Hands-On Testing and Analysis

Hard Drive Evolution – Part I

Evolution Of Man

Since RAID was originally designed to parallelize disk drives for performance and resiliency, it seems pretty obvious that data protection techniques like RAID are constrained by the technology of the disk, and later solid state, drives they protect. It seems appropriate at this point to take a brief detour from explaining how we protect data from problems with disk drives into how the disk drives themselves have evolved.

While the prep school I went to had a Selectric Terminal connected to a mainframe running APL at IBM Poughkeepsie, the first computer I ever got to lay my dirty little hands on, the Chemistry department’s PCP-8i[1] at university, didn’t have any disk storage.  Grad students had access to the two 280KB DECtape drives, but as a lowly freshman, I had to save my BASIC programs with the 10cps paper tape punch on the ASR-33 teletypes we used as terminals.

By the time I was using hard drives regularly, they broke down into two types; 14” ‘high performance” drives that used the SMD interface and the 5 ¼” ST-506 drives that are the direct ancestors of all the disks we use today.

In the next few posts I’m going to discuss the changes that have affected how we as enterprise or storage architects use disks, and eventually, the SSDs that have emulated them.

The first big change was when disk media stopped being removable. The old SMD drives, as shown above, used removable disk packs. Organizations used disk packs to load data on demand for batch jobs and for all the reasons we make copies today from backups to use as a transport medium. By the 80s increasing track density made pack interchangeability impractical.

Then RAID was such a success that disk drive vendors stopped developing new SLEDs just a few years after Patterson Et Al published their seminal paper. While technologies, like voice coil positioners that first appeared in SLEDs would soon become common all of today’s drives owe their lineage to the ST-506.

In these posts, I’ll pay more attention to things like logical block addressing, which changed how we accessed data than to perpendicular magnetic recording or even Winchester heads, that increased bit density w/o requiring any changes in how the disks were handled.

[1] I bought, but have not yet started assembling a PDP-8i replica kit powered by a Raspberry Pi that is supposed to actually run the OS-8 operating system.

  • Well, back in the day, if you were not attending college or working in a corporate or government organization, you really had limited access to disk-based data storage. The largest physical HDD I ever used was an 8-inch, 10MB HDD in an Onyx single-user system. The Onyx computer used a Zilog Z8000 CPU and the OASIS operating system developed by Tim Williams, which was derived from the PICK System which Dick Pick developed for the U.S. Army.

    The Apple III with its externally attached 5MB Profile HDD was Apple’s first “business” microcomputer and its first flop. The IBM XT with its 10MB internal HDD and its 8-bit Intel 8088 (technically 8/16-bit) became the first affordable “business” microcomputer that was wildly successful. It was replaced by the IBM AT with its 16-bit Intel 80286 CPU (later called brain dead by Bill Gates) and a 20MB internal HDD (the CMI made drives IBM supplied suffered high failure rates) but the IBM AT could be ordered without a HDD, so many IBM AT customers sourced their HDDs from other vendors.

    Back in this era of personal HDD storage you had to “marry” the disk controller (usually a WD1003 series) to the HDD by invoking debug to a memory location in the firmware of the disk controller in order to “low-level” format the HDD. Some vendors, like Novell, used a disk formatting procedure that required you to enter the “bad block” locations from the manufacturer’s label on the HDD as part of the process of preparing the HDD for use.

    We have indeed come a long way in the evolution of HDD storage and it doesn’t look like we have come to the end of the road quite yet for the venerable HDD.

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  • Gerald

    If this is an article about the evolution of disk drives, surely it should start with what storage was (Drums etc),before the introduction of the first disk drive in 1957, then what the first disk drives were like, instead of diving straight into PC disk mode

    • admin

      While I’d certainly be interested in reading a full history of data storage from relays and mercury delay lines to present I started in the industry in 1978 so I don’t have any experience with pre-disk, or even early disk, tech and as I wrote at the beginning of the blog I just wanted to explain the parts of disk technology that affect how disk drives are addressed.

      The full discussion of storage evolution you want would be at least 20,000 words, with a typical blog post being just 500, and I don’t have the time, interest or energy for a 40 part series in the middle of the data protection story I’m trying to tell.

      Please let me know when you’ve written the book you’re looking for, I’d be glad to buy a copy.

      – Howard

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