CECS 326 Final Chapters 5 and 6

What is the total data rate per channel for a DMA controller with 5 channels requesting a 32-bit word every 40 ns?

400 Mbps

How fast must the bus be to avoid being a bottleneck with 5 channels operating at 400 Mbps each?

At least 2 Gbps.

What are loadable kernel modules (LKMs) and how do they facilitate device installation without recompiling the OS?

LKMs allow device drivers to be compiled separately and dynamically loaded into the kernel without recompilation.

What role do device descriptors and the Hardware Abstraction Layer (HAL) play in modern operating systems?

They provide a uniform interface for the OS to interact with device drivers.

Why are output files for printers spooled on disk before being printed?

Spooling decouples the slow printer from fast user processes, prevents process blocking, and allows for reordering and retrying.

List two advantages of optical disks compared to magnetic disks.

1. Longer shelf life for archiving. 2. Cheaper per unit for distribution.

List two disadvantages of optical disks compared to magnetic disks.

1. Slower read/write speeds. 2. Typically read-only or write-once.

What are the compatibility issues that arise from redesigning the partition table of a Pentium hard disk?

Existing OSes expect MBR with a maximum of 4 primary partitions, leading to potential bootloader complications.

What is a good consequence of redesigning the partition table for a Pentium hard disk?

Increased flexibility in partitioning.

What happens to the output queued for a display after receiving a DEL (SIGINT) character?

The display driver discards all queued output to avoid displaying irrelevant or incomplete information.

When will UNIX systems using a 32-bit unsigned integer for time wrap around?

In approximately 136 years from January 1, 1970.

What is the seek time for disk requests using the First-Come, First-Served (FCFS) algorithm starting from cylinder 20?

816 ms.

What is the total seek time using the Shortest Seek Time First (SSTF) algorithm starting from cylinder 20?

360 ms.

What is the total seek time using the Elevator (SCAN) algorithm starting from cylinder 20?

348 ms.

What are two advantages of thin client computing?

1. Centralized management for easier updates and backups. 2. Cost-effective hardware for clients.

What are two disadvantages of thin client computing?

1. Performance heavily depends on network reliability. 2. Limited offline functionality.

Why does a notebook computer have better battery life when running text-only UNIX programs compared to the X Window System?

Text mode uses less power as it does not require frequent redraws or keep the display active.

What is the significance of the SIGINT character in UNIX systems?

It is used to stop a process, allowing for real-time response to user intent.

What is the maximum number of partitions supported by the Master Boot Record (MBR)?

Four primary partitions.

What is the purpose of spooling in the context of printing?

To manage print jobs efficiently and prevent blocking of user processes.

What is the impact of using the X Window System on battery life in a notebook computer?

It consumes more power due to hardware acceleration and frequent graphical updates.

What is the maximum value of a 32-bit unsigned integer in seconds?

4,294,967,295 seconds.

Why is the open system call essential in UNIX?

It initializes access to a file and returns a file descriptor for subsequent system calls like read, write, or close.

What would happen without the open system call in UNIX?

The OS would struggle to manage or identify which files are in use, making secure and efficient file access nearly impossible.

How can a simple operating system simulate a hierarchical file system?

By encoding the directory structure into file names using delimiters like slashes (e.g., homeuserdocuments_file.txt).

What happens to a file with a corrupted data block in a contiguous allocation scheme?

The file may lose a significant portion of its data since data is stored in sequence.

What happens to a file with a corrupted data block in a linked allocation scheme?

Only the corrupted block is lost, but it breaks the chain, potentially rendering the rest of the file inaccessible.

What happens to a file with a corrupted data block in an indexed allocation scheme?

Damage is localized; only the corrupted block is affected, and other blocks remain accessible via the index table.

Which allocation scheme is most appropriate for a file size that varies between 4 KB and 4 MB?

Indexed allocation is most appropriate as it supports random access and dynamic file size changes efficiently.

What is one advantage of hard links over symbolic links?

If the original file is deleted, the data remains accessible via the hard link.

What is one advantage of symbolic links over hard links?

Symbolic links can span across different file systems and can link to directories, which hard links cannot.

How many block addresses can be stored in one block of a 4-KB disk using 4-byte addresses?

One block can hold 1024 block addresses (4096 bytes / 4 bytes per address).

What does the free-space bitmap look like after writing five blocks for File B?

1111 1111 1110 0000.

What does the free-space bitmap look like after deleting File A?

1000 0001 1110 0000.

What does the free-space bitmap look like after writing eight blocks for File C?

1111 1111 1111 1111.

What does the free-space bitmap look like after deleting File B?

1000 0000 0001 1111.

What issue arises when Oliver Owl works on the same system being backed up?

His open files may be partially written or inconsistent during the backup, leading to corrupted backups or missing changes.

What type of cache is more suitable for an external USB hard drive: write-through cache or block cache?

A write-through cache is more suitable as it ensures data is immediately written to the drive, reducing data loss risk.

Is the read-ahead technique useful for an application that accesses student records based on user input? Why or why not?

No, read-ahead is not useful here as access is based on random input rather than sequential patterns, leading to unnecessary data fetching.