×
INTELLIGENT WORK FORUMS
FOR COMPUTER PROFESSIONALS

Are you a
Computer / IT professional?
Join Tek-Tips Forums!
• Talk With Other Members
• Be Notified Of Responses
• Keyword Search
Favorite Forums
• Automated Signatures
• Best Of All, It's Free!

*Tek-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

#### Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

# Floppy Disk size (in BIOS)

 Forum Search FAQs Links MVPs

## Floppy Disk size (in BIOS)

(OP)
Assuming that a sector on a floppy disk is 512 bytes long and the floppy is a standard 3.5" disk:
- How many sectors are there per head ?
- How many heads per cylinder(or track??) ?
- How many cylinders on the disk ?

### RE: Floppy Disk size (in BIOS)

(OP)

I found an interrupt that told me:

mov ah,08h ; get params...
mov dl,00h ; ...for floppy drive
int 13h

This gives the following results (in decimal):
max. sector   = 18
max. cylinder = 79 (80 altogether inc. 0)
max. head     =  1 (2 inc. 0)
This appears to be coherent for a 1.44Mb floppy:

512 x 18 x 80 x 2 = 1474560 bytes
(/1024) = 1440 kb
(/1000) = 1.44 Mb

Just to check - is the following diagram (of a floppy, as best as I can do...) correct or am I mistaken as to what cylinder, sector & head are:

#====================#
!        oooo        !
!      oo  : oo      !
!    oo    :   oo    ! <-sector=between..
!  oo      :     oo  !
!  o       :......o  !
!  o      ~       o  !
!  oo    ~       oo  ! <-cylinder=along ~
!    oo ~      oo    !
!      oo    oo      ! <-head=opposite
!        oooo        !      side of disk
#====================#

### RE: Floppy Disk size (in BIOS)

The names are logically assigned, so head refers to the read/write head and for a floppy there are two of those (because a floppy has two sides). A cylinder is a tube, in this case the edge of it: if you place 80 tight fitting cylinders in each other and then take a slice out, you have a disc consisting of 80 cylinders i.e. something like a floppy disk. A sector is a centerpoint angle of a disc. If a disc has 18 sectors, each sector has an angle of 20°.

Regards,
Bert Vingerhoets
vingerhoetsbert@hotmail.com
http://student.vub.ac.be/~bvingerh/
Don't worry what people think about you. They're too busy wondering what you think about them.

### RE: Floppy Disk size (in BIOS)

In conclusion: you were right about sector and head, but I think not about cylinder.
Visualization using the ASCII Art Standard:

#====================#
!        oooo        !
!      oo  : oo      !
!    oo   ~:   oo    ! <-sector=between..
!  oo   ~  : ~   oo  !
!  o  ~    :......o  !
!  o  ~        ~  o  !
!  oo   ~    ~   oo  ! <-cylinder=along ~
!    oo   ~~   oo    !
!      oo    oo      ! <-head=opposite
!        oooo        !      side of disk
#====================#

Regards,
Bert Vingerhoets
vingerhoetsbert@hotmail.com
http://student.vub.ac.be/~bvingerh/
Don't worry what people think about you. They're too busy wondering what you think about them.

### RE: Floppy Disk size (in BIOS)

(OP)

#### Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

#### Red Flag Submitted

Thank you for helping keep Tek-Tips Forums free from inappropriate posts.
The Tek-Tips staff will check this out and take appropriate action.

#### Posting in the Tek-Tips forums is a member-only feature.

Click Here to join Tek-Tips and talk with other members! Already a Member? Login

Close Box

# Join Tek-Tips® Today!

Join your peers on the Internet's largest technical computer professional community.
It's easy to join and it's free.

Here's Why Members Love Tek-Tips Forums:

• Talk To Other Members
• Notification Of Responses To Questions
• Favorite Forums One Click Access
• Keyword Search Of All Posts, And More...

Register now while it's still free!