Computer Science

Computer Science

1. Memory Managment

   • Operating systems have to decide what goes where in memory. They have to make sure that memory is used efficiently and that important data isn't overwritten during the running of a program
   • Virtual Memory
     • Sometimes there are more jobs than there is space in memory to hold them. The operating system then swaps jobs in and out of memory, using a technique called virtual memory.
     • Virtual memory means 'not real' memory. It uses secondary storage (the disk) to hold parts pf a program that are not currently needed. It is slower to access than main memory. A large program may take up too much memory so it is divided into modules.
   • Peripheral Managment
     • A file is a named store of data on a secondary storage medium
     • The operating system is responsible for keeping track of all files in a system. These are stored on secondary storage. They are copied into main memory when needed.

2. Security

   • Viruses are programs that replicate themselves. They attach themselves to legitimate programs. They often have a payload which is designed to do such things as: Damage files, Take control of a computer, Retrieve confidential
     • Some viruses have no payload but can still cause damage
   • Authentication: Where a user sets up credentials to be able to enter their personal account. This usually requires a username and a password
   • Privileges are the rights assigned to users and groups. They may include features like what a particular user can do to files
   • Encryption is used to protect information. The files are transformed in such a way that an unautharised person cannot understand them

3. Programming Software

   • Editors
     • Editors are like cut-down word processes. They allow text to be created, saved, read and change.
     • They are particularly useful for writing the source code of programs
   • Linkers
     • These combine modules of object code (complied program code) into a single executable program
   • Interpreters
     • These convert typed commands into the machine instructions that the processor can understand