Block devices As mentioned, block devices store the contents of memory in blocks of 1024 bytes. They include ram disk, disk drives, and hard disks. The RAM disk The basic 1616 system does not have any floppy disk drives. Instead, a proportion of the 1616’s RAM memory is used as a disk; data is written to memory as if it were being recorded onto a disk. The simulation of a floppy disk using memory is referred to as a ‘RAM disk’. The name of the ram disk is /RD . There are many references to disks and disk files in this manual; the term ‘disk’ in this context does not actually refer to a physical floppy disk but rather to any mass storage device for which a software driver exists in the 1616.
The RAM disk is one such device. Others devices can include one or two 3.5 inch (9 cm) or 5.25 inch (14 cm) disk drives, SCSI hard disks, or SCSI cartridge tape drives. To ensure file integrity the RAM disk data is checksummed under software as it is written in. The checksum is verified whenthe data is read back; if some software (or hardware) malfunction has caused the RAM disk contents to be corrupted, then attempting to read the file whose contents were affected will result in an I/O error being reported. You may vary the amount of memory which 1616/OS allocates for the RAM disk using switches 0 and 1 of the quad switch on the 1616’s PCB as follows:
RAM disk Switch 1 Switch 0 RAM disk selection setting setting size 0 off off 24K 1 off on 104K 2 on off 200K 3 on on 304K It is suggested that you select RAM disk size 2 for the time being. If you have disk drives, then the settings in the MRDRIVERS file on your boot disk will overridethe switch settings as required. The ram disk can occupy up toa megabyte of memory, if you have this much to spare. The major disadvantage of the /RD device is that the contents are lost when the computer is switched off. Why then use it at all? The answer is speed. A ram disk is faster than most physical disks. A typical use is to copy your most often used programs into /RD , and run them from there.
Because you have a permanent copy of your programs on disk or tape, it does not matter that the copy in the ram disk is lost when you switch off. However, when you create a new file, or update the contents of a file, you want it saved in some less transient form. This will be on floppy disk or on hard disk. Files and Directories User Tutorial Manual Page 33