IBM cassette tapes.

From: Tony Duell <ard_at_p850ug1.demon.co.uk>
Date: Wed Jun 16 17:40:15 2004

>
> Hi,=20
>
> Does anyone have technical information of the IBM cassette tapes
> used to load diagnostic programs in systems like the IBM System/7,=20
> IBM System/3 and the original IBM PC 5150 ?

I certainly have that information for the 5150, it's in the Techref (I
have a shelf of said manuals, I may not _like_ PCs, but at least I am
going to have the information on them :-)).

A 0 bit consists of 1 cycle taking a total of 500us (that's 2kHz I
think). A 1 is 1 cycle taking 1000us (1kHz).

The data record consists of :

Leader (256 bytes of all 1's)
Sync bit (a single 0 bit)
Sync byte (Hex 16)
Data block (256 bytes)
CRC (2 bytes)
Data block (256 bytes)
CRC (2 bytes)
etc...


The CRC polynomial is the usual one X^16+X^12+X^5+1

I don't feel like typing in the relevant bits of BIOS source code, though :-)

-tony
Received on Wed Jun 16 2004 - 17:40:15 BST