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先进的编码技术对提高数字磁记录系统的位密度和可靠性作用很大。本文扼安地叙述了编码技术的发展过程,重点介绍改进型调频制(MFM)和成组编码制(GCR)广泛应用后,新提出的几种实用价值较高的游程长度受限码(RLLC):固定长度的按组编码(0,3;8,9;1);可变长度固定变比的按组编码(1,7;2,3;2);可变长度固定变比的位间相关型按位编码[(1,3;1,2;2)或改进的改进型调频制(M~2FM)]和固定长度的位间相关型按位编码[(1,3;1,2;1)或零调制(ZM)]。(0,3;8,9;1)和(1,7;2,3;2)的位密度极限分别比GCR和MFM约高12～23％和20～30％。M~2FM具有比MFM更大的相位余量,是软盘系统的一种倍密度(6.400～6,536位/英寸)实用方案。ZM具有不包含直流成分的独特优点,已在采用旋转磁头的IBM3850大容量磁带存储系统中应用。
Advanced coding techniques have a great effect on increasing the bit density and reliability of digital magnetic recording systems. In this paper, the development of coding technology is described briefly. After the extensive application of MFM and GCR, the newly proposed run length limited codes (RLLCs) ): Fixed-length group-by-group coding (0,3; 8,9; 1); Variable-length fixed ratio by group coding Inter-related bit-coded [(1, 3; 1, 2; 2) or improved modified FM (M ~ 2FM)] and fixed- 2; 1) or Zero Modulation (ZM)]. The bit density limits of (0,3; 8,9; 1) and (1,7; 2,3; 2) are about 12-23% and 20-30% higher than those of GCR and MFM, respectively. The M ~ 2FM has a larger phase margin than the MFM and is a practical solution for double density (6.400 ~ 6,536 bits / inch) of a floppy disk system. The unique benefits of ZM, which does not include DC components, have been used in the IBM 3850 high-capacity tape storage system with rotating heads.