OCR AS/A2 Computer Science Memory Management

Paging

• ADVANTAGES
• No areas where parts of the program cannot be stored as it is physically broken up and areas are of a distinct size
• DISADVANTAGES
• Code may not be large enough to fit into a page and so will waste storage space.
• Conversely, code may be too large and have to be split into multiple parts to fit into pages which means that the computer must jump more often which slows it down

Segmentation

• ADVANTAGES
• Broken up in logical areas in the code so less jumping required between segments
• Will fit code in more places if the segment is the right size
• DISADVANTAGES
• Relies on the operating system to break up the code
• When code is removed the remaining storage space is oddly sized so other parts of a code may not be able to be stored there

Virtual Memory

• A section of the HDD set aside as a method of primary storage
• Used when storage space in RAM has run out to ensure all that needs to be stored is stored
• RAM usually does not have enough space to hold an entire program so less prevalent parts of the program such as parts that aren't needed immediately or are not necessary to completely run the program are stored in VM
• VM is very slow as the CPU must call from a peripheral that relies on an actuator arm which is much slower than electricity
• When space on RAM is severely reduced the computer must transfer data to and from RAM which takes time and slows the computer
• When data is transferred more than the required process is performed, this is called disk thrashing which severely slows the system. This happens when RAM is full or close to being full
• VM is volatile memory so data stored on it is lost when power is lost

Interrupts

• Interrupts are a signal generated by a source such as an input or output to break the execution of the current routine
• Types of interrupts: