Each packet may be transmitted over different routes
- packets may arrive out of order and are reassembled
- Better security as it is difficult to intercept
- Makes more efficient use of data lines as their is no waiting during gaps
Contents of packets:
- Actual data
- Destination address
- Source address
- Packet id / Order number
- Checksum
- Length
- Protocol
File Transfer Protocol (FTP):
- Allows the transfer of large files over a network
- Has built in error checking and re-transmission requests if necessary
Hypertext Transfer protocol (HTTP)
- Allows the transfer of multimedia webpages over the internet
- Allows multiple different web browsers to display and format web pages as
the original author intended
Simple mail transfer protocol (SMTP)
- Allows emails to be sent over a network (server to server)
- Provides a standard way of transferring emails between two different servers
Internet Message Access Protocol (IMAP)
- allows emails to be transferred between computer systems
- provides standard way of transferring emails between two different servers
- messages are retrieved from server to computer
DHCP - Ensures each devices that connects to a network has a unique ip address
- Assigns IP addresses to devices on a network
- Ensures unique and dynamic IP addresses are allocated (automatically)
- allows addresses no longer in use to be automatically returned to the pool of IP
addresses available for reallocation
Universal datagram protocol (UDP)
- Sends data across network/internet with very few error recovery services
- important for video and audio streaming as protocols are designed to handle
occasional lost packets and need to receive new packets rather than retransmission
to prevent buffering.
TCP/IP (Transfer control protocol / Internet protocol)
- Allows networked computers to communicate with each other
- Specifies how signals are routed and transported around a network and reduced need
for gateways to convert signals into different protocols.
- a suite of protocols that control exactly how data is broken down for transmission from sender to receiver, across a network
VoIP
Voice Over Internet Protocol. This protocol allows the Internet to be used
as a phone network; users with microphones and headphones can talk to one
another this way.
Handshaking - When a computer system establishes a devices readiness to communicate
Data representation and data types
No memorization
Organization and Structure of data
The supermarket’s system uses real time transaction processing.
Explain how the stock control system would operate.
- The master file/stock file would be updated as purchased items are processed/scanned at the checkouts.
- Deliveries of goods received from suppliers/central warehouse would be added to the master file/stock file in real time/as they are received.
- Quantities in stock would be compared with a specified minimum quantity each time a purchase is recorded, and items below this stock level would be listed for reordering.
- Items below the stock level will be added to the re-order file which will be updated as transactions take place.
Only one terminal/checkout can update a stock record at a time. Identify the potential problem if customers purchase items with the same stock code at different checkouts at the same time and describe a possible solution to this problem.
- The potential for data integrity to be compromised.
- When one terminal is updating a record, the record will be locked to prevent any other device making changes.
- Further changes to a record will be held in a queue/buffer and processed when the previous update is completed.
Data processing
Inputs:
- Updated meter reading
- New customer / amended customer details
Processes:
- Sorting of transaction file in key field order to match master file.
- Merging of data to update master file
- Calculation of electricity used and cost
Outputs:
- Updated master file
- Customer bills
- Error log
Explain why this hashing algorithm is unsuitable
- Only 10 out of a 1000 memory locations will be accessed
- Product codes will hash to only a few locations so many collisions will be expected.
- Collisions will result in overflow locating a record in overflow will involve slow serial access.
- Will only work up to year 99 before duplicating the year.
Describe a more suitable hashing algorithm
- Delete the last 2 digits ‘20’ and carry out MOD 1000 on the remaining 5 digits.
- Change the hash function to: key field DIV 10 000 so the location is determined by only the first three digits of the product code.
- Modify the hash function so that 20 is not a factor of the modulus, e.g. key field MOD 999
Fixed length and variable length fields
- If records have a fixed length, the position of any record in the file can be calculated by multiplying the record length in bytes by the record sequence number. (There is no fast way of locating a variable length record with a particular sequence number.)
- A fast binary search can be used to locate a fixed length record in a sequential file.
- Variable length records can only be found using a slower linear search method.
- Fixed length records can be quickly updated without affecting other records in the file. There should be empty space present in the record to allow for any increase in the size of the data (e.g. changing an address in a customer record).
- If a variable length record is updated, the size of the record will change. The file will need to be rebuilt and the updated record inserted at the correct point in the sequence.
Variable length records
- Variable length records are preferred when the records in a file are of very different lengths.
- So as to avoid wasting memory / storage / disk space.
- Variable length records are suitable for situations where no searching or updating is necessary e.g. transaction files which will be used later to update a master file.
