Sometimes when you enter EDIT/VIEW of a dataset in ISPF you end up in a BROWSE session instead. It might be because you are trying to edit a load module which is not possible, but more likely it is because the dataset is too large to be edited by ISPF EDIT/VIEW. EDIT/VIEW reads all data in a dataset or member into storage from disk and if your TSO session does not have enough storage availabe ISPF switches to BROWSE instead.
Other vendors of mainframe software and IBM has developed editors that are able to edit almost any size of datasets. Unfortunately these editors are either not available at your installation or it is too complicated to find out if one of them is available. Luckily you can try something much simpler before you start a quest for an alternative editor. you can increase the amount of storage available to your TSO session.
First of all you must leave ISPF and end at the TSO READY prompt. If you do not know how to do this then ask one of your really experienced mainframe colleagues. When you are placed at the TSO READY prompt you must type the command
where you replace <USERID> with your own TSO userid and press Enter. Now the following panel is displayed:
Some of the fields will be filled out (for instance the Userid field), while others may be empty (for instance the Password field which you MUST fill out). The interesting field in this tip is the Size field which I have marked with ???????. Here you can type in a figure in Kilobytes or in Megabytes if you put a M at the end. 64M means 64 Megabytes while 64000 means 64000 Kilobytes. Most likely the field is initialized with a figure less than 16 Megabytes because the TSO systems programmer has decided so. This was a good idea many, many years ago when mainframes did not have gigabytes of central storage. But today where most installations are running z/OS using 64-bit adressing you can use a much larger value without any worries.
My experience is that you must specify a value larger than 64M before you will experience any difference in ISPF EDIT/VIEW. If you use a value of 256M you will be able to edit most datasets using the ISPF editor. I have even seen the value 2000M being used, but do not use such a big value, because z/OS has to allocate an array to keep track of all the storage you are able to allocate even though you do not use it all. If everybody uses 2000M as Size z/OS will be suffocated slowly by TSO users and then editing of any dataset will no longer be an option.
Fortunately it is probably not very often that you need to edit a very large dataset. Therefore you can choose to adjust Size when needed. TSO will remember the value of Size and use it as the value for your future TSO sessions. At some installations you may not be allowed to increase the value of Size. Then you can try using 0M which means unlimited amount of storage. But most lileky this is also not allowed.