Mainframe, MVS and zOS Discussion

Not sure I understand what you mean about a reference link. The point is that required memory must be allocated and present in RAM to be used. The only thing that can reside on a page data set is pages that are not in use. As a result, the working set for a job is a combination of memory resident pa...

In a single CPU situation, then only one instruction stream can be processed at a time. So whatever that does will determine the behavior of the whole machine. When there is more than one processor, the operating system provides a mechanism for serializing access to resources. This is required to en...

The primary difference is that virtual memory is a concept, while cache memory is real, physical memory. As mentioned previously, the z13 has 4 levels of cache memory and then central storage [RAM]. The role of cache memory is to improve the access speed to instructions and data. Each core has a Lev...

Memory refers to "processor storage" while DASD refers to "disk storage". Memory is temporary while DASD is permanent [this is defined by what happens to the data in the event of a power loss]. In addition one can even refer to tape storage if necessary. However the points about ...

DCB parameters will be present only when creating a data set. DCB parameters are ALWAYS present and they are required to be coded within the program. These define the files that the program will use. The DCB parameter in the JCL is only used to override any values that have not been specified withi...

As I mentioned previously, MSU's [Millions of service units per hour] should NEVER be used as a measure of performance or capacity. They are numbers that were made up to account for a basic size of a system and are used to establish software licensing costs. They do NOT reflect actual resources cons...

The blocksize is largely irrelevant. You will find it ranging from 6144 to 13030 to 19069 to 32760. It has little to do with anything in a load library. It doesn't really do anything for efficiency, because only the TXT records in a load module are subject to blocking. Since these records are only r...

The biggest factor in KSDS performance is the number of index and data buffers being used. For random access, index buffers will be important. For sequential processing, data buffers become more important. For online access, most environments utilize a feature called Locally Shared Resources [LSR] w...

One example of opening an empty KSDS can be when a program wants to read a file which is created or maintained by other system. That time you don't know if the VSAM is empty. But it should happen only when the program executes first time, but we still check for the VSAM status code all our life, ri...

MIPS and MSUs are abused terms. The processor measure is never evaluated in MIPS. It is assessed using Service Units and then related by ITR {Internal Throughput Rate]. MIPS is absolutely meaningless without instruction measurements and understanding instruction pipeline flow. MSUs do NOT represent ...

A clarification regarding PRTY. This parameter has nothing to do with job execution nor WLM. The PRTY parameter determines whether or not a job's position on the input queue should be placed ahead of others already in the queue. PRTY has nothing to do with the job's execution since that will be esta...

You cannot simply rewrite the header labels [HDR1 and HDR2). Every tape data set also has corresponding trailer labels [EOV or EOF]. If they are EOV, then you'd have to re-write the labels of every tape in the sequence. In any case, you'd still have to advance through the entire tape to modify the t...

MSU's should never be used for capacity planning. SU's do NOT convert to MSU's because they represent two entirely different metrics. SU's are "charged" to specific units of work so that they represents a normalizing value to determine CPU or I/O usage. MSU's are defined as a capacity metr...

If you have a product like SYSVIEW, OMEGAMON, MAINVIEW, or TMON you can use those products to see your system configuration. If you are authorized to issue operator display commands [such as through SDSF], the D M [Display Matrix] command will show you some of the information you're interested in. T...