Re: Reply to Question???

[sbdocker@acs.ucalgary.ca (Sean Brendan Dockery)]

In article <754702827.AA01642@drharry.UUCP>
Evan.Molnar@f107.n2605.z1.fidonet.org (Evan Molnar) writes:

| -=> On 27 Nov 93  01:56:09, Victoria M Althoff@1:2605/102 said:
| 
| >Does the ProDOS Block Read routine need to know what kind of block it is
| >reading, so that it can find the second sector of a ProDOS or Pascal block?
| >mean, should someone writing a disk data viewer simply assume the lowest com
| >denominator (256-byte sectors) on a disk with an unknown format; or is there
| >some kind of signature that tells the block reader it's dealing with blocks
| >instead of sectors?  Or do blocks always consist of consecutive disk sectors

When you go though GS/OS, the DOS 3.3 FST will read the proper sector.
Although the standard byte count of a block read through the FST is
512, only the first 256 bytes are valid.  (Anyone know if the rest are
zeroed?)

Under ProDOS 8, there is no support for foreign file systems.  As
such, when you read a block, ProDOS will read in two sectors
corresponding to the ProDOS block number, regardless of what type of
disk it is.

Utilities like COPY II+ have kludge code to get around this
limitation, though.

| ProDOS blocks consist of two sectors.  They're simply read in
| one-after-the-other.

They are not simply read in one after the other as they are skewed.
For instance, ProDOS block 0 resides straddled across track 0, sectors
0 and 2.

On no part of the disk are the sectors of the same block consecutive.

| Evan
-- 
Sean Dockery

dockery@griffin.cuc.ab.ca (preferred)
sbdocker@acs.ucalgary.ca (pending expiration)