Random Access
- Explanation of strategy to save records, using hashing to convert a key field value into a memory location/address.
- Explanation of strategy to handle collisions.
- Explanation of strategy to access records.
- If the main file is large and there are few collisions, most records will be found immediately.
- Separate overflow area where records are stored in the next available memory location
- Overflow area can be serial file or linked list
- Searching the separate overflow area is done linearly and may be slow if the area is large
- Progressive overflow within the main file may be used, so records are found very close to their home locations even if overflow has occurred.
- Could be a problem with the random access file if the overflow area becomes too large – main file may need to be restructured with a different hash function.
- Could be faster than obtaining records from the sequential indexed file, where several index blocks must be searched and the required record found amongst other records in a data block.
Indexed sequential
- Explanation of strategy to save records in data blocks on disk, with records sorted into sequential order within each data block.
- Explanation of locating records through use of index block pointers.
- Explanation of multiple levels of index.
- Fast searching using indexes will find the data block containing the required record.
- Could be faster than searching the overflow area of the random access file.
- Easy to add any amount of further records by adding extra data blocks, then setting index pointers.
Overflow
- the overflow area is a separate file.
- the overflow area uses serial storage.
- Records are likely to be stored at or close to the calculated location, so access will be fast.
- If a record is not in the file, this will be known as soon as the first empty location is reached.
- Less total storage space needed
- The main file has a fixed maximum capacity, so storage of further records may be prevented.
A suitable hashing algorithm will map component numbers onto a smaller range of addresses, by generating fewer digit address references.
Use progressive overflow, if the location is occupied use the next available location if the end of the file is reached wrap around and start searching from the beginning again.
Master Files and Transaction files
Master file
- Holds descriptive data; the actual data that is supposed to be processed and holds the resultant data after the process is completed i.e. long term data records which contain data which does not change or data which is periodically updated
- Data is held sequentially, in key field order.
- Example: Customer details for electricity company
Transaction file
- Contains the transactions i.e. changes that are supposed to be made to the data in the master file
- Data is held serially in temporal order i.e. in the order it was collected
- Example: Customer meter readings for electricity company
Multilevel index
- An index is used to improve (read) access times to records
- There is a main that contains the location of the next index
- This process may extend to several levels.
- The last index contains the physical address of the record.
Databases and Distributed Systems
First Normal Form
- All fields names must be unique
- Values in fields sould be from the same domain - each field must only contain teh same type of data
- Values in fields should be atomic - each fields should only contain a single item of data
- No two records may be identical - duplicate records take up space unnecessarily and can cause inconsistencies if updates are not performed on all of them
- Every table must have a primary key - a field or several fields (composite key) that gives each record a uinique identity
Second Normal Form
- The data must be in 1NF
- Remove any partial dependencies - one or more fields depend on only part of the primary key. Can occur if primary key in composite key.
- Fix any M:M relationships created as a result - make sure each table servers a single purpose
Third Normal Form
- Data must be in 2NF
- Remove any transitive dependencies - ensure non-key fields are not dependent on each other
Validation - looks okay
Verification - is correct
Advantages of structuring data in third normal form
- Removing Data duplication, removes duplicated data reducing the size of the stored file.
- Protecting Data integrity, Once redundant data is removed, it is easy to change the data since data is present in only one place.
Reduction of duplicated data decreases the risk of updating some rather than all instances of an item of data.
Distributed Processing
- Distributed processing is the technique of carrying out a large computing task by sharing the processing between computers in different locations.
- Each computer will run its own programs and have its own store of data, but will share data with other computers in the distributed processing network as necessary.
- Computers will be located in health centres and hospitals. These will be linked in a wide area network.
- Each computer will have the software necessary to carry out database operations on patient records, and to display any included images (e.g. ultrasound scans, graphs of heart function…).
- Patient records will generally be held locally at the GP surgery, but additional records may also be held in a hospital when treatment is provided.
- Doctors and other medical staff may access and update information about a patient at any of the locations by means of the network.
- The overall system may provide summary data for the health authority (e.g. the number of patients receiving treatment for particular illnesses, or the waiting times for treatments).
- The system will be able to inform GP’s of the outcomes of hospital treatments carried out on their patients, and any follow-up actions needed.
Data Base Management System
- A database management system stores data accessed by multiple types of user.
- Different users may have different levels of access to different data sets.
- Different users may have different access rights (e.g. read only, read/write).
