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OS · Question Set
Device Management & OS Internals interview questions for placements and exams.
Questions
10
Included in this set
Subject
OS
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Difficulty
Mixed
Level of this set
Go through each question and its explanation. Use this set as a focused practice pack for OS.
Spooling stands for Simultaneous Peripheral Operations On-Line. It uses an intermediate buffer or queue so that data destined to a slower device is stored temporarily and the system can move on. This improves efficiency for devices like printers.
For complete preparation, combine this set with full subject-wise practice for OS. You can also explore other subjects and sets from the links below.
The SCAN algorithm (also called the elevator algorithm) moves the disk arm in one direction, servicing requests as it goes, until it hits one end of the disk, then reverses direction. This approach reduces arm movement and can offer better average wait times than simple methods. In interview settings, explaining the ‘elevator’ metaphor and its trade-offs (for example with SSTF) is valuable.
A device driver is a software component (often part of the OS kernel or a loadable module) that provides an interface between the operating system’s generic I/O framework and the specific hardware device. It handles initialization of the device, data transfer, interrupt handling, power management and clean-up. The OS kernel calls driver APIs to perform I/O, route interrupts to the driver, and manage resources like DMA channels or device memory. For interviews it is useful to highlight how drivers provide abstraction, manage concurrency and ensure safe access to hardware.
DMA allows a hardware controller (the DMA engine) to move data between memory and a device without continuous CPU intervention. This frees the CPU to perform other tasks while large blocks of I/O are transferred. An OS using DMA must coordinate memory buffers, interrupt service routines and bus arbitration. Understanding DMA is often asked in system-level OS interviews because it touches hardware-software boundary.
Polling (or programmed I/O) is when the CPU repeatedly checks (in a loop) a device status to see if it is ready, then performs the transfer. It wastes CPU cycles while waiting. Interrupt-driven I/O is when the device issues an interrupt when ready, and the CPU handles the request via ISR (Interrupt Service Routine). Interrupts reduce wasteful CPU polling but add overhead due to context switching, interrupt latency and complexity. Polling may be suitable for very fast or predictable devices. Interrupts are better for devices with unpredictable latency or that allow CPU to work on other tasks. In interviews, discuss trade-offs: timing, latency, complexity, context switch overhead, CPU utilisation.
When multiple processes need I/O or device access simultaneously the OS must coordinate resource sharing. It does so by maintaining queues (ready queue, I/O queue), using device-queues, scheduling I/O requests, applying locking or semaphores to protect device registers, managing priorities, and ensuring fairness and avoidance of starvation. For example, a print spooler may queue all print requests and let the driver service them one by one. The OS might also use priority or time-slicing for devices. In interviews mention trade-offs: fairness vs throughput, device contention, prevention of starvation, and impact on CPU scheduling.
For an operating system to support hot-plug devices (such as USB drives or external peripherals) it must allow device drivers (often kernel modules) to load and unload dynamically at runtime. This ensures that the system recognizes new devices and removes them safely without rebooting. This topic demonstrates system internals knowledge in interviews.
Buffering is the technique of using a temporary memory area (buffer) to hold data while it is transferred between two devices or between device and memory. It helps decouple producer and consumer speeds (for example when a fast CPU writes to a slower peripheral). Buffering improves throughput, smooths bursts of data and reduces I/O invocation overhead. On the flip side, buffering consumes memory, can introduce latency (data waits in buffer), may cause inconsistency if not flushed correctly, and adds complexity (flush logic, overflow, memory management). Interviewers like it when you discuss both the benefit and trade-offs.
A cache is aimed at reducing access latency by storing copies of frequently used data near the CPU or device; a buffer smooths data transfer by holding data temporarily between two entities with mismatched speeds. These are commonly confused in interview questions, so clearly stating the difference shows clarity.
In a multi-tenant or shared environment the OS must allocate devices fairly and securely among different virtual machines or processes. For example a hypervisor or OS may use IOMMU to partition DMA access, assign virtual functions (SR-IOV) for network cards, isolate GPUs via hardware virtualization, and use quotas or scheduling for access. Challenges include performance isolation (one tenant hogging device), security isolation (preventing DMA attacks or shared memory leakage), scheduling of I/O bandwidth, interrupt sharing, driver compatibility, and load balancing. In interview responses mention these challenges and how OS design or hypervisor can mitigate them — e.g., using hardware partitioning, IO-virtualization, and monitoring of usage.