Memory Management Ibm Os 360
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MEMORY MANAGEMENT Data and programs are stored, usually in
binary form, in a memory subsystem On
early computers, memory subsystem was a single main memory
MEMORY MANAGEMENT Dynamic real memory management
OS/360 magnetic tape was the principal medium for secondary storage, but its sequential nature limited its possibilities for memory management the arrival of disk storage as an economical secondlevel storage with good random access capabilities was the catalyst for a new approach to memory management.
MEMORY MANAGEMENT Dynamic real memory management OS/360
taking advantage of random access disk storage, OS360 provide execution-time binding(In OS360 a set of services provide the link between the application program and the program modules on direct access storage) For
example, during execution, a program can request the appropriate subroutine; only then will it be brought from secondary storage. This defers main memory occupancy until it is actually needed and also allows the selection of the subroutine to be based on the data at hand.
MEMORY MANAGEMENT Dynamic real memory management
OS/360
execution-time binding is important because: this capability offers the potential of reducing the maximum amount of storage required by a program during its execution without the preplanning becoming hopelessly complex the operating system itself can use it to great advantage
MEMORY MANAGEMENT Overview of Memory Management
Techniques Component
Memory Management
Comment
1 partition
Batch-processing model – One job had all available memory until complete
MFT(Multiprocessing with4 to 15 a Fixed number of Tasks.)
Fixed partitions
Number of number of tasks
MVT(Multiprogramming unlimited with a Variable (limitless) number of Tasks)
Variable partitions
Created high degree of external fragmentation
PCP(Primary Program),
# Tasks
Control1
partitions
=
MEMORY MANAGEMENT Memory Structure and Implementation
3 techniques used: Planned overlay structure Dynamic serial structure Dynamic parallel structure
MEMORY MANAGEMENT Memory Structure and Implementation
Planned overlay structure - was utilized when not all of the elements of a program needed to be actively loaded on the system simultaneously
- the programmer was able to segment the program into load modules that need to be present simultaneously in main memory
MEMORY MANAGEMENT Memory Structure and Implementation
Dynamic serial structure - was useful when jobs became more complex
be called
- load modules can dynamically
MEMORY MANAGEMENT Memory Structure and Implementation
Dynamic parallel structure - It creates a task that can proceed in parallel with other tasks, but since it uses the ATTACH and thus requires the processor to go into kernel, or supervisor, mode, its use needs to be limited.
binary form, in a memory subsystem On
early computers, memory subsystem was a single main memory
MEMORY MANAGEMENT Dynamic real memory management
OS/360 magnetic tape was the principal medium for secondary storage, but its sequential nature limited its possibilities for memory management the arrival of disk storage as an economical secondlevel storage with good random access capabilities was the catalyst for a new approach to memory management.
MEMORY MANAGEMENT Dynamic real memory management OS/360
taking advantage of random access disk storage, OS360 provide execution-time binding(In OS360 a set of services provide the link between the application program and the program modules on direct access storage) For
example, during execution, a program can request the appropriate subroutine; only then will it be brought from secondary storage. This defers main memory occupancy until it is actually needed and also allows the selection of the subroutine to be based on the data at hand.
MEMORY MANAGEMENT Dynamic real memory management
OS/360
execution-time binding is important because: this capability offers the potential of reducing the maximum amount of storage required by a program during its execution without the preplanning becoming hopelessly complex the operating system itself can use it to great advantage
MEMORY MANAGEMENT Overview of Memory Management
Techniques Component
Memory Management
Comment
1 partition
Batch-processing model – One job had all available memory until complete
MFT(Multiprocessing with4 to 15 a Fixed number of Tasks.)
Fixed partitions
Number of number of tasks
MVT(Multiprogramming unlimited with a Variable (limitless) number of Tasks)
Variable partitions
Created high degree of external fragmentation
PCP(Primary Program),
# Tasks
Control1
partitions
=
MEMORY MANAGEMENT Memory Structure and Implementation
3 techniques used: Planned overlay structure Dynamic serial structure Dynamic parallel structure
MEMORY MANAGEMENT Memory Structure and Implementation
Planned overlay structure - was utilized when not all of the elements of a program needed to be actively loaded on the system simultaneously
- the programmer was able to segment the program into load modules that need to be present simultaneously in main memory
MEMORY MANAGEMENT Memory Structure and Implementation
Dynamic serial structure - was useful when jobs became more complex
be called
- load modules can dynamically
MEMORY MANAGEMENT Memory Structure and Implementation
Dynamic parallel structure - It creates a task that can proceed in parallel with other tasks, but since it uses the ATTACH and thus requires the processor to go into kernel, or supervisor, mode, its use needs to be limited.
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