The main features of the SYS expanded BIOS are:–
(a) Full screen editing, which allows the cursor to be moved back up to a line
already on the screen, so that the line can be edited and reentered to CP/M. This
feature, also found in all of Gemini’s BIOSs for Nascoms and Geminis, is most
unusual if not unique for CP/M systems.
(b) Screen dump to the CP/M list device, so that an image of the screen can
easily be printed. (Also now in Gemini’s own BIOSs.)
(ec) Automatic screen paging, so that information does not roll off the top of
the display before it has been read.
(d) Support of the Nascom screen display or the Gemini Video Card. An
additional keyboard is supported on the Video Card.
(e) Support of the Nascom keyboard or an ASCII encoded keyboard. On the Nascom
keyboard, the action of the Shift key may be reversed by pressing Control/Enter.
The % (% = ‘at’) key when not shifted may be used as a Tab key or as an
alternative Control key. A number of command strings may be automatically
generated by pressing the GRAPH key and a letter, and this simplifies the entry
of several commonly used commands.
(f) Full support for the CP/M IOBYTE option.
(g) Support for both serial (Teletype compatible) and parallel (Centronics
type) printers. A variety of options are available including handshaking and
automatic handling of form feeds so that printers without a page throw mechanism
will operate correctly.
(h) Ability to automatically identify single density disks in drives B, C and
D. The primary format supported is the SD Systems format, extended to also use
the second side of the disk. This format was used by the Gemini/Henelec GM805
single density disk system. Special versions can be generated which instead allow
alternative single density formats to be used. These are the Cromemco SS/SD, RML
SS/SD and Xerox 820 SS/SD formats. In each case these formats require 40 track
drives which are not supported. You must take care to access only the first 35
tracks of the disk if you use these formats.
(i) Ability to read and write other double density disk formats. Special
versions can be generated which allow an alternative double density format for
disks in drive B. At present, Superbrain QD (DS/DD) format, Nascom SS/DD 80 track
(only with a Shugart compatible interface 96 t.p-i drive) and Rair DS/DD formats
(3) Optional read after write checking for all changes to disks. This gives
greater security while decreasing performance.
(k) Standard disk software supporting Winchester hard disks (see note on
availabiility), standard eight inch floppy disks, Pertec, ‘‘Shugart compatible’,
and Micropolis five inch disks.
(1) Support of a virtual disk which appears exactly like a real disk but is in
fact additional memory. This can use the standard 64K page mode allowing either
additional RAM cards, each of up to 64K. This option is now also included in
Gemini’s own BIOSs. An alternative option allows the use of MAP memory cards with
up to one megabyte of memory. These operate either in 32K pages with the Nascom 2
or Gemini GM811 CPU cards, or in full memory mapped mode with the Gemini GM813
(m) Warm boot from the virtual disk, which makes this process very fast.
(n) Extensive messages are displayed when SYS is executed, describing the
configuration for which it has been generated and the main features included.
(0) Most features are set by easily understood assembly options, allowing
either a small simple BIOS or a large advanced BIOS to be generated to the exact
requirements of the user.
"Fixed’ Screen Edit
A new feature of SYS which requires some explanation is the ‘fixed’ screen
edit mode. At the moment if you enter screen edit mode, edit a line and press
Return, the system returns to normal. But back in the days of NAS-SYS you were