Post B4T2QD5Cm4VfCaotg8 by wrosecrans@mstdn.social
 (DIR) More posts by wrosecrans@mstdn.social
 (DIR) Post #B4SosTQIDVrOd8GaFk by argv_minus_one@mastodon.sdf.org
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       TIL that the #IBMPC didn't come with just #MSDOS. It had *four* operating systems available from the start.I imagine that's why it was designed to boot from disk, and not a fixed ROM operating system like the #Macintosh.The four original IBM PC operating systems were:* #ROM #BASIC* UCSD p-System, an OS built around a #bytecode interpreter for #Pascal* CP/M-86, an x86 version of #CPM* #IBM PC #DOS, a knock-off of CP/M from a little-known company called #Microsoft#retrocomputing
       
 (DIR) Post #B4SowoatRhAtRuILce by domi@donotsta.re
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       @argv_minus_one CP/Mfrom the startgiant asterisk :) it took them like a year until the port got to the market. big reason why history went like it did.
       
 (DIR) Post #B4T2QCZefNGxck3hVA by gloriouscow@oldbytes.space
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       @argv_minus_one calling ROM BASIC an operating system is a very charitable interpretation
       
 (DIR) Post #B4T2QCpFjNkWP7M9oW by gloriouscow@oldbytes.space
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       @argv_minus_one it cannot even access your floppy drives
       
 (DIR) Post #B4T2QD5Cm4VfCaotg8 by wrosecrans@mstdn.social
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       @gloriouscow @argv_minus_one  The lowest spec PC at launch didn't even have floppy drives.  In 1981, that was still a credible microcomputer.  Needed to upgrade to at least 32 K of RAM to get supported disk drives and DOS.The expectations around a minimum viable product in those days were still bare minimal.
       
 (DIR) Post #B4T2QDHy0ciZqAn5ZQ by gloriouscow@oldbytes.space
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       @wrosecrans @argv_minus_one This is a hotly debated topic among PC nerds.  "Did anyone actually ever buy a PC without a floppy drive?" you are correct it was an option. You could set them dip switches to 0 floppies.IBM published exactly one title on cassette, a copy of the IBM PC Diagnostics.  This happens to be the only commercial release of any software for the PC on cassette.I feel like if anyone did they had to be a remarkably undemanding type of consumer.  "So, what kind of software titles are available?"  "Uh, you can run the diagnostics.""Stop. You had me at diagnostics."
       
 (DIR) Post #B4T2QEFsPsdkpyovx2 by gloriouscow@oldbytes.space
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       @wrosecrans @argv_minus_one To elaborate on why you need 32K of RAM to use a floppy disk -The PC BIOS boots from a floppy by reading the boot sector into the 512 bytes starting at 7C00h; which is 31744 decimal.  This is more than 16k, if you needed me to point that out.Meaning if you only had 16K of installed, the PC just does a DMA transfer to nowhere and then jumps right in, YOLO and all.I suppose it is unfair to say that 32K of RAM is strictly required. There is an very small but not still nonzero chance that enough cosmic rays bombard the system at that exact moment that the CPU executes a valid program there anyway.
       
 (DIR) Post #B4T2QEpgGlHQd1ZWl6 by gloriouscow@oldbytes.space
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       @wrosecrans @argv_minus_one there is a dumb party trick you can pull though, you can set the dip switches for 16K but actually have 32K installed, this at least lets DOS boot.After booting DOS 1.0 will still think you only have 16K of RAM so you can properly enjoy a somewhat fraudulent 16K IBM PC experience.