Sunday brain tickler

Chuck Guzis cclist at
Mon Jan 9 17:37:51 CST 2017

On 01/09/2017 02:58 PM, allison wrote:

> Low majik there...   8 bytes of 7 bit ascii means one free bytes
> worth of bits, to do that start with an 8byte area as 64 bits and
> stuff the bits.   The only question is are the left justified or
> right a few minutes by hand can discover that. Done that way 9
> characters fit in 8 bytes.

> Another allocation scheme is one page per track, about 1200-1500
> bytes, or about 35 pages for a 35track floppy.   So each tack is a
> page and the file header has the page name and a linked list to the
> next.

There are actually 16 150-byte sectors (4 byte header in the form of DB
TT SS CC where CC is the arithmetic sum of TT and SS, followed by 151
bytes of data, with the last byte being the simple sum of bytes 1-150
modulo 256. Encoding is simple FM, with no "funny" missing clock bits.

The sectors are ordered in two groups of 1200 bytes:

0,11,6,1,12,7,2,13 and 8,3,14,9,4,15,10,5

There are 70 groups on the disk, obviously.

I've learned that the 103 was a 32KB 8080 system, so not so sophisticated.

It's the filename encoding that has me stymied, not the data retrieval


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