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Why were floppy disks and hard disks chosen as the boot device for most PCs (only recently replaced by NAND flash)?

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    ... because what else would those computers use? Flash memory didn't exist back then.
    – Renan
    Commented Jun 1 at 19:15
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    Somehow I fail to see any basic research about media history (as well as common sense) applied with this question.
    – Raffzahn
    Commented Jun 3 at 12:07

4 Answers 4

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  • Because tape was too slow and flash drives didn't exist.

  • "Thin clients" were diskless PCs that booted from the network. The antique option for Network Boot PROM was still there, the last time I looked.

  • What other boot device would you suggest? An Iomega Zip drive? All available boot devices were listed in the BIOS options, or else they couldn't be selected for the as a boot device.

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Boot media has requirements to be instantly available, reasonably sized and reliable. Floppy disks were a jack-of-all-trades medium, performing adequately in all technical and economic senses: fast, random access, reasonably large, read write, removable, common off the shelf part. Later, hard disks became cheaper, more reliable, and were much faster and with larger capacities than floppy disks could provide. Successive successful replacements for boot media, such as SSDs, supplant floppies and hard disks by performing their use cases better; allowing the user to boot quickly, or housing the complete operating system itself to store and manipulate documents, and configure and alter software as they please.


I think your question is lacking a few qualifiers - what I think you're really asking is why floppy disks and later hard disks were chosen as the boot device for PCs over the alternatives. And are you asking about industry, business or the home, which are different scenarios?

Let's look at some alternatives to floppy disks and hard disks.

Digital tapes have the capacity but are expensive and not great for random access. Admittedly I don't know much about them beyond that. The early PCs didn't have a large amount of RAM, so loading a large operating system from a cassette with a huge capacity and going back and forth in little chunks for drivers or applications makes not a large amount of sense.

Audio cassette tapes are inexpensive but unreliable and exceptionally slow. RC:SE has a question about that: Did computer games for Commodore 64 really take "25 minutes" to load "if everything went alright"? . The summary is that simple arcade games can take half an hour to load from audio cassette. Useless.

(Rewritable) ROM is fast and relatively big so let's look deeper into that. Your observation of NAND Flash is appropriate since strictly speaking all PCs from the earliest to the most modern do begin execution with a form of ROM, or something playing the role of ROM.

In the original PCs, for many decades, this would be the BIOS ROM: a physical set of mask ROM chips holding the initial set-up sequence and routines for interfacing with peripherals and mass storage devices. The original PC didn't have to boot from floppy disks - it could boot straight into its own IBM BASIC editor environment stored in ROM, just like a Commodore 64 or a ZX Spectrum. The IBM PC could boot from floppy disks, and the code necessary to do so would be stored in the IBM BIOS' ROM. The original PC didn't support hard disks directly, but supported ways for the user to supply additional ROMs in controller cards that would augment the system to support further mass storage devices.

A PC booting off detachable ROM cartridges like a video game console doesn't sound out of the question, does it? IBM thought so, so they developed the IBM PCjr computer which did take software cartridges.

enter image description here

Image by 'Binarysequence'. https://commons.wikimedia.org/wiki/File:IBM_PC_Jr_BASIC_Cartridge.jpg

But compared to floppy disks, cartridges are more expensive and of little use for transferring documents. Mask ROMs were smaller and more expensive to produce. A ROM cartridge allows you to use that piece of software, and that's all, but people wanted to use arbitrary programs as and when they pleased.

Personal computers that booted from ROM that had built in applications would have had to have been of exceptional quality in order to succeed. In the case of the Commodore Plus/4, that was not the case. But in the case of handheld devices like the Psion series of personal organisers - such as the Psion Series 3, 5 and Siena, the CPU hardware, keyboard and ROM software would be a workable match and the product would sell.

You've suggested bubble memory below. There is an open question on that :) What happened to bubble memory - is it still being sold? My understanding is for first stage booting mask ROM is massively more convenient (bubble requires over a minute of physical warm up time before it becomes usable (!)) and conventional semiconductors were always more cheaper and productive to manufacture. For second stage booting, floppy disks are considerably cheaper than bubble, and instant also. I saw a photo of a bubble memory expansion card for the IBM XT PC, so it wasn't completely forgotten, but it wasn't the right tech at the right time for booting.

A bubble memory based floppy drive emulation development card by Intel for the IBM PC is mentioned on this page connecting through the floppy drive interface. So if you'd like to second stage boot from a bubble memory device, it seems you could. It was always being considered by big companies as an option it wasn't a pragmatic one.

That exhausts the typical options for a 1980s device. CD-ROMs would become available later on and progressively cheaper, but as a late-coming read only medium, it would have to have been faster or cheaper or more convenient to displace hard disks as a boot medium. No doubt in certain industrial scenarios an authenticated read-only boot medium is exactly what you want. For a home or office user, you'll most likely be wanting to use a complete operating system with the option to add new software and write documents, so any alternative boot media will be competing with the concept of a large, versatile fixed hard disk or removable floppy disk.

