4 Files and Directories This chapter explains about block devices in 1616/OS . Block devices, despite their crass name, are one of the really handy things about computers, because they help youmanipulatelargechunksofinformationwhateverwayyouneed. Blockdevices store the contents of the computer memory in chunks called blocks, each of which is1024 bytes long. Theyinclude disk drives, hard disks,and ram disks. Incontrast, character devices such as the keyboard and printer manipulate memory contents on a byte at a time basis. This chapter explains that computers store information in named files, and groups the files in directories.
It explains the different types of block devices, such as ram disks, disk drives, and hard (or fixed) disks, their advantages and disadvan- tages. It tells you about hierarchical file systems, directory names, filenames, and pathnames. It introduces some easy commands for using block devices. Although you do not actually have access to a disk drive or hard disk until you expand your Applix 1616, the inbuilt ram disk (known as /rd ) obeys exactly the same commands, so it is possible to run the system without a real disk drive. However, the contents of /rd are destroyed once you switch off the computer, making this an insecure system.
Although cassettes were the only choice a decade ago, today all serious users try to obtain disk drives as soon as they can. You will find more detailed discussion of setting up disk drives in the Disk CoProcessor Manual and the User Disk Manual . Background Since the contents of the memory in a modern computer disappear when power is switched off, some method of storing files and programs more permanently is required. This method is, unfortunately, almost always on some magnetic media (and thus relatively slow by comparison with the electronics in the computer).
The magnetic media the 1616 can handle includes cassette tapes, floppy disks, Small Computer Systems Interface (SCSI) hard disks, and other SCSI devices. SCSI is one of several standard styles of interfaces (connections) to magnetic storage devices for computers. Others you may encounter (not used by Applix) include ST506, SMD, ESDI and IDE. Eachfileorprogramthatisstoredneedstohaveanamebywhichitcanbeidentified by the user, and this is known as its filename . On the Applix, the filename can be up to 31 letters long, so you should use descriptive names. Upper and lower case letters are treated as if they were the same, while spaces and control characters are removed.
You are not allowed to use the ‘ / ’ character within a filename. Files and Directories User Tutorial Manual Page 31