The document discusses memory management techniques in operating systems. It describes how the memory manager allocates primary memory to processes, maps process address spaces to physical memory, and minimizes access time. It also discusses logical versus actual address spaces and paging techniques. The memory manager keeps track of allocated and free memory locations. It determines how much memory to allocate to processes and which process gets memory access at what time.

1. Memory Management
This section describes memory management techniques, logical v/s actual address space and
various paging techniques.
emorymanagementisthe functionalityof anoperatingsystemwhichhandlesor
managesprimarymemory.Memorymanagementkeepstrackof eachand every
memorylocationeitheritisallocatedtosome processoritis free.Itcheckshow
much memoryisto be allocatedtoprocesses.Itdecideswhichprocesswill getmemoryatwhattime.It
tracks wheneversome memorygetsfreedorunallocatedandcorrespondinglyitupdatesthe status.
Memory Manager
The purpose of the memorymanageris
 To allocate primarymemoryspace toprocesses
 To map the processaddressspace intothe allocatedportionof the primarymemory
 To minimize the accesstime usingacosteffective amountof primarymemory
Memory managementprovidesprotectionby using two registers,a base registerand a limitregister.
The base registerholds the smallestlegal physical memoryaddress and the limit registerspecifiesthe
size of the range.For example,if the base registerholds300000 and the limitregisteris1209000, then
the program can legallyaccessall addressesfrom300000 through411999.
M

2. How at execution time address binding is done in OS?
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I am readin Galvin's Operating System book. In memory management's
address binding it said about 3 types of address binding. compile time, load
time, execution time. And about Execution time address binding:" The
physical address are computed at the time of execution." But my question is
that these computations for the physical address is for the memory's base
address to load the process into memory. To execute the process first it has
to be loaded into memory. For that it requires some physical memory address.
Then how at execution time these addresses are computed? I am confused.
Can some provide explanation for this.
Thanks
operating-system
share| improve this question asked Jun 1 '11 at 15:10
poddroid
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3 Answers
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You are correct in your thinking. The difference between load-time and run-
time binding is that in run-time every time there is a memory lookup it goes
through a "relocation register" which is like the base register and then you add
an offset.
In load-time binding it does the same thing but subsequent lookups don't
require evaluation of this register. The addresses are set when it is first pulled
into memory. Hence if the base address changes you need to re-load the
whole process to fix up all the relocatable addresses.

3. In the case of run-time, you can move the process around in physical memory
and not need to worry about re-loading it to fix the mapping up because every
time there is an access to memory it maps it then.
Load-time binding results in matching logical/physical addresses but run-time
results in differing logical/physical addresses.
I hope this is clearer for you. I've just started learning about Memory
Management too :)
share| improve this answer answered Oct 5 '12 at
11:13
I King
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When it says that the actual base address is generated at execution time it
means that that the address in RAM (physical address) is determined at
execution time from the virtual address using the MMU. This whole address
conversion is done on the fly. For executing the process the starting virtual
address has to be known. When the process is to be run its virtual page table
is loaded in the MMU and then the MMU quickly calculates the physical
address(in RAM) and the execution goes on with MMU generating physical
addresses from page tables. Consider reading Tanenbaum's Modern
Operating Systems. I find it better.
share| improve this answer answered Jun 2 '11 at
19:29

4. lovesh
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Execution time address binding usually only applies to variables in programs
and is the most common form of binding for scripts, which do not get
compiled. In this scenario, the program requests memory space for a variable
in a program the first time that variable is encountered during the processing
of instructions in the script. The memory will be allocated to that variable until
the program sequence ends, or unless a specific instruction within the script
releases the memory address bound to a variable.