- Access is password protected
- Different classes of password give different amounts of access. Tasks carried out by IT staff may include:
- Setting up the database tables, queries and reports for different classes of user.
- Database maintenance and performance management.
- Allocating user names and managing passwords.
- Making regular backups of the data, and restoring data in the event of loss.
- Monitoring use of the network through access logs, and identifying unacceptable or unauthorised use.
- Maintaining security through installing virus checking and firewall.
- Providing encryption of confidential data.
- Updating hardware and software as necessary to maintain the system.
- Providing help desk facilities
- Providing training facilities for users.
Data base normalisation
- is a way of structuring data according to theoretical rules
- normalising data usually reduces data duplication/redundancy
- avoids danger of inconsistency / maintains integrity 4x1
- avoids danger of data being lost during update
- avoids wasting processing time
- probably enables easier maintenance of the database
- allows different views of the data.
- 1NF makes field atomic, avoids duplication of items
- 2NF Each field depends on the whole primary key
- 3NF All data items depend on nothing but the primary key.
The operating system
Data Compression
- is reducing the amount of memory a file uses
- the level of file compression is measured using a compression ratio. A compression ratio is the size of the compressed file divided by the original file size
- Compression algorithms are used to employ different methods to reduce file size depending on the type of file
- There are two main types of file compression algorithms, lossy and lossless
- lossy compression algorithms reduce a file size but some data is lost during this process and cannot be retrieved.
- lossless compression algorithms reduce a files size without the loss of any data and the original file can be retrieved.
- JPEG is a lossy compression method for images
- PNG is a lossless compression method for images
CPU scheduling
- is a process that allows one process to use the CPU while the execution of another process is on hold due to unavailability of any resource like I/O etc, therefore making full use of CPU.
- Whenever the CPU becomes idle, the operating system must select one of the processes/jobs in the ready queue to be executed. The selection process is carried out by the CPU scheduler.
- The scheduler selects from among the processes in memory that are ready to execute, accoridng to set priorities, and allocates the CPU to one of them.
Priority based scheduling
- if new higher priority processes keep coming inot the ready queue, then the processes waiting in the ready queue with lower priority mau have to wait long durations before execution. Possibly leading to indefinite blocking or starvation.
- The concept of aging can be used to prevent starvation of any process. Where the priority of a low-prioroty job is incremented as waiting time increases.
Batch Processing
- system in which a series of repetitive processing operations are carried out together
- processing is carried out without user intervention
- may be carried out at times when a computer system is otherwise not in use, such as at weekends or during the night
- an example of batch processing would be a payroll or billing system.
Real time transaction
- a system in which transactions are processed immediately as they occur
- real time transaction processing can avoid multiple bookings
- real time transactions may be made simultaneously from different computer terminals (e.g over internet)
- The file should be locked during update, to prevent corruption of a record by simultaneous changes by more than one user
- an example of real time transaction would be booking a hotel room or airline seat
States of a process in a multi tasking computer
- Ready, the process is loaded into the main memory and waits to be allocated CPU time for its execution. Processes that are readu for execution by the CPU are maintained in a queue for ready processes
- Run, the process is chosen by CPU for execution and the instructions within the process are executed by any one of hte available CPU cores.
- Blocked or waiting, whenever the process requests access to I/O it enters the blocked or wait state. The process continues to wait in the main memory. Once the I/O operation is completed the process goes to the ready state.
Kernal
Process management
- Proces execution, including the allocation of processor time and termination is controlled by the kernel so the system makes efficient use of the CPU and functions properly.
Memory management
- The kernal keeps track of the sections of memory that are currently allocated, manages the release of memory once processes have been executed and allocates / re-alocates memory to new processes that are ready for execution
Device management / I/O communication
- Manages all the systems devices via communication with dievice driver software. All user inputs and all process outputs are handled by the kernel
Interrupt handling
- Higher priority processes that are ready for execution will generate an interrupt signal, or request for CPU access. The kernel will handle the interruption of current processing, enable the CPU to process the higher priority event and then manage the return to the interrupted process
applications that support unicode standardised character sets
- The alternative is to use 8 bit ASCII character sets which will support 256 bit patterns and only 128 characters and therefore cannot support two or more alphabets in the same document, which is a likely requirement for language translation. A standardised Unicode character set uses between 8 and 32 bits per character enabling over a million different bit combinations / codes that can be used to represent the various characters that are used in most / all of the world’s languages.
Types of operating systems: Multitasking
- A method of organising computer use that allows several tasks or applications to be available at the same time.
