COS3721 - Operating Systems And Architecture EXAM PACK WITH SHORT SUMMARY

Chapter 1 2018 S2 A1 What is the purpose of interrupts? How does an interrupt differ from a trap? Can traps be generated intentionally by a user program? If so, for what purpose?  An interrupt is a hardware-generated change of flow within the system. An interrupt handler is summoned to deal with the cause of the interrupt; control is then returned to the interrupted context and instruction.  A trap is a software-generated interrupt. An interrupt can be used to signal the completion of an I/O to obviate the need for device polling. A trap can be used to call operating system routines or to catch arithmetic errors. 2018 S2 A1 Describe some of the challenges of designing operating systems for mobile devices compared with designing operating systems for traditional PCs.  The greatest challenges in designing mobile operating systems include:  Less storage capacity means the operating system must manage memory carefully.  The operating system must also manage power consumption carefully.  Less processing power plus fewer processors mean the operating system must carefully apportion processors to applications. 2018 S2 A1 Identify several advantages and several disadvantages of open-source operating systems. Include the types of people who would find each aspect to be an advantage or a disadvantage.  Open source operating systems have the advantages of having many people working on them, many people debugging them, ease of access and distribution, and rapid update cycles.  Further, for students and programmers, there is certainly an advantage to being able to view and modify the source code.  Typically open source operating systems are free for some forms of use, usually just requiring payment for support services.  Commercial operating system companies usually do not like the competition that open source operating systems bring because these features are difficult to compete against.  Some open source operating systems do not offer paid support programs. Some companies avoid open source projects because they need paid support, so that they have some entity to hold accountable if there is a problem or they need help fixing an issue.  Finally, some complain that a lack of discipline in the coding of open source operating systems means that backward compatibility is lacking making upgrades difficult, and that the frequent release cycle exacerbates these issues by forcing users to upgrade frequently.