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H  Harmony (National Research Council of Canada)
Harmony is a multitasking, multiprocessing operating system for realtime control, developed at the National Research Council to serve a need for a flexible system for realtime control of robotics experiments and for other applications of embedded systems where predictable temporal performance is a requirement. Harmony is extensible, configurable and portable, both across different target computers (typically assembled from single-board computers), and across different development hosts.


Helios (Perihelion Distributed Software)

Helios is a micro kernel operating system for embedded and multiprocessor systems. The operating system is modular in design and can scale from an embedded runtime executive up to a fully distributed operating system.


Hive (Stanford University Flash Project)

The Hive OS Team is designing an operating system that is able to operate effectively in a traditional supercomputer environment as well as in a general-purpose, multiprogrammed environment. The latter environment poses significant challenges since general-purpose environments typically contain large numbers of processes making many system calls and many small I/O requests.


HP 3000  (outdated)
HP 3000 MPE and MPE/iX 


HPFS (OS/2 file system)
HPFS is the file system of OS/2, distributed by IBM.
The High-Performance-Filesystem HPFS was obsolete right
at the time of its introduction into the market. It had the
directories organized in multiple bands on the disk so that the
physical ways for the heads on the disk were optimized in
directory-operations. Directories were placed in such a way that the
mean way between data-area and directory-area was optimized. The 3 main
time-consuming factors which slow down disk-acces should get optimized
this way: step-time,head-settle-time and disk-latency(this is the time
the disk needs to rotate until the desired sector is under the head).
Although it gets easily forgotten that every cache has to be filled at
least once before it can function as a cache(which means on the other
hand that operations which reference an item only once have no benefit
from caching), the upcomming of note-worthy caches but more a new type
of disks made this system old-fashion: disks which show to the outside
an geometry which is (very) different from their internal real geometry.
This started when harddisks became intelligent and the disk-manufacturers
could implement a variable-sector scheme to improve the capacity of the
disk. It is clear that a system, which tries to optimize physical ways
gets fooled by a disk which behaves in such a way. (The sentence with
the cache-topic is not to be taken verbatim: caches are a complex
subject. With read-ahead caches the statement may be false!)
R.B.


HURD (Free Software Foundation GNU Project)

Related to: Mach
The HURD is the operating system being developed by the Free Software Foundation as the basis for the GNU Project, which has already produced such well known tools as Emacs and GCC. The Hurd is a personality for the Mach micro-kernel which exports a bevy of services to the application. The Hurd will provide the standard UNIX interface, but should also be much more flexible than standard UNIX.


Hurricane

The Hurricane operating system is a hierarchically clustered operating system implemented on the Hector multiprocessor. Hierarchical clustering manages the system resources in clusters, using tight coupling within a cluster, and loose coupling across clusters. Distributed systems principles are applied by distributing and replicating system services and data objects to increase locality, increase concurrency, and to avoid centralized bottlenecks, thus making the system scalable.

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