In the early 1990s businesses were increasingly trying to move from mainframe/minicomputer solutions to those that could be hosted on desktop PCs. But getting a computer on every desk was very expensive, both in costs of initial expense and maintenance.
An interesting mid ground of sorts could be had by connecting inexpensive, and often existing, dumb terminals to one single beefed up desktop microcomputer, and sharing applications.
Unix solutions could be found, but at the time those required very expensive software licenses, usually very expensive proprietary hardware, and exceedingly high development and maintenance costs. Essentially throwbacks to the minicomputer. Various multitasking DOS solutions existed, such as Digital Research Concurrent DOS 386
, and VM/386. But... well, DOS!
Again, a midground was IBM and Microsoft's new OS/2
product, which evolved from Microsoft's earlier attempts at making a multitasking DOS
, and was to be the successor to DOS and Windows 2.
But OS/2 was only a multitasking OS, not multi-user.
Until Citrix Systems came along:
Released in 1991 by Citrix Systems, Citrix Multiuser is a customized version of Microsoft OS/2 1.21 that turns it in to a real multi-user operating system. With Citrix Multiuser, users can connect and simultaneously run character cell based applications from remote serial terminals. To prevent users from interfering with each other, it adds security permissions to devices and files. It can use multi-port serial port boards like the Digiboard, or any serial device that has OS/2 1.21 drivers.
An interesting promotional video is on youtube, that shows how it could be used: https://www.youtube.com/watch?v=UxJ0T0C7p4g
And a 1991 byte Magazine review is here: http://jonudell.net/archive/citrixFirstImpression.html
Citrix Multiuser OS/2 does *not* support running Presentation Manager based application or DOS executables, and programs can not use graphics modes. It also does not have support for networking. (it looks like you can install LAN Manager, but it won't use that for communications.) Another limitation is that text-mode applications can not use a mouse.
Although it can not run DOS applications, many familiar text mode DOS applications had already been ported to OS/2. A few examples include: WordPerfect, Lotus 1-2-3, Microsoft Word, HyperAccess, Oracle, Paradox, and R:base.
Unfortunately for Citirx Systems, this product was released just days before the IBM-Microsoft separation, which was an almost instant fatal blow as Citrix was licensing OS/2 code through Microsoft.
As a result, Citrix Systems had to backtrack and instead focused on making MS-DOS multi-user until eventually they released a Windows NT based version.
Installation was a bit of a headache -
To install on a faster computer, you must first apply the OS/2 speed
patches described here to the boot disk:
http://www.os2museum.com/wp/installing- ... ualbox-vm/
To summarize, replace all occurrences of:
B8 F4 01 BB C8 00 F7 E3 F7 F1
B8 F4 01 BB C8 00 F7 E3 90 90
It currently will not install in PCem (or some real hardware apparently) due to a known bug with OS/2's FDISK. Unlike normal OS/2, Citrix Multiuser's setup will not let you skip that.
The CSD update disks must be installed from maintenance mode. To do that, use the Citrix Multiuser OS/2 boot disk, and after install starts from the second disk, hit escape.
I managed to get it running in VirtualBox 4.x. Fortunately VirtualBox will accept either 1.2mb or 1.4mb images and they "just work". When I initially tried to resize the install images to 1.44mb using WinImage, it didn't seem to like that for some reason. There is probably some way to convert those or perhaps I just did something wrong. Otherwise, with other emulators you might have to check and configure 1.2mb disk support. On real hardware you can write a 15-sectors 1.2mb image to a 3.5" disk but you have to make sure the disk is formatted properly. The Corrective Service Disks are on 1.44m disks.
This also includes "Multiuser Link", a telecommunications program that Connects a PC
running DOS or OS/2 to a Citrix Multiuser system via standard RS-232C serial directly or with a modem.
This provides some extra optimizations not available with other terminal types. It supports ZMODEM file transfers, dial-up and direct connection, SSA/CUA compliant menuing user interface, context sensitive help, ICA (Intelligent Console Architecture) and ASCII terminal emulation, full color and sound, and local PC printing from the Citrix Multiuser host.
In conclusion this is an interesting and, in its time, potentially useful application built on a stripped-down version of OS/2.