File management systems: device drivers and basic file systems

Question

Page 526 of the textbook Operating Systems – Internals and Design Principles , eighth edition, by William Stallings, says the following:

At the lowest level, device drivers communicate directly with peripheral devices or their controllers or channels. A device driver is responsible for starting I/O operations on a device and processing the completion of an I/O request. For file operations, the typical devices controlled are disk and tape drives. Device drivers are usually considered to be part of the operating system.

Page 527 continues by saying the following:

The next level is referred to as the basic file system, or the physical I/O level. This is the primary interface with the environment outside of the computer system. It deals with blocks of data that are exchanged with disk or tape systems.

The functions of device drivers and basic file systems seem identical to me. As such, I'm not exactly sure how Stallings is differentiating them. What are the differences between these two?

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EDIT

From page 555 of the ninth edition of the same textbook:

The next level is referred to as the basic file system, or the physical I/O level. This is the primary interface with the environment outside of the computer system. It deals with blocks of data that are exchanged with disk or tape systems. Thus, it is concerned with the placement of those blocks on the secondary storage device and on the buffering of those blocks in main memory. It does not understand the content of the data or the structure of the files involved. The basic file system is often considered part of the operating system.

Answer 1

Break this down into layer:

Layer 1) Physical I/O to a disk requires specifying the platter, sector and track to read or write to a block.

Layer 2) Logical I/O to a disk arranges the blocks in a numeric sequence and one reads or writes to a specific logical block number that gets translated into into the track/platter/sector.

Operating systems generally have support for a Logical I/O and physical I/O to the disk. That said, most disks these days do the logical to physical translation. O/S support for that is only needed for older disks.

If the device supports logical I/O the device driver performs the I/O. If the device only supports physical I/O the device driver usually handles both the Logical and Physical layers. Thus, the physical I/O layer only exists in drivers for disks that do not do logical I/O in hardware. If the disk supports logical I/O, there is no layer 1 in the driver.

All of the above is what is appears the your first quote is addressing.

Layer 3) Virtual I/O writes to a specific bytes or blocks (depending upon the O/S) to a file. This layer is usually handled outside the device driver. At this layer there are separate modules for each supported file system. Virtual I/O requests to all disks using the same file system go through the same module.

Handling Virtual I/O requires much more complexity than simply reading an writing disk blocks. The virtual I/O layer requires working with the underlying disk file system structure to allocate the blocks to a specific file.

This appears to be what is referred to in the second quote. What is confusing to me is why it is calling this the "physical I/O" layer instead of the "virtual I/O" layer.

Everywhere I have been Physical I/O and Logical I/O are the writing of raw blocks to a disk without regard to the file system on the disk.