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Questions and Answers
What is the size of a byte in bits?
Why do most computers not have an instruction to move a bit?
Which statement best describes the relationship between bytes and bits?
In what context is a byte considered the smallest convenient chunk of storage?
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What is a likely reason for computers having instructions to move bytes but not bits?
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What is often cited by computer manufacturers as the size of a megabyte?
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How do computer manufacturers typically round the definition of a gigabyte?
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What rounding convention do computer manufacturers use for defining megabytes and gigabytes?
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Which of the following statements is true regarding the size of a gigabyte?
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What misconception about size definitions do some people hold regarding megabytes and gigabytes?
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Study Notes
Byte, Megabyte, Gigabyte
- A byte is 8 bits
- It’s the smallest chunk of storage managed by most computers
- Most computers lack instructions to move single bits, but have instructions to move bytes
- Computer manufacturers round up the size of megabytes to 1 million bytes and gigabytes to 1 billion bytes.
- Network measurements are an exception, they use bits as data is transmitted bit by bit.
Symmetric Multiprocessing Architecture
- Each processor performs all tasks.
Asymmetric Multiprocessing Architecture
- Each processor is assigned a specific task.
Dual-Core Design
- A dual-core design includes multiple chips and multiple cores.
- Systems containing all chips include:
- A chassis containing multiple, separate systems.
Operating-System Operations
- The bootstrap program is simple code to initialize the system and load the entire kernel.
- The kernel loads the system daemons (services that run outside of the kernel)
- The kernel is interrupt driven by hardware or software
- Hardware interrupts are triggered by devices.
- Software interrupts are triggered by:
- A software error (e.g., division by zero)
- A request for a system service (system call)
- Other processes like an infinite loop, processes modifying each other or the operation system.
Multiprogramming and Multitasking
- Multiprogramming (used in Batch systems) is needed for efficiency
- A single user cannot keep the CPU and I/O devices busy at all times
- Multiprogramming organizes jobs (code and data) so the CPU always has something to execute
- A subset of all jobs in the system is kept in memory
- One job is selected and run via job scheduling
- When ready, the OS switches to another job.
- Timesharing (multitasking) is a logical extension where the CPU switches jobs frequently so users can interact with a job while it’s running. This creates interactive computing
- Response time should be less than 1 second
- Each user has at least one program executing in memory
- Program in memory is called a process
- If several processes are ready to run at the same time, there is CPU scheduling
- If processes don’t fit in memory, swapping moves them in and out of memory to run.
- Virtual memory allows execution of processes that are not fully in memory.
Dual-Mode and Multimode Operation
- Dual-mode operation allows the OS to protect itself and other system components
- User mode and kernel mode
- Mode bit identifies whether the system is running user or kernel code
- Some instructions are privileged and can only be executed in kernel mode
- System calls change the mode to kernel, and returning from a call resets it to user mode.
- Increasingly, CPUs support multi-mode operations.
Transition from User to Kernel Mode
- Timers to prevent infinite loops and process hogging resources
- Timers are set to interrupt the computer after a certain time period
- To keep track of the time, a counter is used that’s decremented by the physical clock
- The operating system can set the counter (via a privileged instruction)
- When the counter reaches zero, an interrupt is generated
- This is used to reclaim control from a process exceeding its allocated time or to terminate the program.
- The timer interrupt provides a transition from user mode to kernel mode.
Process Management
- A process is a program in execution.
- Amazon EC2 (Elastic Compute Cloud) has thousands of servers, millions of virtual machines, and petabytes of storage available across the Internet, and costs are based on usage.
- Cloud Computing:
- Public cloud - available via internet to anyone willing to pay.
- Private cloud - run by a company for its own use.
- Hybrid cloud - includes both public and private cloud components.
- SaaS (Software as a Service) - one or more applications available via the internet (i.e., word processor)
- PaaS (Platform as a Service) - software stack ready for application use via the internet (i.e., database server)
- IaaS (Infrastructure as a Service) - Servers or storage available over the internet (i.e., storage available for backup use)
Computing Environments - Cloud Computing
- Cloud computing environments are composed of traditional operating systems, VMMs (Virtual Machine Monitors), and cloud management tools.
- Security is required for internet connectivity, such as firewalls, and load balancers to spread traffic across multiple applications.
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Description
Test your knowledge on computer architecture concepts including byte and memory sizes, symmetric and asymmetric multiprocessing, and dual-core designs. Understand the fundamentals of operating systems and their operations in this comprehensive quiz.
