See ./epsonCPMdirectory.html for an illustrated and more extended version of this text.

Epson CP/M 2.2 format QX-10, TF-20 (HX-20, PX-4, PX-8)

The floppy format is:
- 40 tracks, 
- double sided, 
- double density, 
- 256 byte sectors,
- 16 sectors per track,
- track 0 - 3 are reserved for system files,
- track 39 is never used,
- the directory is located at the first 8 sectors of track 4, containing 8 extends each (64 extends in total),
- a physical extend can contain up to two logical extends, containing 256 records of 128 byte max,
- a block is 2048 bytes, or 16 records, or 8 sectors.
This leaves 139 blocks available on an empty disk.
The PX-4 RefMan reports:
Number of directory entries:  64
Storage available for user:   278B bytes

Files larger than 32 kByte are stored in multiple extends. In theory one file could span all 64 extends,
but in practice for this disk geometry it is limited to 8.7 extends. This makes the Xh byte always 0.

A directory extend consists of 32 bytes organized as:
St F0 F1 F2 F3 F4 F5 F6 F7 E0 E1 E2 Xl Bc Xh Rc
Al Al Al Al Al Al Al Al Al Al Al Al Al Al Al Al


St      is the status; possible values are:
        0x00-0x0F: used for file, status is the user number
	(0x20: used for disk label)*
	(0x21: used for date-time stamp for the files in the previous three directory extends)*
        0xE5: unused

F0 - F7 is the file name (bit 0 - 6)
E0 - E2 is the extension (bit 0 - 6)
        E0 (bit 7): read-only file
        E1 (bit 7): system file
        E2 (bit 7): archived file (maybe only CP/M 3?)

Xl      Extend number (bit 1 - 5) and Records in extend (bit 0, as overflow of Rc)
Bc      Effectively always 0. 
Xh      Effectively always 0.
Rc      Records in extend (bit 0 - 7, but higest value used is 128, 0x80)

Al      are the block numbers ranging from 0x01 to 0x8B. A value 0 means this allocation is not used.

*) found in CP/M Plus enabled disks; QX-10 only

Other sources:
http://www.cpm8680.com/cpmtools/cpm.htm
http://groups.google.nl/group/comp.os.cpm/browse_thread/thread/2e8160b267bf6fd5/c19799cfbedf8e61?lnk=gst&q=directory+format+group%3Acomp.os.cpm#c19799cfbedf8e61
http://www.seasip.demon.co.uk/Cpm/format22.html
PX-4,HX-40 Operating System Reference Manual, II-359

fjkraan,2010-03-26