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The Memotech MTX Series



There were a number of different disk upgrades available for the MTX range, including various floppy disk interfaces as well as a hard disk option for the FDX, called the HDX. The hard disk upgrade was very expensive though, and I'm not sure if (m)any were actually sold; here, I am going to concentrate on the floppy disk drive options.

Floppy Disk Systems

A word about floppy disk technology

It should be remembered that floppy disk drive heads make contact with the media (diskette), in contrast to a hard disk, where the heads "fly" over the surface of the disk platters. As the floppy media ages, particularly lower quality media, it can degrade in a number of ways, including breakdown of the magnetic coating, mould inside the protective jacket, etc. These issues, as well as specs of dust, can lead to scoring of the media which can not only effect the particular diskette in use, but also any other media subsequently put into the drive if the debris gets deposited on the read/write heads.

It is a good idea to closely inspect any old diskettes that you plan on putting into the floppy drive before use. It is also important to periodically clean the drive heads to clear any accumulated magnetic oxide particles and dust that would otherwise damage the media and/or drive.

The design and construction of 3.5" floppies means that they are much less prone to these problems than 5.25" floppies are.

Memotech Floppy Disk Options

Disk Operating System

All of the disk system released by Memotech use the same underlying software, i.e., they are ALL based on the Memotech CP/M system.

CP/M Systems

When running under CP/M, operation of the Memotech disk systems is as you might expect and is pretty much the same as floppy disk operations on other CP/M systems. Starting the system requires that the system is booted from a system disk which loads the CP/M system into memory as described in more detail on my CP/M Structure page.

In short, the disk system ROM looks for the boot sector of a system disk and loads the essential parts of CP/M, including the disk configuration definitions, into RAM. On an FDX system, once the system is loaded, the boot disk can be swapped for non-bootable program and data disks as needed. To ensure that CP/M is made aware of the disk change and can properly update the directory structure, the user "logs on" to the new disk by issuing a <ctrl><C> command from the command processor. (This is not the case for SDX disk systems - see the SDX page for more details.)

Under CP/M, the first two tracks on the disk are reserved for CP/M and store the BIOS, BDOS and CCP. Since the tracks are reserved, there is no penalty for making every user disk a system disk and being able to boot from it.

Non-CP/M Systems

Memotech's non-CP/M disk systems operate in a very similar manner, but with some important differences that the user must be aware of. Unlike other 1980's home computers, such as the BBC micro, the disks used for Memotech's BASIC disk systems must ALL contain a bootable CP/M operating system disk.

After the system and disk drive(s) have been powered on, the user must explicitly restart the disk system by issuing a "ROM x", (where "x" is 3 or 5), command from BASIC to initialise the disk system, load the essential parts of the disk system into RAM and read the disk directory. To cater for differences between the CP/M and non-CP/M systems, the non-CP/M ROM patches the disk code as required during the boot process.

If the disk is changed, another "ROM x" command must be issued to make the system aware of the new directory contents.

When preparing a new disk for use, the USER FORMAT and USER SYSCOPY commands must be used to make the disk bootable which requires that the user already has a bootable disk from which to copy the system files. As with the CP/M system, there is no reduction in the usable space on the disk by doing this.


Credits : Some of the information on the operation of the SDX was posted by Andy Key in the Memotech Group on Facebook


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