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Summary COS3721 ASSIGNMENT 1 SOLUTIONS 2023
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- University Of South Africa (Unisa)
ASSIGNMENT 1 ASWERS FOR COS
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Assignment 1 Total marks 100Question-1 Coverage : Chapter 1 [10]
1) Direct memory access is used for high-speed I/O devices in order to avoid increasing the
CPU’s execution load.
a. How does the CPU interface with the device to coordinate the transfer? (2)
~ The CPU can initiate a direct memory Access (DMA) operation by writing values into special
registers that can be independently accessed by the device. The device initiates the corresponding
operation once it receives a command from the Central Processing Unit (CPU).
b. How does the CPU know when the memory operations are complete? (2)
~ It gets interrupted to indicate the completion of the operation. Both the device and the CPU can
be accessing memory simultaneously. The memory controller provides access to the memory bus in
a fair manner to these two entities
c. The CPU is allowed to execute other programs while the DMA controller is transferring
data. Does this process interfere with the execution of the user programs? If so, describe
what forms of interference are caused. (4)
~ The process does interfere with the program, The CPU might be unable to issue memory
operations at peak speeds since it has to compete with the device in order to obtain access to the
memory bus.
~ DMA can lead to memory fragmentation. This can cause performance issues when the CPU
attempts to allocate or access memory.
2) Describe two challenges of designing operating systems for mobile devices compare with
designing operating system for traditional PCs. (2)
~ Less processing power and fewer processors mean the operating system must carefully share
processors to applications.
~ Less storage capacity means the operating system must manage memory carefully.
Question 2: Operating-system structures [12]
1) Describe three general methods for passing parameters to the operating system. (6)
~ Pass parameters in registers
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