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Thursday, June 20, 2013

Explain the single and multiple partition techniques?

There are a number of allocation techniques available and all have different properties and allocate memory based on different principles. One prominent type of allocation is the partitioned allocation. 
- In partitioned allocation the primary or the main memory of the system is divided into a number of contiguous memory blocks which are commonly known as the memory partitions. 
- Each of these partitions consists of all the information that might be required for carrying out a specific task. 
- The task of allocating these memory partitions to various jobs and processes and de-allocating them after use is the duty of the memory management unit.  
But partitioned allocation cannot be carried out by the help of software alone. 
It requires some hardware support. 
- This support prevents interference of the various jobs in to each other and with the operating system as well. 
- For example, a lock and key technique was used by the IBM system/ 360. 
- Some other systems made use of the registers called the base and bound registers containing the partition limits and these were also used for flagging if any invalid access was made. 
- Limits register was used by the UNIVAC 1108 having separate base and bound data and instructions. 
- A technique called the memory interleaving was used by this system for placing so called I banks and d banks in different memory modules. 

Partitions are of two types namely:
Ø  Static partitions: These are defined at the boot time or IPL (initial program load) or sometimes by the computer operator. An example of system using static partitions is IBM system/360 operating system multi-programming with MFT (fixed number of tasks).
Ø  Dynamic partitions: These are created automatically for the specified job. An example is of the IBM system/ 360 operating system multi-programming with MVT (variable number of tasks).

- The hardware typed memory such as the base and bound registers (GE – 635, PDP – 10 etc.), Burroughs corporation B5500 etc. is used for relocating the memory partitions. 
- The partitions that can be relocated can be compacted to form larger contiguous memory chunks in the main memory. 
- Some systems allow for swapping out the partitions to the secondary storage and in turn to some additional memory.
The partitioned allocation offers two types of allocation techniques namely:
  1. Single partition techniques
  2. Multiple partition techniques

- Single partition techniques are the ones that are used for the single time sharing partition for swapping in and out the memory partitions. 
- These techniques are used by the IBM’s TSO (time sharing option). 
- The multiple partition techniques are used in the multiple time sharing partition. 
- In DOS systems when the disk is partitioned, each of the memory partitions act as if it is an individual disk drive. 
- Partitioning is useful for the systems where there are more than one operating system. 
- Partitioning techniques are meant for increasing the efficiency of the disk. 
Hard and soft partitioning is used on the apple Macintosh computers. 
- The creation, relocation and deletion of the memory partitions can be harmful for the data. 
- That’s why it is good to have back up of the data stored on your system. 
Several issues have to be considered if you want to install more than one operating system on your computer. 
- Day by day disks are becoming less expensive and bigger. 
- You can go for separate disks for storing data and installing Oss. 

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