SLR4 - Systems Software

Operating System

A platform for software to run, interacts woth the hardware and prevents a user interface

Functions of an OS

• Peripheral management
• File management
• Security
• Interrupt handling

Types of virtual memory

Paging and Segmentation

What is paging

Physical memory split into equal sized blocks

What is segmentation

Logical divides in memory, variable sized blocks

Why is virtual memory needed

So more programs can be opened than the Physical RAM allows.

What is thrashing

Spending more time moving data/instructions that executing them

What is an interrupt

A signal from the control bus that stops the current process for a more important task

Software Interrupts

• Division by 0
• Out of memory
• Expired time slice

Hardware Interrupts

• Power lost
• Peripheral needs attention
• Buffer nearly empty

What happens when an interrupt is called?

1. Is the importance greater than the current instruction
2. Contents of registers put on the stack
3. Instructions for interrupt are loaded
4. Interrupt executed
5. Contents of the stack are put back on the registers

When does the Interrupt Register check for interrupts

After the FDE cycle

What are the benefits of scheduling

To maximise the use of the processor

Which scheduling algorithms use time slicing

• Round Robin
• Shortest remaining time
• Multi level feedback queue

Which scheduling algorithms dont use time slicing

• First come first serve
• Shortest job first

What are the types of OS

• Distributed
• Embedded
• Multi-Tasking
• Multi-User
• Real time

What is a distributed OS

Processing is sent out to multiple processors across a network (Very Fast)

What is an embedded OS

Used in embedded systems, very specialised

What is a multi-tasking OS

Gives the impression of multiple processes at once uses time slicing

What is a multi-user OS

Multiple uses at once, personal data is kept loaded

What is a real time OS

Guaranteed execution timel, input processed immediately. Built to cope, Eg. Heart rate monitor

How does the BIOS start the computer

1. POST - Power on self test (Checks hardware)
2. Loads bootstrap
3. Loads the OS

What is the purpose of device drivers

Translates instructions from the OS into specific hardware instructions

What are the types of virtual machine

1. Emulator
2. Interpreter

What is an emulator

Simulates the hardware of another PC

What is an interpreter

Intermediate code as a result of compilation is translated into instructions for a specific machine

What are the pros and cons of an interpreter

• Allows programs to run on different architechures
• Slower to execute (No good for real time OS)