Caption: FIGURE 8: The file writing time in sequential access
In SCAN or second phase (steps from 2b to 2c), it verifies if final object's scores are not duplicate; then, it executes a sequential access
for each list [S.sub.i], and stops when a different score is found in each list.
To recoup the added cost of a disk library, it should deliver high enough sequential access
to replace ten or more tape drives.
Host Data Connect already supported the main IMS database organizations - HISAM (Hierarchical Indexed Sequential Access
Method), HIDAM (Hierarchical Indexed Direct Access Method), HDAM (Hierarchical Direct Access Method), SHISAM (Simple Hierarchical Indexed Sequential Access
Method), HSAM (Hierarchical Sequential Access
Method) and SHSAM (Simple Hierarchical Sequential Access
It may be noted that a sequential access
to semantic and phonological information is a frequent feature of current models of speech production.
A sequential access
stream resulting from a tight loop, for example, may not allow sufficient lead time between the use of block b and the request for block b + 1.
Of portability I will have more to say later, but we all access information in books randomly by riffling their pages (which is why we prefer books over the "sequential access
" of microfilm), and publishers assist us in this activity with tables of contents, indexes, running heads, chapter titles and subheadings.
Of course, there's a cost involved, even for die least expensive CD recorders, but you don't really want to back up hundreds of megabytes of files to floppies nor would you enjoy putting up with the sequential access
of streamer tapes when you have to restore a file or two.
RBASE and dBASE have a behavior similar to COBOL where sequential access
without indices is much faster.
Using iSMART's disk usage information, such as read/write, random and sequential access
, and block sizes, users will also be able to verify that they bought the ideal product for their specific application, fine tune software settings for better performance, and even save money by ensuring that they choose the most suitable drives for their applications in the future.
Some architectural issues remain facing traditional tape storage and include: 1) the time to first byte of data (milliseconds for disk and seconds for tape); 2) tape supports sequential access
only (disk supports random and sequential access
); and 3) the recovery time for data is longer for tape than for mirrored or replicated disk (minutes or hours on tape compared to seconds normally for mirrored disk).