Victor 9000

From: A.R. Duell <>
Date: Thu Jun 19 19:49:15 1997

> I thought the idea of variable speed drives was to have the same
> number/sized sectors on each track? Perhaps I goofed there too...

Let's go through this logically.

Virtually all standard floppy drives (and a lot of 'classic' hard
drives) rotate at a cosntant speed, which for the purposes of this
discussion I'll take as 300rpm (The speed of a 'standard' low density
5.25" disk). So, the disk takes 0.2s to rotate once.

Most controllers write the bits to the disk at a constant rate. There are
thus a constant number of bits sent out in 0.2s, and thus a constant
number of bits (or equivalently a constant number of sectors of a given
constant size) written in one revolution of the disk.

However, the outer tracks are longer than the inner ones (a simple matter
of geometry). So, data bits on the outside tracks take up more area on the
disk than ones on the inner tracks. Now, assuming we only need a constant
area to store a single bit, it's obvious that space is being wasted on the
longer outside tracks.

There are 2 ways rounds this. The one used by Commodore on the 1541 and
the 8050 (and AFAIK all other classic Commodore drives) was to keep the
disk turning at a constant speed (300rpm IIRC) and to write the data bits
faster on the outer tracks. Thus, they could write more data in that
constant 0.2s I mentioned earlier.

The one used by Victor (I believe, I've not seen a Technical Manual) was
to keep the data rate constant, but to slow the disk down when writing to
the outside tracks (or equivalently to speed it up on the inner ones). The
result was that there was more time to write data to the outside tracks,
so (at a constant data rate) you could fit more on the disk.

In neither case was the number of sectors per track constant (obvious if
you require all sectors to be of the same size, which makes writing the
file system a lot easier).

> Uncle Roger "There is pleasure pure in being mad

The gates in my computer are AND,OR and NOT, not Bill
Received on Thu Jun 19 1997 - 19:49:15 BST

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