1.  Field of the Invention
The present invention relates to an apparatus and method for recording and reproducing data, which can be applied to a disk drive apparatus, and more particularly to a technology capable of recording video data while reproducing the same or other video data. 
2.  Background of the Invention
A magnetic tape is a popular recording medium for recording video data such as a TV program and a video cassette recorder (hereinafter referred to as VCR) which records video data onto the magnetic tape has spread very widely.  The VCR is used not only to record TV programs but also to replay a video tape on which movies or other programs (hereinafter sometimes referred to as programs including TV programs). 
The above described VCRs have the following problems and demands.  First, when a plurality of programs are recorded on one video tape, a considerable amount of time is spent for a fast-forward or rewind to search a heading of a program to be reproduced.  This is because the magnetic tape is a recording medium which is not suitable for random-accessing.  Further, some viewers may want to record a TV program while watching this TV program from a desired point of time, or to record a TV program while watching another TV program previously recorded.  Although such desires mean that the viewers want to have a video recorder having a simultaneous recording and reproducing function, conventional VCRs have no such function. 
An example of a digital video unit which would be effective for the above described problems is disclosed in Japanese Laid-Open Patent Application No.  Hei 11-504175.  This digital video unit include a digital video tape recorder and a hard disk drive.  In this digital video unit, data is once recorded on a hard disk at the time of data recording, and then the data is transferred and copied to a digital video tape.  When the data is to be reproduced, the data recorded on the digital video tape is once recorded on the hard disk, and then transferred to a display.  According to the description of Japanese Laid-Open Patent Application No.  Hei 11-504175, the random-accessible hard disk is used to realize quick reproducing from any point of a recorded program, and it is possible to reproduce a program recorded on the digital video tape while recording a different program.  Accordingly, the digital video unit disclosed in Japanese Laid-Open Patent Application No.  Hei 11-504175 may be effective for satisfying the demands of the viewers. 
However, the above digital video unit requires two facilities, i.e. a recording and reproducing apparatus for digital video tapes, and a hard disk drive, which results in high cost.  Although the digital video unit is functionally superior to analog VCRs widely used, the analog VCR is inexpensive and, therefore, the high cost of the digital video unit obstructs its spread.  Consequently, there is a need for an apparatus which is random-accessible and capable of performing simultaneous recording and reproducing with a single recording medium.