Why Is The Bottom Of My Foot Numb

Processing in Heritage / 1

Before a hard drive, Heritage / 1 will be V-tapes for storage. I mentioned that a V-TAPE is (or will be) a 3.5-inch diskette with a file system (owner) designed to simulate a magnetic tape.

So far, I imagined that a V-TAPE only hosts to a file, but this is a waste of space, obviously it is quite possible, therefore, to design the file system so as to allow more than one file for V -TAPE. Suppose that is the case, then my choice will host one or more of a V-TAPE. I think in the case of databases (or data files in general) prefer a single file by V-TAPE and these files will grow over time, while for several files preferred programs by V-TAPE and that they are fixed length so I can make better use of disk space.

The reader will wonder what is problem if the diskette is a random access medium. The answer is that a V-TAPE is no such thing as its file system forces you to behave like a tape and is as such qie no-brainer. The tape is a sequential access medium, can personally do not but only inserts data at the end to add or replace the file in its entirety. From there to host several files on one tape impossible to update them. I am aware that these procedures look archaic in the ear of a modern man, but this is it: to savor the past problems.

DATABASES

will adevertido the curious reader of history that the old computer centers employing a large number of tape drives. I think not so much to increase the total capacity of the system but, rather, to allow operation with a large number of files simultaneously.

Take the case of an application of typical database. Today we are used to design databases in line with the relational model, we think of "stalemate" divided into "columns", we set vínclulos between them, and we worry about the "plumbing" underlying it as the employee DBMS (MySQL, MS SQL Server, etc) is responsible for those underage. The truth is that almost all modern DBMS creates a disk file for each "table" in our database, so an application, which typically employs a large number of tables, use a large number of files on disk.

We will not use disk, but V-tapes, and we have seen that each file uses a V-TAPE for themselves, so that a large number of files means a large number of V-TAPES, which is the same as saying: a large number of readers of diskettes. This imposes a serious constraint to the design of our databases, you must use the least amount of "Tables."

Incidentally, we will not use the Relational Model, but as this is the hierarchical role in times of Heritage / 1.

PERMANENT FILES AND FILES MOTION

Here is a concept lost in time because today, updating a file on disk is no problem. But this was not the case at the time of the tapes.

We have seen that the only way to update a tape that contains multiple files is to replace all their new versions, ie the tape in its entirety. In practice, this means, rather, read the old tape while creating a new one with the new data (Using two tape drives) ... remember that in those days, memory was limited and quite possibly not enough to accommodate a file in its entirety.

intersante The moral of this story is that the updating of files on tape is something to be avoided. One way to minimize it is by the use of "permanent files."

Consider the case of a Personal Monitoring System. There are a lot of information about each employee, but does not recruit or lay off workers on a daily basis, so that information is not very amenable to change. These files are called "permanent."

In contrast, there is frequently changing information such as hours worked per day, holidays, etc.. This information is saved in "files of movement." The daily task is to update system files and then generate outputs motion based on these, with reference to the permanent. For example, the output "Pedro Perez has 4 hours of exta time these days" is generated on the basis of continuous information on Pedro Perez (including their normal working hours) and hours worked which were recorded daily (motion).

The advantage of using permanent files is that we can store more than one file on the same tape, saving readers. In case you need to update (recruitment of new employees, for example), there to produce a new tape (permanent) which is an updated version of the old.

The moral is this: The system must be designed movements trying to concentrate on the smallest possible amount of files, maximizing the use of permanent files.

PROGRAM FILES

We are made to the idea that our PC is a "solve it all" and therefore must accommodate a vast number of programs but only a few we use in daily practice. This follows from the fact of being, our PC, (and as its name suggests) a "Personal Computer."

In the industrial world is more common to find computers (even PCs) dedicated to a single function, but even in such cases their operating systems (Windows, Linux, etc.) come with a huge amount of pre-installed programs to provide various services and even applications platform.

This is not (permanently) for Heritage / 1, as it was not that of their counterparts back in the early 70s. If

Heritage / 1 service with a public library, for example, would be devoted entirely to keep the library catalog, ie one and only one application for the rest of your life.

recidirían data files in various V-TAPES perennial mounted in their respective readers. Two V-tapes would be earmarked for additional programs: one for the OS (H1-OS) and one for the application itself. Whenever

had to start the system, the operator would enter the "Loader" in memory using the console for it and this little program is responsible for H1-OS loaded into memory from V-TAPE. Surely H1-OS consists of several files of programs, all of them city residents in the same V-TAPE ... or maybe take a few and then the operator has to do juggling changing V-Tapes in various readers over the load.

with the OS already running, the ride operator V-TAPE of the application, and hit command, instruct H1-OS to load in memory. By then the V-TAPES data would be mounted in their respective readers and clients of the library could then make use of the system from terminals installed in the lounge.

How many readers?

I thought about a initial SUPPLIES 8-V-TAPE readers. This magic number comes from a very simple consideration: that is what fits comfortably in 19 inch rack. Surely one will be reserved for the OS, so I have 7 to my database applications, whatever they are.

Interestingly, I am designing a simple database to solve a particular problem persornal and so far, I'm just taking up 5 files ... so the restriction has not proved to be too severe ... so far.