lecture-03-layering-naming-filesystem-design.pptx

Lecture 03: Layering, Naming, and Filesystem Design

Principles of Computer

Systems Spring 2019

Stanford University

Computer Science

Department Lecturer:

Chris Gregg

PDF of this

and if you want to flip the boolean, you need to write the entire byte back to memory.

A similar concept exists in the world of hard drives. Hard drives are divided into

sectors (we'll assume 512 bytes), and are sector-addressable: you must read or write

entire sectors, even if you’re only interested in a portion of each.

Sectors are often 512 bytes in size, but not always. The size is determined by the

physical drive and might be 1024 or 2048 bytes, or even some larger power of two if

the drive is optimized to store a small number of large files (e.g. high definition videos

for youtube.com)

Conceptually, a hard drive might be viewed like this:

Lecture 03: Layering, Naming, and Filesystem Design

Thanks to Ryan Eberhardt for the illustraons and the text used in these slides, and to Ryan and Jerry Cain for the

content.

Lecture 03: Layering, Naming, and Filesystem Design

2 public:

3 size_t getNumSectors() const;

4 void readSector(size_t num, unsigned char data[]) const;

5void writeSector(size_t num, const unsigned char data[]);

6 };

Throughout the lecture, you may hear me use the term block instead of sector.

Sectors are the physical storage units on the hard drive.

The filesystem, however, generally frames its operations in terms of blocks

(which are each comprised of one or more sectors).

If the filesystem goes with a block size of 1024, then when it accesses the

deck will do precisely that).

Lecture 03: Layering, Naming, and Filesystem Design

Lecture 03: Layering, Naming, and Filesystem Design