- The operating system will allow users to have several tasks apparently running at the same time, with the user switching freely between tasks or applications.
- Concept of time sharing - The switching occurs when the time slice of currently executing process ends.
Types of operating sytems: Multiprogramming
- A multi-programming operating system allows multiple processes to reside in main memory where only one program is running.
- The aim is to optimise CPU use by reducing CPU idle time.
- Concept of context switching - The switching is done when the currently executing process halts, such as when waiting for I/O, and the CPU is allocated to some other process.
Purpose of partitioning main memory (fixed, variable and dynamic partiontining)
- Processes must be allocated an exclusive area of main memory. An allocated area of memory cannot be used by a second process until the first process is complete and de-allocated from memory.
- Fixed partitioning is the system of dividing memory into non-overlapping sizes that are fixed. A process may be loaded into a partition of equal or greater size and is confined to its allocated partition.
- Small processes with respect to the fixed partition sizes results in occupied partitions with lots of unoccupied space left. This unoccupied space is known as internal fragmentation.
- Variable partitioning is a system for dividing memory into non-overlapping but variable sizes. More flexible than the fixed partitioning configuration, where small processes are allocated to small partitions and large processes allocated to larger partitions.
- Dynamic partitioning. Partitions are made during run-time according to process’s need instead of partitioning during system configuration. The partition size varies according to the need of the process so that internal fragmentation can be avoided to ensure efficient utilisation of RAM.
Memory buffering
- Memory buffering - the temporary storage in memory of information / processes that are waiting to be executed / processed - whilst other information / process is being processed / executed.
Double buffering
- Double buffering - The use of two buffers increases the throughput of a device and helps prevents bottlenecks
Master file and transaction file
Inputs:
- Updated meter reading
- New customer / amended customer details
Processes:
- Sorting of transaction file in key field order to match master file.
- Merging of data to update master file
- Calculation of electricity used and cost
Outputs:
- Updated master file
- Customer bills
- Error log
Operating System:
- Providing a user interface, typically using windows, icons, menus and pointers (WIMP).
- Providing an interface to peripheral devices such as keyboard, mouse, speakers, printer…
- Running software programs, by loading program code and data into RAM then activating the CPU to execute the program.
- Allowing multiple programs to be active at the same time, by sharing processor time.
- Providing an interface for local or wide area networking.
- Allowing the configuration of hardware, such as: screen resolution, mouse movement response.
- Providing device drivers to allow new peripherals to be installed.
- Controlling the storage of files in secondary storage, and displaying a catalogue of programs and data files.
- Providing security to prevent unauthorised access or alteration of data.
- Allowing multiple users to have personal secure access through a password system.
- Responding to system errors in a way which minimises data loss.
- Displaying previews of common file types, such as: images, video, sound, text.
- Handling on-line updates to the operating system.
Real time processing
- Real time transaction processing involves direct updating of the master file immediately an event occurs.
- Real time processing can avoid double booking (e.g. hotel rooms, theatre seats…)
- Real time gives an accurate current view of the data (e.g. shop stock control, so staff are immediately aware if running low on stock)
- Real time systems involve more complex algorithms - e.g. to reserve seats temporarily whilst the customer enters payment details, but free the seats again if payment not made.
Batch Processing
- Batch processing uses a transaction file to record events, then the master file is updated at the end of each period (day/week…)
- Batch processing is a simpler/faster system to operate. Transactions can simply be stored in the order received, with all processing carried out later.
- Batch processing can be carried out automatically at times when the computer system is not otherwise in use (e.g. at night).
Principles of high-level scheduling (states of process and teh role of time-slicing and polling)
- Processing is controlled by a scheduler.
- The currently active programs will be held in a job queue (runnable state).
- Each program will receive a slice of processing time when it reaches the front of the queue (running state).
- If a program requires slow input or output, it will temporarily leave the job queue (blocked state).
- Input/output will be handled by the spooling system while the processor continues to process other jobs.
- The scheduler will poll the blocked jobs, to check when input/output is completed and the job can re-join the job queue.
- Efficiency can be improved by providing multiple job queues, so that users experience minimum delays.
- Description of a queue strategy, e.g. Smaller jobs enter a fast queue. Larger jobs are held in a main queue and only receive processor time when the fast queue is empty (analogy with the fast checkout queue in a supermarket for customers with few items).
- Polling to check the state of input / output devices
Interrupts
- interrupts are signals to the operating system / CPU requesting attention.
