COS2621 Final Exam Notes
Write notes on memory management:
• Main memory is divided into two parts, one part for OS and one part
for the program currently being executed.
• In a multiprogramming system, the user part of memory is subdivided
to accommodate multiple processes.
• The task ...
Write notes on memory management: Five sequences of hardware events occurring when I/O device completes I/O
operation:
• Main memory is divided into two parts, one part for OS and one part
for the program currently being executed. 1. The device issues an interrupt signal to the processor
• In a multiprogramming system, the user part of memory is subdivided 2. The processor finishes execution of the current instruction before
to accommodate multiple processes. responding to the interrupt
• The task of subdivision is carried out dynamically by the OS and is 3. The processor tests for an interrupt, determines that there is one then
known as memory management sends an acknowledgement signal to the device that issued the
• Effective memory management is vital. interrupt allowing the device to remove the Interrupt signal.
• Memory needs to be allocated efficiently to pack as many processes 4. The processor prepares to transfer control to the interrupt routine. It
into memory as possible. saves necessary info (the status if the processor - contained in PSW
register, the location of the next instruction contained in the counter)
5. The processor loads the program counter with the entry location of
Explain the term ‘gate’ in a digital logic circuit: the interrupt handler program that will respond to this interrupt.
• A gate is a device that implements a simple Boolean or logical function
such as if A and B are true then C is true. They control data flow What Shortcomings of ASCII led to development of Unicode:
• Unicode was invented to supersede ASCII, As ASCII could only support
Explain 2 ways to make computerised multiplication more efficient: a limited number of characters, (2^7 due to them being 7-bit), and did
not support multiple languages past English.
• 1. Performing a running addition on the partial products rather than • Unicode supports substantially more characters, and supports a much
waiting till the end wider variety of languages.
• 2. Save time on generation of partial products using add and shift
3 methods used to increase processor speed:
• Increase the hardware speed of the processor. This is fundamentally
Four reasons peripheral devices aren’t connected directly to the system bus: due to shrinking the size of the logic gates on the processor chip, so
more gates can be packed together more tightly allowing an increase
• Wide variety of peripherals with various methods of operation, and
in clock rate.
impractical to concorporate the necessary logic within the processor
• Increase size and speed of caches interposed between the processor
to control a range of devices
and main memory. Dedicating a portion of the processor chip itself to
• Data transfer rate is often slower than memory or processor, thus
the cache, cache access times drop significantly
impractical to use a high-speed bus
• Make changes to processor organisation and architecture that
• Data transfer rate is sometimes faster, and mismatch would lead to
increase the effective speed of instruction execution. This typically
inefficiencies
involves the use of parallelism in one form or another.
• Peripherals often use different data formats and word lengths than
the computer to which they are attached
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