NEW 1.2.1 Operating Systems

Which of the following is the best definition of a multi-user operating system?

• An operating system intended to serve and process data as it comes in, typically without buffering delays

• Any operating system designed to allow multiple processes to be carried out at the same time

• The software is spread over a collection of independent and physically separate computers

• Any operating system designed to allow multiple users to connect from different locations or computers at the same time

Answer explanation

A multi-user operating system is one which allows multiple users to log in and connect to a central server from different locations or computers at the same time. Specially designed for the sharing of resources such as files, programs or hardware (printers, scanners etc.)

What happens when a computer runs out of RAM?

• Virtual networks can be used

• Virtual storage is used

• Virtual servers are used

• Virtual memory is used

Answer explanation

The physical RAM in a computer can rarely hold all the open applications and data, including the operating system. Therefore part of the secondary storage is used as a temporary memory store. When code needs to be executed it is paged in to the RAM. When it is not executing it can be paged to the storage.

Which of the following devices found in the home is NOT an embedded system?

• Electronic coffee maker

• Personal laptop

• Washing machine

• Central heating boiler

Answer explanation

An embedded system is any computer systems with a dedicated function within a larger mechanical or electrical system.

What type of operating system would you recommend for an aircraft auto-pilot system?

• Real time

• Embedded

• Distributed

• Multi-user

Answer explanation

A real time operating system is intended to process data as it comes in, typically without buffering delays. This is vital with certain critical applications such as medical monitoring systems, aircraft, missile and car management systems. Real time operating systems usually have plenty of redundancy. That means the CPU and memory can never be at maximum capacity.

Which of the following is a non pre-emptive scheduling algorithm?

• Shortest remaining time

• Multi-level feedback queues

• Round robin

• First come first served

Answer explanation

Scheduling algorithms are classified as either 'pre-emptive' or 'non pre-emptive'. 'Pre-emptive' algorithms are able to interrupt a job during its running state and move it into a ready state. 'Non pre-emptive' algorithms are not able to interrupt a job during its running state and must wait for it to finish before loading another.

What are virtual servers?

• A server design specifically for virtual reality programs

• A server which can only operate in the cloud

• The process of using software to create multiple instances of a server

• A server that handles virtual memory

Answer explanation

In a virtual server environment if a server fails, a server application such as email is simply run by another server. This happens automatically, so no technical support is necessary and there is no down-time. In bigger applications such as dedicated servers for online games, it allows for load balancing where servers can spin up and shut down as the player base grows and shrinks at different times of the day.

What is a virtual machine?

• An interpreter that translates intermediate code

• A computer system which runs software in the cloud

• A design for a hypothetical machine

• A computer in the cloud

Answer explanation

A virtual machine is an abstraction of an underlying hardware architecture allowing programs written for one type of system to work on other systems. Regardless of the operating system or actual hardware present, a virtual machine creates a predictable environment for programs and translates intermediate code into machine code for the system it is executing on. The most popular example is the Java Virtual Machine (JVM) installed on all devices running Java programs. This allows the same Java program to run on any architecture running the JVM. Remember in exams not to use the brand name 'Java' though in your explanation!

Why is virtual memory used?

• To store the most frequently used instructions and data in the processor, speeding up the computer

• To allow access to documents in the cloud, anytime, anywhere

• To extend the storage capacity of the computer

• To allow more programs to execute than could be possible with the physical RAM available

Answer explanation

The physical RAM in a computer can rarely hold all the open applications and data, including the operating system. Therefore part of the secondary storage is used as a temporary memory store. When code needs to be executed it is paged in to the RAM. When it is not executing it can be paged to the storage.

Using part of the hard disk as if it were RAM is known as what?

• Virtual memory

• Virtual server

• Virtual reality

• Virtual network

Answer explanation

When memory is low in order to continue to multi-task, the processor pages instructions and data not being used by the currently executing process to the hard disk. This is known as virtual memory.

One disadvantage of virtual memory is:

• It requires a lot more configuration than primary memory

• It slows the computer down because of the extra data transfer needed

• It uses up a lot more RAM instead of hard disk space

• If the remote server is not available you cannot access your files

Answer explanation

Instructions and data in virtual memory still need to be transferred into the RAM to be executed by the CPU. As virtual memory is stored on a hard disk, this slows the computer down because the hard drive is a slow component, especially if it uses a mechanical read-write head.