- interrupts may have different priorities
- operating system / CPU will suspend the current program(s) in order to deal with the interrupt (then resume the program(s) from the point reached).
Hardware interrupts: Mouse click or mouse move, Keyboard key press, Printer ready for further data, Printer out of paper/ink…, Disk drive data transfer completed, Power failure
Software intterupts: Mathematical error in program, such as ‘division by zero’, File handling error in program such as file not ‘found’, Execution of program completed., User termination of program by CTRL/ALT/DEL or ESC.
Compression
- Data compression is reducing the amount of memory a file uses.
- The level of file compression is measured using a compression ratio. A compression ratio is the size of the compressed file divided by the original file size.
- A compression algorithms are used to employ different methods to reduce file size depending on the type of file.
- There a two main types of file compression algorithms lossy and lossless.
- Lossy compression algorithms reduce a file size but some data is lost during this process and cannot be retrieved.
- Lossless compression algorithms reduce a files size without the loss of any data and the original file can be retrieved.
Buffering is the temporary storage of data during input, output or internal transfer of data in a computer system.
- Buffering is required because components of a computer system operate at different speeds.
- Fast components (such as the CPU) can carry out other tasks whilst waiting for data to be transferred through the buffer to a slow device (such as a hard drive).
A double buffer is more efficient than a single buffer.
- One buffer can be filling whilst the other is emptying.
An interrupt is a signal to the CPU that attention is required.
- Interrupts may be generated by hardware devices or by software processes.
- keyboard key press, causing the CPU to accept characters which may be transferred to a word processing document, spreadsheet…
- mouse click, causing the program to activate a menu choice…
- printer completed processing data, causing the CPU to transfer the next block of data to the printer.
- disk drive completed transferring data, causing the CPU to initiate transfer the next block of data.
- a running process has completed, so the CPU can reallocate resources
- a process has timed-out, so can be terminated by the CPU.
- a program has requested data, so the CPU initiates a data input from a disk file.
- a file error has occurred, so the CPU suspends the data transfer and displays a warning message on screen.
- the user has requested a process to close, so the CPU updates the screen display and reallocates resources.
Mainframe computer
- multi-programming, multi-user operating system: a single computer has a number of separate users, running separate processes from different terminals.
- time-slicing, with each process receiving small amounts of processor time, repeated as necessary
- active processes may be running (currently receiving processor time), runnable (able to run when the processor is available) or suspended.
- an example of a suspended process: e.g. awaiting completion of data input/output, awaiting linking of a DLL code module…
- Description of two different designs of scheduler: single queue with equal job priority, multiple job queues, e.g. with small fast jobs given priority over large slow jobs.
- Use of polling, to check when suspended jobs are ready to re-join the job queue.
- Storage protection ensures that programs in RAM do not interfere with each other.
- Backing store disks provide virtual memory to extend the job queue.
- A separate spooling system handles input/output operations, with connections to individual terminals.
- A large mainframe computer will have multiple processors, and may run a number of process threads simultaneously.
Distributed Processing
- Distributed processing is the technique of carrying out a large computing task by sharing the processing between computers in different locations.
- Each computer will run its own programs and have its own store of data, but will share data with other computers in the distributed processing network as necessary.
- Computers will be located in health centres and hospitals. These will be linked in a wide area network.
- Each computer will have the software necessary to carry out database operations on patient records, and to display any included images (e.g. ultrasound scans, graphs of heart function…).
- Patient records will generally be held locally at the GP surgery, but additional records may also be held in a hospital when treatment is provided.
- Doctors and other medical staff may access and update information about a patient at any of the locations by means of the network.
- The overall system may provide summary data for the health authority (e.g. the number of patients receiving treatment for particular illnesses, or the waiting times for treatments).
- The system will be able to inform GP’s of the outcomes of hospital treatments carried out on their patients, and any follow-up actions needed.
Modes of operation
- Gas Billing Batch processing. Bills are issued regularly in response to meter readings.
- Traffic Lights Real time control processing. Traffic lights have timed intervals, and may also react to the arrivals of traffic.
- Theatre Booking Real time transaction processing. To avoid double bookings, the ticketing database is updated immediately payment is made.
interrupts
- Clock sends interrupt at the end of the time slice
- Disk controller sends interrupt when file transfer completed
- Printer sends interrupts to spooling system
- Processor sends interrupt if a software error occurs
- Terminals send interrupts if key pressed/mouse clicked
how polling operates in spooling
- operating system periodically checks the progress of jobs suspended in the spooling system, / availability of I/O devices
- allows jobs to re-join the runnable queue when input/output is completed.
input and output buffers in spooling
- Concept that there is a difference in device speed between the spooling system disk and the mainframe processor, printer, or user terminals
- A buffer is a small block of memory inside hardware devices such as printers, keyboards and hard drives.
