HP MPE/iX 6.x Operating System File Structure, File Types, The adjustment the File System mak es for odd-byterecord sizes is important

for data. If the ￿le is binary , the byte is accessible. Figure 6-13 belo w, shows how the File System handles odd-b yte record sizes in Compatibility Mode for device

Figure 6-13. Odd-byte Record Sizes

The adjustment the File System mak es for odd-byte record sizes is important

when reading tapes created on other systems. If the tape has actual odd-b yte length records that are blocked, you cannot specify the exact b yte length and bloc king factor and obtain accurate results, because y ou will get a cumulative e￿ect of each successive record being \o￿" by more bytes. It is a recommended practice to handle the bloc k as one large logical record in one block and then programmatically pull apart the odd b yte lengths. You can use the DEBLOCK option of FCOPY for this purpose.

File Structure

When you create a ￿le, the File System imposes a structure and access method on the con tent of the ￿le. Access to records in a ￿le are dictated b y the ￿le type speci￿ed at ￿le creation. Important factors in creating a ￿le are discussed belo w.

File Types

Depending on your intended use of the ￿le, y ou can specify the follo wing ￿le types:

Standard ￿le, whic h is the most common t ype of ￿le. It is structured as a group of records, beginning with record 0 and ending with record n-1 , where n is the maximum speci￿ed in the ￿lesize option. The Standard ￿le t ype is the default created when y ou ￿rst open a ￿le. Examples of Standard ￿les are Editor ￿les and program ￿les.

KSAM ￿le. Keyed Sequential Access Method (KSAM) is a method of organizing records based on the content of key ￿elds within the records. Eac h record in a KSAM ￿le con tains a primary k ey ￿eld; the contents of the primary k ey ￿eld determine the primary logical

File System 6-25