--- /dev/null
+.\" Believe it or not, reportedly there are nroffs which do not know \(en
+.if n .ds en -
+.if t .ds en \(en
+.TH CPM 5 "November 26, 2007" "CP/M tools" "File formats"
+.SH NAME \"{{{roff}}}\"{{{
+cpm \- CP/M disk and file system format
+.\"}}}
+.SH DESCRIPTION \"{{{
+.SS "Characteristic sizes" \"{{{
+Each CP/M disk format is described by the following specific sizes:
+.RS
+.sp
+Sector size in bytes
+.br
+Number of tracks
+.br
+Number of sectors
+.br
+Block size
+.br
+Number of directory entries
+.br
+Logical sector skew
+.br
+Number of reserved system tracks
+.sp
+.RE
+A block is the smallest allocatable storage unit. CP/M supports block
+sizes of 1024, 2048, 4096, 8192 and 16384 bytes. Unfortunately, this
+format specification is not stored on the disk and there are lots of
+formats. Accessing a block is performed by accessing its sectors, which
+are stored with the given software skew.
+.\"}}}
+.SS "Device areas" \"{{{
+A CP/M disk contains three areas:
+.RS
+.sp
+System tracks (optional)
+.br
+Directory
+.br
+Data
+.sp
+.RE
+The system tracks store the boot loader and CP/M itself. In order to save
+disk space, there are non-bootable formats which omit those system tracks.
+The term \fIdisk capacity\fP always excludes the space for system tracks.
+Note that there is no bitmap or list for free blocks. When accessing a
+drive for the first time, CP/M builds this bitmap in core from the directory.
+.\"}}}
+.SS "Directory entries" \"{{{
+The directory is a sequence of directory entries (also called extents),
+which contain 32 bytes of the following structure:
+.RS
+.sp
+.ta 3n 6n 9n 12n 15n 18n 21n 24n 27n 30n 33n 36n 39n 42n 45n
+St F0 F1 F2 F3 F4 F5 F6 F7 E0 E1 E2 Xl Bc Xh Rc
+.br
+Al Al Al Al Al Al Al Al Al Al Al Al Al Al Al Al
+.sp
+.RE
+.\"{{{ St = status
+\fBSt\fP is the status; possible values are:
+.RS
+.sp
+0\*(en15: used for file, status is the user number
+.br
+16\*(en31: used for file, status is the user number (P2DOS)
+or used for password extent (CP/M 3 or higher)
+.br
+32: disc label
+.br
+33: time stamp (P2DOS)
+.br
+0xE5: unused
+.sp
+.RE
+.\"}}}
+.LP
+.\"{{{ F0-E2 = file name and extension
+\fBF0\*(enE2\fP are the file name and its extension. They may consist of
+any printable 7 bit ASCII character but: \fB< > . , ; : = ? * [ ]\fP.
+The file name must not be empty, the extension may be empty. Both are
+padded with blanks. The highest bit of each character of the file name
+and extension is used as attribute. The attributes have the following
+meaning:
+.RS
+.sp
+F0: requires set wheel byte (Backgrounder II)
+.br
+F1: public file (P2DOS, ZSDOS), forground-only command (Backgrounder II)
+.br
+F2: date stamp (ZSDOS), background-only commands (Backgrounder II)
+.br
+F7: wheel protect (ZSDOS)
+.br
+E0: read-only
+.br
+E1: system file
+.br
+E2: archived
+.sp
+.RE
+Public files (visible under each user number) are not supported by CP/M
+2.2, but there is a patch and some free CP/M clones support them without
+any patches.
+.LP
+The wheel byte is (by default) the memory location at 0x4b. If it is
+zero, only non-privileged commands may be executed.
+.\"}}}
+.LP
+.\"{{{ Xl, Xh = extent number
+\fBXl\fP and \fBXh\fP store the extent number. A file may use more than
+one directory entry, if it contains more blocks than an extent can hold.
+In this case, more extents are allocated and each of them is numbered
+sequentially with an extent number. If a physical extent stores more than
+16k, it is considered to contain multiple logical extents, each pointing
+to 16k data, and the extent number of the last used logical extent
+is stored. Note: Some formats decided to always store only one logical
+extent in a physical extent, thus wasting extent space. CP/M 2.2 allows
+512 extents per file, CP/M 3 and higher allow up to 2048. Bit 5\*(en7 of
+Xl are 0, bit 0\*(en4 store the lower bits of the extent number. Bit 6
+and 7 of Xh are 0, bit 0\*(en5 store the higher bits of the extent number.
