Quantum XP32150 SCSI Hard Drive (1995) teardown  - Page 1
Forum section: electronics / general

author: sonnytiger
author_rank: Frequent Contributor
timestamp: January 11, 2014, 02:30:43 pm
content: Similar to theCD-ROM teardown(they are from the same machine) a little more interesting (and shorter!).As usual please answer some of my questions if you can, I love learning new stuff.Thanks for watching!

author: SeanB
author_rank: Super Contributor
timestamp: January 11, 2014, 02:36:35 pm
content: Still have a PCI SCSI controller ( Adaptek) sitting around doing nothing, and still have some SCSI disks ( even a 2G and a pair of IBM 1G Deathstars, of which one works and one is dead) along with a SCSI scanner and SCSI Zip drive. I used to use them as scratch drives, as they were fast enough to handle it, and were not on the same bus so did not give contention. The one Deathstar was swap space.

author: sonnytiger
author_rank: Frequent Contributor
timestamp: January 11, 2014, 09:12:16 pm
content: Cool, fun use for them. Was a SCSI port really necessary for a scanner? Doesn't seem like it would need all the bandwidth though maybe it did back then.

author: free_electron
author_rank: Super Contributor
timestamp: January 12, 2014, 12:31:19 am
content: The TI chip is the SCSI interface controllerThe bog guy is the main processor, the phillips chip the read/write channelThe static rams are loaded with firmware at powerup. The flashchip holds just enough code to start the motors, load the heads and go find the real driveware. That is then loaded into the srams and then the drive is ready to roll.They do this because flash chips were slow and expensive. The flash chip has a 150ns access time while the sram can do it in 70nsThey use sram for the firmware as they cannot have timing flutter due to refresh cycles needed like with drams.The channel is an analog block containing signal conditioning , shaping and the error correction/ prediction logic . Most likely PRML. This is where the black magic happens that finds the bits in the noisy signal coming from the heads.The openings in the drive covered by that plastic sheet are for the drive formatter. On one side of the drive there should be a metallic stick covering a rectangular hole.During manufacturing they stick an additional head in there and write a pilot signal at the outermost edge of one platter. The formatter grabs the head arm mechanically (they do not use the voice coils) and writes the servo information and sector markers. The pilot signal tells us where we are on a turn.The pilot is a simple square wave with one pulse missing. The missing pulse tells us where a revolution begins then cou ting ticks gives you an idea where you are angularly.They write the pilot so that the length of each pulse is exact. Meaning that the last pulse of the revolution should line up perfectly with the first one..That signal is then used for speed control once the motors are energised. The discs are rotated mechanically without using the motor while writing the pilot.Once the pilot is ready we can power the motor, look at the frequency of the squarewave read by the pilot head and use that to control the motor speed. Faster moter is faster pi,ot. The missing puls tells you where a revolution begins.Now we can place heads in position and write track and sector markers. This again done mechanically.The platters spin on their own, but the heads are moved mechanically.Once those markers are therr we can remove the pilot head, seal the drive ,spin up and use the read write heads to know where we are as we can see the markers flyby. Now we can start writing error correction data, do a format of empty space, check for bad areas, build the relocation tablesand much more. Lastly the driveware is written in the resrved areas ( typically 5 copies exist) as well as the relocation tables are stored.This drive may be to old but typically also other data is saved such as flying height and head biassing offsets can be stored to compensate for large magnetic disturbances.After this the drive is formatted and goes through a 24 to 48 hour burn-in

author: wilheldp
author_rank: Regular Contributor
timestamp: January 12, 2014, 01:40:30 am
content: Design a hard drive or two in your day, Vincent?

author: SeanB
author_rank: Super Contributor
timestamp: January 12, 2014, 01:59:12 pm
content: The drive will not spin up until it gets a spin up command from the controller, which then turns on the motor and gets the drive ready. You have to send the command after power up otherwise the drive does nothing until it gets a spin up command from the controller. These were often used in an external case with a SCSI lead to plug it into as computer. They did nothing until the computer was connected and powered on.

author: sonnytiger
author_rank: Frequent Contributor
timestamp: January 12, 2014, 08:58:47 pm
content: Thanks for the info, that was awesome! Thanks for letting me know why it doesn't spin up, I actually found PCI SCSI controller lying around, maybe it will support the 8 bit interface this guy (and the CD-ROM) are using.

author: peter.mitchell
author_rank: Super Contributor
timestamp: January 13, 2014, 06:43:39 am
content: Quote from: SeanB on January 12, 2014, 01:59:12 pmIt's also good if you have 32 of them in an enclosure and you want to stagger the spin up so the power supply doesn't shit itself.

author: sonnytiger
author_rank: Frequent Contributor
timestamp: January 13, 2014, 04:34:42 pm
content: no doubt, 50A at 12V isn't easy to supply for most power supplies