Why, is easy.... CMS was developed in the '60s. There was no concept of PCs or their disk structure at that time. Memory was very expensive (hence the 512 byte blocks) and disk was too expensive to waste. Most of what was going to be under CMS was files like we xedit with. Not data files. The CMS minidisk structure is very efficient and very forgiving with crashes. It is very rare that a crash would corrupt a minidisk. And when CMS was put with CP, the only concern was being able to have multiple smaller minidisks mapped to a larger volume as efficiently as possible. Back in the early '70s, a programmer might cost you $10k. A MB of main memory might cost you $1M. With that type of cost difference, you solved what problems you could, with manpower. Most of us laughed when VSAM was announced. Buffers....in memory? Forget that garbage! We are paging too much as it is. In '79 with the R*star white paper (when relational database concept was defined). Never going to work! Direct I/O! Now that works! I laugh at a lot of things we use to believe. And in 10 years, I will laugh at what I believe now<G> Tom Duerbusch THD Consulting
>>> LOREN CHARNLEY <[EMAIL PROTECTED]> 3/15/2007 10:30 AM >>> John, I have a PFKEY set up in MAINT to list mdisks in different ways, one of which might be what you are looking for. I actually run this every time I up date the directory and run an edit on it, I can spot an overlap on files easily this way also. PF06 DELAY DISKMAP USER#DIRMAP USER(GAPFILE INCLUDE LINKS#DIRECTXA (EDIT Loren Charnley, Jr. IT Systems Engineer Family Dollar Stores, Inc. (704) 847-6961 Ext. 7043 (704) 708-7043 [EMAIL PROTECTED] -----Original Message----- From: The IBM z/VM Operating System [mailto:[EMAIL PROTECTED] On Behalf Of McKown, John Sent: Thursday, March 15, 2007 10:43 AM To: [email protected] Subject: Historical curiousity question. This is not important, but I just have to ask this. Does anybody know why the original designers of VM did not do something for "minidisks" akin to a OS/360 VTOC? Actually, it would be more akin to a "partition table" on a PC disk. It just seems that it would be easier to maintain if there was "something" on the physical disk which contained information about the minidisks on it. Perhaps with information such as: start cylinder, end cylinder, owning guest, read password, etc. CP owned volumes have an "allocation map", this seems to me to be an extention of that concept. Just curious. -- John McKown Senior Systems Programmer HealthMarkets Keeping the Promise of Affordable Coverage Administrative Services Group Information Technology The information contained in this e-mail message may be privileged and/or confidential. It is for intended addressee(s) only. If you are not the intended recipient, you are hereby notified that any disclosure, reproduction, distribution or other use of this communication is strictly prohibited and could, in certain circumstances, be a criminal offense. If you have received this e-mail in error, please notify the sender by reply and delete this message without copying or disclosing it. ----------------------------------------- ************************************************************ NOTE: This e-mail message contains PRIVILEGED and CONFIDENTIAL information and is intended only for the use of the specific individual or individuals to which it is addressed. If you are not an intended recipient of this e-mail, you are hereby notified that any unauthorized use, dissemination or copying of this e-mail or the information contained herein or attached hereto is strictly prohibited. If you receive this e-mail in error, notify the person named above by reply e-mail and please delete it. Thank you.
