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1Clear out junk files and repair common Windows errors2Scan for outdated or missing drivers - takes under a minute3Repair Windows errors before they cause bigger problemsA sequential-access storage device retrieves or writes data by moving through consecutive storage locations in order. A tape drive is the standard example: reaching a particular item can require the drive to pass earlier data first.
What does “sequential access” mean?
The term describes how a device reaches data, not how an application organizes information. In IBM’s TS4500 glossary, sequential access is processing information on a tape cartridge in a way that requires access to consecutive storage locations, or logical blocks, on the medium. IBM’s glossary also identifies a tape drive as a Sequential Access Device in SCSI terminology.
This does not mean that every file must contain records in a meaningful top-to-bottom order. It means that locating a storage position involves proceeding through locations in sequence.
How a tape drive accesses data
A tape drive reads and writes data on magnetic tape. To reach a particular piece of data, it may need to move the tape past preceding data and physically position itself at the requested location. Oracle’s Secure Backup glossary describes tape drives as sequential-access because they must read preceding data to reach a particular item. Oracle Secure Backup 19 glossary
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That positioning can take time. IBM notes that tape drives may need time to locate data physically. It also explains that changing a file stored on tape can result in blocks being appended at different tape locations, which may slow later reads. IBM Storage Archive LE performance considerations
Sequential access versus direct access
| Feature | Sequential access | Direct access |
|---|---|---|
| How data is reached | The device processes consecutive storage locations; reaching later data can involve passing earlier data and positioning the medium. | The device can access nonconsecutive locations directly. |
| Typical example | Magnetic tape drive. | Disk drive, called a direct access storage device (DASD) in IBM z/OS materials. |
| Practical effect | Locating an individual item may take time, so tape is commonly used for workflows such as backup and archiving. | Supports direct access to a requested location or dataset. |
The comparison is about the device, not necessarily the order of the data. IBM explains that some datasets on disks may be stored sequentially even though disks support direct access. In the cited z/OS context, only sequential datasets can be stored on magnetic tape. IBM: Where are data sets stored?
Where sequential-access storage is used
Tape is used in storage workflows that write or retrieve data in larger sequences, including backup, archiving, migration, database backup, and off-site transfer. IBM Storage Protect lists these activities among physical-tape uses. IBM Storage Protect: Data storage devices
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“Sequential access” is a description of access behavior, not a claim that tape is the only possible sequential-access storage type. IBM Storage Protect’s device taxonomy also includes sequential-access disk. The conventional SCSI example of a Sequential Access Device, however, is a tape drive.
What is a tape cartridge?
A tape cartridge packages magnetic tape so it can be handled and used without separating the tape from its container. Compatibility depends on the tape format and the drive; a cartridge is not automatically usable in every tape drive. IBM DS8000 glossary
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