- A buffer holds data sent from a device.
- Double buffering can be used for emptying one buffer while filling the other.
- There is no delay while an interrupt is being processed.
- The device will have a much higher active time
The need for different types of software systems and their attributes
Computer Aided Design (CAD)
- To run specialised graphics software able to carry out the geometric calculations
necessary to produce accurate 2D and 3D screen representations / models; that
can be viewed and manipulated from all angles.
- To improve the efficiency / productivity of the design process; by enabling early
visualisation of design proposals, improve record keeping through better
documentation and version control and promote team working through better
communications.
Computer Generated Animations
- A medical animation - a short educational film, usually based around a physiological
or surgical topic, rendered using 3D computer graphics and most commonly
used as an instructional tool for medical professionals or their patients.
- Education and training. A popular tool in classroom teaching and learning and in
work related training. Use of animation can increase interest & motivation in
learning.
- Forensic animation - The use of computer animation, stills, and other audio visual
aids to recreate incidents to aid investigators and help solve cases.
Expert System
- An expert system uses an inference engine, knowledge base of facts and rules for decision
making.
- Facts and rules should be produced by a specialist with relevant expertise, using the best
available information.
- The user is asked a series of questions. Subsequent questions may vary according to
the answers given.
- Question sequences should be designed so as to gather the necessary information needed for
decision making for all valid sets of input values.
- The user interface should be user-friendly, with adequate help and error trapping during data
entry.
- The system should generate results on screen or on paper in a format which is clearly
understandable to the user.
- The system should list its results in order of suitability, or indicate a relative value or score
for each.
- The system should explain its reasoning in reaching its decisions, so that the accuracy of
the results can be evaluated.
A-Level System
- The expert system allows more students to receive advice than is possible with interviews
alone.
- Students may investigate career/course options using the expert system as preparation before
an interview, to make best use of interview time.
- The expert system can be regularly updated with the latest career/course information.
- Students may feel more comfortable using an expert system rather than consulting a careers
advisor in person, e.g. if they were very uncertain about choice of career and didn’t feel
ready to discuss this yet.
- The expert system can be made available at any time of the day, and from any location by
internet.
- Staff costs will be lower than if additional careers advisors are employed.
Robots in Manufacturing:
- Accurate assembly, e.g. circuit boards.
- Carrying out unhealthy or dangerous activities, e.g. car body welding or spray painting.
- Repetitive operations, e.g. packing food items in boxes.
- Warehouse functions, e.g. collecting selected items from shelves.
- Lower prices due to reduced manufacturing costs.
- Consistent quality due to accurate manufacturing.
- Faster delivery times.
- Quicker innovation for new products.
- Need for retraining of the workforce to operate new technology
- Cost of specialist technicians and programmers
- Risk of breakdown of a complex system affecting production
- Cost of adapting factory premises for automation / Initial setup costs
- Risk of malicious damage by hackers
Input/Output Control Systems
- Monitoring speed, then applying power or braking as necessary.
- Monitoring geographical location, and applying brakes on entering a station.
- Monitoring the track ahead, and applying brakes if an obstruction is detected.
- Monitoring the state of the carriage doors, and not moving from the platform
if doors are open.
- Monitoring fire warning systems and taking emergency action if a fire is detected.
Safety Risks of Data Transfer
- A safety critical system is one in which a malfunction or failure of computer hardware or
software could potentially put persons at risk of injury.
- Exhaustive testing of systems must be carried out before they are brought into
service.
- Systems should have redundancy where possible (e.g. a backup computer can be
brought into use immediately if the main computer fails).
- Systems should be designed to be fail-safe (e.g. a train will safely come to a halt if a
malfunction is detected).
- Regular maintenance and testing should be carried out (e.g. of outdoor cabling which
might be affected by rainwater, or control equipment on a train which might be affected
by vibration)
- High levels of security must be maintained, to guard against malicious attacks.
Driverless trains:
- No possibility of human error (for instance passing a signal at red)
- Train’s control system could apply the brakes at/before a red signal
- Obstruction / train ahead detection could be included
- Could govern the maximum speed
- Could prevent starting with any doors open
- No driver so save salaries, plus no sickness, lateness etc.
