Unix
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The document discusses memory management techniques used in early UNIX operating systems, noting that pre-3BSD systems used swapping exclusively to handle memory contention among processes. It then describes how later Berkeley UNIX systems primarily used paging and demand paging, where when a process needs a page not in memory a page fault occurs and a frame is allocated to load the page from disk. The document also provides details on the data structures used to manage paging, including page table entries, disk block descriptors, and tables to track page frames and swap space usage.
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Network Security Lec5
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Network Security
Network SecurityFederal Urdu University The document discusses network security and cryptography. It covers symmetric encryption, public key cryptography, cryptographic algorithms like DES and AES, and cryptanalysis techniques. It also describes the Feistel cipher structure, which partitions the plaintext into blocks and performs multiple rounds of substitutions and permutations using subkeys. Feistel ciphers include algorithms like DES.
Os Linux Documentation
Os Linux DocumentationFederal Urdu University The document summarizes Linux memory management. It discusses that Linux uses a three-level page table structure for virtual memory management. It implements a demand paging system with no working set concept. For physical memory management, it uses buddy allocation and maintains different memory zones. It employs clock replacement policy for page replacement and uses modified LRU to determine which pages to replace.
Os Linux
Os LinuxFederal Urdu University Linux memory management uses a combination of physical memory, virtual memory, and paging. It uses a buddy system to allocate and free physical memory pages. Each Linux process gets 3GB of virtual address space, with the remaining 1GB reserved for page tables and kernel data. Linux uses demand paging and maintains lists of frequently and infrequently used pages. It employs a clock replacement algorithm and uses both local and global page replacement policies.
Maria Managment Spectrum
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Zohaib Dfd
Zohaib DfdFederal Urdu University The document describes data flow diagrams (DFDs), including what they are, their purposes and uses, and the different types of DFDs. DFDs show the flow of data through a system and are used to model systems for requirements analysis, design, documentation and more. They contain processes, data stores, external entities and data flows. The different types of DFDs include context diagrams, level-0 diagrams, and more detailed lower-level diagrams.
Zeeshan Estimation
Zeeshan EstimationFederal Urdu University The document discusses software project estimation, including an overview of estimation techniques and methods. It describes decomposition techniques like software sizing and problem-based estimation. Cost estimation models like SLIM and COCOMO are explained, along with their advantages and drawbacks. Accurate estimation is important for software project implementation, costing, producing quality products on time, and solving future problems.
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Zahid AsdFederal Urdu University Adaptive software development (ASD) is an agile process that replaces the traditional waterfall model with a speculate, collaborate and learn cycle. It is mission focused, feature based, iterative, time-boxed and risk driven. The basic ASD life cycle speculates without predicting the future, collaborates to maintain the workplace, and learns through small mistakes in iterative cycles.
Umar Erd
Umar ErdFederal Urdu University Entity relationship diagrams (ERDs) are a graphical representation of entities and their relationships in a database. ERDs were developed in 1976 by Peter Chen and introduced by Charles Bachman. An ERD uses objects, attributes, and relationships to model how data is connected. Relationships can be one-to-one, one-to-many, or many-to-many. Cardinality and modality are also expressed to define maximum numbers and whether relationships are optional or mandatory.
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Sidra Agile Software Process
Sidra Agile Software ProcessFederal Urdu University Agile software processes are characterized by unpredictable requirements that change over time. Agile methods promote iterative development in short cycles with customer involvement and frequent review. The Agile Manifesto from 2001 defines key agile principles including valuing individuals, collaboration, response to change, and working software over documentation. Popular agile methods include scrum, extreme programming, feature-driven development, and lean software development.
Muzammil Prescriptive Vs Agile Process Models
Muzammil Prescriptive Vs Agile Process ModelsFederal Urdu University The document compares prescriptive and agile software engineering approaches. Prescriptive approaches describe how software should be developed through defined processes and guidelines. They aim to facilitate planning, improve quality and control. However, they can be rigid and inappropriate for environments where requirements change rapidly. Agile approaches emphasize adaptability, speed, and informal processes suited for unpredictable environments. While prescriptive models strive for structure and control, agile prioritizes vales like communication and feedback to enable flexibility. The choice of approach depends on factors like requirement volatility and need for structure versus flexibility.
