Operating Systems · Unit 9
Input Output and Disk Management
Exam-focused notes for Input Output and Disk Management (Operating Systems, BIT204): what the TU syllabus asks and how it has actually been tested, with 10 solved past questions from this unit.
What this unit covers
- Device controller definition
- DMA definition and purpose
- DMA working mechanism
- Memory mapped I/O
- Interrupt based I/O
- DMA based I/O comparison
- Device independent I/O software
- Disk scheduling algorithms
- RAID definition and levels
- Disk error handling and formatting
Device controller definition
Discuss about controller and memory mapped I/O.Differentiate between interrupt based I/O and DMA based I/O.[5+5]
Note: No specific curriculum notes were found for this topic. The answer below is based on standard, correct Computer Organization and Architecture concepts as taught in BSc CSIT programs. --- (a) Controller and Memory Mapped I/O An I/O Controller (also cal...
Full solved answer →Disk error handling and formatting
Describe about error handling and formatting in disk management. [5]
Note: The reference notes did not contain specific content on this topic. The following answer is based on standard Operating Systems concepts as taught in BSc CSIT curriculum. --- Disk formatting is the process of preparing a disk for use by the operating ...
Full solved answer →Disk scheduling algorithms
Suppose that a disk drive has the cylinder numbered, 0 to 199 is currently serving a request at cylinder 143. The request queue is kept in the FIFO order 25, 17, 119, 197, 194, 15, 182, 115, and 183. What is the total head movement needed to satisfy these request for the following disk scheduling algorithm. a) FCFS b) SSTF [5]
- Cylinder range: 0 to 199 - Current head position: 143 - Request queue (FIFO): 25, 17, 119, 197, 194, 15, 182, 115, 183 --- Service order: 143 → 25 → 17 → 119 → 197 → 194 → 15 → 182 → 115 → 183 From To Distance -------------------- 143 25 118 25 17 8 17 11...
Full solved answer →Suppose that a disk has 100 cylinders, numbered 0 to 99. The drive is currently serving a request at cylinder 45. The queue of pending request, in FIFO order is: 88, 72, 13, 74, 48, 9, 22, 50, 35 and 30. What is the total distance (in cylinders) that the disk arm moves to satisfy all pending request for each of the following disk scheduling algorithms? a) FCFS b) SCAN c) SSTF[10]
- Total cylinders: 0 to 99 (100 cylinders) - Current head position: 45 - FIFO request queue: 88, 72, 13, 74, 48, 9, 22, 50, 35, 30 --- Serve in FIFO order: $45 \to 88 \to 72 \to 13 \to 74 \to 48 \to 9 \to 22 \to 50 \to 35 \to 30$ Move Distance -------------...
Full solved answer →When does interrupt concur? Suppose that a disk drive has the cylinder numbered from 0 to 199. The head is currently at cylinder number 53. The queue for services of cylinders is as 99, 183, 37, 122, 14, 124, 65 and 67. What is the total head movement in each of following disk algorithm to satisfy the requests? (a) FCFS (b) SSTF (c) SCAN[10]
An interrupt is a signal to the CPU from hardware or software indicating that an event needs immediate attention. When an interrupt occurs, the CPU suspends the currently executing process, saves its state, and transfers control to an Interrupt Service Rout...
Full solved answer →Memory mapped I/O
What is memory mapped I/O? Explain about device independent I/O software. [5]
Memory Mapped I/O is a method of performing input/output operations between the CPU and peripheral devices in which the I/O devices are mapped into the same address space as the main memory. - In this scheme, a portion of the memory address space is reserve...
Full solved answer →RAID definition and levels
What is RAID? Explain Level-2 and Level-3 RAID. [5]
RAID (Redundant Array of Independent Disks) is a data storage technology that combines multiple physical disk drives into a single logical unit to achieve one or more of the following goals: - Improved performance (through parallelism/striping) - Fault tole...
Full solved answer →DMA working mechanism
Explain the working mechanism of DMA. [5]
DMA (Direct Memory Access) is a technique that allows I/O devices to transfer data directly to/from main memory without involving the CPU for each byte/word of the transfer. A dedicated hardware unit called the DMA Controller manages this transfer. --- Comp...
Full solved answer →DMA definition and purpose
What is DMA? Explain how it works in brief with suitable diagram. [5]
DMA (Direct Memory Access) is a feature of computer systems that allows certain hardware subsystems (such as disk controllers, network cards, or sound cards) to access main memory (RAM) independently of the CPU. It enables data transfer between I/O devices ...
Full solved answer →How does DMA help in I/O management? Explain. [5]
Direct Memory Access (DMA) is a technique that allows I/O devices to transfer data directly to or from main memory without the continuous involvement of the CPU. A special hardware unit called the DMA controller manages these transfers. --- Without DMA, the...
Full solved answer →Make Unit 9 stick
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