+.\"}}}
+.LP
+.\"{{{ Rc, Bc = record count, byte count
+\fBRc\fP and \fBBc\fP determine the length of the data used by this extent. The
+physical extent is divided into logical extents, each of them being 16k
+in size (a physical extent must hold at least one logical extent, e.g. a
+blocksize of 1024 byte with two-byte block pointers is not allowed).
+Rc stores the number of 128 byte records of the last used logical extent.
+Bc stores the number of bytes in the last used record. The value 0 means
+128 for backward compatibility with CP/M 2.2, which did not support Bc.
+.\"}}}
+.LP
+.\"{{{ Al = allocated blocks
+\fBAl\fP stores block pointers. If the disk capacity is less than 256 blocks,
+Al is interpreted as 16 byte-values, otherwise as 8 double-byte-values.
+A block pointer of 0 marks a hole in the file. If a hole
+covers the range of a full extent, the extent will not be allocated. In particular,
+the first extent of a file does not neccessarily have extent number 0.
+A file may not share blocks with other files, as its blocks would be freed
+if the other files is erased without a following disk system reset. CP/M returns
+EOF when it reaches a hole, whereas UNIX returns zero-value bytes, which makes
+holes invisible.
+.\"}}}
+.\"}}}
+.SS "Time stamps" \"{{{
+P2DOS and CP/M Plus support time stamps, which are stored in each fourth
+directory entry. This entry contains the time stamps for
+the extents using the previous three directory entries. Note that you
+really have time stamps for each extent, no matter if it is the first
+extent of a file or not. The structure of time stamp entries is:
+.RS
+.sp
+1 byte status 0x21
+.br
+8 bytes time stamp for third-last directory entry
+.br
+2 bytes unused
+.br
+8 bytes time stamp for second-last directory entry
+.br
+2 bytes unused
+.br
+8 bytes time stamp for last directory entry
+.sp
+.RE
+A time stamp consists of two dates: Creation and modification date (the
+latter being recorded when the file is closed). CP/M Plus further
+allows optionally to record the access instead of creation date as first
+time stamp.
+.RS
+.sp
+2 bytes (little-endian) days starting with 1 at 01-01-1978
+.br
+1 byte hour in BCD format
+.br
+1 byte minute in BCD format
+.sp
+.RE
+.\"}}}
+.SS "Disc labels" \"{{{
+CP/M Plus support disc labels, which are stored in an arbitrary directory
+entry.
+The structure of disc labels is:
+.RS
+.sp
+1 byte status 0x20
+.br
+\fBF0\*(enE2\fP are the disc label
+.br
+1 byte mode: bit 7 activates password protection, bit 6 causes time stamps on
+access, but 5 causes time stamps on modifications, bit 4 causes time stamps on
+creation and bit 0 is set when a label exists. Bit 4 and 6 are exclusively set.
+.br
+1 byte password decode byte: To decode the password, xor this byte with the password
+bytes in reverse order. To encode a password, add its characters to get the
+decode byte.
+.br
+2 reserved bytes
+.br
+8 password bytes
+.br
+4 bytes label creation time stamp
+.br
+4 bytes label modification time stamp
+.sp
+.RE
+.\"}}}
+.SS "Passwords" \"{{{
+CP/M Plus supports passwords, which are stored in an arbitrary directory
+entry.
+The structure of these entries is:
+.RS
+.sp
+1 byte status (user number plus 16)
+.br
+\fBF0\*(enE2\fP are the file name and its extension.
+.br
+1 byte password mode: bit 7 means password required for reading, bit 6 for writing
+and bit 5 for deleting.
+.br
+1 byte password decode byte: To decode the password, xor this byte with the password
+bytes in reverse order. To encode a password, add its characters to get the
+decode byte.
+.br
+2 reserved bytes
+.br
+8 password bytes
+.sp
+.RE
+.\"}}}
+.\"}}}
+.SH "SEE ALSO" \"{{{
+.IR mkfs.cpm (1),
+.IR fsck.cpm (1),
+.IR fsed.cpm (1),
+.IR cpmls (1)
+.\"}}}
projects / debian / cpmtools / blobdiff