For the PC, what are the differences between MFM, RLL, IDE, EIDE, ATA, ESDI, and SCSI hard drives?
Here is a summary of the common hard drive types found in PCs and clones: MFM (Modified Frequency Modulation) This is the original type of hard drive found on PCs. MFM refers to the method of recording bits onto the media of the drive. These drives adhere to the ST-506 hard drive controller standard, which is based on early Seagate drive controllers. RLL (Run Length Limited) RLL drives and controllers also adhere to the ST-506 standard, and are a modification of the basic MFM recording. RLL recording involves squeezing more bits into a track. This is accomplished by using a larger number of sectors (27 rather than 17 or 19), and requires a better quality drive medium than that required for MFM. RLL recording results in a roughly 50% increase in capacity over MFM recording, given the same physical hard drive. It is the controller card that determines whether a drive is used with MFM or RLL encoding. MFM drives may be low-level formatted using an RLL controller, and vice versa. However,
