On 9/19/2025 2:31 PM, Go Canes wrote:
On Fri, Sep 19, 2025 at 12:07 PM home user via users
<[email protected]> wrote:
On 9/17/2025 1:27 PM, Go Canes wrote:
On Wed, Sep 17, 2025 at 2:48 PM home user via users
>> A drive is divided into sectors, which are divided into blocks. Am
I right?
>
> Correct, although you usually don't care about sectors. In fact, most
> modern spinning disk drives *lie* about the number of sectors and
> their size. Only the block size and number of blocks is normally
> relevant.
Sorry, but I had a bit of a brain-fart there.....
Originally a disk was magnetically divided into *cylinders*, cylinders
were divided into tracks, and tracks divided into sectors/blocks.
- a disk would have one or more platters
- each platter typically has a surface on top and bottom
- there is a read/write head for each surface
- a contiguous group of sectors on a single surface of a platter forms a track
- all of the tracks in the same location on all the surfaces forms a cylinder
- so to read a specific sector:
- o the read/write head assembly has to be positioned to the correct cylinder
- o the disk has to rotate until the desired sector is under the read/write head
- o finally the sector can be read
- o in terms of computer time, the above takes an eternity
One of the issues with these original disks is that the inner-most and
outer-most cylinders held the same amount of data even though the
outer-most cylinder was larger (i.e. larger circumference). This was
one of the original ways they started squeezing more space out of
disks - the disk no longer physically had the conventional magnetic
structure, and used its own internal logic to convert between what the
computer expected and what it actually used. Hence disks started
"lying" about the # of heads and cylinders.
There is probably an article on wiki or google that covers this
history much better than I summarize here.
I remember them stacks of platters... 1970s, Xerox Sigma-7.
Those were my student (B.S.) days.
--
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