File system 2
Basic:
Devices are named by the system as:
- 1 letter indicating device type (D=disk,M=tape)
- 1 letter indicating controller type (K=SCSI,Q=IDE,R=RAID)
- 1 letter indicating controller instance
- 1 or 3 digits indicating device instance (for SCSI it is the SCSI unit)
Examples:
- DKA300:
- SCSI disk unit 3 on first SCSI controller
- MKB0:
- SCSI tape drive unit 0 on second SCSI controller
- DQA1:
- IDE disk on first IDE controller
File types:
VMS file system is *NOT* byte stream based.
Among other things it has file organization and record format.
File organization:
- sequential
- normal file of records
- index sequential
- a database like file where records has 1-10 keys and can be accessed
both sequentially and by key
- relative
- you dont want to know
Sequential files can have several different record formats:
- Variable length
- Normal variable length records. Physical stored as 2 byte with length + record + 0 or 1 nul byte
to pad to an even number of bytes.
- VFC
- Very similar to variable length. Files created by DCL has this format. Physical stored as
2 byte with length + 2 bytes control information + record + 0 or 1 nul byte
to pad to an even number of bytes.
- Stream
- DOS/Windows format. Physical stored as record + CR + LF.
- Stream LF
- Unix format. Used a lot by C and Java software. Physical stored as record + LF.
- Stream CR
- Old Mac format. Physical stored as record + CR.
- Fixed length
- Used by binary files. Physical stored as record + 0 or 1 nul byte
to pad to an even number of bytes.
- Undefined
- Block file. Practically never used.
For a file to be consistent the files actual content and the
meta information in the file header must match.
Using ASCII or IMAGE in FTP is extremely important on VMS.