8 "disc geometry

[Enrico email.it]

Hi at all. I have few questions on how the geometry is calculated.


1) I would like to understand. this table represents an 3740 IBM standard
disk

D: Drive Characteristics
1944: 128 Byte Record Capacity
243: Kilobyte Drive Capacity
64: 32 Byte Directory Entries
64: Checked Directory Entries
128: Records / Extent
8: Records / Block
26: Sectors / Track
2: Reserved Tracks

Its DPT is:

1A00 03 07 00 F200 3F00 C000 1000 0200

Or:
SPT = 001A = The number of 128 byte records per track.
BSH = 03 = The block shift count.
BLM = 07 = The block mask.
EXM = 00 = The extent mask.
DSM = 00F2 = Disk storage maximum (the largest block number).
DRM = 003F = Directory maximum (the largest directory entry).
DAB = 00C0 = Directory Allocation Block AL1: = 00 & AL0: = C0 [0C0H]
CKS = 0010 = Directory check size.
OFF = 0002 = Track offset (number of reserved tracks).

I already know there are 26x128x77 = 256256 bytes
But how does this table represent them?

1944 sectors x 128 bytes = 248832 bytes = 243x1024 is the capacity actually
available for the files
The system takes 26 sects/track x128 bytes/sect x2 sects= 6656 bytes

So 256256 - 248832 = 768 bytes
They are for the directory
but how does this number come out?

2) I have instead this table of a BASF 6104 Floppy Disk Drive managed
through a Shugart SA-1403 SASI Controller:

B: Drive Characteristics
9216: 128 Byte Record Capacity
1152: Kilobyte Drive Capacity
64: 32 Byte Directory Entries
64: Checked Directory Entries
2048: Records / Extent
128: Records / Block
512: Sectors / Track
1: Reserved Tracks

Its DPT is:

0002 07 7F 0F 4700 3F00 8000 1000 0100

SPT = 0200 = The number of 128 byte records per track.
BSH = 07 = The block shift count.
BLM = 7F = The block mask.
EXM = 0F = The extent mask.
DSM = 0047 = Disk storage maximum (the largest block number).
DRM = 003F = Directory maximum (the largest directory entry).
DAB = 0080 = Directory Allocation Block AL1: = 00 & AL0: = C0 [0C0H]
CKS = 0010 = Directory check size.
OFF = 0001 = Track offset (number of reserved tracks).

Oddly, the controller seems to manage the drive as 32 sect/tracks x256
bytes/setc x77 trakcs x2 heads

In this case I don't know exactly the parameters of the diskette

9216 sectors x 128 bytes = 1.179.648 bytes = 1.152x1024 is the capacity
actually available for the files
The system takes 512 setcs/track x32 bytes/sect x1 tracks = 16.384 bytes

In case 1 the gross capacity is 256256 while in case 2 which is it?

3) what could be the correct parameters to insert in 22disk in order to
transfer files between a type 2 disk and msdos?


Thanks a lot at all who will wish to answer to me.

Enrico