Muzammil Agile Vs Prescriptive
Muzammil Agile Vs PrescriptiveFederal Urdu University The document is Muhammad Muzammil's final proposal on the topic of Agile vs. Prescriptive Software Engineering. It includes an abstract thanking his teacher for guidance. The proposal contains sections on software processes, prescriptive and agile approaches, comparing the two, and references. It provides definitions of prescriptive processes and agile methodology, explaining that prescriptive processes prescribe set activities while agile is more adaptive. It also compares the waterfall and agile methodologies.
Khurram Spiral
Khurram SpiralFederal Urdu University The spiral model is a software development process that combines elements of both design and prototyping in an risk-driven iterative process. It consists of four phases - planning, risk analysis, engineering, and customer evaluation - that are repeated until the product is completed. The spiral model is well-suited for medium to high-risk projects where requirements are uncertain or likely to change. It allows for user feedback at each cycle to refine requirements and manage risks.
Hira Xp
Hira XpFederal Urdu University This document provides an overview of Extreme Programming (XP), an agile software development methodology. It discusses XP practices like planning with user stories, making frequent small releases, designing for simplicity, pair programming, testing with unit and acceptance tests, and having an on-site customer. The goal of XP is to satisfy customers through iterative development, lightweight processes, and team collaboration.
G4 Group
G4 GroupFederal Urdu University This 3 sentence summary provides the high level information from the document:
The document from the G4 Group welcomes students and wishes them a happy future life after they are divided into specializations for their programs. The group apologizes if they have hurt anyone and thanks all the students from the BSCS 4th batch.
Faisal Incremental Model
Faisal Incremental ModelFederal Urdu University The incremental model is a method of software development that combines elements of the waterfall model with iterative prototyping. It involves developing a software product incrementally until final delivery. The model has five main phases - communication, planning, modeling, construction, and deployment. Each phase builds upon the previous one by adding more features and functionality based on customer feedback. While more flexible than the waterfall model, the incremental model can be challenging to implement due to integration issues between builds and determining the optimal number of builds.
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- 1. Subject : Operating System Group Members :Muhammad Shakeeb ( IS/17122-Aut -FO7 M )Syed Zeeshan Nasir ( IS/17133-Aut –F 07 M )Faisal Muhammad ( IS/17122-Aut –F07 M)Class : BsCS 4th -B
- 3. • Process A's virtual address space• Physical memory• Process B's virtual address space
- 4. Memory ManagementThe initial memory management schemes were constrained in size by the relatively small memory resources of
- 5. UNIX was developed on the PDP machines
- 6. Pre 3BSD system use swapping exclusively to handle memory contention among processes
- 7. If there is too much contention, processes are swapped out until enough memory is available
- 8. Allocation of both main memory and swap space is done first-fit Paging Berkeley UNIX systems depend primarily on paging for memory-contention management, and depend only secondarily on swapping
- 9. Demand paging – When a process needs a page and the page is not there, a page fault tot he kernel occurs, a frame of main memory is allocated, and the proper disk page is read into the frame
- 10. A page daemon process uses a modified second-chance page-replacement algorithm to keep enough free frames to support the executing processes
- 11. If the scheduler decides that the paging system is overloaded, processes will be swapped out whole until the overload is relieved PagingPage table entry
- 13. Page frame data table
- 14. Swap use tablePage Table Entry and Disk Block DescriptorPage TableRegionDisk Block DescriptorPage Table EntryPage Table EntryDisk Block Descriptor
- 15. Contains the physical address of page and the following bits:Valid: whether the page content legalReference: whether the page is referenced recentlyModify:whether the page content is modifiedcopy on write: kernel must create a new copy when a process modifies its content (required for fork)Age: Age of the pageProtection: Read/ write permissionPage Table Entry
- 16. Disk Block DescriptorSwap Device number as there may be several swap devicesBlock number that contains page
- 17. Page Frame Data Table Entry Swap use Table entry
- 18. 11
- 19. Replacement policy