Doctor expert systems
- expert system is a software system / type of artificial intelligence
- it is based on facts (Knowledge base)
- it is based on rules (Inference engine)
- can replace the human agent Describe
- would help the doctor reach a diagnosis
- might help them to diagnose unusual conditions / more reliable / up-to-date
- final decision remains with the doctor
- might cause doctors to lose their jobs / doctor does not have to be present
- might save doctors time
* may be legal or ethical issues
- de-skilling
Forecasting Weather
- Inputs from thousands of weather stations e.g. satellites, balloons, ships etc / from huge
geographical area / whole world
- Requires the processing of a huge amount of data
- Requires comparison with huge amounts of historical data
- Requires very complex calculations
- Will require large, complex programs
- Processing has to be done very quickly as weather forecasts are no use if out-of-date
- Weather is often extremely unstable / chaotic / hard to predict
- May require very good graphics for visual representation
Selling Apps on internet
- Can receive feedback on the app
- Can provide updates as soon as they become available
- Can reach potential massive market so app can be sold at cheap price
- App is downloaded so no postage or package costs
- No physical media required so app can be cheaper (more profit)
- Can generate revenue from advertising on free apps
- Can target niche market by exploiting global marketplace
- Environmental benefits improve green credentials for the company
- Can sell directly to customers so no commission to third party app store
- Payment is received immediately
- Programmer could receive recognition of successful app and be ‘head hunted’ and find a very good job
- Can download and use immediately
- Can download anytime (24/7)
- Save time and/or money travelling to shop to buy
- Can read other customer’s reviews before buying
- Can download again if app is lost/corrupted or new device
- Can access updates as soon as they become available (not twice)
- Potential massive market so app can be bought at cheap price (not twice)
- App is downloaded so no postage or package costs (not twice)
Open Sources Software
- Free licence / General public licence
- Relaxed / non-existent copyright restrictions
- Built using community co-operation
- code is available for all to view, debug, rewrite
- free from commercial pressures
- frequent integration with other software packages
- several versions
- high modularisation
Virtual Learning Environment
- Software system designed to help teachers and pupils in the management and use of learning
resources
- Could contain details about homework / coursework / assignments
- school newsletter / achievements made by student
- feedback from teachers
- additional / background teaching materials
Intranet
- can only be accessed by members of organisation
Data security and integrity process
Cyber attacks
Implications on individuals.
- Email accounts, social media sites, and other personal information have been compromised.
- Cyber-attacks affect personal data and privacy, as well political, economic, and social systems.
- The implications for the average person range from identity theft to financial losses to reputational damage resulting from non-consensual data broadcasts.
- Many cyber-attacks are extremely personal. Hacked emails, social accounts, webcams, and mobile phones provide some of the numerous attack vectors for domestic assailants.
- Due in large part to the proliferation and accessibility of digital weapons, spyware and other surveillance tools can be implanted, and have been used in cases ranging from cyber bullying to domestic abuse.
Implications on society.
- On domestic and international politics, integrating cyber-attacks with data that contain a mixture of real and false information to influence public opinion / election results.
- Theft of business patents and processes cause detrimental impacts on businesses, with measurable financial and productivity implications.
- Usernames, passwords, credit card data, health records – malicious use of this data by criminals can result in the organisations the data was stolen from suffering from loss of reputation, fines, falling sales, and legal proceedings.
- Hackers gaining access to everyday public and utility services in order to cause havoc and disrupt society constitutes a genuine threat to UK national and infrastructure security.
- Hackers gaining access national security and military systems to cause havoc and hold nations to ransom.
Security measures
- Turn on firewalls, use anti-virus / antimalware software
- Password rules. Strong passwords are one of the first lines of defence. Make regular password updates mandatory and use strong passwords.
- Update regularly. Any connection to the Internet is vulnerable. Keep every connection, operating system, and application up to date with patches and enhancements.
- Implement VPNs for all connections. Networks that are protected only by generic security measures are more vulnerable to attack. Implement virtual private network (VPN) connections and make their use easy and mandatory when using public Wi-Fi services.
- Retire unused services When systems are no longer needed, delete the applications, logins, and user credentials associated with them. Turn off unused software features such as a video chat function to limit potential for unauthorised access.
Symmetric (single key) and asymmetric (double-key) encryption methods
- Single key encryption can be faster in use. Double key encryption takes longer to encrypt a document, and longer to decrypt, due to the large amount of calculations involved.
- It can be faster to set up a single key encryption system than a double key system, as the programming involved may be simpler.
