IBM Corp has developed a new technique for squeezing more data onto disk drives and is using it first in a new 2.5 drive that stores 810Mb – not quite a record if Data Storage International Inc’s claim to have completed design of a 1Gb 2.5 drive stand up to scrutiny (CI No 2,396). The new No-ID sector format eliminates the need to store disk-sector identification information with each sector, holding it instead in memory in the disk controller. The housekeeping data typically takes up 10% to 15% of the total storage area, depending on how big the sectors are. In combination with magnetoresistive heads, the technique increases storage capacity 28%, IBM claims. Eliminating the need to read the identification data also cuts read and write times. IBM notes proudly that ID fields have been essential features of disk drives since the company invented the devices in 1956. The No-ID sector format uses the drive’s servo system to locate the data sectors and stores a defect map of the disk in the controller’s memory, and also eliminates the need for a recovery area at the end of each track in which the head can switch between read and write modes. The increase in density is made possible by the fact that the head does not need to read an ID field before writing: it is not possible to move the head between these two positions fast enough to be able to read the fields during writing, so track widths had to be limited to enable reliable off-centre reading of the ID-fields, whereas with the new technique, tracks can be as close together as the magnetoresistive head will allow. The new 2.5 platters therefore store 5,050 tracks per inch, up from 4,300. The new 810Mb drive has three platters and comes in AT and Fast SCSI-2 versions. The DVAA 2810 is an AT drive with 8.3M-byte per second data transfer rate, the DVAS 2810 is the Fast SCSI-2 one, with 10M-byte per second transfer. The platters spin at 3800rpm; average seek time is 14mS. Out now in volume, each costs $795 for samples.
