Section 2 Systems Software
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Where is the operating system stored?
Permanent storage, e.g. hard disk
How is the operating system brought from secondary to primary storage?
A program called the loader (which is stored in ROM) copies the OS from storage to RAM
What 5 things does an os do aside from the UI?
Memory management Interrupt service routines Processor scheduling Backing store management Management of all input and output
How does paging work?
Memory is divided into 4Kb fixed pages. When data is stored in memory, a program may take up a number of consecutive addresses. A table is then made to map the physical memory address to the logical memory address.
What is segmentation?
Segmentation is the logical division of address space into varying segments (different sizes). As with paging, you can load a part of the program into memory initially.
Why does a full RAM cause a computer to slow down?
The computer has to swap pages in and out of RAM and secondary storage, it ends up doing this most of the time which tanks performance, this is known as thrashing.
What is meant by multi - tasking in a single core processor
When a processor with one core breaks down a large problem into small chunks and does those one after another to give the appearance of carrying out several tasks simultaneously.
What does the schedular do?
The schedular is a module in the operating system that makes sure processor time is used as efficiently as possible
What are the objectives of the schedular? (4)
Maximise throughput Be fair to all users on a multi user system Provide acceptable response time to all users Ensure hardware resources are kept as busy as possible
What is backing store management?
The operating system keeps track of the locations in storage that are free so new files can be uploaded there. It also needs to know where files are stored so they can be quickly accessed
What does your computer do when talking to a peripheral (i.e. a printer) in order to not reduce performance?
It sends the data to be transferred to a buffer so that the CPU can continue on another task. This is to compensate for the difference in speeds between the CPU and the printer.
What is a distributed operating system?
A distributed operating system is a form of parallel processing where the operating system divides up tasks among multiple computers (often servers) to provide more power than a single large server
What two operating systems do mobile devices have?
Mobile operating system Real-time operating system
What’s the purpose of the real time os in a smartphone?
It controls the low level hardware in a phone such as the radio or gps.
What are the main features of an os in a conventional household embedded system (4)
It will have a minimal user interface It will accept input from sensors and output to control devices Limited RAM so no complex memory management system No permanent data storage devices to be managed
What will the features of the os in a real time system be? (I.e. airbus a320)
Must respond very quickly to inputs or sensors Must be able to deal with many inputs simultaneously Must have fail safe mechanisms if hardware fails It must incorporate redundancy (if one part fails, switch to another)
Where is the bios stored?
EPROM (erasable programmable read-only memory)
What does the bios do?
It’s primary purpose is to initialise and test the system hardware components and then load the os
What does a driver do?
Provides a software interface for a particular hardware device like a printer
Why might an apple device install a different driver to a windows device for a printer?
Drivers are hardware specific and os specific
Def virtual machine
A virtual machine is any instance when software is used to take on the function of the machine often to emulate different hardware
What two categories of software are there?
Systems software, application software
What is system software?
The software needed to run the computers hardware including the os and utility programs
Give 2 main functions of an os
Resource management - managing computer hardware Providing a UI