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1.引言用成组编码记录(GCR)方式提高磁带记录密度引起了国内外的注意。成组编码记录方式采用不归零制记录1和0,但要求先将数据进行同步编码,使得记录的编码后数据在每一道中相邻的0的个数至多为2。在 IBM 6250位/时系统中,同步编码采用“四变五”方案,即将4位数据转换为5位数据,在这五位中至多2个0相邻,边上至多1个0。在读出时,从带面读出的是经过同步编码的数据,故需要经过译码才能得出原来的数据。对于四变五同步编码,这种同步译码为“五变四”即将5位数据还原为4位数据。为了提高可靠性,当记带时,在同步编码
1. Introduction The use of group code recording (GCR) to improve tape recording density has attracted domestic and international attention. Group coded records using non-return zero record 1 and 0, but requires the first data synchronization encoding, making the recorded encoded data in each lane adjacent to the number of 0 up to 2. In the IBM 6250 bit / time system, the synchronization encoding uses a “four-to-five” scheme that converts 4 bits of data to 5 bits of data, up to two of which are 0 adjacent and up to one zero on the edge. Read out from the tape surface is read through the synchronous encoding of data, it needs to be decoded to get the original data. For four-to-five simultaneous encoding, the simultaneous decoding of “five to four” about 5-bit data is reduced to 4-bit data. In order to improve the reliability, when the recorded tape, in the synchronization code