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Top Forums UNIX for Dummies Questions & Answers Not quite related to Unix but CP/M file structure... Post 302149083 by Legend986 on Tuesday 4th of December 2007 09:03:11 PM
Old 12-04-2007
Aha... That paper was wonderful... Smilie Thanks a lot... Now I understand the real reason behind that classification... But even then, what dictates the fact that "CP/M can support only disks as large as a floppy?" The paper just discusses taking into account a disk with 102,400 bytes divided into 800 128-byte CP/M sectors.

Ok the disk allocation map, as the paper says, contains 16 1-byte address pointers. The following is a paragraph from the paper itself:

Quote:
bytes. The technique CP/M uses is to cluster sectors groups of 8 sectors each (see Figure 4). so that there into are a maximum of 100 groups per disk and the address pointers represent group numbers. (On larger disks,CP/M simply uses larger clusters in each group.) Group number 0 includes sectors l-8 of track 3. group 1 includes sectors 9-16 of track 3, group 2 includes sectors 17-20 of track 3 and sectors l-4 of track 4. and so on.
The paper clearly says that there are 16 1-byte address pointers and each represents one group => there are 16 groups and a group includes 8 sectors => 128 sectors in total. But there are 800 sectors... Smilie I know I'm missing something but I don't understand what I'm missing....
 

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dir_ufs(4)							   File Formats 							dir_ufs(4)

NAME
dir_ufs, dir - format of ufs directories SYNOPSIS
#include <sys/param.h> #include <sys/types.h> #include <sys/fs/ufs_fsdir.h> DESCRIPTION
A directory consists of some number of blocks of DIRBLKSIZ bytes, where DIRBLKSIZ is chosen such that it can be transferred to disk in a single atomic operation, for example, 512 bytes on most machines. Each DIRBLKSIZ-byte block contains some number of directory entry structures, which are of variable length. Each directory entry has a struct direct at the front of it, containing its inode number, the length of the entry, and the length of the name contained in the entry. These entries are followed by the name padded to a 4 byte boundary with null bytes. All names are guaranteed null-terminated. The maximum length of a name in a directory is MAXNAMLEN. #define DIRBLKSIZ DEV_BSIZE #define MAXNAMLEN 256 struct direct { ulong_t d_ino; /* inode number of entry */ ushort_t d_reclen; /* length of this record */ ushort_t d_namlen; /* length of string in d_name */ char d_name[MAXNAMLEN + 1]; /* maximum name length */ }; ATTRIBUTES
See attributes(5) for a description of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Interface Stability |Unstable | +-----------------------------+-----------------------------+ SEE ALSO
attributes(5), ufs(7FS) SunOS 5.10 16 Apr 2003 dir_ufs(4)
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