hard drive sectors

Each track is further broken down into sectors. A sector is normally the smallest individually-addressable unit of information stored on a hard disk. Each sector of data on the hard disk contains 512 bytes, or 4,096 bits, of user data (1 byte=8 bits it is octal). In modern drives the larger outer tracks hold more sectors than the smaller inner ones. All information stored on a hard disk is recorded in tracks. The tracks are marked by number, starting from zero, starting at the outside of the platter and increasing in number as you go in.

The first PC hard disks typically held 16 sectors per track. Details as below from Seagate

Capacity:Speed:Average Read Time: Cylinders:Heads:Sectors: 85.7 MB3500 rpm16 ms74814  (Physical Only 2 Heads)16

Resource:  Examples: 16 (e.g. the st9100ag), 17 (e.g. the st325ax), 24 (e.g. the st9190ag), 27 (e.g. the st280a), 28 (e.g. the Maxtor 8051A), 29 (e.g. the st1162a), 32 (e.g. the st9051a), 34 (e.g. the st3195a), 35 (e.g. the st3283a), 36 (e.g. the st1239a), 38 (e.g. the st3211a), 47 (e.g. the st9150ag), 50 (e.g. the st3291a), 51 (e.g. the st9385ag), 52 (e.g. the st9240ag), 53 (e.g. the st3271a), 55 (e.g. the st2274a), 56 (e.g. the st2383a), 59 (e.g. the st9550ag), 60 (e.g. the st9300ag), 61 (e.g. the st1401a), 62 (e.g. the st3385a), 63 (e.g. the st3270a).

(Please go to Seagate website to get the details of above HDD.)

A sector includes only 512 Bytes?
In addition to these bits (512 Bytes of user data), an additional number of bits are added to each sector for the implementation of error correcting code or ECC (sometimes also called error correction code or error correcting circuits). These bits do not contain user data; rather, they contain information about the data that can be used to correct any problems encountered trying to access the real data bits.

Block Mode: More than one sector can be transferred on each interrupt notification. Newer drives allow you to transfer as many as 16 or 32 sectors at a time. These sectors are known as Clusters. On some systems you will find an option in the system BIOS called block mode. You may set it on BIOS.

Block mode is a performance enhancement that allows the grouping of multiple read or write commands over the IDE/ATA interface so that they can be handled on a single interrupt.

Example of a BIOS option for the IDE Block Mode feature (boxed in red)