In <[EMAIL PROTECTED]>, on
02/10/2006
at 11:41 PM, Johnny Luo <[EMAIL PROTECTED]> said:
>MVS(Multiple Virtual Storage) is the basic concept for
>z/os.However,after entering
>the mainframe world for eight months I still cannot understand it
>thoroughly
There are people on this list who offer training for a reasonable fee.
>1,MVS allow different task to have their own address space.While the
>number of address space increases in system,the total amount of
>virtual storage can become very big.
Yes, you need to size your local paging to accommodate it.
>With 31-bit addressing,the max size of real storage or auxiliary
>storage is 2G.
No, the max size of *central* storage is 2 GiB, but neither real
storage nor auxillary storage is so limited.
>So,the max size of virtual storage=max real storage+max auxiliary
>storage=4G
No. The max size of a single address[1] space is 2 GiB, but the total
size of virtual storage is limited only by the local paging data sets.
> Does this mean that the total size of all the address spaces
>cannot exceed 4G although
>in theory each address space can have a max size of 2G?
It would if your assumptions were correct, but they are wrong.
>2,Take a TSO user's address space for example.Suppose its size is
>5M.Whenthe user logon to tso, the address space is established
>which means 5M virtual storage space is allocated for
>this address space.
Not quite. A 5MiB region is allocated, but that doesn't mean that
there is 5 MiB allocated within that region.
>So this 5M space is being mapped using real storage plus auxiliary
>storage even if the user doesn't do any job after logon?
No; there is no page frame backing up an unallocated page of virtual
storage.
In <[EMAIL PROTECTED]>, on
02/11/2006
at 12:18 AM, Johnny Luo <[EMAIL PROTECTED]> said:
>Yes,that's where I got puzzled.If you can have unlimited paging data
>sets,it meas that you have unlimited auxiliary storage.But just like
>real storage,you must assign each piece of aux a unique address to
>identify it.
Yes, but that address is just[1] data set number and slot within data
set.
>And if your aux exceed 2G,how can you address
>it?
The same way as if the aux were smaller: data set number and slot
within data set.
[1] I believe that a data space can be 4 GiB.
[2] The actual encoding might be different, but in principle that's
what it is.
--
Shmuel (Seymour J.) Metz, SysProg and JOAT
ISO position; see <http://patriot.net/~shmuel/resume/brief.html>
We don't care. We don't have to care, we're Congress.
(S877: The Shut up and Eat Your spam act of 2003)
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