Modern hard disk drives use one of two interfaces: IDE (ATA) – Integrated Drive Electronics (also called ST506 drives) and its variants (EIDE – Enhanced Integrated Drive Electronics, or the SCSI (Small Computer System Interface). You can tell immediately by looking at the back of the hard disk which interface is being used.
1. IDE hard disks use a 40-pin connector, and SCSI hard disks normally use either a 50-pin or a 68-pin or 80-Pin connector.
2. Note: Older MFM (MODIFIED FREQUENCY MODULATION), RLL (RUN LENGTH KIMITED) and ESDI (ENHANCED SYSTEM DEVICE INTERFACE) hard disks used two data connectors, one 34 pins and the other 20 pins.
3. The cable usually has a red stripe to indicate wire #1 and the hard disk uses markers to indicate the matching pin #1.
Led Connector: Originally, hard disks shipped with a faceplate (or bezel) on the front. The hard disk was mounted into an external hard drive bay (in place of a floppy disk drive) and an LED was visible on the front of the drive to indicate when the disk was in use. It was quickly realized that having the disks mounted internally to the case made more sense, but the LED was still desirable. So an LED was mounted to the case and a wire run to a two-pin connector on the hard disk itself. On newer systems that run with integrated IDE controllers on the motherboard, the LED is connected to a special connector on the motherboard itself.
Drive Bay: The entire hard disk is mounted into a physical enclosure designed to protect it and also keep its internal environment sealed from the outside air. This is necessary because of the requirement of keeping the internal environment free of dust and other contamination that could get between the read/write heads and the platters over which they float, and possibly lead to head crashes.
DRIVE BAYS are where internal hard drives are mounted inside the PC. They come in internal and external versions, based on whether they allow access from the exterior of the case, and also in two standard sizes: 5.25″ and 3.5″.
Now, we have rough understanding of the HDD components now and how these parts work in architecture. But you may find the importance of the microprogram inside the HDD. No matter how precise the HDD design, they are a stack of meaningless mechanical parts.