Information and Communication Technology File Access Modes Tsang Wing Luen S4C (28)
File Access Modes • Sequential Access Mode • Direct Access Mode • Also called Random Access Mode
Sequential Access Mode • Not common • Has to wind the tape until the desired record is underneath the read head • Need longer time and unpredictable • Mainly used for back up and recover of database and files of servers • E.g. magnetic tapes
Direct Access Mode • When the target location is moved underneath the read/write head, the reading or writing process operation can proceed.
Hard disk • The most common storage • Most essential secondary storage device • Has high reliability, speed and capacity • Need shorter time and predictable to access data (access time: around 10ms) • Besides hard disk, floppy disk, optical disk and USB flash drive also support direct access mode.
Optical disks • Operate in direct access mode • Limited in capacity and speed of data access • Used for storage of multimedia files • E.g. DVD-R, DVD-RW, CD-R, CD-RW