IDK Flashcards
Late 1940s:
No operating system. The programmer was also the user. Programs and data were entered in binary by means of switches on the front of the machine. Each switch represented one bit. Output was by means of lights, with each light representing one bit. The programmer did everything that an operating system does today.
1950s:
The introduction of specialist operators, who were not programmers themselves, but who tended the machine, fed the programs to the machine, and delivered back the output. They used punch machines to encode their programs as a series of holes in stiff cards, which the computer could read and interpret. The operators acted as a human interface between the programmer and the hardware.
1960s:
Human intervention was a serious source of delay in the system. Loading and unloading punched cards, starting and stopping devices – all of this slowed things down. So instead of giving verbal commands to a human operator, the programmer punched instructions on control cards, which were inserted at the appropriate places before and after the program cards and the data cards. These commands were written in specially developed job control languages.
Late 1960s and 1970s:
First attempts to provide interactive use of a computer.
Computer users found that programs were growing in size and required more memory. The initial solution was to break programs up into little chunks, each of which would fit in the available memory at any one time.
Larger memory - timesharing
The issue of protecting one program from another became more and more important (OS job!)
1980s: and 1990s:
1980s: Networking and communication
1990s: Move to open systems. Previously, operating systems had been developed specifically for particular hardware platforms, e.g. MS-DOS for the PC. Now there is a move to build generic operating systems (e.g. Linux) which will run on any hardware.
What is an operating system?
The operating system is itself a program, which is written, compiled, tested and debugged just like any other program. This program is run whenever a computer is switched on. It is almost always done automatically – no special command is required – so users may not be aware that it happens every time they switch on a machine. It stays running all the time until the machine is switched off.
Operating system is software which makes the hardware more useful and more user-friendly.
What does an operating system do?
Provides an environment which helps others to do productive work
Helps a user to develop and run programs, by providing a convenient environment
Starting and stopping programs, and sharing the CPU between them
Managing memory:
. which parts of memory are in use and which are free
. provides mechanisms by which programs can ask for more memory or give back memory they no longer need
.Input and output
.covers up the differences between alternative makes and models of devices
.overlaps input and output with processing
What is Kernel?
Central component or heart of operating system
Interface between hardware components and software applications
Makes the software to interact with the hardware to get a specific task done.
It decides the amount of resources (RAM, GPU,… ) to be used by every application.
It decides on what programs to be executed and on what order.
It has separate space on memory so it functions independently.
It acts as a central authority which guides memory and keeps eye on all the hardware and software data flow.
System call: Every process which starts on a system, demands the resources from kernel.
CPUs operate in at least two different modes:
User Mode: the CPU can only execute a subset of its instructions – the more common ones, like add, subtract, load and store, etc. If a program is executed in user mode, it does not have access to memory, hardware and such resources .
Kernel Mode: the CPU can execute all of its instructions, including extra privileged instructions. If a program is executed in Kernel mode, it has direct access to memory, hardware and such resources .
Monolithic kernel : user services and kernel services both are kept in the same address space (entire OS is in kernel space), larger than micro kernel, less access time and fast execution, hard to extend, higher performance, higher risk of system crash. Linux uses monolithic kernel.
Microkernel : user services and kernel services are kept in separate address space, smaller in size (minimum code in kernel space), greater access time and slow execution, easily extendable, lower responsibility. Windows use hybrid (Micro + Monolithic)
Batch Systems
Earliest systems developed
Data and the commands to manipulate the program and data are all submitted together to the computer in the form of a ‘job’.
Little or no interaction between users and an executing program.
Example: Payroll processing & Bank or credit card statements - no need for any operator interaction once the job has been started
Interactive systems
Most common mode of computing using keyboard, mouse and screen.
Significant improvement on batch systems, as it is now possible to intervene directly while a program is being developed, or as it is running.
Single user: Multitasking & Interactive computing on a single-user basis such as Windows, MS-DOS and OS/2.
Multi-user: Interactive computing on a multi-access or Multi-user basis (using different terminals) such as Unix, Linux, Windows 10, Ubuntu, Mac OS.
Type of Operating Systems
General Purpose OS: A given environment may want a bit of everything. For example, a timesharing system may support interactive users, but also include the ability to run programs in batch mode.
Network OS: To share resources such as printers and databases across a network, such as Windows NT Server.
Distributed systems: The most recent development in operating systems, meeting the requirements of a multi-user system. Essentially, it consists of a group of machines acting together as one. When a user starts a program, it may actually run on the local machine. But if that computer is heavily loaded, and the operating system knows that another machine is idle, then the job may be transferred to that idle machine.
Specialist systems: Dedicated to processing large volumes of data, which are maintained in an organized way such as real-time operating system, banking system
