Computing - AS Level

Definitions & What Is(s) - Work In Progress

Batch Processing - A processing mode in which data is gathered first, then processed at a later time.

Data Integrity Checking

• Validation - Checks whether data is logically correct. (i.e. numbers put in an "Amount" field, text into "Name")
  
• Verification - Checks whether data is correct/what is meant to be input. (i.e. No typos, data put into the correct record)
  

Data Transmission

• Serial - Transmission of data through one data stream.
  
• Parallel - Transmission of data through many data streams.
  
• Simplex - Transmission of data in only one direction.
  
• Half Duplex - Transmission of data in multiple directions, but only one direction at a time.
  
• Duplex - Transmission of data in multiple directions. (Simultaneous)
  

Files

• Indexed Sequential -
  
• Random - Records are assigned a unique value using a hashing algorithm, and these records are identified and accessed by this unique value.
  
• Sequential - Records in file are stored according to a logical order. (i.e. ascending, by letter)
  
• Serial - Records in file are stored in no particular order. (i.e. chronological)
  

Hardware - The physical components of a computer system.

Information Systems

• Interactive - A system where data held in the system can be edited by the user.
  
• Passive - A system where it allows only the viewing of information.
  

Input Device - Any device that allows data to be input into the processor.

Operating System

• Batch -
• Real-Time -
• Single-User -
• Multi-User -
• Network -

Output Device - Any device that allows the processor to convey the results of its processing.

Protocol (Network) - A set of rules/instructions that allows communication between different devices to be possible.

Real-time Processing - A processing mode in which data is immediately processed as it is retrieved.

Software - A collection of programs that govern the functions of a computer system.

Storage Device -

User Interface

• Command Line User Interface - User interface which requires user to input commands to peform tasks.
  
• Form-Based User Interface - User interface which looks like a question-and-answer form, with textual answers filled in automatically validated textboxes. Selection and/or multiple choice are done through radio buttons, checkboxes, or drop-down lists.
  
• Graphical User Interface - User interface which consists of icons, windows, menus, etc.
  

Utility Software

• Disk Formatting - Software which divides up the surface of a disk into more easily manageable sectors.
  
• File Compression - Software which reduces the size of individual files without any loss of data in the files.
  
• File Handling - Software which manages files stored in a computer system.
  
• Hardware Drivers - Software which acts as a translator, allowing communication between the operating system of a computer system and its peripherals.
  
• Virus Checker - Software which checks files on a computer system for viruses.
  

Concepts - Work In Progress

Buffers & Interrupts in Transferring Data from Primary Memory to Hard Drive

• Buffer filled from primary memory.
• Processor carries on with other task while hard drive empties buffer and stores data.
• When buffer is empty, interrupt sent to processor (From hard drive/buffer) requesting buffer to be refilled.
• Processor decides according to importance of interrupt whether to suspend current job and carry out interrupt or to store interrupt for later execution.
• Processor refills buffer from primary memory.

Check Sums - Method of Checking Errors During Transmission of Data

• Individual bytes of data are added together.
• An algorithm is applied to the above result.
• Result of algorithm is attached to data to be sent.
• When data is received, repeat calculation and check whether the result of this calculation matches the one attached to data.
• If there are no errors, both values will match.

Maintenance of Stock Levels of Goods in a Warehouse Using Stock Control Software

• Barcodes read as goods arrive/leave.
• Number in stock is incremented if arriving, decremented when leaving.
• Software checks number in stock against reorder number.
• After every transaction, when number in stock below reorder level, then create order.
• Order made is stored as boolean 1 (True) until order delivered.

Algorithms

• You may use pseudo code, flowcharts, or even normal English to write your algorithms. (Note: If possible, do not do flowcharts; they're a waste of time)
• Do not forget to declare & initialize your variables if you are making any.
• There is no need to declare variables already stated in the question.
• You will get your marks only if you can understand what you just wrote.
  
• There are only 3 looping statements: for-next, repeat-until, and while-endwhile; so don't make your own fancy statement because most likely nobody would understand!
• If there is a simpler way of solving the problem, (i.e. Lesser number of instructions, is easier to be understood) then do it simpler!
• Do not use language-specific syntax; (e.g. Instead of writing '==', write "is equal to") you must make sure that even the average guy can understand what you're writing. (At least in the wording)
• Properly indent different blocks of code; this is the convention when writing algorithms and it makes these algorithms easier to read.
• Make sure it answers the question!