Re: Reply to Question???

[ag471@yfn.ysu.edu (Eric S. Ford)]

In a previous article, Evan.Molnar@f107.n2605.z1.fidonet.org (Evan Molnar) says:

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

True, but only pertains to particular disk formats.  ProDOS was developed to 
work with other block oriented devices and thus be independent of format.  Any
block device having its own ROM is addressed, by ProDOS, with a 'block read'
request and the device executes and returns the data.  ProDos doesn't need
any format info for such devices.  For disks, in particular the 5.25 disks,
there is a built-in driver in ProDos which responds to the 'block read' 
request.  I believe the 3.5 drives (particularly the UniDisk 3.5) has onboard
ROM and is accessed by 'block read'.


-- 
Eric S. Ford    ag471@yfn.ysu.edu