-----Original Message-----
From: IBM Mainframe Discussion List [mailto:[EMAIL PROTECTED] On Behalf
Of Bruce Black
Sent: Wednesday July 20 2005 09:30
To: [email protected]
Subject: Re: capacity of largest drive
>
>
>The maximum track capacity is then 65,535 bytes.
>
No, the max size of a single record (block) is 65535 and most access methods
only support up to 32760. But you can write multiple records per track, up
to 255 (the record number is 1 byte).
The maximum value of any variable is whatever is the smallest allowable
value for that variable in any of the places where that variable is stored or
manipulated. There are many 2-byte fields used to hold track size, and they
could all go up to 65535. The largest track size IBM has offered commercially
for M/Fs is the 3390 with 56664 usable bytes (unless you want to write a
full-track R0, which is not very often a good idea). Since no real 3390
tracks
have been manufactured for many years now and since all controllers have
learned how to map blocks, tracks, and cylinders to wherever the controller
microcoders feel like mapping them, the maximum size of a virtual track can
theoretically be increased to 65535 through new microcode algorithms. Then
access
methods could be taught how to use this larger capacity.
Bill Fairchild
----------------------------------------------------------------------
For IBM-MAIN subscribe / signoff / archive access instructions,
send email to [EMAIL PROTECTED] with the message: GET IBM-MAIN INFO
Search the archives at http://bama.ua.edu/archives/ibm-main.html