You haven't considered network booting, which would have been possible with network cards. Why didn't that become common? In some business environments I would expect it did - thin clients being almost a conceptual progression from dumb terminals. But in the home, it would require a whole second computer to boot off, defeating the point of a single 'solves all your problems! recipes! accounts!' machine that PCs have been marketed as since their beginning.

Other kinds of later personal computing devices do boot from read-only media or non-removable ROM, but without there also being an easy-to-use type of removable writable media associated with them for the user to do work on them, they're not typically referred to or thought of as PCs. Tablet PCs, handheld PCs, games consoles, and so on. I've already mentioned personal organisers, like the Psion series above. Organisers became organiser-phones, then just smartphones, running a heavily protected base kernel in PROM, with applications in NAND in another partition. If the economics worked out, removable block device flash units could have been common for booting PCs, like on the Nintendo DS and Switch, but as it is floppy drives and hard drives were bigger and cheaper first so that's what was used (and I'm aware that's a circular argument!).

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    Back in the 1980's I used a photolithography mask making machine that booted up off of paper tape. (Yes, there were spare boot tapes available if it were to get shredded in the mechanism late at night, which was when I was using it.)
    – Jon Custer
    Commented May 31 at 18:27
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    Hard to say - it has been a long time and I have a mind like a steel sieve at this point. Likely the university got it used, so a 1970's system. My guess would be a PDP-6 system integrated into the system by the mask maker manufacturer. Pictures of the (a) PDP-6 paper tape reader look not-wrong (can't say it looks perfectly right)l
    – Jon Custer
    Commented May 31 at 18:32
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    I noticed you tagged the original question 'Google'. I'm not sure what you mean in this context. Do you mean Google Chromebook or Pixel or something else?
    – knol
    Commented May 31 at 22:41
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    Google's servers in 1999 were a pile of off shelf PCs, workstations and servers. blog.codinghorror.com/google-hardware-circa-1999
    – knol
    Commented Jun 1 at 7:33
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    Google was an experimental software project in 1999, not an experimental hardware project. Why would they use anything other than standard, therefore inexpensive parts? And being an always-available online service, what they booted from and how fast it was wouldn't have been business-sensitive to Google themselves at that point. Maybe you might be interested in looking into something like weather modeling supercomputers (a random guess?) if you suspect that large servers would have pursued other types of hardware?
    – knol
    Commented Jun 2 at 8:52
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I am going to assume by "most PCs" you mean the IBM PC and more or less compatible computers and their followers. If not, define what you mean by PCs.

Floppy disks were the only boot device for first PCs because hard drives for PCs did not yet exist.

PCs had no suppot for hard drives until hard drives became available for PCs and they came with adapter cards that expanded the BIOS to access the drives or motherboard BIOSes supported hard drives directly.

May not be retro any more, but after hard drives, booting from other devices became available, such as network (provided by BIOS expansion on network card), ATAPI CD drives and other ATAPI devices such as Zip and LS120 drives, and then from USB drives.

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  • AFAIK it was standard industry practice and not limited to IBM PCs.
    – Yuhong Bao
    Commented May 31 at 18:33
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    @YuhongBao Both the Acorn Archimedes and Atari ST are examples of professional-level OSes that sit entirely in ROM; the Macintosh and to a lesser extent the Amiga also shipped with a fair amount of ROM providing a fair amount of the libraries that underlie their environments. Though, notably, the earliest of those examples sits a full three years after the launch of the PC, after a corresponding reduction in the price of ROMs.
    – Tommy
    Commented May 31 at 18:49
  • @Tommy Original Mac did work from ROM. Disk were only needed for patches and add ons.
    – Raffzahn
    Commented Jun 3 at 12:02
  • @Raffzahn I think that if you start an original Mac without a disk in the drive, it'll just show you the floppy disk with the question mark in it. I cannot currently prove this however, so I'll have a quick search and possibly find out that I'm wrong.
    – Tommy
    Commented Jun 3 at 15:07
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    @Tommy True, it looks for the system file within the system folder. It contains fonts, icons and other localized resources. IIRC a dummy file will do it. After that it looks for the finder to be executed. But it's been a good 40 years since I played with that - so I may miss some detail. In any case, everything of the OS is in ROM.
    – Raffzahn
    Commented Jun 3 at 21:38
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Many early PCs came without disk drives of any type (either floppy or hard). Many either required toggling in some initial program code via front panel switches (as with the original Altair boxes, and the Cosmic Elf, etc.), or booted from ROM, on the motherboard, or in a cartridge, into a monitor or a Basic interpreter (Apple I and early Apple II models, Commodore Pet, TRS-80 Model 1, and many others.).

When more sophisticated file systems and operating systems for PCs were developed, floppy drives (8 inch and later 5.25 inch) were one of the cheapest and thus affordable random access storage mechanisms available.

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