64 bit operating system

64 bit os means os is capable of accessing 64 bit address space & hence have corresponding RAM available.
it is due to the restriction of space on motherboard that we cannot accomodate such large ram 2^64 .Hence we use ram of about 8gb & max 16 gb .

some facts on memory management n file management

Reduce storage overhead in access control in memory management by giving access permission to group of user.

A File Control Block (FCB) is a file system structure in which the state of an open file is maintained. An FCB is managed by the operating system, but it resides in the memory of the program that uses the file, not in operating system memory. This allows a process to have as many files open at one time as it wants to, provided it can spare enough memory for an FCB per file.

process scheduling

Multiprocessing aims that maximum of the CPU should be utilized.Whenever some process is waiting ,at that time cpu is free and os give cpu to some other process.
Almost all cpu resources all scheduled before their use.

Ready queue : A newly arrived process is stored in ready queue from where CPU allocation is done by os to execute the process

PCB stores this ready , wait or active status of process.
The entry of all the PCBs of the current processes is in : Process table

Non Pre-emptive scheduling:
1)process switches from running to wait
2)process terminate
A new process must be executed in non preemptive scheduling.


Pre emptive scheduling:
1-When a process switches from the running state to the ready state (for
example, when an interrupt occurs)

2-When a process switches from the waiting state to the ready state (for
example, at completion of I/0)

Windows 95 onwards and mac uses preemptive scheduling