Higher Grade Computing Studies
7. Systems Software
System Software
• This software is used to provide the computer system
with all of the instructions it needs to function correctly.
In modern computer systems, the system software is a
large collection of programs, including the operating
system, utilities and program translators.
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Higher Computing
Computer Systems
S. McCrossan
Higher Grade Computing Studies
7. Systems Software
Single User OS - System Software
• A single user operating system handles communication with
the user, manages memory storage, manages filing on backing
store, deals with input/output communications with peripherals
and schedules the processors time on tasks.
• Older computers often had their operating system in ROM. This
meant that it was ready as soon as the computer was switched on.
It is impossible to corrupt the system.
• But very difficult to upgrade it as it involved changing the ROM
chips on the motherboard.
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Higher Computing
Computer Systems
S. McCrossan
Higher Grade Computing Studies
7. Systems Software
Single User OS - System Software
• Most modern computers keep their operating system on hard
disk and load it in to RAM on startup.
• Even the modern disk-based operating systems need a small part
of ROM – the bootstrap loader – which is the program that the
processor runs on startup and whose task is to load in the rest of the
operating system from the hard disk.
• The main advantage of this is that it is very simple to upgrade the
operating system.
• The main disadvantage is that other programs can corrupt the
operating system.
Higher Computing
3
Computer Systems
S. McCrossan
Higher Grade Computing Studies
7. Systems Software
Single User OS - System Software
• There are basically five layers/modules to a single-user operating
system;
User level
• User interface
• File Management
• Input/Output Management
• Memory Management
• Kernel
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Machine level
Higher Computing
Computer Systems
S. McCrossan
Higher Grade Computing Studies
7. Systems Software
Single User OS – User Interface
• The operating system has to take user commands from the
keyboard, mouse etc., interpret the commands and pass them to the
appropriate part of the operating system that deals with the
command. If the command cannot be understood, a suitable error
message should be given
• The most common styles include:
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• Form Filling
• Menu driven
• Command and GUI
• Natural language
Higher Computing
Computer Systems
S. McCrossan
Higher Grade Computing Studies
7. Systems Software
Single User OS - File Management
• The operating system supervises the creation, deletion and
updating of files.
• A directory has to be kept
which keeps track of where
files are stored.
Directory
• It has to maintain the
hierarchical directory
structure
Sub-directory
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Higher Computing
Computer Systems
S. McCrossan
Higher Grade Computing Studies
7. Systems Software
Single User OS - Input/Output Management
• The main problem is that all the peripherals work at different
speeds and have different characteristics. The I/O system hides
these differences and makes them all appear to operate in a similar
manner.
• It is the task of the I/O system to do all the actual data transfers
and issue the appropriate control signals to the peripherals.
• If extra hardware is bought, say a printer, then the printer
manufacturer will supply the appropriate software (driver) to
control that peripheral.
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Higher Computing
Computer Systems
S. McCrossan
Higher Grade Computing Studies
7. Systems Software
Single User OS - Memory Management
• The operating system has to decide where programs and data will
be placed in memory.
• Memory Protection - in a multi-tasking environment, it has to
keep track of what stage each program is at and ensure that no
process tries to access the memory space of a different process.
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Higher Computing
Computer Systems
S. McCrossan
Higher Grade Computing Studies
7. Systems Software
Single User OS – Kernel (Process Management)
• The separate activities within the main memory are each called
'processes'. The Kernel is responsible for controlling all the
processes running within memory. It has to decide which of the
tasks in a multi-tasking environment gets to use the processor.
• In a single-program operating system it only has to choose
between the operating system itself and the package being run.
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Higher Computing
Computer Systems
S. McCrossan
Higher Grade Computing Studies
7. Systems Software
Utility Program
• Utility programs are those programs that are used to
enhance the operating system.
• Disk formatting programs - used to prepare the surface of
writeable media for use.
• Disk defragmentation tools - reorganises the files are laid
out on the disk so that the blocks are near to each other.
• File compression - reduce the amount of space that a file
takes up on disk.
• Virus checking tools – see next topic.
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Higher Computing
Computer Systems
S. McCrossan
Higher Grade Computing Studies
7. Systems Software
Graphic File Formats
• JPEGs – use lossy compression.
• GIFs – use lossless compression.
• TIFFs – used to convert bitmap images.
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Higher Computing
Computer Systems
S. McCrossan