HDDs (Was: PDP-11/45 RSTS/E boot problem

Liam Proven lproven at gmail.com
Wed Feb 20 06:49:23 CST 2019

On Tue, 19 Feb 2019 at 22:00, Fred Cisin via cctalk
<cctalk at classiccmp.org> wrote:
> Yes.
> I was thinking in terms of slightly older drives than that, particularly
> 5.25"
> Getting at the slider on newer drives wouldn't be practical.

Probably not. I suspect that ITRO 90+ % of the people I work with have
never seen a 5¼" hard disk. CD-R or DVD, yes, but they're possibly
unaware that HDs used to come in that formfactor.

I've had arguments with people over the meaning of "full height" and
"half height" before, because to them, the physically biggest drive
they've ever seen, in ancient kit (to them), is a CD drive. So
logically that _must_ mean "full height" because nothing is bigger,
therefore they redefined all the terms in their heads...

> The RAMAC came out in 1956?  The platters are 24" diameter.  Each platter
> was almost 100K!  But, with 50 platters, it maxed out at almost 5MB.
> When Nikita Khruschev made a peace mission to USA, they took him on a tour
> of the RAMAC facility.  But, they wouldn't let him go to DisneyLand! (THAT
> had repercussions in the Cuban missile crisis)

11 years before I came out, then.

I've seen and played a bit with some machines with 8" floppies, but I
think that's the biggest. I never saw the VAX 11-780 I learned Fortran

> You could run Xenix on an XT!

True, but I think it wasn't a lot of use for commercial multiuser
accounts systems. They were the main market for Xenix for my
employers, early in my career. My 1st job sold Tetra, mainly

Checks... huh, later bought by Sage:

Later, I worked for places that sold other things, like SystemsUnion.
Happily a market I left long ago and have forgotten about.

> The stock IBM XT HDD controller (Xebec) had physical solder pads for drive
> type, and supported 5MB, 10MB, 15MB, and 25MB drives.  The 25 was, of
> course, best (if you could get one) and would permit a 10MB DOS partition
> dual booting with 15MB Xenix.  Was that the first "dual boot" in the
> PC world?  (or was there a CP/M-86 dual boot option once they added HDD
> support?)

DOS+ could dual-boot with PC DOS, as I recall. I think CDOS could too.
So, probably.

I'm quite glad the XT was fading away as I got into the PC business.
They were weird and constrained.

Still, not knowing about them means people working on PCs now don't
know where it came from...
> I used a lot of ST4096 drives.  Needed a second AT power supply for the
> second one.

Ha! Yes, I can believe that. IBM did under-spec the PSUs, though.

> I use 2TB 2.5" 7.5mm Seagate/Samsung drives for MP4s of movies in
> laptops and with a Seagate GoFlex-TV (media streamer with SATA slot)
> But, I finally filled 2TB
> Currently, that is the largest 7.5mm 2.5" drive available.  But SSDs are
> now available in 2TB, so when that price comes down, . . .
> Heard about the NSA Utah Data Center?
> https://nsa.gov1.info/utah-data-center/
> That's a LottaBytes!


Reminds me... I should buy a few more tibs, consolidate and rearrange
some stuff.

I wonder why megs and gigs caught on, but there's no common shorthand
for terabytes?

Liam Proven - Profile: https://about.me/liamproven
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