Today most general-purpose operating systems employ paged virtual memory. A page is a unit of logical
address space, and a frame is a same-size unit of physical memory. By means of a page table data structure,
which maps pages to frames, the operating system maps logical addresses to physical addresses. The advantages
of virtual memory include a very large logical address space, and a higher degree of multiprogramming.
The file system is a very visible feature of any operating system. We discussed various file management
systems, including systems based on linked allocation of file blocks and systems based on indexed allocation
of file blocks. Newer file systems are incorporating journaling of transactions in order to better insure file
system stability.
REVIEW QUESTIONS
6.1 What is the advantage of managing I/O with interrupts? If an active typist is typing 30 words per minute
into a word processor, and the computer operates at one million machine instructions per second, how
many machine instructions can be executed in the time it takes a character to be typed on the keyboard?
6.2 Explain why a DMA channel would or would not be useful in a computer without an interrupt-based
I/O system.
6.3 What scheduling concept was critical to the development of timesharing computers, and has remained
an important part of scheduling for interactive computer systems?
6.
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