Changes
/* Vortex Disk Format */
* First 9K contain two System Tracks (eg. CP/M Bootstrap)
* Next 4K contain directory (see Note)
* Next 720K 704K are data (allocated in 4K blocks) (aka 4K clusters)
* Last 3K are unused (due to 4K allocation size)
Note: According to the manual, the directory can hold 128 entries under VDOS2.0 (whole 4K used), but only 64 entries under VDOS1.0 (only half of the 4K area used).
