I don't follow your comparison of PDS/e and Unix filesystems.
If I saw correlation of Linux filesystems with PDS, I glossed over it as
stoopid. (Here again, I feel your pain.)
My understanding is that PDS is (historically) a means of segmenting one
data set into related chunks. They're "related" because they're all
members of the same data set.
The real "filesystem" for MVS is the catalog, and the "files" are the
data sets, whether partitioned or not. Hopefully the VTOC and the
catalog match-up. That's not always required.
PDS are also flat, unless something has changed recently.
PDS is more like the partition table on a PC disk. (Though the latter
doesn't use names, per se, and tends to have less "members".)
You're absolutely right: a Unix filesystem is a file containing files.
There the similarity to PDS ends.
Unix filesystems have two important features: inodes and directories.
The inodes are usually invisible. The directories connect inodes with
names, which is what people see.
A hard link is where two files (by name) refer to the same inode. A
symbolic link is a special kind of Unix file that names another file.
Here's a neat trick: you can make a hard link to a sym-link.
There are only a handful of actual file *types*:
* plain file
* directory
* character special (like a terminal)
* block special (like a disk drive or partition thereof)
* symbolic link
* and a couple others added by OMVS ... really
As I recall, other Unix vendors added their own special types. But I've
slept since then and memory is fuzzy (or maybe I dreamed it).
Not all "filesystems" mountable on a Linux system properly implement
inodes and directories. They therefore lack some functionality in
practice; it can be significant.
Some features of Unix (and Linux) filesystems are a step up from
historical MVS data sets. It is sadly still possible to have a data set
with no time stamp.
So you can count that as one thing Unix did that MVS has learned
afterward. (Not a slam on z/OS. Just keeping things in perspective.)
-- R; <><
On 7/29/23 12:28, Jon Perryman wrote:
Can anyone provide the definition of MAINFRAME? The ARS Technica article is
complete nonsense because the mainframe is a state of mind and nothing to do
with reality. Can anyone prove me
wrong?https://arstechnica.com/information-technology/2023/07/the-ibm-mainframe-how-it-runs-and-why-it-survives/.
The IBM z16 is just 4 motherboards containing 16 CPU and many PCIe slots. Linux
will run on an IBM z16. Is a PC also mainframe? Forget zPDT because I suspect
it still uses a PCIe zCPU card. I can't say with any certainty, but I suspect
that z/OS will run on a PC by using Hercules. What is the definition of
MAINFRAME?
1. CPU does not make a mainframe: The smallest IBM z16 (39 user cores of the 64
cores) is the same as an AMD Ryzen 4.2Ghz CPU (64 user cores of 64 cores). The
largest IBM z16 (200 user cores of the 256 cores) is the same as 4 AMD Ryzen
CPU on 1 motherboard (256 user cores of the 256 cores). Both are CISC CPU (AMD
uses X86 instructions versus IBM z instructions). IBM Telum (5.2Ghz) has a
slightly faster clock than AMD Ryzen (4.2Ghz) but is offset by the 25% extra
user cores. IBM z16 has 4 motherboards for 16 CPU and the same AMD Ryzen would
need 1 motherboard for 4 CPU.
2. Hardware does not make a mainframe. IBM z16 has PCIe and ram which are also
on every modern motherboard. IBM z16 chooses not to include other hardware
(e.g. SATA, IDE, WIFI and more). Motherboards choose not to have 1,600 PCIe
slots. IBM could allow PCIe graphics cards, mice, keyboards and more.
Essentially, IBM z16 and AMD Ryzen can implement the same hardware if there was
enough customer demand.
3. OS does not make a mainframe. Linux running on z16 doesn't make it mainframe
Linux. There's nothing stopping Linux from taking advantage of every z16
hardware feature (e.g. 1,600 PCIe slots) but no one is willing to build the
Linux software. IBM hasn't duplicated z/OS software features in Linux.
4. Software does not make a mainframe. IBM sells DB2 for Linux and DB2 for
z/OS. DB2 for Linux runs on all hardware including z16. With Linux, you can
still run DB2 on z16 but large customers choose DB2 for z/OS.
ASK YOURSELF: Other than design philosophy, name 1 fundamental difference
between IBM z16, AMD Ryzen and the software.
ASK YOURSELF: Since design philosophy is the only difference, name the
philosophy that makes a mainframe.
Despite the story's false claims for z/OS relevance, it is ignorance in the
Linux community that makes IBM z/OS relevant. Specifically, it's the lack of
design in Linux. Consider DB2 for Linux and DB2 for z/OS which are the same
product both from IBM and available on an IBM z16. Linux people tell you they
provide the same results, but they ignore the intrinsic capabilities of z/OS
design. DB2 for Linux supports high availability and large databases but it
requires knowledge of big data solutions, Linux