- Single key encryption may not be secure if the key value has to be transferred over the internet and is intercepted by an unauthorised person.
- Double key encryption avoids the security risk by only revealing the public encryption key to the sender. The private decryption key is held securely by the receiver and not revealed.
- Single key encryption suitable for personal use in encrypting files on a single computer. No transfer of the key value to another user needed.
- Single key encryption is suitable for use within an office or work group, where the key value can be transferred during personal meetings or over a secure local area network.
- Double key encryption is more suitable for transfer of confidential data over the internet (such as credit card details), e.g. on-line hotel/airline bookings or shop purchases.
Protecting the security and integrity of data and computer system
- The hotel should consider physical security. Keep the computer in a locked area when staff are not present. CCTV might be used to monitor the reception area.
- Individual members of staff should have user names and passwords.
- Access to the network by different users should be recorded in a log file.
- Staff should receive training and sign a code of conduct regarding computer use and confidentiality of data.
- Staff may be given different levels of access to the computer system, according to their job roles.
- Some staff may have read-only access to booking data.
- Sensitive data such as bank account details should be held on the computer system in encrypted format.
- All client data transmitted by e-mail should be sent in an encrypted format.
- If the hotel accepts bookings and payments from its web site, then customers should be able to submit their data through a secure encrypted system.
- The hotel should introduce an efficient backup system, with copies of data made daily. Backup data should be stored off-site, either on a portable storage device or using the ‘cloud’.
- A transaction file should be kept, to help in restoring data in the event of loss.
- The hotel must implement improved security in order to conform with the Data Protection Act.
Types of malicious software
- Viruses. Viruses are programs that can replicate themselves and be spread from one system to another by attaching themselves to host files. They are used to modify or corrupt information on a targeted computer system.
- Worms. Worms are self-replicating programs that identify vulnerabilities in operating systems and enable remote control of the infected computer.
- Spyware. Installed by opening attachments or downloading infected software. Spyware can be used to collect stored data without the user’s knowledge.
- Trojans. A Trojan is a program that appears to perform a useful function, but also provides a ‘backdoor’ that enables data to be stolen.
- Virus and spyware checking software should be installed and kept up to date.
- A firewall can protect against unauthorised access to the computer system.
- E-mail attachments should not be opened unless from a trusted source.
- Users should be cautious of fraudulent e-mails asking for passwords, or fraudulent telephone callers asking for particular web pages to be loaded.
- Password hierarchy
- Access levels
- User policies
Risks during transfer of data
- Data sent over the internet may be intercepted. Sensitive data should be encrypted.
- Data is particularly at risk if sent or received at public Wi-Fi locations. Password protection should be used.
- Data sent by post (e.g. on a DVD or on a USB memory stick) may be intercepted.
- The storage medium should be password protected. Sensitive data should be encrypted.
Biometric data
- Biometric data refers to measurement and recording of some physical characteristic of a person,
- which can be used to uniquely identify that person.
- Facial recognition data. Measurements of the distances between key points on the face, e.g. eyes, nose, ears.
- Fingerprint data. Patterns of whirls and loops in the fingerprint pattern.
- Iris scan data. Colour pattern of the iris at the front of the eye.
- Hand Geometry – identifies users by the shape of their hand.
- Palm vein – patterns of the blood vessels in their palms.
- Signature recognition – characteristic writing style.
- Voice pattern recognition – characteristic frequencies of spoken sounds.
- Human Gait – so you can tell by the way they walk.
- Ear canal.
- Body Odour identification.
- Data capture (e.g. by photography or scanning)
- The data would be digitised and stored on a database.
- During access, data would again be captured and compared to the reference record stored in the database.
- A decision made, based upon the comparison.
Voice recognition and biometric data
- The voice print of each employee will initially be recorded when they join the company.
- This is stored in a secure format (encryption).
- On attempted entry to the building, the original voiceprint record is compared with the current voice print of the employee.
- If they match, entry is permitted.
- A number of attempts are permitted.
- More secure as it is difficult to replicate the data / unique voice print.
- Can’t be lost, stolen or forgotten.
- Can’t be phished or tricked out of someone.
- Can speed up queues at the entrance / exit.
- Not always reliable under some circumstances, e.g. background noise.
- People’s voice change over time.
- Privacy concerns.
- Expensive to set-up.
Disaster planning
- To aid a rapid recovery from disaster, periodic / regular backups should be made, with files archived offsite and/or in a fire-proof environment. An alternative system (computer-based or manual) should be available, as should a back-up power supply.
